Abstracts No.57: 1999 Selwyn Symposium: Geological Catastrophism, 1999, Melbourne

Geological Society of Australia

ABSTRACTS Number

57

"Geological Catastrophism" 1999 Selwyn Symposium and Medal Presentation Victoria Division of the Geological Society of Australia Lyle Theatre, Redman Barry Building University of Melbourne Friday, October 29,1999

Geological Society of Australia, Abstracts Number 57 "Geological Catastrophism" 1999 Selwyn Symposium Abstract Volume, Melbourne, October 1999 Victoria Division Geological Society of Australia ISSN 0729 01IX Number 57 National Library of Australia Cataloguing-in-Publication data

"Geological Catastrophism" 1999 Selwyn Symposium Abstract Volume Victoria Division of the Geological Society of Australia University of Melbourne Friday, October 29, 1999 Compiled by: Kerry A. Hegarty and Robert A. Mooney Example citation for papers in this volume: Archbold, N., 1999, Extinction, evolution, catastrophism and uniformitarianism. Geological Society of Australia, Abstracts No 57, pp 55. © Geological Society of Australia Inc.

Copies of this abstract volume may be obtained from: Ms. Misha Frankel, Business Manager, Geological Society of Australia, 706 Thakral House, 301 George St., Sydney, NSW 2000 More information about membership and activities of the Geological Society may be obtained from: Victoria Division GPO Box 2355V Melbourne, VIC 3001 or phone (02) 9290-2194

^^Geolqgical

Catastrophism^^

Four invited lectures to commemorate the 1999 Selwyn Symposium md Medal Presentation 2pm Friday, October 29"^ 1999 Lyle Theatrey Redman Barry Building University of Melbourne

Our four invited speakers Professor Neil Archbold, Deakin University Ms. Marion Anderson, Monash University Dr. Bob Musgrave, LaTrobe University Professor Ray Cas, Monash University

Our congratulations to Dr. Bill Birch 1999 Selwyn Medalist Our thanks to Dr. Walter C. Pitman Lamont-Doherty Earth Observatory, New York 1999 Selwyn Public Lecture '^Noah's Flood: The Geological Evidence" 6:30pm Copland Lecture Theatre University of Melbourne October 29^, 1999

Selwyn Subcommitee: Kerry Hegarty (Chair), Gus Bravo, Ingrid Campbell, Lex Ferguson, Monty Grover, Bob Musgrave, Meredith Orr, John Waters

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

This important event on the Victoria Division calendar would not have been possible without the generous support of the following Societies, individuals, government and educational groups and industry:

DE B E E R S

A D I A M O N D IS FOREVER STOCKDALE PROSPECTING LIMITED Stockdale Prospecting 60 Wilson Street PO Box 126 South Yarra, VIC 3141 Phone: 9863-5222 ic@spl.oz.au

Geotrack International Pty Ltd 37 Melville Road Brunswick West, VIC 3055 Phone: 9380-1077 www.aeotrack.com.au

SCIENCE ENGINEERING TECHNOLOGY Petroleum Exploration Soclely of Australia Vtotorla/Tasmania Branch

Petroleum Exploration Society of Australia Victorian/Tasmanian Division PO Box 317 Collins Street West Melbourne, VIC 8007 Phone: 9412-5016 www.latrobe.edu.au/wvvw/pesa

V I C T O R I A N GOVERNMENT I N I T I A T I V E

Department of State Development Science, Engineering & Technology GPO Box 4509RR Melbourne, VIC 3001 Phone: 9651-9038 www.innovation.vic.gov.au

THE UNIVERSITY OF

MONASH UNIVERSITY Monash University Department of Earth Sciences Wellington Road Clayton, VIC 3800 Phone: 9905-4879 www.earth.monash.edu.au

MELBOURNE School of Earth Sciences Melbourne University Victoria 3010 Phone: 9344-7761 www.met.unimelb.edu.au

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

... and more sponsors we would like to thank...

Mr Bob Foster Bob Foster Consultancy Phone: 9525-6335 mail@fsb.com.au

Victorian Institute of Earth And Planetary Sciences C/o Department of Earth Sciences Monash University Clayton, VIC 3168 Phone: 9905-1530 www.earth.monash.edu.au/~vieps/ Great Central Mines 210 Kings Way South Melboume, VIC 3205 Phone: 9234-1100 www.gcm.com.au

Australian Society of Exploration Geophysicists Victoria Branch c/o Pasminco GPO Box 1291K Melbourne, VIC 3001 Phone: 9288-9188 www.aseg.org.au

Geological Society of Australia 706 Thakral House 301 George St. Sydney, NSW 2000 Phone: (02) 9290-2194 www.gsa.org.au

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

Con0mtulations to Dr. Bill Birch 1999 Selwyn Medalist from the Victoria Division^^ Geolo£fiml Society of Australia Bill Birch obtained his PhD at Melbourne University in 1976, with a thesis on the volcanic rocks in the Palaeozoic cauldron complexes of central Victoria. Bill and his colleagues were the first to interpret these rocks as products of major ashflow eruptions. The work drew attention to the remarkable preservation of the Devonian volcanic complexes and their unusual mineralogical features including cordierite and garnet abundance. This interest in igneous rocks later encompassed other felsic, mafic and alkaline occurrences in Victoria. In 1974 he began work at the Museum of Victoria, with responsibilities for the mineral, rock and meteorite collections. He has overseen the amalgamation of the Museum's mineral collection with those of the Geological Survey of Victoria and the University of Melbourne. Bill's numerous notes, papers and books cater to enthusiastic amateurs as well as professionals. He has codescribed twenty new mineral species, including three from Victoria (ulrichite, selwynite and wycheproofite), seven from Broken Hill, and five from other Australian localities. His main contributions centre on microprobe analyses obtained in the Melbourne University Geology Department, where he has been an Honorary Associate since 1983. His current projects include studies of several meteorites from Victoria and a new edition of the book Minerals of Broken Hill. Bill Birch has involved himself in organisations spanning all levels of interest and expertise in mineralogy and geology. These include the Geological Society of Australia, The Mineralogical Society of Victoria, The Gemmological Association of Australia and the International Mineralogical Association. In the Victoria Division of the Geological Society of Australia, he served as Treasurer and was Chairman in 1987 to 1989. During his Chairmanship he organised the publication of the current edition of "Geology of Victoria" and expedited the completion of "Victorian Geology Excursion Guide". He currently chairs the subcommittee responsible for producing the new "Geology of Victoria".

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

ALFRED RICHARD CECIL SELWTN (1824-1902) The Selwyn Memorial Lecture was introduced in 1984 to commemorate the work of A.R.C Selwyn, the first Government Geologist of Victoria. This year represents the 144th anniversary of the Government Geological Survey in Victoria. In recent years the Lecture has followed a symposium, involving invited speakers on a significant theme for Australian geology, to celebrate Selwyn's work. Alfred Selwyn was bom in Somerset, England in 1824 and had a strong Church of England upbringing. He was educated in Switzerland where he developed an enthusiasm for geology. At the age of 21, he joined the Geological Survey of Great Britain although not a university graduate. He began work under the direction of A.C. Ramsay in North Wales and was soon entrusted with the independent mapping of large areas containing key Silurian rocks. The discovery of gold in Victoria in 1851 led Governor La Trobe to ask the Colonial Office in London for "a gentleman possessed of the requisite qualifications and acquaintance with geological science and phenomenon." Selwyn was awarded the post at an annual salary of 500 pounds and arrived in early December 1852. Almost immediately he commenced a series of wide ranging reconnaissance trips during which he studied the geology of Victoria with excursions into Tasmania and South Australia. Among many of the early records, the Geological Survey holds and original water coloured version of his 1856 map of the Yarra Basin and Western Port. Selwyn set up the Geological Survey proper in 1856 and gathered around him and trained a team of geologists including Alpin, Ulrich, Wilkinson, Daintree, Taylor, Brown and Etheridge. They subsequently occupied senior positions in all mainland State Geological Surveys and became renowned in the early annals of Australian geology. Selwyn and his team established the 6 mile x 9 mile Victorian quarter sheet mapping programme of which 65 were produced. Selwyn was a silent and reserved man of indomitable disposition who carried out his plans in spite of all hindrances and achieved an amount of work that few could emulate. However, conflict arose from the overlapping activities of mining surveyors. The Survey often held views on scientific standards, and policies opposed to those of the colonial officials and legislators, in particular that of R. Brough Smyth, Secretary of Mines. Consequently, Selwyn resigned in 1869 and the Survey was disbanded for a year. Selwyn left Australia and was appointed the Director of the Geological Survey of Canada on the retirement of Sir William Logan. He filled this office with distinction from 1869 until his retirement in 1894. The Murchison Medal of the Geological Society of London was awarded to him in 1876. Other honours followed in Great Britain but the only recognition from Australia was the Clarke Gold Medal from the Royal Society of New South Wales in 1884. He is commemorated in Victoria by this annual lecture instituted by the Geological Society of Victoria. 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

1999 Selwyn Public Lecture '"Noah's Flood: The Geological Evidence^' Dr. Walter C. Pitman Lamont-Doherty Earth Observatory Senior scientists from Lamont Doherty Earth Observatory, Dr. Walter C. Pitman and Dr. William B. F. Ryan have outstanding credentials in the geological sciences. Walter is well known for his contributions in scientific works and novel concepts in relation to such things as eustatic sealevel rise, fundamental aspects related to the theory of plate tectonics in the 1960's and 70's and his pioneering work in the reconstruction of plate geometries and motion. It is with great pleasure that the Victoria Division welcomes Dr. Pitman who will tell us more about his latest pioneering endeavours with Bill Ryan. They have documented geological evidence that the Black Sea was once an inland body of freshwater lying below sea level some 7500 years ago. Their evidence suggests that the Mediterranean flooded into the nowBlack Sea with tremendous force causing a fantastically rapid rise in shorelines and displacement of inhabitants. The geological evidence for this event "that changed history", oft referred to as Noah's Flood, will be the focus of Dr. Pitman's presentation. 6:30 pm Friday, October 1999 Copland Lecture Theatre University of Melbourne

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29* "Geological Catastrophism"

