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- 4 Feb 23 NOAA: Tsunami: Asteroid Impact - 66 Million Years Ago - brilliant animation
- 8 Dec 22 Livescience: Colossal 'planet killer' asteroid sparked mega-tsunami on Mars, and now we know where it landed.
- 29 Mar 21 Bisouv: Researchers suggest Lomonosov crater could be more evidence of mega-tsunami on Mars + JGR (2019): The Lomonosov Crater Impact Event: A Possible Mega‐Tsunami Source on Mars.
- 8 Jan 19 LiveScience: Dinosaur-Killing Asteroid Triggered Mile-High Tsunami That Spread Through Earth's Oceans.
- 28 Mar 17 Cosmos: Mars may have experienced a giant tsunami -
Evidence suggests a tsunami rolled across Mars, lending strong support
to the theory that the planet was once covered by ocean.
- 21 May 16 Nature Scientific Reports: Giant tsunamis washed over ancient Mars - Meteorite impacts triggered enormous waves in now-vanished ocean + Tsunami waves extensively resurfaced the shorelines of an early Martian ocean
- evidence for two enormous tsunami events possibly triggered by bolide
impacts, resulting in craters ~30 km in diameter and occurring perhaps
a few million years apart. The tsunamis produced widespread littoral
landforms, including run-up water-ice-rich and bouldery lobes, which
extended tens to hundreds of kilometers over gently sloping plains and
boundary cratered highlands, as well as backwash channels where wave
retreat occurred on highland-boundary surfaces...
- 15 Oct 13 Steve Ward has simulated the Eltanin impact. (Youtube)
- 22 Dec 12 Steve Ward has created a brilliant computer simulation of the Chicxulub impact and tsunami on Youtube. More simulations here.
- 21 Jun 10 Nature: Modelling Mars in a Texan torrent - see also Tsunami book gives a better understanding of ancient floods on Mars Science of Tsunami Hazards Vol 20 No 1 (2002) + Process Geomorphology research.
- 10 Dec 09 NewSci: Mega-flood filled the Mediterranean in months - revealed a gorge 200 kilometres long and 250 metres deep, cutting through the Strait... (hydraulic erosion on a big scale)
- 4 May 09 BBC: Ancient tsunami 'hit New York' - a space impactor may have set off the massive wave...
- 29 Apr 09 EurekaAlert: Contrary to recent hypothesis, 'chevrons' are not evidence of megatsunamis (but see Mega Tsunami of the World Oceans: Chevron Dune Formation... from 4th Alexander von Humboldt International Conference - The Andes: Challenge for Geosciences and Chevron Dunes from the Holocene Impact Working Group)
- 21 Apr 09 New Scientist: Asteroids won't raise killer waves - but mind the splash (see also Asteroid impacts: the extra hazard due to tsunami from Science of Tsunami Hazards, 1999)
- 21 Nov 08 Discovery: Did Asteroid Cause Ancient N.Y. Tsunami? (thanks Steve Ward - see link to his computer simulation)
- 12 Mar 08 Mader Consulting - Book available 'Numerical modeling of water waves' - second edition. It documents in the problems and limitations of the various modeling methods. 2008 UPDATED DVD AVAILABLE Free to Book Owners + Parts of Chapter 6
- 12 Sep 07 : A possible Plio-Pleistocene tsunami deposit, Hornitos, northern Chile (Eltanin impact? thanks Nicolás González)
- 19 Jul 07 New Scientist: Dam-busting 'megaflood' made Britain an island - All the bedrock landforms we see are characteristic of a megaflood," NOT A TSUNAMI but an example of catastrophic erosion caused by water. See also Glacier Garden Lucerrne, Switzerland - Potholes - These impressive potholes were formed at the bottom of the glacier by the sheer force of the water. As is still the case in alpine glaciers today, the melt water initially flowed on the surface of the ice before seeping into the glacier through fissures. At the bottom of the glacier the water was under tremendous pressure. As the flow of water gathered speed, vortices with speeds of up to 200 km/h began to form. + THE FORMATION OF A GLACIAL POTHOLE. (however, note that water alone can cause rock erosion in a very short time - sand and gravel need not be present)
- 30 Jan 07: Excellent presentation by Steve Ward on the tsunami hazard (19Mb Quicktime movie)
- 16 Nov 06 AGU 2006 Abstract: Holocene Indian Ocean Cosmic Impacts: The Megatsunami Chevron Evidence From Madagascar
- 15 Nov 06 ABC Radio: Researchers claim link between tsunamis and outer space + NY Times: Ancient Crash, Epic Wave (thanks David Morrison) + SMH: Big splash theory says meteors hit regularly.
