SETI bioastro: Tsunami book helps explain ancient Martian floods

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From: LARRY KLAES (ljk4@msn.com)
Date: Tue Mar 26 2002 - 09:32:46 PST


TSUNAMI BOOK GIVES A BETTER UNDERSTANDING OF ANCIENT FLOODS ON MARS

by Michael Paine <mpaine@tpgi.com.au>

Science of Tsunami Hazards, Volume 20, No 1 (2002)
http://epubs.lanl.gov/tsunami/ (not online until mid April). A PDF version
of this paper includes colour photographs and can be downloaded from
http://www4.tpg.com.au/users/tps-seti/spacegd7.html#news

This article was originally planned as a review of the book "Tsunami: The
Underrated Hazard" by Ted Bryant (Cambridge University Press, 2001).
However, a review by Japanese tsunami expert Kenji Satake appeared in Nature
on 24 January 2002 so I decided, instead, to describe my own investigations
to verify some of the phenomena that are set out in the book.

The book

Ted Bryant is an Associate Professor at the University of Wollongong, on the
south east Australian coast. He is a geoscientist with an interest in
geomorphology. Bryant had studied the coastal features of the area since the
late 1960s. Some things did not add up. He remembers the day in 1989 when he
was examining fresh boulders jammed into a crevice in a cliff well above the
height of any possible storm waves. After eliminating all other explanations
he and his colleague, Bob Young, "were left with the preposterous hypothesis
that one or two tsunami
waves had impinged upon the coast". Bryant began to gather other evidence of
these mega-tsunami, including the overwashing of a headland 130m high.

It is fair to say that many researchers were sceptical about Bryant's
claims. They picked on isolated items of evidence and provided alternative
explanations for the unusual features. It seems, however, that none of the
critics have actually visited the dozens of interesting
sites and considered the convergence of evidence which leads to the
conclusion that mega-tsunami have struck the south east Australian coast in
recent times.

Eventually Bryant decided to set out his research in a book. As well as
describing the mechanisms of alteration of coastal landforms he
comprehensively covers a wide range of topics concerning tsunami: historical
accounts around the world, the physics of tsunami, causes of tsunami and a
review of the risk to coastal populations. Sakate's review in Nature is
mostly complimentary but cautions that "the quality and depth varies greatly
from chapter to chapter" and that "parts of the book lack vigour and
consistency". I do not have the knowledge to make such judgements but I
found the book fascinating and it certainly triggered my curiosity. The
description of bedrock scouring, in which large chunks of rocky headlands
are torn away in a matter of minutes was amazing. Sakate commented that "a
modern example of bedrock scouring would also have made Bryant's arguments
more convincing". I had the same thoughts, and set out to investigate this
phenomenon.

Surprising sources of information

An internet search led me to an unlikely source - the Creation Research
Society. It seems that members of this Society are keen to demonstrate that
modern erosional landscapes, such as the Grand Canyon, could have been
formed in a few thousand years. Fortuitously they have gathered
together recent examples of bedrock scouring by catastrophic floods. The
paper "The 1993 Mid-West Floods and Rapid Canyon Formation" by Dr Glen
Wolfrom describes sudden erosional effects at three locations. Wolfrom
reports that water from a spillway "acted like a chisel, a drill, a grinder
and a thousand bulldozers all in one". His pictures show where huge chunks
of bedrock are missing from the streambed below dam spillways.

Another source that popped up from an internet search was research on
Martian geology. I have a long-standing amateur interest in Mars so this
source caught my attention. The Viking spacecraft that orbited Mars in the
early 1970s took pictures of Martian channels that had signs of catastrophic
flooding. Dr Mary Bourke from Oxford University in the UK has studied the
geomorphology of ancient floods in Central Australia as an analogue for
those features on Mars. In one paper she describes erosion of bedrock
including "scour holes generated by macroturbulent vortices" - evidently a
similar process to that which generated the whirlpool features at Bass
Point.

Dr Vic Baker from the University of Arizona also studies the Martian
features and has compared them with the strange landforms of the Washington
Scablands in the USA. I contacted Dr Baker by email and, to my surprise, he
told me he would be visiting Ted Bryant in Wollongong the following week. A
quick call to Dr Bryant confirmed that I could tag along while Dr Baker was
shown the tsunami signatures of the area. Fierce rainstorms and dense fog on
the two hour drive to Wollongong could not deter me from joining the tour.

Now if you intend to visit Wollongong yourself and want to experience that
moment of realisation that a mega-tsunami is the only logical explanation
for the coastal landforms then I suggest you read no further because I am
about to reveal some of Ted Bryant's tantalising evidence.

The clues

The northern side of Bass Point is covered by a thick, jumbled layer of
sand, crushed shells, pebbles and boulders - clearly subjected to severe
mechanical action. The explanation is that they have been dumped there when
a mega-tsunami swept over the headland from the south east. We then crossed
to the rugged, exposed south east face of the headland. Here, carved into
the rock, are two giant donut-shaped whirlpool features some 50 metres
across. One is complete and has a central plug (Figure 1). The other is
about three-quarters complete and looks as if a it was being quarried when
work suddenly ceased (Figure 2). Bryant's explanation is that when the
tsunami overwashed the headland giant whirlpools were formed. The outer
edges of the whirlpool started to form secondary vortices ("kolks") that
were highly erosional and tore out chunks of bedrock in a circular path. For
the second whirlpool the tsunami finished before the full circle could be
completed.