1999 Selwyn Symposium Speakers invited Speaker #1: "Extinction, Evolution, Catastrophism and Uniformitarianism" Professor Neil Archbold School of Ecology and Environment Deakin University Rusden Campus Clayton, VIC 3168 narchie@deakin.edu.au phone: 9244-7448 Invited Spealcer #2: "Catastrophic Flooding on Mars" or "But we don't have the wood to build an Ark!" Ms. Marion Anderson Department of Earth Sciences Monash University Wellington Road Clayton, VIC 3168 marion@maiLearth.monash.edu.au phone: 9905-4896 Invited Speaker #3: "Catastrophism and the Earth's Interior! It's not all calm under the surface" Dr. Bob Musgrave Department of Earth Sciences LaTrobe University Bundoora, VIC 3083 R.Musgrave@lati'obe.edu.au phone: 9479-2145 Invited Speaker #4: "The catastrophism of volcanic phenomena: never underestimate the scale and the effects" Professor Ray Cas 1998 Selwyn Medalist Department of Earth Sciences Monash University Wellington Road Clayton, VIC 3168 rcas@mail.earth.monash.edu.au phone: 9905-4897

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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9

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Professor Neil Archbold School of Ecology and Environment Deakin University : Rusden Campus Clayton, VIC 3168 nafchie@deakin.edu.au 9244-7448

. 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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EXTINCTION, EVOLUTION, CATASTROPHES AND UNIFORMITARIANISM Neil Archbold School of Ecology and Environment, Deakin University, Rusden Campus, Clayton, Victoria 3168 Introduction During the final decades of the Twentieth Century, the concept of major (global) catastrophes randomly punctuating earth history, with concomitant impacts on the evolution of earth based life, has captured the minds of earth scientists and others. The implications of rapid global change and the question of the possibility of such changes being triggered by human activity, have given rise to a range of human causation 'neocatastrophist' proposals including global climate change (warming), associated rises in sea levels and impending mass extinctions. This review examines the anatomy of mass extinctions, with particular reference to the largest known extinction event in earth history - that of the end Permian. The implications of mass extinctions on evolutionary theory and the concepts of catastrophism and uniformitarianism are then considered in terms of Kuhnian paradigm shifts or ongoing gradualistic theoretical change. Perhaps it is as Henry de la Beche (first Director of the Geological Survey of Great Britain) wrote when comparing the catastrophist and gradualist models. The difference in the two theories is in reality not very great; the question being merely one of intensity of forces, so that probably, by uniting the two, we should approximate nearer the truth,' quoted by Palmer (1999:64). Anatomy of Mass Extinctions • the end Permian Extinction is the outstanding feature of the fossil record and the obverse of the coin to evolution. Without both, biostratigraphy would not work. Extinction was first recognised in the modem sense at the turn of the nineteenth century by Leopold Chretien Frederic Dagobert de Cuvier (known as Georges, after a dead brother). Episodes of profound extinction were used by John Phillips in 1841 (see Figure 1) to define the end of the Palaeozoic and Mesozoic Eras (see Palmer, 1999, for a rigorous review of the history of extinctions and their recognition). Erwin (1993) identified six key events in the history of life on Earth: 1. The Origin of Life (3.8 - 4.0 Gyr) 2. The Origin of Eukaryotes (1.5-2.1 Gyr) 3. The radiation of animals (540 Myr) 4. The invasion of the Land (Ord. - Dev.) 5. The end - Permian mass extinction 6. The end - Cretaceous mass extinction Other events also occurred, as noted by Erwin, but I would note that the extinction of the Vendian multicellular animals probably coincided with number 3. 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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Extinction events through the Phanerozoic (recognised by 1986), and the biodiversity crashes of 'the big 5' extinction events, are shown in Figures 2 and 3 (after Hallam and Wignall, 1997). Fine tuning by recent work has added to our recognition of minor to moderate mass extinctions as, for example, with the recognition of the end Maokouan event in the Permian (Figure 4).

C.fiKOZOIO LIFK. •

MESOZOIO UF£«

/ > I

PALJEOZOIO LIFE.

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9 9

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Figure 1. The diversity of life according to John Phillips (after Erwin, 1993:6) 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

12

Pliocene M.. Miocene U. Eocene

T

Maastrichtian 100-

Cenomanian

K

Aptian Trthonian

§

Pliensbachian

200^

Norlan

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U. Permian

CO

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Frasnian U.Silurian Ashgillian M. Caradocian

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U. Botomian

Extinction events as summarized by J.J. Sepkoski in 1986 (after Hallam & Wignall, 1997:5)

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29"' "Geological Catastrophism"

13

500<0 E <0

E

600

400

200

Geological Time (Myr) Figure 3.

Marine family diversity for the Phanerozoic as shown by Raup & Sepkoski in 1982 (after Hallam and Wignall, 1997:3)

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29*^ "Geological Catastrophism"

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RADIOLARIANS FISHES/ CONODONTS AMMONOIDS

Figure 4.

Extinctions at the end of the Maokouan Stage (after Hallam & Wignall,

1997:115).

Organisms c^n be classified in terms of their responses to extinction events, all of which consist of three phases - extinction, survival and recovery. Hence, taxa are classified as extinct, holdover, progenitor, disaster, survivors, Elvis and Lazarus (Figure 5). The end-Permian extinction, familiar to the present author because of the near demise of the Brachiopoda, is of major significance because even the Insecta, the most diverse class on Earth today, did not escape the holocaust (Figure 6). This was the only time they have been affected by such an event. Their fossil record is good (perhaps surprisingly, but only the Lepidoptera have an underrepresented record), with over 1263 families. Apart from a 35 million year gap in the Latest Devonian - Early Carboniferous, their record is better than that of the vertebrates. They are expansive survivors because of low rates of extinction.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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RECOVERY PHASE

I I

SURVIVAL PHASE I I

EXTINCnON PHASE

EXTINCT TAXA

Figure 5.

HOLDOVER fROGBNITOR TAXA TAXA

DISASTER TAXA

SURMVORS

ELVIS TAXA

lAZARUS TAXA

Classification oftaxa during the three stages of an extinction event (after Hallam & Wignall, 1997:14).

Many high level taxa were badly affected by the end-Permian extinction. Rugose and tabulate corals, bryozoans, echinoderms (crinoids, echinoids and blastoids), foraminiferids and ostracods (the dysoxic, deeper water forms survived), brachiopods, gastropods, bivalves, ammonoids, tetrapods, photosynthetic plankton and megaflora were all profoundly affected. Only nautiloids and fish show little effect or even an increase in diversity. A 'fungal spike' is known and reflects an opportunistic occurrence in turn reflecting the extinction of many insects and a rotting earth - the Gotterdammerung Scenario of Hallam & Wignall (1997:114). What was the trigger for the end-Permian event? Evidence for a bolide impact is poor and controversial to non-existent. A combination of massive volcanism and oxidation of peat is possible followed by the triggering of global warming, in turn following by anoxic oceans and productivity collapse (Figure 7). Proposed causes for mass extinctions are varied. The tabulation in Figure 8 is conservative and bolide impacts are probably more significant (Palmer, 1999) but they are not a universal cause of extinction events.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29* "Geological Catastrophism"

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Uz

Figure 6.

U"f'

I'll.,

Diversity of fossil families within insect orders for the Phanerozoic Eon (after Labandeira & Sepkoski, 1993:311).

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

17 Coal oxidation in southern Gondi»-ana

I

Negative swing or5i3C

Elevated rates of continental weathering

atmosphcrk C02 rise

Rise of Sr Isotope ratios

Negative swing ofSiK)

Decreased circulation in oceans and lowering oT oxygen levels leading to oceanic stagnation

CI.OBAI. WARMINC

X

Sudden decline of nutrients: productivity colhipse

ICruption of Silierittn Traps

MASS EXTINCnON

I

Cosmopolitan faunas

I Acritaixrh blooms

z

I

Negative spike of 5t3C values

Eutrophic oceans Black shales accumulate in oceanic settings

Figure 7. Flow chart for the global warming - marine anoxia model for the end Permian mass extinction (after Hallam S: Wignall, 1997:141). Bolida impact Late Precambrian Ute Early Cambrian Bkxnere boundaries Ute Ashgill Rasnlarhfamennian Devonian-Carboniferous Late Maokouan End-Penmlan End-Triassic Early Toarcian Cenonwiian-Turonian End-Cretaceous End-Palaeocene Late Eocene

Volcmnltm

Coolino

Warming

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Figure 8. Proposed causes of the main Phanerozoic mass extinction events (after Hallam & Wignall, 1997:249).

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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m w

18 A Joker in the deck

A new card in the deck of geological processes for the last 30 years is that of events external to the Earth, ie. the impact of asteroids and comets. The term astrobleme is now seldom seen (a pre-computer database term?) but space exploration has provided much new data. Halley in 1694 had argued that multiple collisions with comets had occurred, each destroying whole 'races' but with survivors which 'flourished anew'. Data from space may be statistically treated (as reviewed by Palmer, 1999) and results indicate some 5 impacts of 10km+ size objects over the last 500 Myr, 2-3 impacts of 1km size objects over the last 1 Myr and 10+ impacts of 0.5 km objects over the last 1 Myr. In the Twentieth Century, the following have been recorded: 1908 Tunguska (no crater but an area the size of Belgium destroyed) 1937 Estonia 8.5m crater 1947 Sikhote-Alin 100 craters, largest 14.0 m 1990 Sterlitamak 5.0m crater Neocatastrophism and Neouniformitarianism

By the Twentieth Century, uniformitarianism was considered to be the equivalent of gradualism and catastrophism was treated as the pariah which invoked religious fundamentalism. The recognition that gradualism is not always appropriate when interpreting the geological record and the mechanisms of biological evolution (see Eldredge, 1996 for a comprehensive overview of the 'punctuated equilibrium' debate, and much more) has resulted in a proliferation of words such as 'neocatastrophism' and 'neodarwinism'. Palmer (1999) has convincingly shown that the simplistic views of classical catastrophism and uniformitarianism and their chief protagonists, invariably provided in writings of this century up to the 1980's, are gross simplifications of the historical data. The myth propagated by Charles Lyell and others was that catastrophism owed much to 'preconceived ideas than to observation' whereas uniformitarianism was 'derived from logical deduction'. Lyell's concept of uniformitarianism was that of a dual definition. It combined a notion of 'actualism' (that physical processes operate according to unchanging laws) and 'substantive uniformitarianism' (earth's present state is typical of its entire history). The latter implied that because no global catastrophes had occurred in historical time none had ever occurred and hence, uniformitarianism took on the mantle of gradualism. It is true that the early catastrophists (eg. Cuvier, Buckland and Sedgwick) often invoked new supernatural creations of life through time but so also did Lyell (man was a special creation) and Hutton. They should be seen as men of their times - both groups were influenced by religion. Hallam, in 1989 noted the two components of uniformitarianism and concluded that it is possible to use actualistic methods and come to catastrophist conclusions. Hutton (1788:302), it should be noted, was clearly no gradualist - 'in thus accomplishing a certain end, we are not to limit nature with the uniformity of an equable progression, although it be necessary in our computations to proceed upon equalities'. The Twentieth Century has seen the supernatural realm removed from catastrophism and uniformitarianism. Catastrophism has been recast as 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

19 'neocatastrophism' yet uniformitarianism has remained - arguably it should have become known as neouniformitarianism, but are these new words required? Perhaps the final words can be quoted from that nineteenth century materialist, T.H. Huxley, who warned Darwin in private not to follow Lyell and ascribe Lyell's gradualism to evolution. T o my mind there appears to be no necessary theoretical antagonism between Catastrophism and Uniformitarianism. On the contrary, it is very conceivable that catastrophes may be part and parcel of uniformity. Let me illustrate my case by analogy. The working of a clock is a model of uniform action; good time-keeping means uniformity of action. But the striking of a clock is essentially a catastrophe; the hammer might be made to blow up a barrel of gunpowder, or turn on a deluge of water; and, by proper arrangement, the clock, instead of marking the hours, might strike at all sorts of irregular intervals, never twice alike in the intervals, force, or number of its blows. Nevertheless, all these irregular and apparently lawless catastrophes would be the result of an absolutely uniformitarian action; and we might have two schools of clock-theorists, one studying the hammer and the other the pendulum,' (quoted by Palmer, 1999:345).