- 24 Aug 06 Steve Ward: New simulation of Eltanin impact 2 million years ago.
- 13 May 06 New Scientist: Tsunami risk of asteroid strikes revealed. Natural Hazards: A Quantitative Assessment of the Human and Economic Hazard from Impact-generated Tsunami. Preprint here.
- 13 May 06 Selection of recent papers from Science of Tsunami Hazards (PDFs):
- Confirmation and Calibration of Computer Modeling of Tsunamis Produced by Augustine Volcano, Alaska
- Experimental Modeling of Tsunami Generated by Underwater Landslides
- Sage Calculations of the Tsunami Threat from La Palma - We
find that while high-amplitude waves are produced that would be highly
dangerous to nearby communities (in the Canary Islands, and the shores
of Morocco, Spain, and Portugal), the wavelengths and periods of these
waves are relatively short, and they will not propagate efficiently
over long distances.
- 19 Mar 06 LPSC2006: RUNUP FROM IMPACT TSUNAMI.
- 5 Mar 06 Steve Ward: New movies of encounter with asteroid Apophis in 2036: Apophis strikes the Pacific ocean just north of Panama + Apophis zooms by Earth missing by just 2500 km.
- 6 Dec 05 Steve Ward: New impact tsunami movies include blast-wave effects (~3Mb MOV): 10 km diameter Chicxulub + 1 km diameter off Southern California
- 22 Oct 05 NewSci (subs): The future of Atlantic tsunamis
+ page 62 of the paper edition (22 Oct 05) has an ad for "Project
Scientists - Australian Tsunami Warning System".
- 20 Oct 05 Essay by Steve Ward & Simon day: Tsunami Thoughts
- 5 Aug 05 Nature: Hurricanes
whip up huge waves - 40-metre
monsters [but their period is too short to cause castastrophic erosion]
- 6 Jul 05 The Australian Museum Society: Tsunami and Sydney: a long-term relationship - Dr Edward Bryant, University of Wollongong - Thursday 7 July, 2005, 6.30pm for 7pm at the Australian Museum, Sydney.
- 26 May 05 Glencairn Insurance: The
Asian Earthquake/Tsunami Disaster An Insurance Perspective (2Mb
PDF) - "Santa Cruz, for example, has experienced a number of tsunamis
from distant earthquakes in the last 60 years and is also at risk from
local tsunamis generated by submarine landslides..." (thanks Steve Ward)
- 11 May 05 Quaternary Science Reviews (abs): Evidence
for three North Sea tsunamis at the Shetland Islands between 8000 and
1500 years ago.
- 11 May 05 San Gabriel Valley Tribune: Tsunami
danger real, but remote, study says Southern California faces a
real tsunami threat from offshore earthquakes and submarine
landslides...(CC)
- 6 May 05 Livescience: New
Method Predicts Monster Waves (not tsunami)
- 5 May 05 Tsunami modeller Steve Ward has prepared two
movies of potential impacts by asteroid 2004MN4 off the coast of
the USA. A-MOV
and B-MOV
- 4 Apr 04 BBC: Flood theory - A tsunami could have hit Bristol and south Wales in 1607 (CCNet)
- 2 Apr 05 LiveScience: Potential
Southern California Tsunami Could Cost up to $42 Billion.
- 21 Mar 05 Indy Star: Study
sees tsunami risk in the Caribbean - Ten destructive tsunamis have
been generated in the past 500 years. Nearby undersea landslides are
the likely cause.
- 11 Mar 05 LPSC05: OFFSHORE
BREAKING OF IMPACT TSUNAMI: VAN DORN WAS RIGHT.
- 25 Feb 05 Science (regn): Ancient
Alexandria Emerges, By Land and By Sea - subsidence was brought on by a lethal
combination of earthquakes, tsunamis, and the slow but relentless
sinking of heavy foundations into unstable soil.