This mechanism is still regarded as speculative by Sakate. I was unable to
find a modern example of such an action, where before and after pictures of
the changes to bedrock are available. There are however, several other
examples of these erosional whirlpools in the Wollongong area. They do not
appear to be associated with any localised weakness in the rock but do have
similarities in the surrounding terrain - these would influence the
formation of vortices during overwashing by a mega-tsunami.

I tend to think of the whirlpool mechanism as being similar to a rock-face
tunnelling machine that has a large rotating head with smaller rotating bits
on the circumference (action movies such as "Total Recall" and "Die Hard
with a Vengeance" have examples of these machines).

Bryant then showed us the clinching evidence. We clambered over the rock
formations to a valley that had a group of boulders at one end. The boulders
were imbricated (stacked like a pile of fallen dominoes). He explained that
the boulders had been carried from the seaward side of a ridge that was more
than six metres above sea level. He pointed out that one of the boulders had
oyster shells attached - it had been scooped up from the shoreline by a
tsunami, carried over the top of the ridge and dumped against the other
boulders (Figures 3 and 4). The shells had been dated to 1500AD, just 270
years before Captain Cook sailed up the east coast of Australia!

After Bass Point we travelled to several spots along the south coast to see
other examples of strange erosion, imbricated boulders and huge sand
deposits in odd places. It is difficult to think of any other explanation
than mega-tsunami for this wide range of features.

The cause

What could have caused the mega-tsunami that struck the south east coast of
Australia five hundred years ago? Ted Bryant's book describes the four
causes of tsunami: earthquakes,
undersea landslides, volcanic eruptions/explosions and cosmic (asteroid or
comet) impacts with the ocean. Of these cosmic impacts and giant landslides
are the most likely causes of mega-tsunami. Landslides are a possible cause
of the Australian mega-tsunami. The shallow continental shelf extends tens
of kilometres from the coast then drops off steeply to depths of 4
kilometres in some places. Major rivers such as the Shoalhaven and
Hawkesbury deliver sediment to the edge of the shelf and this might
periodically tumble down the continental slope. Apparently a thorough survey
of the continental slope that might pick up signs of past landslides only
recently got underway.

In the book Bryant refers to the work of Ward and Asphaug when considering
the possibility that cosmic impacts might have caused mega-tsunami. Their
work suggest that for Sydney the average interval between 10m+ tsunami
caused by cosmic impacts is about 80,000 years (based on Bryant Figure
9.10). My own investigations of tsunami from cosmic impacts led to a paper
in the Science of Tsunami Hazards (Vol 17, No. 3 1999). In that paper I
pointed out major differences between researchers in the estimates of long
range wave heights from impact-generated tsunami. Using the more
conservative estimates of Crawford and Mader I estimate that, for Sydney,
the average interval between 10m+ tsunami from cosmic impacts is about 1
million years. Even the most pessimistic frequency derived from the work of
Ward and Asphaug would not account for frequency of large tsunami
established by Bryant - perhaps every 500 years. There remains, however, the
possibility of an unusual series of impacts such as a barrage from the
breakup of a comet. There are signs of such an event occurring several
thousand years ago (Steel 1995) but it does seem unlikely that "frequent"
ocean impacts large enough to devastate the coast of Australia were not
accompanied by similar large impacts in the northern hemisphere, including
some that would have left impact craters on land. On the other hand the last
major Australian tsunami event, that occurred around 1500AD, has some
coincidences. The largest recorded death toll from a meteorite fall occurred
in China in 1490AD - more than ten thousand died in the city of Ch'ing-yang
Shansi (Lewis 2000). There is also evidence of impact generated fires and
tsunami in New Zealand at this time (Bryant's book).

Finally there is speculation about the enigmatic Balls Pyramid rock outcrop
near Lord Howe Island, between Australia and New Zealand. It is a stunning
sight in the middle of the ocean and looks to me like a giant stone tool
that has had shards flaked off to give a ragged edge (Figure
5). The odd thing is that the vane-like island is aligned in the same
direction as the mega-tsunami that hit Bass Point and possibly the South
Island of New Zealand. In discussions during our tour, Bryant pointed out
that a tsunami tens of metres high could cause the strange features
observed on Balls Pyramid.

My recommendation is that people living near the coast read Bryant's book
and go out looking for some of the tsunami signatures that he describes. You
may discover unsettling evidence that our populated coastlines are
surprisingly vulnerable to these giant waves. An interactive map of the New
South Wales tsunami features, with many new photographs, is now available
at:

http://www.uow.edu.au/science/geosciences/research/tsunami/tsunami_nsw.htm

References

Baker V. and Milton D. (1974) 'Erosion by Catastrophic Floods on Mars and
Earth', Icarus 23:27-41.

Bourke M. and Zimbelman J. (2000) 'Australian Paleoflood Systems: An
Analogue for Martain Channel Systems', Proceedings of 31st Lunar and
Planetary Science Conference.

Byrant E. (2001) Tsunami: The Underrated Hazard, Cambridge University Press

Lewis J. (2000) Comet and Asteroid Impact Hazards on a Populated Earth,
Academic Press.

Paine M. (1999) 'Asteroid Impacts: The Extra Hazard Due to Tsunami', Science
of Tsunami Hazards, Vol 17, No. 3 pp155.

Sakate K. (2002) 'Making Waves on Rocky Ground', Nature Vol 415, 24 January
2002 pp369.

Steel D. (1995) Rogue Asteroids and Doomsday Comets, Wiley & Sons.

Wolfrom G. (1994) 'The Midwest Floods and Rapid Canyon Formation', Creation
Research Society Quarterly 31(2): 109 September 1994.


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