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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REFERENCES

Eldredge, N., 1996. Reinventing Darwin. The Great Evolutionary Debate. Phoenix, London, 244 pp. Erwin, D.H., 1993. The Great Paleozoic Crisis: Life and Death in the Permian. Columbia University Press, New York, 327 pp. Hallam, A & Wignall, P.B., 1997. Mass Extinctions and their Aftermath. Oxford University Press, Oxford, 320 pp. Hutton, J., 1788. Theory of the Earth; or an investigation of the Laws observable in the composition, dissolution, and restoration of land upon the globe. Transactions of the Royal Society of Edinburgh 1:209-304, 2 plates. Labandeira, C.C. & Sepkoski, J.J. Jr., 1993. Insect diversity in the fossil record. Science 261:310-315. Palmer, T., 1999. Controversy Catastrophism and Evolution. The Ongoing Debate. Kluwer Academic / Plenum Publishers, New York, 452 pp.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

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CC

Catastrophic Flooding on MarsJ>J> or ^^But we don^t have the wood to build an Arkr Ms. Marion Anderson Department of Earth Sciences Monasli University Wellington Road Clayton, VIC 3168 marion@mail.earth.monash.edu.au Phone:9905-4896

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29* "Geological Catastrophism"

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CATASTROPHIC FLOODING ON MARS OR "BUT WE DON'T HAVE THE WOOD TO BUILD AN ARK!" Marion Anderson Department of Earth Sciences, Monash University, Clayton 3168

The History and Mythology of Water on Mars Mars has been a fascination for mankind since the earliest recorded history. To the ancient Babylonians and Sumerians the red planet was a great wolf, Nergal, with fangs dripping with plague and death - the caretaker of the underworld. To the Romans, Greeks and Egyptians, Mars (Ares, Horns) was the personification of the god of war, its red colour identified with the blood of corpses on battlefields. To modern man it is a solid ball of rock, its secrets unfolding with every picture sent back from the Viking, Pathfinder, Sojourner and Global Surveyor probes. It is only a matter of time before we set foot on its surface to better understand the genesis of the solar system, and the place of our own planet Earth within it. The motivation to travel to Mars will in part be the result of the pioneering work of several early astronomers and writers. Theories about the presence of water and flooding on Mars date back to the 19th Century. The Italian astronomer Giovanni Schiaparelli produced the first map of the surface of Mars in 1887. The map showed what appeared to be dark lines connecting some of the larger features. He called them "canali", meaning channels. The Italian word "canali" was frequently mistranslated into English as "canals", manmade features which were commonly used for transporting goods throughout Europe at the time. Inspired by the publicity about Schiaparelli's map, in 1897 H. G. Wells had the first version of his novel "War of the Worlds" published in Pearson's Magazine. Invaders from the dying planet Mars come to Earth, and on the brink of extermination the human race is saved by the bacteria in our atmosphere infecting and killing the hostile Martian forces. In 1910 the American astronomer Percival Lowell published "Mars as the Abode of Life". In this work he took Schiaparelli's "canali" and by long nights of observation turned the planet Mars into the home of a dying civilisation, their cities connected by vast networks of canals channelling water from the ice-covered poles to support the thirsty population. Edgar Rice Burroughs' Barsoom novels made travel to the planet Mars an easy task, all you had to do to travel across space was to reach out your arms and utter a heartfelt wish to be there. Once on the planet you were again in the realm of a dying civilisation, only this time there were lascivious princesses, four armed green Martians, giant white apes, and great tales of daring-do.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

23 It's a bit harder to get to Mars now than in Burroughs' books, but the images that have been returned from the landers and orbiters in the closing years of the 20th century are showing us a planet, which while apparently scarce in princesses and dying cities, is just as rich in food for the imagination.

Figure L

Viking Orbiter map of Mars showing significant features. VL = Viking Lander, MP = Mars Pathfinder, Image courtesy NASA.

The Channels of Mars Since the fly-by spacecraft Mariner 4 took images of the Northern Hemisphere of Mars in 1965, and Mariner 9 sent back global images of Mars in 1972, there has been speculation on whether Mars once had a surface covered in water. Many of the Mariner images showed what appear to be fluvial landforms. These landforms are broad meandering channels, predominantly located in four regions: - south of Amazonis Planitia (Mangala Vallis, Ma'adim Vallis, A1 Quahira Vallis) - in Xanthe Terra, between the chaotic terrain to the south and Chryse and Acidalia Planitiae to the north (Shalbatana Vallis, Simud Vallis, Tiu Vallis, Ares Vallis) - north of Lunae Planum, between Xanthe Terra and the Tharsis Montes (Kasei Vallis) - throughout the fretted terrain near Deuteronilus Mensae and Nilosyrtis Mensae, north of Syrtis Major (Auquakuh Vallis, Huo Hsing Vallis) (Mutch et al 1976). Sharp and Malin (1975) created the term "outflow channels" for these landforms to distinguish them from terrestrial fluvial features. They described the channels as ranging in size from a few kilometres up to tens of kilometres across, with many appearing to start at discrete sources in the chaotic terrain at the southern end of the Valles Marineris.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

24 The channels have few tributaries, but many branch and rejoin (after the fashion of braided river flows). They show a number of bedforms consistent with high volumes of water flow, have sinuous streamlined walls, and enclose teardrop-shaped islands. The channels tend to be deeper close to their sources than downstream, suggesting a catastrophic outpouring of liquid from a single source. The observed bedforms include plucked zones, longitudinal scour, and inner channel cataracts. (Carr 1996)

Figure 2. Tiu Vallis, from its source in the Hydaspis Chaos fi W, 28°W) to the end of the detectable channels (20°N, 37"^) Viking Orbiter image, courtesy of Mike Caplinger, Malin Space Science Systems.

Higher resolution images from the Viking orbiters in the mid 1970s allowed the first detailed maps to be made of the whole planetary surface, down to a resolution of 200 metres per pixel (picture element). The Viking images also 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

25 reinforced the presence of these fluvial landforms, giving more information about the potential source and sink areas for the floods. Images currently being received from the Mars Global Surveyor in orbit around Mars, from its Mars Observer Camera (MOC), have a resolution of up to 1.5 metres per pixel. This increase in resolution is enhancing our knowledge of many of the landforms, while at the same time destroying theories about the formation of others. The largest concentration of outflow channels is around the Chryse Planitia (20°N, 45°W). This is a broad plain, with a low concentration of craters suggesting that the surface is relatively young and has been reworked or covered since the heavy bombardment in the early stages of Mars' history. The plain is almost completely surrounded by cratered highlands, except to the north, where the channels appear to drain into the northern lowlands. The topography of the plain is generally flat, with elevations on average 1 km below the Mars datum. The Chryse Planitia channels (including the Tiu Vallis and Ares Vallis) start either in the cratered uplands, or in the chaotic region between 20°S to 5°N, and 15° W to 50° W. The chaotic terrain to the north east of the Valles Marineris consists of areas where the ground appears to have collapsed to form large collections of fallen blocks. These collapsed regions appear to be up to 12 km below the surrounding terrain, and the Ares and Tiu Valles appear to flow northwards out of these chaos regions. (Carr 1996) Other channels flow out of the Valles Marineris canyon system (Ophir, Hebes, Candor and Ganges Chasmas), and recent images of these areas show heavily layered terrain consistent with sedimentary layers forming over long periods of time (MSSS releases MOC2-59a, -59b, -59c, -59d, -59e; MOC2-15A, -15B, 15C). The largest of all the outflow channels is Kasei Valles, draining from Echus Chasma, a flat-floored, broad, north-trending depression just north of the Valles Marineris. This is thought to have carried the highest flow volume of all the outflow channels. (Carr 1996) The channels in all regions show some similarity of landforms, although many differ in the sub-sets of landforms displayed. The Chryse channels are distinctive by the presence of islands, surrounded by streamlined scour channels. These islands often form around a crater or another topographic obstruction. The erosion around the islands has created pointed prows upstream, and tapering tails downstream, while the flow is clearly indicated by the scourmarks. The channels also show the presence of deep grooves, several hundreds of metres across and tens of metres deep, consistent with catastrophic flood erosion patterns.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

26 The channels of the Elysium region originated along the north and northwest flanks of the Elysium rise, from graben-like depressions radial to the rise. These grabens widen into true sinuous flow channels to the north, and also show teardrop islands similar to those described above. Channels in the Eastern Hellas region are similar in morphology to those around Chryse. Mangala Vallis emerges from a graben in this region, but then becomes wider and more sinuous as it extends northwards, until it crosses the plains-upland boundary when it becomes too indistinct to trace further. (Carr 1996) From the analysis of cratering densities over the surface of Mars, and comparison with the density and geologic timescales created for the Moon, the history of Mars has been divided into a number of epochs. The dates of each epoch are not fixed yet, as it will require sample return missions before the dates can be more accurately estimated, but there are two main schemes: Epoch Amazonian Hesperian Noachian Table 1.