- 15 Jan 05 ABJournal: Asteroid
Could Cause Tsunami, LANL Scientist Says - "If we had a monitoring system in the
Indian Ocean, maybe 75,000 lives could have been saved in this recent
disaster," Gisler said. "It's just ridiculous when you look back that
the money wasn't spent." (CC)
- 10 Jan 05 LA PALMA TSUNAMI:
DEBUNKING THE MEGA-HYPED TIDAL WAVE STORY (author not named) +
University of Southampton (Aug 04): Canary
Islands landslides and mega-tsunamis: should we really be frightened?
(CCNet)
- 7 Jan 05: This page earns Griffith Observatory
Star Awards.
- 3 Jan 05 Financial Express - New Delhi,India: TSUNAMI
alarm: desi model or global club?
- 1 Jan 05 SMH: Anger
rises in India over lack of warning - Seismologist Arun
Bapat says he has been warning of the risk of a tsunami for
decades, yet no one was listening. "There have been four
tsunamis in India in the last 100 years, and it is well-known that
an earthquake of such a large magnitude generates a tsunami. There was
no system in place."
- 1 Jan 05 World News: Tsunami
predicted, not heeded - Scientists
at the Pacific Tsunami Warning Centre in Honolulu had forecast Sunday's
massive tsunami within 15 minutes of the Indonesian earthquake, but did
not know who to pass the information to. A tsunami warning that could
have saved thousands of lives was issued, but not acted upon, more than
an hour before giant waves hit Sri Lanka and southern India... In Sri
Lanka, which suffered the biggest loss of life in the tsunami, crowds
had come to the beaches to watch the sea after word spread that it was
producing larger-than-normal waves... None of the countries most
severely affected had a tsunami warning mechanism.
- 31 Dec 04 Livescience: Tsunami
Kills Few Animals in Sri Lanka (speculative) + Deadly
Tsunamis Rival Waves of the Past.
- 29 Dec 04 Japan Times editorial: Catastrophe
without warning.
- 29 Dec 04 Copy of "The
Great Earthquake and Tsunami of 26 December 2004 in Southeast Asia"
by Dr. George Pararas-Carayannis temporarily added due to his website being overloaded. - 29 Dec 04 Space.com: Arthur C. Clarke, in Sri Lanka, Calls Tsunami 'Disaster of Unprecedented Magnitude'
- 27 Dec 04 Links to TerraDaily
articles on the SE Asian Tsunami.
- 27 Dec 04 Channel News Asia: No
warning system in place for tsunami-hit countries: USGS (map of
affected areas).
- 27 Dec 04 SMH: Tsunami smashes Asia, more than 11,300 dead - One of the most powerful earthquakes in history hit Asia yesterday,unleashing a tsunami which devastated coastal areas of Sri Lanka,India, Indonesia and tourist isles in Thailand, killing more than 11,300 people.
- 27 Dec 04 STH Abstract (1999): Tsunamis
along the coastlines of India.
- 26 Dec 04 Yahoo (posted just a few hours after the item below): Indonesia Quake Sparks Fatal Tidal Waves One of the world's most powerful earthquakes in years (magnitude 8.5) rocked northern Indonesia on Sunday and launched tidal waves that slammed shorelines across Asia, killing some 300 in Sri Lanka and almost 100 in Indonesia, officials said... Waves crashed into coastal villages over a wide area of Sri Lanka — some 1,000 miles west of the quake's epicenter
- 26 Dec 04 Yahoo: One of World's Largest Quakes Hits Near Australia - The earthquake measuring 8.1 on the Richter
scale hit near Macquarie Island in the Southern Ocean, more than 500
miles southeast of Tasmania... The earthquake could have caused a
tsunami, but no noticeable changes in water levels had been reported in
Tasmania or New Zealand.
- 8 Dec 04 LiveScience: Mystery of Deadly 1946 Tsunami Deepens
- 5 Nov 04 Deep Sea Research: Special issue on ocean impacts (Vol 49 No 6, Published 2002)
- 3 Nov 04 AGU Annual Meeting - search for "tsunami": Tsunami Hazards and Probabilistic Analyses + Quantifying Tsunami Impact on Structures + Inundation Modeling for Probabilistic Tsunami Hazard Assessment + Probabilistic Risk Analysis of Run-up and Inundation in Hawaii due to Distant Tsunamis
- 30 Oct 04 BBC: Tidal wave threat 'over-hyped'
- 18 Oct 04 Tsunami
Society: The Third
Tsunami Symposium has been
postponed one year to May 2006!
