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Megatsunamis @ the London `Catastrophes` conference
August 17, 2002The modern world appears secure in its knowledge of hazards. However tsunamis today are smaller and less frequent than they were in prehistory.
Professor Ted Bryant argues geological evidence along the Australian coast is testament to past catastrophic tsunamis. The size of these tsunamis is beyond the capability of earthquakes, while their regional extent rules out submarine landslides. Only meteorite or comet impacts with the ocean, he believes, could generate tsunamis big enough to produce these features.
Radiocarbon dating along the southeast coast of Australia indicates that these giant tsunamis have occurred at a periodicity of around 400-500 years throughout the Late Holocene. One recent tsunami around AD 1500 stands out - an event that affected over 400 km of the Australian coastline and is also recorded on the east coast of New Zealand and on Lord Howe Island in the middle of the Tasman Sea. Aboriginal and Maori legends allude to a cosmogenic source for this event (or one like it). The Maori legends can be dated around AD 1500 based upon the evidence for occupational burning on the South Island. In addition, cultural changes among Aborigines in Australia after this time lend support to the idea that there was a substantial tsunami. Presently, the point of impact of the bolide responsible for the disaster has not been determined, but it probably lies southeast of New Zealand. If the observed periodicity of cosmogenic tsunamis in the southwest Pacific region is valid, then today's coastlines exist tenuously within a narrowing temporal window.
Although the Pacific coastlines regularly experiences destructive tsunamis, the shores of the North Atlantic are a far less likely location for past megatsunamis. However, around 7000 years ago, one of the world`s largest submarine slides triggered a giant tsunami that travelled across the North Atlantic and Norwegian Seas. It is not known if the slide was generated by a large offshore earthquake or by gas release from within the slide sediments; but deposits from the resulting tsunami have been found in western Norway, Scotland, Faeroe Isles and as far south as eastern England.
Professor Alastair Dawson reports on new computer modelling of the slide and tsunami estimates that show the giant wave had an average velocity of c. 35m/s and that the bulk of the sediment mass moved in as little as two days. Modelling of the tsunami runup at the coast suggests that in western Norway, the generation of the tsunami was associated with an initial drawdown (lowering) of sea level at the coast in the order of -8m quickly followed by a sea surface rise in the order of +16m.
Geological studies of coastal deposits in Scotland and Norway attributable to the tsunami indicate that runup varied with the shape of the local coastline, but that in parts of the Shetland Isles, it may have been as much as between +25/+30m above sea level.
Geological Society of London, The
Although the Pacific coastlines regularly experiences destructive tsunamis, the shores of the North Atlantic are a far less likely location for past megatsunamis. However, around 7000 years ago, one of the world`s largest submarine slides triggered a giant tsunami that travelled across the North Atlantic and Norwegian Seas. It is not known if the slide was generated by a large offshore earthquake or by gas release from within the slide sediments; but deposits from the resulting tsunami have been found in western Norway, Scotland, Faeroe Isles and as far south as eastern England.
Professor Alastair Dawson reports on new computer modelling of the slide and tsunami estimates that show the giant wave had an average velocity of c. 35m/s and that the bulk of the sediment mass moved in as little as two days. Modelling of the tsunami runup at the coast suggests that in western Norway, the generation of the tsunami was associated with an initial drawdown (lowering) of sea level at the coast in the order of -8m quickly followed by a sea surface rise in the order of +16m.
Geological studies of coastal deposits in Scotland and Norway attributable to the tsunami indicate that runup varied with the shape of the local coastline, but that in parts of the Shetland Isles, it may have been as much as between +25/+30m above sea level.
Geological Society of London, The
Tsunami News and Current Tsunami Events RSSUncertain future for elephants of Thailand
Worries over the future of Thailand' s famous elephants have emerged following an investigation by a University of Manchester team.
A world novelty for an improved tsunami early warning
After completing their simulation component in the German-Indonesian Tsunami Early Warning System (GITEWS), the team for tsunami modelling of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association has presented the currently leading software system for tsunami events with the potential for catastrophe.
Stress Buildup Precedes Large Sumatra Quakes
The island of Sumatra, Indonesia, has shaken many times with powerful earthquakes since the one that wrought the infamous 2004 Indian Ocean tsunami. Now, scientists from the California Institute of Technology and the Indonesian Institute of Sciences are harnessing information from these and earlier quakes to determine where the next ones will likely occur, and how big they will be.
Big quakes spark jolts worldwide
Until 1992, when California's magnitude-7.3 Landers earthquake set off small jolts as far away as Yellowstone National Park, scientists did not believe large earthquakes sparked smaller tremors at distant locations.
1 year after Solomon Islands, scientists learn barrier to earthquakes weaker than expected
On the one year anniversary of a devastating earthquake and tsunami in the Solomon Islands that killed 52 people and displaced more than 6,000, scientists are revising their understanding of the potential for similar giant earthquakes in other parts of the globe.
Scientists obtain core samples from subsea fault system off Japan
The third expedition of the Integrated Ocean Drilling Program's Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) completed its mission off the Kii Peninsula today.
Newly discovered active fault building new Dalmatian Islands off Croatian coast
A newly identified fault that runs under the Adriatic Sea is actively building more of the famously beautiful Dalmatian Islands and Dinaride Mountains of Croatia, according to a new research report.
Thousands of Crop Varieties from Four Corners of the World Depart for Arctic Seed Vault
At the end of January, more than 200,000 crop varieties from Asia, Africa, Latin America and the Middle East-drawn from vast seed collections maintained by the Consultative Group on International Agricultural Research (CGIAR)-will be shipped to a remote island near the Arctic Circle, where they will be stored in the Svalbard Global Seed Vault (SGSV), a facility capable of preserving their vitality for thousands of years.
Rich nations' environmental footprints tread heavily on poor countries
The environmental damage caused by rich nations disproportionately impacts poor nations and costs them more than their combined foreign debt, according to a first-ever global accounting of the dollar costs of countries' ecological footprints.
Deep-ocean researchers target tsunami zone near Japan
Rice University Earth scientist Dale Sawyer and colleagues last month reported the discovery of a strong variation in the tectonic stresses in a region of the Pacific Ocean notorious for generating devastating earthquakes and tsunamis in southeastern Japan.
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