Hartmann-Tanaka dates (Gyr) 1.80-0.00 3.50-1.80 4.60 - 3.50

Neukum-Wise dates (Gyr) 3.55 - 0.00 3.80 - 3.55 4.60 - 3.80

Martian Epochs and Absolute Age Ranges based on Cratering Densities (After Tanaka et al 1992)

The majority of the outflow channels are Hesperian in age - they formed after the period of heavy bombardment, but still early in Mars' history - although one channel feeding out of the Elysium Planitia region shows almost no superimposed impact craters, and possibly dates from the Amazonian (Carr 1996, Scott etal 1992). The Source of the Waters A number of suggestions have been made for the origin of the water that created these outflow channels. Rain is unlikely, as there are almost no of tributary structures present in the majority of the channels. Another possibility is they formed as the result of freeze-thawing of water saturated ground. The most likely source is catastrophic outpourings of groundwater, either as a result of an aquifer rupturing as the result of an impact, or where an aquifer broke through to the surface. Another potential source is the catastrophic failure of a lake wall. The presence of groundwater on Mars has been used to explain many of the landforms observed, although under today's temperature and pressure conditions any groundwater present would be in the form of ice in the Martian regolith. Measurements of regolith porosity at the Viking lander sites yields a total global pore volume of approximately 8x10^ m^, or sufficient pore space to store a global layer of water 550 metres deep (Squyres et al 1992). This figure can be further refined if the topography of Mars is modelled, taking selfcompaction into account, resulting in a planetary groundwater depth of approximately 400 metres (Clifford 1993). 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

27

At the lowest points on the planet, in the Hellas region, the groundwater level is above the topographic contours, resulting in the chance of episodic floods if a high-pressure aquifer was punctured. Such outbreaks would be eventually selfsealing, both as a result of the local lowering of groundwater levels and the refreezing of the water-saturated regolith (Carr 1979, Clifford 1993). This would allow the gradual building of a lake within a canyon region that may eventually breach its end wall, resulting in a catastrophic flood, and forming outflow channels such as Mangala Vallis, originating in the Eastern Hellas region. Sharp and Malin (1975) suggested that Mangala Vallis formed from the breaching of a large lake, located at its headwaters, with the subsequent overflow and catastrophic failure of the reservoir walls. Where low-lying topography was ruptured, either by an impact, or by collapse of overlying regolith, the groundwater would escape to the surface, fed by the hydraulic pressure within the water-saturated layers (Carr 1996). Collapse outbreaks may have formed the chaotic terrain at the start of the Tiu and Ares Valles, and in the graben-fed channels in the Elysium region. A few minor channels in the Chryse region appear to originate from impact structures. The Voiume of Floodwaters Kasei Valles is one of the large outflow channel systems, appearing to drain from Echus Chasma (80° W, 1° N) northwards towards the plains. It covers a distance of over 1000 km, and has a cross sectional area of approximately 3.12x10'^ m^ (based on Viking Orbiter data). Robinson & Tanaka (1990) calculated the upper limit for the Kasei Valles discharges to be 1.23.5x10^ m^s"^ , in a flood that had a width of 83 km, an average depth of 347 metres, and a maximum depth of 1280 metres. The flood is proposed to have been the result of the breaching of a wall in a temporary lake that formed in Echus Chasma, part of the Valles Marineris canyon network. Earlier calculations of the flow velocities of the Maja, Ares and Mangala Valles (if assumed to be 100 metres deep) were 3 x l 0 W s ' \ 7 x l 0 W s " \ and 2 x l 0 V s ' ^ respectively (Baker 1982, Komar 1979). In order to understand the magnitude of these flood events it helps to take a look at known catastrophic terrestrial floods; the Pleistocene (15,000 years old) Lake Missoula floods in eastern Washington, USA, the Pliocene (5.33 million years ago) filling of the Mediterranean Basin, and the recent (7,600 years ago) flooding of the Black Sea. The floods from Lake Missoula that carved the Channelled Scablands (the Spokane Floods) created similar fluvial patterns to those seen in these channel regions of Mars as a result of a series of up to 30 wall-collapse outbreaks from meltwater-fed glacial Lake Missoula. The deposits of these floods were used as a model for the surfaces that could be expected by the Mars Pathfinder, and a version of the Sojourner rover was trialed on the Ephrata Fan deposits. The Lake Missoula outbreaks have been estimated to have peak discharge volumes

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

28 of up to 1.7x10^ up to one hundred times smaller than those of the Martian floods (O'Connor & Baker 1992). A recent version of this type of glacially-dammed outbreak flood was the jokulhlaup (glacial outburst) from the Grimsvotn volcano in Iceland on 5th November 1996. Volcanic activity melted the overlying Vatnajokull glacier, creating a huge lake within the 35 km^ volcanic caldera, the floodwaters held in place by the remaining overlying ice. When the water pressure had risen high enough and the breakout finally occurred, the flow is estimated to have been 55,000 m^s'\ smaller than that of the Lake Missoula floods, but the highest flow this century. (Source: http://www.eldhom.is/eruption/Grimsv.htm). It is clear from studies of the Scabland deposits that the maximum flow of each of the discharges would have been a short-term event, and each breakout would not have lasted more than a few days. This is also considered to be the case for the Amazonian floods on Mars (Baker 1973, Baker 1982). However, Carr (1996) notes that even if the Martian floods were only short-lived phenomena they still would have been able to transport up to 4x10^ km^ of sedimentary material in 6x10^ km^ of water from just the Chryse basin alone. It is estimated by Ryan and Pitman (1999) that the rate of flow involved in the breaching of the Bosphorus dam, and subsequent catastrophic flooding that resulted in the filling of the Black Sea, was 50 km^ per day, or 5.8x10^ The entrance to the Mediterranean at Gibraltar, 5.33 million years ago, was significantly larger than the entrance to the Black Sea at the Bosphorus. At its narrowest, the entrance at Gibraltar was 10 miles wide, and 300 metres deep, compared to 0.4 miles and 80 metres for the Bosphorus. A conservative estimate of the flooding of the Mediterranean made by Ken Hsii and William Ryan in 1973 was that it took less than 10 years to fill the Mediterranean basin with more than 1 million cubic kilometres of water (Ryan W. B. F., 1999, pers comm). This corresponds to a flow rate of 2.8x10^ m^s"\ making it the largest flooding reliably recorded on Earth and a flood of the same order of magnitude as the Maja, Ares and Mangala floods on Mars. Getting into the dirt

In order to better evaluate the likelihood of flooding on Mars, the Sagan Pathfinder and Sojoumer Rover were deployed into the area thought to be the mouth of the Tiu and Ares Valles. The images they sent back were a rich source of speculation, with arguments both for and against flood deposits from the same set of data. The topography of the landing site from orbit showed it to be an area of relatively smooth plains, with scattered hills that appeared to be remnants of an eroded surface, a number of nearby impact craters and the resulting debris, and clear evidence of aeolian deposits around many of the topographic high points. On the ground the site was found to show pronounced ridge and swale structures, with amplitudes as high as 5 metres and with crest to crest measurements of 15-25 metres. The trends of these ridges were southwest to 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^^ "Geological Catastrophism"

29 northeast and south to north, consistent with the flow directions evaluated from the Viking and Mariner images of the area. The rocks near the Pathfinder lander ranged from a few centimetres to a few metres in size, with some distant boulders being up to 7 metres in size. The mean diameter of the five largest boulders near the landing site is 1.8 metres. In shape they ranged from angular (assumed to be crater ejecta) to rounded (assumed to be the result of rounding during the floods). A number of rocks showed what appeared to be imbrication, with the direction of imbrication again consistent with the predicted flow directions. Subsequent aeolian action has carved flutes and grooves into larger exposed boulders, and left wind tails around all rocks observed. (Golombek et al 1997) A hard pale layer lies just under the aeolian dust across much of the site. Tests using the resistance of the Sojourner rover wheels suggest it is consistent with a compacted or an indurated layer, with some believing it to possibly be an evaporite.(Smith et al 1997) The gradient of the landing site is between 1 km in 400 km and 1 km in 1000 km, resulting in a flow velocity of 8 m/s, and a flow depth of between 10-20 metres. These are consistent with the values previously calculated for the flood plains as a whole, with discharges of between 10^ and 10^ This represents a drop in velocity of one to two orders of magnitude from previous flow calculations for the Ares and Tiu floods. (Smith et al 1997) The initial evaluation of the site was that the rock types, distribution, slope and geomorphology appeared to be consistent with the previously proposed flood theories. Subsequently other theories have been proposed to explain the boulder distribution - these will be discussed later. So where did the water go?

Following the initial reports of these flood deposits, a concerted search was made for evidence of the standing bodies of water that would have formed on Mars at the ends of the outflow channels. Parker et al (1989) identified shore features in the lower resolution Viking Orbiter images of West Deuteronilus Mensae as being wave terraces, beach ridges, arcuate or cuspate patterns, and coastal plains features such as ice-wedge polygons and pingos. This suggested the presence in the northern plains regions of a liquid or ice-covered sea at some time in the past. Further coastal geomorphological features were identified in the northern lowland basin region by Parker et al (1993). They suggested that lacustrine or marine deposition provided the simplest explanation of the observed features. However, closer analysis of the potential shorelines, in a paper released on 1st October 1999 by Malin and Edgett, has shown that there is no evidence for the previously inferred shoreline features. It suggests that the features were interpretations of the shadowed regions in the Viking images, and clearly 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

30 shows that when 'shorelines' are imaged by the Mars Global Surveyor, at resolutions five to ten times better than that provided by the Viking images, no traces of the wave terraces and beach ridges are visible. Topographically, there is still evidence that there is a basin region to the north of the flood plains consistent with water flowing northward from the chaos regions through the channelled regions. A single north polar ocean was suggested by Head et al (1998) based on data obtained from the Mars Orbiter Laser Altimeter (MOLA) and two potential shorelines previously proposed and mapped by Parker et al (1989, 1993). Head et al noted a significant change in surface roughness between the areas outside the boundaries of one of the two shorelines, and were able to form an equipotential surface which would contain an ocean with a volume of 1.5x10^ km^ consistent with the total volume of water proposed by Carr (1996), and the volume proposed by Baker et al (1992) of 8x10^ km^ (equivalent to a global ocean layer with a depth of about 100 metres). Aharpnson et al (1998) also used MOLA data to investigate the roughness of the Northem Plains, and noted that the variation in surface roughness in the Amazonis Planitia, where the Tiu and Ares Valles are located, is less than 2 metres over a 100 km baseline, with the rest of the northem hemisphere plains showing slopes of typically 1°. The only other planetary surfaces that show this elevation variation, and are also depositional, are oceanic abyssal plains and some sedimentary basins. It still seems possible that while no evidence appears to currently exist for geomorphological features produced by the dynamic action of ocean shorelines, the north polar region could have acted as a temporary holding basin for the proposed catastrophic floodwaters until they had time to dissipate back into the regolith, evaporate into the atmosphere, or freeze onto the polar caps. If the duration of holding was short enough, no large shoreline features would have been produced, and any small features that were created would have been eroded by aeolian processes in the intervening billion years or so. So, was it water at all?