- 15 Oct 04 Financial Times (subs reqd): Shock Waves - Fears that a volcanic eruption in the
Canary Islands could send a 25-metre-high tsunami crashing into the US
coast have been gaining momentum. But rival scientists dismiss the
prediction as a hugely unlikely worst-case scenario. Who do we believe?
... And even if the La Palma tsunami were not to be quite so immense,
it would still be classified as a flood, explains Bob Hartwig, chief
economist of the Insurance Information Institute in New York. And
floods are, generally, not covered under most property insurance. As
far as catastrophic events go, insurance companies are more worried by
what lurks in the heavens. "Meteors," says Hartwig, "they're covered by
insurance, but not factored into premiums. If a meteor similar to the
one that hit Siberia in 1908 were to hit western Europe or the
north-east United States, we could go bankrupt."
- 15 Sep 04 Astrobiology Magazine: Surfing the Wave A tsunami, a series of large
waves caused by the disruption of seawater, is one
of the many hazards of living on Earth. Bill McGuire, Director of the Benfield Hazard Research Centre, says that a mega-tsunami could cause death and destruction to both the eastern and western Atlantic coasts. [Prof McGuire claims that the Tsunami Society does not have volcano experts but see the link to Dr. George Pararas-Carayannis's paper below (17 Aug).]
- 7 Sep 04 Japan Times: Quakes injure 42; tsunami flip 14 boats
- 3 Sep 04 Science (subs): Tibet's
ancient flood - this one was "one of the most erosive events in
recent Earth history". See this thesis page
by David Finlayson.
- 1 Sep 04 Geology (abstract): Megatsunami
deposits on Kohala volcano, Hawaii, from flank collapse of Mauna Loa
(thanks Steve Ward). See also Modeling the 105ka
Lanai Tsunami (4.5Mb PDF) and this animation by Steve Ward
(large quicktime file - see snapshot at right). Steve also has an animation of a
Mt St Helens landslide.
- 19 Aug 04 Uni Wollongong: Interactive
map of Australian Tsunami features.
- 19 Aug 04 Guardian: Britain
being battered by waves hurling giant rocks
- Storms are causing waves that are ripping giant boulders from the top
of cliffs in exposed areas and hurling them inland.
- 17 Aug 04 George Mason Uni: Run To The Hills! La Palma "mega-tsunami" + Dr. George Pararas-Carayannis: EVALUATION OF THE THREAT OF MEGA TSUNAMI GENERATION FROM POSTULATED MASSIVE SLOPE FAILURES OF ISLAND STRATOVOLCANOES ON LA PALMA, CANARY ISLANDS, AND ON THE ISLAND OF HAWAII + Royal [Bemuda] Gazette: Expert downplays tsunami threat.
- 11 Aug 04 Mader Consulting: new book available 'Numerical modeling of water waves' - second edition. It documents in the problems and limitations of the various modeling methods.
- 10 Aug 04 ABC: Scientist
warns of tsunami in the making BUT Tsunami Society: MEGA TSUNAMI HAZARDS
- We would like to halt the scaremongering from these unfounded
reports [that collapse of volcano flanks might cause ocean-wide
"mega-tsunami"]. Also reported in the
Guardian (thanks Duncan Steel).
- 28 Jul 04 SciAm: Old
Rivers More Active in Youth ... rapid erosion over a relatively
short 20,000-year span. Abstract
from Science 23 Jul 04.
- 27 Jul 04 Yahoo: Ship-Sinking Monster Waves Are Widespread -- ESA (not tsunami)
- 1 Jun 04 Geology: River
incision into bedrock: Mechanics and relative efficacy of plucking,
abrasion, and cavitation. Geological Society of America Bulletin:
Vol. 112, No. 3, pp. 490–503 (2000!).
- 28 May 04 AGU: Ocean-Scale
Tsunami Propagation: Boussinesq Approximations.
- 9 Mar 04 ScienceNews: Killer Waves.
Thanks Steve Ward.
- 10 Feb 04 NZ Herald: Expedition hunts giant meteor [sic]. Thanks Steve Ward.