Since the first Mariner images were analysed, there have been counter arguments for the role of water in the formation of the outflow channels. They can be broken down into a number of different hypotheses: ice flow, mass or debris flow, and CO2 supported mass flow. Lucchitta (1982) proposed the concept of ice flows to explain the morphology and nature of the chaotic terrain, suggesting that pre-existing water-carved valleys provided channels for either glacial flows or outwash from glacial melting. The lack of glacial moraines and tills identified to date in the Global Surveyor images makes this hypothesis increasingly unlikely. The possibility of some or all of the flow geomorphology being the result of lava flows has been raised since the work of Carr (1974) and Schonfeld (1977). 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

31 This possibility was later considered by Carr (1996) as being unlikely given the morphological differences between typical lava channels (deep and generally straight) and the observed outflow channels (wide and sinuous), but recent images from the Global Surveyor seem to have proved the lava theories right, in one basin at least. The Elysium Basin region was originally thought to be an ancient lake, now higher resolution images from MGS show it to be composed of lava flows. This means that Marte Vallis may no longer be a purely fluvial structure. It is suggested that it may once have been a fluvial valley that later acted as a conduit for a lava flow (McEwen et al. 1998) The suggestion that the flows may have been lubricated by CO2 was originally made by Sagan et al. (1973) and has recently been revived by Hoffman (1999), where he suggests that the outburst floods of the Amazonian can be successfully explained by modelling turbulent gas-supported flows, using terrestrial pyroclastic surges and submarine turbidites as analogues. This model requires a warming of the whole planet in the Amazonian, leading to the collapse and sublimation of CO2 ices in the regolith, as well as a significant increase in atmospheric pressure. At present, this seems unlikely. Chapman and Kargel (1999) argued that while there is significant evidence for water having played a part in the geomorphology of the Pathfinder landing site and the Ares Vallis region in general, there was insufficient evidence for it to be the result of a single flood event, suggesting instead the possibility of a combination of flood, mass flow, glacial and aeolian processes. This view was partly supported by Tanaka (1999) who points out that water flow rates as previously calculated are unable to emplace the metre sized boulders seen at Pathfinder site, as Komatsu and Baker (1997) suggested flow rates sufficient to transport boulders up to, but not exceeding, one metre in size. Tanaka proposed a debris flow origin for the current rocks found in the Tiu Vallis, while allowing a catastrophic flooding origin for the original canyons of the whole Xanthe Terra region, with subsequent debris flows being steered through preexisting water-cut channels. It is interesting to note that even though many of these alternative hypotheses propose arguments that explain the presence of rocks on the surface from transport other than water, most rely on the flows being transported through pre-existing water-carved valleys. The state of the art Despite the lack of oceans, at the Fifth Intemational Conference on Mars, in July 1999, the majority of presenters and researchers still appear to favour the concept of catastrophic flooding on Mars. Carr (1999) and Malin & Carr (1999) support the presence of water-cut outflow channels, with MOC images of the Nanedi Vallis suggesting that the river that cut the valley was fed primarily by groundwater. The analysis of the morphometry of the Chryse channels by Williams et al (1999) suggests that the

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

32 channels may in some cases flow uphill, implying either violent floods, or later tectonic warping of the Chryse region. Golombek et al (1999) in studying erosion rates at the Mars Pathfinder landing site argue for the presence of a catastrophic flood, with the climate at the time of the flood being significantly warmer and wetter than it is now. Ivanov & Head (1999) still support the possibility of a North Polar basin, based on MOLA data and profiles, with the circum-Chryse outflow channels emptying to the basin. More data is being obtained on a daily basis from the Mars Global Surveyor, and despite the loss of the Mars Climate Orbiter, the images being returned from the Surveyor will go a long way in the next few years to decide the fate of the theories regarding catastrophic flooding on Mars. The Mars Polar Lander, due to land on rolling plains near the South Polar cap on December 3rd 1999 will examine the soil types at the landing site, determine its composition and the subsurface ratios of CO2 to water ice. In addition it will monitor the seasonal changes at the landing site. Future missions will be dedicated to further analysis of the flood topography, as well as the possibility of life on Mars. Perhaps in a few years time we will be able to answer the question "did Mars once experience floods of the magnitude of those that filled the Mediterranean and the Black Sea?" for once and for all.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

33 REFERENCES

Aharonson, O.; Zuber, M. T.; & Neumann, G. A., 1998, "Mars: Northern hemisphere slopes and slope distributions", Geophysical Research Letters, 25, 4413-4416 Baker, V. R., 1973. "Paleohydrology and sedimentology of Lake Missoula flooding in eastern Washington", Geological Society of America Special Paper 144, 1-79. Baker, V. R., 1982 "The Channels of Mars", University of Texas Press, Austin Baker, V. R.; Carr, M. H.; Gulick, V. C.; WiUiams, C. R., & Marley, M. S., 1992, "Channels and Valley Networks", in "Mars", Keiffer, H. H., et al, eds.. University of Arizona Press, Tuscon, 493-522 Carr, M. H., 1974, "The role of lava erosion in the formation of Lunar Rilles and Martian Channels", Icarus, 22, 1-23. Carr, M. H., 1979, "Formation of Martian flood features by release of water from confined aquifers", Journal of Geophysical Research, 84, 2995-3007 Carr, M. H., 1996, "Water on Mars", Oxford University Press, Oxford Carr, M. H., 1999, "Global History of Water on Mars", The Fifth Intemational Conference on Mars, July 18-23, 1999 Chapman, M. G., & Kargel, J. S.; 1999, "Observations at the Mars Pathfinder site; Do they provide "unequivocal" evidence of catastrophic flooding?", Journal of Geophysical Research, 104, 8671-8678 Clifford, S. M., 1993, "A model for the hydrologic and climatic behaviour of water on Mars", Journal of Geophysical Research, 98,10973-11016 Golombek, M. P.; Cook, R. A.; Economou, T.; Folkner, W. M.; Haldemann, A. F. C.; Kallemeyn, P. H.; Knudsen, J. M.; Manning, R. M.; Moore, H. J.; Parker, T. J.; Rieder, R.; Schofield, J. T.; Smith, P. H., & Vaughan, R. M., 1997, "Overview of the Mars Pathfinder Site Mission and Assessment of landing Site Predictions", Science, 278, 1743-1748 Golombek, M. P., & Bridges, N. T., 1999, "Climate change on Mars inferred from erosion rates at the Mars Pathfinder landing site". The Fifth Intemational Conference on Mars, July 18-23, 1999 Head, J. W., HI; Kreslavsky, M.; Hiesinger, H.; Ivanov, M.; Pratt, S, & Seibert, N., 1998, "Oceans in the past history of Mars: Tests for their presence using Mars Orbiter Laser Altimeter (MOLA) data". Geophysical Research Letters, 25, 4401-4404 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29* "Geological Catastrophism"

34 Hoffman, N., 1999, "White Mars: A global evolution model for Mars' surface based on CO2", The Fifth International Conference on Mars, July 18-23, 1999 Hsii, K. J., 1983, "The Mediterranean was a Desert: A Voyage of the Glomar Challenger". Princeton University Press, Princeton Komar, P. D., 1979, "Comparisons of the hydraulics of water flows in Martian channels with flows of a similar scale on Earth", Icarus, 37, 156-181 Komatsu, G., & Baker, V. R., 1997, "Paleohydrology and flood geomorphology of Ares Vallis", Journal of Geophysical Research, 102, 4151-4160 Lucchitta, B. K., 1982, "Ice sculpture in the Martian Outflow Channels", Journal of Geophysical Research, 87, 9951-9973 Malin, M. C., & Carr, M. C., 1999, "Groundwater formation of Martian valleys". Nature, 397, 589-591 Malin, M. C.; & Edgett, K. S., 1999, "Oceans or seas in the Martian northern lowlands: High-resolution imaging tests of proposed coastlines". Geophysical Research Letters, 26, 3049 McEwen, A. S.; Edgett, K. S.; Malin, M. C.; Keszthelyi, L., & Lanagan, P., 1998, "Mars Global Surveyor Camera Tests the Elysium Basin Controversy: It's Lava, Not Lake Sediments," Geological Society of America Annual Meeting, October 29, 1998. MSSS images: Mars Global Surveyor - Mars Orbiter Camera Release: MOC2-15A, -15B, 15C; http://www.msss.eom/marsjmages/moc/ll_10_97__release/1303/index.html Mars Global Surveyor - Mars Orbiter Camera Release: MOC2-59a, -59b, 59c, -59d, -59e; http://www.msss.com/marsjmages/moc/7_20_98_marineris_rel/index.html Mutch, T. A.; Arvidson, R. E.; Head, J. W., HI; Jones, K. L., & Saunders, R. S, 1976, "The Geology of Mars", Princeton University Press, Princeton, New Jersey. O'Connor, J. E., & Baker, V. R., 1992 "Magnitudes and implications of peak discharges from glacial Lake Missoula", Geological Society of America Bulletin, 104, 267-279 Parker, T. S.; Saunders, R. S., & Schneeburger, D. M., 1989, "Transitional morphology in West Deuteronilus Mensae, Mars: Implications for modification of the lowland/highland boundary." Icarus 82, 111-145 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

35 Parker, T. S.; Gorsline D. S.; Saunders, R. S.; Fieri, D., & Schneeburger, D. M., "Coastal Geomorphology of the Martian northern plains". Journal of Geophysical Research, 98, 11061-11078 Robinson, M. S., & Tanaka, K. L., 1990, "Magnitude of a catastrophic flood event at Kasei Valles, Mars", Geology, 18, 902-905 Ryan, W., & Pitman, W. C., 1999, " Noah's Flood: The New Scientific Discoveries About the Event That Changed History", Simon & Schuster, New York Sagan C.; Toon, O. B., & Gierasch, P. J., 1973, "Climate change on Mars", Science, 181, 1045-1049 Schonfeld, E., 1977, "Martian Volcanism", Proceedings Lunar & Planetary Sciences Conference, Vm, 843-845 Scott, D. H.; Chapman, M. G.; Rice, J. W., & Dohm, J. M., 1992, "New Evidence of lacustrine basins on Mars: Amazonis and Utopia Planitia", Proceedings Lunar & Planetary Sciences Conference, 22, 53-62 Sharp, R. P., & Malin, M. C., 1975, "Channels on Mars", Geological Society of America Bulletin, 86, 593-609 Smith, P. H.; Bell, J. F, HI; Bridges, N. T.; Britt, D. T.; Gaddis, L.; Greeley, R.; Keller, H. U.; Herkenhoff, K. E.; Jaumann, R.; Johnson, J. R.; Kirk, R. L.; Lemmon, M.; Maki, J. N.; Malin, M. C.; Murchie, S. L.; Oberst, J.; Parker, T. J.; Reid, R. J.; Sablotny, R.; Soderblum, L. A.; Stoker, C.; Sullivan, R.; Thomas, N.; Tomasko, M. G.; Ward, W., & Wegryn, E., 1997, "Results from the Mars Pathfinder Camera", Science, 278, 1758-1764 Squyres, S. W.; Clifford, S. M.; Kuzmin, R. O.; Zimbelman, J. R., & Costard, F. M., 1992, "Ice in the Martian regolith", in "Mars", Keiffer, H. H., etal, eds., University of Arizona Press, Tuscon, 523-554 Tanaka, K. L.; Scott, D. H., & Greeley, R., 1992, "Global Stratigraphy", in "Mars", Keiffer, H. H., et al., eds.. University of Arizona Press, Tuscon, 345382 Tanaka, K. L., 1999, "Debris-flow origin for the Simud/Tiu deposit on Mars", Journal of Geophysical Research, 104, 8637-8652 Williams, R. M, & Phillips, R. J., 1999, "Morphometry of Circum-Chryse outflow channels: Preliminary results and implications". The Fifth International Conference on Mars, July 18-23, 1999

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36

^^Catastrophism and the Earth^s InteriorI I f s not all calm under the surface^^ Dr. Bob Musgrave Department of Earth Sciences LaTrobe University Bundoora, VIC 3083 R.Musgrave@latrobe.edu.au Phone: 9479-2145

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29"' "Geological Catastrophism"

37 CATASTROPHISM AND THE EARTHS INTERIOR! IT'S NOT ALL CALM UNDER THE SURFACE

Bob Musgrave Department of Earth Sciences, LaTrobe University, Bundoora, VIC 3083 Introduction

In the last few decades earth scientists have come to appreciate that - basic as it is to our understanding of most geological processes - the Principal of Uniformitarianism is not applicable to all aspects of geological history. The present ceases to be the key to the past when the past event being contemplated is catastrophic. Palaeontologists have always implicitly realised this - the basis of many of the major divisions of geological time is the catastrophe of global mass extinction. Other branches of the earth sciences have been slower to take this idea in - at the forefront of "catastrophic geology" have been the studies of the sudden inundation of the Mediterranean and Black Seas, the "dam-break" origin of the U.S. scablands, and studies of bolide impact features. If Earth processes have traditionally been considered to proceed at a slow and steady pace, the deep internal geophysical behaviour of the Earth has been seen as the most stately of all. Below the zone of seismic activity, all was usually regarded as quiet. The geophysical signal of the deep interior, the geomagnetic field, may exhibit both short term secular variation and longer term reversals of polarity, but these were seen as slightly more complex twists on otherwise "simple" magnetohydrodynamics in the fluid outer core - the sort of behaviour that could be simulated by a pair of self-exciting dynamos (Rikitake, 1958). More recently, we have come to realise just how complex and non-linear chaotic - the behaviour of the outer core really is. Supercomputer modelling is beginning to simulate the patterns seen in secular variation, and even to indicate how magnetic reversals occur. But beyond non-linear behaviour, the earth's field periodically exhibits something more dramatic - a complete change in its modus operandi, where a pattern of more and more frequent polarity reversals abruptly stops, and is replaced by a long interval of constant polarity. To magnetostratigraphy, this is as dramatic and profound a change as a mass extinction is to biostratigraphy. And if the geological evidence for bolide impacts is the "smoking gun" for at least some mass extinctions, the "extinction" of polarity reversals may have an equally dramatic geological corollary - the eruption of massive plume heads. Some background... Non-linear behaviour characterises the Earth's magnetic field on a variety of timescales (Figure 1). Secular variation of the geomagnetic field - changes in the local direction and intensity of the field, typically amounting to about 0.2% of the total field per year - shows highly complex and non-repeated fluctuations superimposed on roughly cyclic behaviour, with a period of the order of 10^ 10 years. On a far longer timescale, the earth's magnetic field periodically inverts its polarity, between a "normal" field (similar to the present 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

38 geomagnetic field) and a "reversed" field (in which a compass would point south). These reversals occur at quasi-random intervals from about 20 000 years to more than 10 million years, and are completed in geologically short times (< 10 000 years).

60

Quaternary

Palaeocene

Pliocene

Q> c Ss

Mtestrichtian

10

70

Miocene iS 20& Q>

Campanian - 80 Santonian

HnniflSfla

Oligocene

•30

Xuronian

90

Cenonnanian

o c

100

8)

8

iS 7R OJ Q.

Eocene

Albian

110 Aptian Palaeocene

Figure 1,

Early Cretaceous to recent magneto stratigraphy of Cox (1982). Note the long interval of constant normal polarity during the early to middle Cretaceous - the Cretaceous superchron - and the increasing frequency of reversals of polarity since that time. Are we due another catastrophic "magnetostratigraphic extinction" - and will it be linked to massive LIP volcanism?

Although the pattern of polarity reversals appears random on a 10-million-year scale, broad cycles in the frequency of reversals are evident on 100-millionyear scales. Polarity reversals have increased from <0.2 reversals/m.y. in the late Cretaceous to around 4 reversals/m.y. in the late Cainozoic. An exceptionally long interval of constant polarity occurred in the Cretaceous, between 105 and 85 Ma, when polarity remained normal (the "Cretaceous Normal Superchron"). An even longer interval of constant polarity, in this case reversed, spans the late Carboniferous and Permian, from 290 to 235 Ma. Termed the Kiaman Superchron, this long reversed interval was first identified in rocks from the upper Carboniferous and Permian of New South Wales (Mercanton, 1926; Irving & Parry, 1963; Irving, 1966). Both the Cretaceous

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

39 and Kiaman Superchrons are an order of magnitude longer than any other known polarity intervals. A second feature of polarity reversals, which initially appears unrelated, has been observed in studies conducted during the last few years. Detailed studies of rapidly deposited sediment sequences spanning the most recent major change in polarity (780 ka) indicate that the field during the transition behaved as though it were produced by magnetic poles wandering from their reversed position to their present position. Surprisingly, the path followed by the poles appears not to be fully random, but to be restricted to two narrow bands, one passing through the Americas and the other through east Asia and Australia. The same paths were seen to be followed irrespective of the geographic position of the sampled sediments, and similar observations have been made for other recent polarity reversals. While it is generally agreed that the geomagnetic field arises from convection systems within the electrically conducting liquid-iron outer core, simple linear mathematical models are generally inadequate to describe the field. Some form of asymmetry in the convection systems is required to produce a poloidal field and to initiate polarity reversals and secular variation. Two contributions to asymmetry have been suggested; radial asymmetry due to shear flow within the outer core, and zonal asymmetries produced by local irregularities in heat transmission across the core - mantle boundary. Both mechanisms have been recently confirmed by seismic tomography. Shear results from the slightly faster rotation of the inner core compared to the mantle (Song & Richards, 1996). Irregularities in the thickness and temperature of the boundary layer at the base of the mantle (the D" layer) provide the local temperature asymmetry.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29"^ "Geological Catastrophism"

40

Age (Ma) Ot=

i

^

.y og

K J

^ ^ ^ J m l "Magnetic radiation" "Magnetic extinction" 200-

Tr P C 1

§

S.

"Magnetic radiation" 300-

"Magnetic extinction"

D S

Normal superchron

O

Reversed superchron

H

Alternating polarity

C

Figure 2,

Poorly known

Patterns of superchrons and periods of rapidly alternating magnetic polarity. To magnetostratigraphers, the onset of a superchron is as a mass extinction is to biostratigraphers - a sudden decline in the "diversity" of magnetic polarity behaviour, followed later by the equivalent of a radiation - the recovery of rapid variability in the outer core dynamo.

Local temperature differences in the D" layer represent the pooling of ancient subducted slabs from long-lived subduction zones - particularly those of the "ring of fire" on the eastern and western margins of the Pacific - which can be traced below their long-known expression in the uppermost 700 km of the mantle, right down to the core-mantle boundary (Grand et al., 1997). At the core-mantle boundary the slabs accumulate, apparently producing the irregular D" layer. This layer is thickest below the regions where the slabs from the longest-lived subduction systems are arriving - in positions corresponding to the zonal bands followed by the magnetic poles during recent reversals. The association suggests that some effect of the D" layer - probably its lower temperature - controls the behaviour of core convection during polarity reversals. Mantle plumes - responsible for the eruption of flood basalts and hot-spot volcanoes - may arise from the D" layer, as a mechanism by which slab material eventually returns to the upper mantle after it thermally equilibrates and so becomes buoyant. It has been suggested that the outbreak of multiple "large igneous provinces" (particularly the Ontong Java and Manihiki Plateaus in the Pacific) may represent a period of substantial reduction of the D" layer; the coincidence of these events with the beginning of the Cretaceous long normal polarity interval may represent a fundamental change to the symmetry 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

41 of the outer core convection system as a result of the changed boundary thermal conditions, resulting in a marked reduction in the frequency of reversals until continued subduction has once again built up a significant thickness (or nonuniformity in thickness) of the D" layer (Tarduno et al., 1991). If irregular topography in the D" layer controls asymmetric behaviour in outer mantle convection cells, this should be expressed in features of the secular variation. We might expect, for example, that the field during the Kiaman or Cretaceous long polarity intervals would exhibit much smaller magnitude secular variation. Accumulation of slab material preceding one of these phases of mantle overturn will have been controlled by a different geographic distribution of subduction, and so the magnetic poles during a transition at this time should have migrated along distinctly different pathways to modem transitions. Another approach to understanding the non-linear behaviour of the field has been supercomputer finite-cell modelling of outer core magnetohydrodynamics, which can simulate changes in flux patterns on a yearly basis over periods long enough to represent multiple polarity reversals (Glatzmeier & Roberts, 1995a, 1995b). Such models are strongly controlled by variations in outer core shear and core-mantle heat transfer (Glatzmeier et al, 1997), and have the potential to be integrated with the seismic tomography evidence described above. An important output of the modelling conducted so far is the apparent link between noisy activity of the field on secular-variation timescales and the frequency of polarity reversals; secular variation appears to be greatly reduced in magnitude, and the field much closer to a true axially-geocentric dipole, during extended periods of constant polarity (McFadden et al, 1995). An obvious means to test the validity of the magnetohydrodynamic modelling, and to provide constraints that could help link the supercomputer modelling to the tomographic observations, would be a measure of the magnitude and structure of secular variation during one of the two periods of extended constant polarity, for comparison with the well studied secular variation of the modem field. Indeed, attempts have been made to examine the secular variation during both the Cretaceous and Kiaman Superchrons (Tauxe et al, 1997; Rochette et al., 1997), but these were limited by the lack of a geological record of the field at anything better than a few-thousand-year scale; even the most rapidly deposited lake or marine sediments preserved from the Mesozoic or Palaeozoic usually represent hundreds to thousands of years within the minimum resolvable thickness of a palaeomagnetic sample (e.g., Acton et al, 1997). Determining the magnitude and cyclic stmcture of secular variation in such studies involves complex deconvolution over many secular variation cycles, with debatable information content. A far better test would be possible if a rock sequence from one of the longconstant polarity intervals that recorded changes in the past field on a very rapid timescale - essentially year-by-year - could be found. The oversampling involved - yearly changes in the field are less than the resolution possible for palaeomagnetic directions - allows very substantial smoothing, resulting in the 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