- 16 Dec 03 Science Now (subs): The Case for Monstrous Hawaiian Waves - Abstract of McMurtry's talk, More details on Hawaii tsunami studies
- 1 Dec 03 USNews.com: A blast from heaven? (debate over a recent mega-tsunami in the South Pacific - thanks Steve Ward) + GSA: DID A BOLIDE IMPACT CAUSE CATASTROPHIC TSUNAMIS IN AUSTRALIA AND NEW ZEALAND? (abstract) + “Mystic Fires of Tamaatea”: Attempts to creatively rewrite New Zealand’s cultural and tectonic past, by James Goff, Journal of the Royal Society of New Zealand - 17 Jan 04 Earth2Class: DID A BOLIDE IMPACT CAUSE CATASTROPHIC TSUNAMIS IN AUSTRALIA AND NEW ZEALAND?
- 18 Nov 03 Santa Cruz Sentinel: UCSC seismologist prepares for tsunami.(CC)
- 12 Nov 03 NewsDay: EXPERTS
SEEK TRAIL TO MARK ICE AGE FLOODS (in NW USA) (CC)
- 29 Aug 03 NASA DPS 2003: Assessing
the Human Hazard from Impact-generated Tsunami - by Chesley and
Ward.
- 24 Aug 03: International Seminar/Workshop on Tsunami - “In Memoriam 120 Years Of Krakatau Eruption – Tsunami And Lesson Learned From Large Tsunami“ August 26th – 29th 2003, Jakarta and Anyer.
- 23 Aug 03 Economist: The next big wave - tsunami detection (CC)
- 7 Aug 03 Nature (abstracts): Unusually
large earthquakes inferred from tsunami deposits along the Kuril trench.
Details
here.
- 19 Jul 03: Steve Ward has created a great new animation of the Eltanin ocean impact.(5Mb Quicktime movie)
- 18 Jul 03 Space.com:
Small Stony Asteroids Will Explode and Not Hit Earth, Study Shows.
Based on a Nature
article (abstract). See also these
discussions on CCNet and this press
release. In esssence, the overall risk to mankind is not greatly
affected by this new work - there will be fewer oceans impacts but more
airbursts above the land.
- 4 Jun 03 SciAm: 2880
Asteroid Impact Simulation Suggests Tsunamis Could Hammer Atlantic
Coast. (1.1km asteroid hitting 600km off the US coast).
- 28 May 03 UCSC: Massive
tsunami sweeps Atlantic Coast in asteroid impact scenario.(NNN)
- 18 Mar 03 Uni Arizona: Worried About Asteroid-Ocean Impacts? Don't Sweat The Small Stuff [note there are many other good reasons for finding asteroids down 200m, even if they don't cause ocean-wide tsunami] (NNN)
- 25 Feb 03 LPSC2003 Abstracts (selection):
- Impact Tsunami Calculations: Hydrodynamical Simulations vs. Linear Theory [#1195]
- Impact-generated Tsunamis: An Over-rated Hazard [#2013]
- Numerical Modeling of the Eltanin Impact [#1101]
- 24 Feb 03 Nature (13/2): Long-lost wave report sinks asteroid impact theory (see also CCNet)
- 24 Jan 03 Tsunami Society: MEGA TSUNAMI HAZARDS - We would like to halt the scaremongering from these unfounded reports [that collapse of volcano flanks might cause ocean-wide "mega-tsunami"]
- 12 Dec 02: SCIENCE OF TSUNAMI HAZARDS - Vol 21 No2 released (advanced computer modelling of asteroid impacts).
- 24 Oct 02 ABC (Australian TV): Asteroid Tsunami 8pm tonight - Australian scientist Ted Bryant says it’s not the infrequent big space rocks we really should be concerned about - it’s the smaller ones. Bryant takes Catalyst reporter Graham Philips to the cliff tops of the coastline around Wollongong and finds geological features that he claims were made by Tsunami’s that in turn were caused by asteroid impact.
- 16 Aug 02 Nando Tines: RESEARCHER STUDIES FOLKLORE FOR CLUES ABOUT TSUNAMI (CCNet)
- 5 Jun 02 SpaceDaily: New Wave Supercomputers Catch Big Waves (tsunami from asteroid impacts).AAS abstract. LANL Press Release (NNN)
- 26 Apr 02: Science
of Tsunami Hazards Vol 20 No 1 (2002) 'Tsunami
book gives a better
understanding of ancient floods on Mars' (800K PDF).