42 elimination of the noise which usually obscures palaeo-secular-variation records. Such studies are familiar enough for sediment sequences from the last few million years, but a study from one of the long-polarity intervals would be exceptional in rocks of this age, and probably unique. A suitable target for such a test is the late Carboniferous Seaham Formation, a glacigene sequence in the Hunter Valley in NSW (Campbell et al., 1969). This contains a series of sections in which mudstones showing fine laminations altemate with fine sandstones on about a 1-cm scale. Given the usual interpretation that the Seaham Formation does include sequences of glacial varves, it is an ideal target. Its age places it near the beginning of the Kiaman interval, so it should preserve secular variation under conditions where the D" layer is thinnest and most uniform. It may even preserve a complete or partial polarity reversal, allowing a direct study of zonal transition behaviour. Studies of this type using carefully selected targets are critical to furthering our understanding of deep-seated catastrophes. The bottom line,For geomagnetists, a study of the year-by-year secular variation during a Superchron will be equivalent to the discovery of the iridium anomaly in the Cretaceous-Tertiary boundary shale - a tantahsing view of an "instant" of geological time, when catastrophic events changed the way the Earth functioned.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

43 REFERENCES

Acton, G.D., Clement, B.M., Lund, S.P., Okada, M., Williams, T., and the Leg 172 Shipboard Scientific Party, 1997. Eos, 78, no. 46 (AGU Fall Meeting), p. F181. Campbell, K.S.W., Engel, B.A., McKelvey, B.C., Roberts, J., and Nashar, B., 1969. The Geology of New South Wales, J. Geol. SocAust, 16,1, 245-265. Glatzmeier G.A., & Roberts, P.H., 1995a. Phys. Earth Planet. Inter., 91, 63. Glatzmeier G.A., & Roberts, P.H., 1995b. Nature, 377, 203. Glatzmeier, G.A., Roberts, P.H., & Coe, R.S., 1997. Eos, 78, no. 46 (AGU Fall Meeting), p. F194. Grand, S.P., van der Hilst, R.D., & Widiyantoro, S., 1997. GSA Today, 7, no. 4, 1-7. Irving, E., 1966. J. Geophys. Res., 71, 6025-6051. Irving, E., and Parry, L.G., 1963. Geophys. J., 1, 395-411. McFadden, P.L., Merrill, R.T., McElhinny, M.W., and Lee, S., 1995. J. Geophys. Res., 96, 3923-3933. Mercanton, P.L., 1926. Terrest. Magnetism Atmospheric Elec., 31, 187-190. Rikitake, T., 1958. Proc. Cambridge Phil. Soc., 54, 89-105. Rochette, P., Vandamme, D., Vlag, P., Simon, L., & Feraud, G., 1997. Eos, 78, no. 46 (AGU Fall Meeting), p. F194. Song, X., & Richards, P.G., 1996. Nature, 282, 221-224. Tarduno, J.A., Sliter, W.V., Kroenke, L., Leckie, M., Mayer, H., Mahoney, J.J., Musgrave, R., Storey, M., and Winterer, E.L., 1991. Science, 254, 399403. Tauxe, L., Constable, C, & Pick, T., 1997. Eos, 78, no. 46 (AGU Fall Meeting), P.F193.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 19* "Geological Catastrophism"

44

^^he mtastrophism of volcanic phenomena : never underestimate the scale and the ejfects^^ Professor Ray Cas 1998 Selwyn Medalist Department of Earth Sciences Monash University Wellington Road Clayton, VIC 3168 rcas@mail.earth.monash.edu.au phone: 9905-4897

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct iS^ "Geological Catastrophism"

45

THE CATASTROPHISM OF VOLCANIC PHENOMENA: NEVER UNDERESTIMATE THE SCALE AND THE EFFECTS Ray Cas Earth Sciences Dept., Monash University, Wellington Rd Clayton, Victoria 3168 Introduction Volcanic processes have been fundamental to the origin and evolution of the Earth. Volcanic processes formed the crust, volcanic gases sourced the atmosphere and oceans, and it is now considered that life originated in subsurface, or subterranean volcanic hydrothermal systems (Davies, 1998). Volcanic rock systems also host a wide range of magmatic and hydrothermal mineral deposits, and geothermal energy is a major source of power. Of all the known geological processes, volcanic phenomena are amongst the most catastrophic. The effects are not always instantaneous. The scale of the phenomena can vary from local to global spatially, and temporally from instantaneous to years, or even hundreds to thousands of years after a major eruption. Volcanic eruptions can lead to major destruction of property, loss of life, and even major extinctions. Processes associated with volcanic terrains can be subdivided into those that are syn-eruptive to those that are post-eruptive. Syn-eruption processes include primary eruptions and derivative sedimentary or gravitational surface processes, and post-eruptive processes consist wholly of the latter. Primary eruptive processes include effusive lava forming processes, and explosive eruptions. Lava forming processes Most lava forming eruptions are not instantaneously catastrophic, because the rates at which lavas are erupted and their flow velocities are not high enough. However, lavas, especially low viscosity basaltic lavas (and in the Archaean komatiite lavas), can flow long distances, and spread over large areas, so devastating the landscape over which they flow. For example, in Hawaii, an eruption has been nearly continuously active for 16 years, producing large new lava flow fields that have destroyed and buried several townships. The largest lava forming systems are basaltic flood basalt provinces. These cover areas of up to 10^ kmsl and have volumes up to 10^ - 10^ kms^. Individual flood basalt lavas are known to have flowed up to 500 kms from vent, and have volumes of 700 kms^ To achieve these flow distances, it was thought that flood basalts must have been high velocity, and therefore very turbulent flow systems (Figure la). If this were true, then flood basalts would have been instantaneously catastrophic. Turbulent flow however causes significant heat loss and this increases the viscosity of the lava to the point of 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

46 causing the lava to solidify (Ho & Cashman, 1997; Keszthelyi & Self, 1998). Under tranquil laminar flow conditions, a surface crust forms on the lava surface, so insulating the interior tube lava from heat loss. Such a laminar flow crust-tube system is more conducive to long distance flow than turbulent flow (Figure lb). Cas et al (in press) have also concluded similar results for ultralow viscosity Archaean komatiite lavas. A major consequence of the new model for flood basalt systems, magma discharge rates must have been lower, and eruptions must have lasted considerably longer than previously thought, probably tens of years. The effects of this on climate are considerable, as discussed further below. The new model also explains why some basalt and komatiite lavas are anomalously thick given their low viscosity. Final preserved lava flow thicknesses do not represent the actual thickness of the lava flow front at the time of flow and emplacement. Lava flow fronts are thin compared with the interiors. Flows progressively thicken as lava is injected through the interior tube under the crust towards the advancing flow fronts.

(b) Lava tube - crust laminar flow model

Progressive flow inflation and thiclcening

Lava tube

Figure 1.

(a) Schematic representation of the early flood basalt flow model depicting flows as highly turbulent, high velocity, essentially catastrophic flows, (b) Schematic representation of the new non-catastrophic laminar flow, crust-tube flow model for basaltic flood lavas.

Explosive eruptions Explosive eruptions generally produce buoyant eruption columns and downwind plumes of gas, ash, pumice and lithic debris, that rise into the atmosphere through explosive thrust, turbulent convection, and density controlled buoyancy (Figure 2a). Columns may be over 50 kms high. Two general groups of pyroclastic phenomena and deposits form. First, as

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

47 convective turbulence wanes, fallout deposits mantle the landscape. These can be metres to tens of metres in thickness near vent, and can be deposited hundreds to thousands of kms from vent. Crops and buildings are destroyed by the effects. Micron size ash in size may remain suspended in the stratosphere for years, and together with released volcanic gases, can produce significant climatic effects. The second major explosive volcanic phenomenon and deposit type are pyroclastic flows and their deposits. Pyroclastic flows are variably turbulent, hot, gravity controlled flows of gas, ash, pumice and lithic debris. The volumes of their deposits range up to 1000 km^ and more (Lipman et al. 1997), their witnessed flow velocities are over lOOkm/hr, the calculated velocities for some of the most violent are 600km/hr, and the maximum flow distances are up to 250 kms. Single event deposits may be tens to hundreds of metres thick. For example, the June 15, 1991 eruption of Mt. Pinatubo produced almost 7 km^ of pyroclastic flow deposits in 6 hours, and the deposits are up to 200 m thick in places. Pyroclastic flows are the most destructive and catastrophic primary volcanic processes known. They are capable of destroying all man- made structures instantaneously, and causing massive deaths instantaneously. For example, pyroclastic flows from the eruption of Mt. Pelee on Martinique in 1902 completely destroyed the town of St. Pierre and killed 30,000 people. There were only 2 survivors, who were safely locked up in strongest building in town, the gaol.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

48 Pyroclastic flows form when eruption columns become too dense, due to high solids contents, and collapse gravitationally (Figure 2b; e.g. Mt. Pinatubo, 1991), and when viscous, high relief gas rich lava domes collapse gravitationally or explosively (e.g. Mt. Unzen, Japan, 1991-1995).

(b)

(a) p column atmosphere

p column >p atmosphere WIND

400

Figure 2.

- 600m^

s'^

pumice flow

(a) Buoyant eruption column of hot gas, ash, pumice and lithic debris that rises above a vent during a major, maintained, explosive eruption due to the low bulk density of the column relative to the atmosphere, the initial explosive thrust and momentum from the vent and the convective energy of the column. Fallout deposits extend hundreds or more kilometres from the vent, (b) Collapsing eruption column due to overload of solids, causing a dynamic turbulent pyroclastic flow of gas, ash, pumice and lithic debris.

Volcanic eruptions and climate change Explosive eruptions release large volumes of fine suspended ash into the stratosphere. This suspended ash may remain suspended for years, and if the volumes are large enough, may lead to an increase in the albedo of the Earth's atmosphere, and reduced solar insolation. Both explosive eruptions and lava forming eruptions may release large volumes of gases to the atmosphere. Release of H2O and CO2 may in large enough quantities affect albedo and/or enhance the atmosphere "greenhouse" effect. The "aerosol" gases, especially SO2, have two effects. SO2 readily combines with H2O to produce H2SO4 vapour droplets (Figure 3). These significantly affect albedo. In addition, H2SO4, and HCl and HE produced by the combination of CI2 and E2 with water, can lead to hemispherically, and even globally significantly acid rain, and both HCl and HE reduce O3 levels. Both increased albedo and acid rain can produce crop or food chain failure, producing short term catastrophism for both lower and higher order organisms.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

49

Increased Planetary Albedo Stratosphere

hv&OH

Heterogeneous Chemistry NgOg HNO3 . CIONO2 CIO HCI

n ^ l P ^ ^ , - . warding Nucleation and Particle Growth Rainout H2O. HCI. Ash

Removal Processes

Cirrus Modification

Infrared Surface cools

Figure 3,

Schematic diagram showing interaction between volcanic gases and atmosphere in effecting climate change (from McCormick, et al, 1995).

Long lived reductions in albedo can induce, or accelerate climate change. Examples of the effects of ash and aerosol release into the atmosphere include: • Mt. St. Helens, U.S.A., 1980 (Rampino et al, 1988) • 0.3 megatonnes of H2SO4 • Negligible surface cooling • El Chichon, Mexico, 1982 (Rampino & Self, 1984) • 20MtH2S04 • surface cooling, -0.2°C • Mt. Pinatubo, Philippines, 1991 (McCormick, et al, 1995) • 30MtH2S04 • surface (tropospheric) cooling . -0.5"C globally -0.7°C in northern hemisphere • Krakatau, Indonesia, 1883 (Rampino & Self, 1992) • 50Mt.H2S04 • Surface cooling of >-0.7°C • Toba, Indonesia, 73 ka (Rampino & Self, 1992) • 1000 (-5000) Mt. H2SO4 • surface cooling of - 3-5°C for 3-4 years • ?acceleration of glacial stage • Roza flood basalt, U.S.A., 14.7 Ma (Thordarson & Self, 1996) • 12,500 Mt.H2S04 • 710'^ year long eruption • ?- 5-15®C surface cooling • volcanic winter • also 710 Mt. HCI, 1780 Mt. HP 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

50

•

• significant O3 depletion Major flood basalt events • ^ each 30 Ma • ?coincide with major impact events • ?coincide with significant/major extinction events (e.g Permian extinction, Siberian flood basalts) (Rampino, 1987) • cooling and acid rain destroys food chains

Rice (1990) and Coffin & Eldholm (1993) attribute warming periods (e.g. K/T boundary) to excess release of CO2 derived from accelerated mantle convection and sea floor spreading, and flood basalt events. Catastrophic Surface Processes Associated With Volcanic Terrains Landslides and debris avalanches Stratovolcanoes are large steep sided volcanoes (e.g. Mt. Fuji) that rise 2-3 kms above their bases often with slopes of 20"" or more. Since the spectacular eruption of Mt. St. Helens in 1980, which commenced with a major landslide (Figure 4), it has become apparent that many, perhaps half of the world's stratovolcanoes have experienced these destructive phenomena. Because of the high potential energy of the slide masses, often given extra momentum by concomitant explosive thrust, the initial landslide masses quickly disintegrate into rock flows or debris avalanches. Debris avalanches can travel at velocities up to hundreds of kms/hour, and can flow up to tens of kms from source. Although they are gravitationally controlled, they are also capable of surmounting substantial topography. The Mt. St. Helens debris avalanche travelled almost 30 km from source (Voight et al 1981). The largest known volcanic debris avalanche is the Socompo Volcano debris avalanche in Chile, which flowed 40 kms from source, and has an estimated surface area of 600 kms^ (Francis etal 1985).

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

51

?5Q0

\ 2000

1500

D

i 1

V>N V^N

::^

8000

J \ —

8000

4000

Figure 4. Cartoon representation of the initial stages of the Mt. St, Helens eruption on May 18, 1980, showing initial landslide collapse of the bulging northern face, succeeded by the lateral blast flow and development of a buoyant eruption column (from Moore and Albee, 1981). Tsunamis

Tsunamis are large solitary waves of water caused by processes capable of rapidly displacing large volumes of water in large lakes or oceans. Mechanisms include sudden sea floor displacement or faulting (e.g. the Sissano event, PNG, 1998; sudden collapse of submarine calderas), major landslides 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

52 from volcanic edifices into the sea, and the passage of large volume pyroclastic flows into the sea (Figure 5).

ih)

4

ul'i^f^'

Figure 5. Experimental tsunami or solitary wave resulting from the passage of a density current, simulating a pyroclastic flow into the body of water (from Monaghan et al 1999).

Major tsunamis up to 20 m high were generated during the 1883 eruption of Krakatau, probably by a combination of causes (sea floor faulting, caldera collapse, explosive displacement, entry of pyroclastic flows into the sea). I

Svn- to post-eruptive torrent floods, hvperconcentrated flood flows, "lahars"

The deposition of large volumes of unconsolidated pyroclastic debris of the slopes surrounding volcanoes by pyroclastic debris on the slopes surrounding volcanoes by pyroclastic fallout and pyroclastic flows creates another major hazard. Significant rainfall for years after such an eruption will remobilise this pyroclastic debris into torrent flows of hyperconcentrated flood flows. The increased sediment load upsets hydrological regimes, leading to choking of channels, aggradation of the beds of rivers, and spreading of the beds on to flood plains, transforming single river channels into braid plains kilometres wide. The agricultural plains and villages around Mt. Pinatubo were buried 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

53 under debris after the 1991 eruption. It is likely to be 20 years until the rivers regain equilibrium (Figure 6).

Mount Pinatubo 1,000

E

I

800

4-

Actual Low

o

^O

—

—Best fit

600 +

•o

c o

400-o tn "cS 3 C C <

2 0 0 --

t

1990

Figure 6.

t

i

I

M

I

2010

Graph showing exponentially declining river sediment yield after the eruption of Ml Pinatubo on June 15, 1991. The sediment is almost all remobilised volcanic ash. It will take 20 years after the eruption for the rivers to achieve equilibrium (from Philippine Institute ofVolcanology and Seismology).

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29^ "Geological Catastrophism"

54 REFERENCES COFFIN, M.F. & ELDHOLM, O. 1993. Large igneous provinces. Scientific

American 269(3), 26-33.

CAS, R.A.F., SELF, S. and BERESFORD, S. in press. The behaviour of the fronts

of komatiite lavas in medial to distal settings. Earth Planetary Science Letters.

DAVIES, P. 1998. The fifth miracle: the search for the origin of life. Penguin

Books, Australia.

FRANCIS, P.W., GARDEWEG, M., RAMIREZ, C.F. & ROTHERY, C.F. 1985.

Catastrophic debris avalanche deposit of Socompa volcano, northern Chile. Geology 13, 600-603.

Ho, A.M. and CASHMAN, K.V. 1997. Temperature constraints on the Ginko flow of the Columbia River Basalt Group. Geology 25, 403-406. L. and S. SELF, S. 1998. Some dynamical and thermal considerations for the emplacement of long basaltic lava flows. J. Geophys.

KESZTHELYI,

Res. 103, Bll, 27,447-27,464.

LIPMAN, P., DUNCAN, M. & BACHMANN, O. 1997. Comagmatic granophyric

granite in the Fish Canyon Tuff, Colorado: Implications for magma-chamber processes during a large ash-flow eruption. Geology 25, 915-918.

MCCORMICK, M.P., THOMASON, L.W., & TREPTE, C.R. 1995. Atmospheric effects of Mt Pinatubo eruption. Nature 373, 399-404. MONAGHAN, J.J, CAS, R.A.F., Kos, A.M. AND HALLWORTH, M. 1999. Gravity currents descending a ramp in a stratified tank. J. Fluid Mech. 319, 39-70. MOORE, J.G. & ALBEE, W.C. 1981. The 1980 eruptions of Mount St. Helens,

Washington. Topographic and structural changes, March-July 1980 photogrammetric data. U.S. Geol. Surv. Prof. Pap. 1250, 123-141.

NISBIT, E.G. 1995. Archaean ecology: a review of evidence for the early

development of bacterial biomes, and speculations of the development of a global-scale biosphere. In: Coward, M.P. & Ries, A.C. eds. Early Precambrian Processes. Geological Society Special Publication 95, 27-51.

RAMPINO, M.R. & SELF, S. 1992. Volcanic winter and accelerated glaciation following the Toba super-eruption. Nature 359, 50-52. RAMPINO, M.R. & SELF, S. 1984. The atmospheric effects of El Chichon. Sci.

Am. 250, 48-57.

RAMPINO, M.R., SELF, S., STOTHERS, R.B. 1988. Volcanic winters. Annual Review of Earth & Planetary Sciences 16, 76-99. 1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29"' "Geological Catastrophism"

55 RICE, A. .1990. The role of volcanism in K/T extinctions. Geological Society of Amercia Special Papers 244, 39-56 SELF, S. & KING, A.J. 1996. Petrology and sulfur and chlorine emissions of the

1963 eruption of Gunung Agung, Bali, Indonesia. Bulletin of Volcanology 58,

263-285

THORDARSON, TH. & SELF, S. 1996. Sulfur, chlorine and fluorine degassing

and atmospheric loading by the Roza eruption, Columbia River Basalt Group, Washington, USA. Journal of Volcanology & Geothermal Research 74, 49-73.

THORDARSON, TH., SELF, S., OSKARSSON, N., & HULSEBOSCH, T. 1996. Sulfur,

chlorine, and fluorine degassing and atmospheric loading by the 1783-1784 AD Laki (Skaftar Fires) eruption in Iceland. Bulletin of Volcanology 58, 205-225.

VoiGHT, B., GUCKEN, H., JANDA, R.J.., & DOUGLASS, P.M. 1981. The 1980

eruptions of Mount St. Helens, Washington. Catastrophic rockslide avalanche of May 18. US. Geol Surv. Prof Pap. 1250, 347-378.

1999 Selwyn Symposium, Geological Society of Australia (Vic Division), Friday Oct 29"" "Geological Catastrophism"