- 26 Apr 02 NYT: EXPERTS FIND CLUES TO CAUSE OF DEADLY PACIFIC TSUNAMI.(CCNet) See also this STH paper by Watt (PDF)
- 12 Apr 02 The Guardian: A last wave goodbye - An asteroid landing in the ocean would produce the tsunami to end them all, says Duncan Steel. But see below.
- 3 Apr 02 UniSci: Superfloods Controversial, But Aid Flood Prediction - The massive flood cut deep canyons, stripped away soils, and carried boulders all the way from Idaho to what is now Portland, Ore. In 48 hours, it transformed the landscape of the Pacific Northwest.
- 30 Mar 02: Science of Tsunami Hazards now has its own website with abstracts for SECOND TSUNAMI SYMPOSIUM.
- 29 Mar 02 Space.com: Mars, Like Earth, Sculpted by Super Eruptions and Epic Floods
- 31 Oct 01: Ted Bryant's book Tsunami: the underrated hazard is now available in Australia. It provides a comprehensive reference to the subject of tsunami: mechanisms for generation, evidence of past tsunami in coastal landforms and the effects on humans over millenia. See review on 26 Mar 02.
- 20 Sep 01 SFC: Threat of killer waves - Recent scientific studies show the power of tsunamis (thanks Steve Ward)
- 9 Sep 01 BBC: Giant wave hit ancient Scotland.
- 29 Aug 01 BBC: Giant wave devastation feared (Landslide generated - but there are considerable differences in the tsunami estimates) + MSNBC (more cautious!) + Discovery.
- 5 Mar 01 ABCNews: Computers Predict Tsunami - NOAA Scientists See Big Wave in West Coast's Future.
- 11 Oct 2000 BBC: Action urged over giant wave threat (see comments above). Mega-tsunami - Horizon BBC TV.
- 18 Jul 01 ABCNews: Threat of Giant Waves? - Scientists suspect that an earthquake-triggered tsunami that killed more than 2,000 people in Papua New Guinea two years ago on Monday was bolstered by an undersea landslide.
- 5 Oct 2000 BBC: Giant wave could threaten US - A collapsing volcano in the Atlantic could unleash a giant wave of water that would swamp the Caribbean and much of the eastern seaboard of the United States. Also in New Scientist. But Tsunami expert Charles Mader advises "... the La Palama landslide generated wave would have a short wavelength and a short period (less than 10 minutes) wave that would rapidly decay to a deep water wave before it got to US coasts. I told Horizon that a La Palama landslide would not be a threat to the U.S. -- that did not fit into their script!"
- 30 May 2000: Seafloor Off Mid-Atlantic Coast Highly Charged with Gas - ...possible cracks along the outer continental shelf off the mid-Atlantic coast might lead to a tsunami-causing landslide ... discovered that the entire area is charged with gas.
- June 2001: New book on tsunami by Ted Bryant.
- May 2001: 'The Asteroid Tsunami Project at Los Alamos' by Jack Hills and Patrick Goda, Science of Tsunami Hazards, Vol 19 No.1 (2001) 55-65. Describes the effects ocean impacts by asteroids 5km and 10km in diameter. The authors indicate there is uncertainty about their earlier work involving smaller asteroids and that they are developing improved models. They point out that localised tsunami effects can be delayed and peaks can occur well after the first wave arrives.
- Sep 2000: 'The mitigation, management and survivability of asteroid/comet impact with Earth' by V. Garshnek, D. Morrison and F. Burkle, Space Policy (Vol 16 (2000) 213-222) (not online) - uses estimates of risk and fatalities from Table 1 below and refers to this page.
- Jan 2000: For alternative estimates of hazards to a populated Earth see my Space.com article Simulating Armageddon on your PC and this extra information.
- Dec 1999: This analysis is also described in my paper
"Asteroid
impacts: the extra hazard due to tsunami" (200K PDF) in the Science
of Tsunami
Hazards, Volume
17 Number 3 1999 (PDF 9.4Mb) available
from LANL.
- Nov 1999: For a less technical description of asteroid tsunami please see my Space.com article Asteroids and tsunami: GOOD NEWS AND BAD and references.
- Aug 1999. Water crater explained. June 99: Risk to inhabited regions revised - area of devastation for 500m & 1km asteroids reduced. Consequences of 2km impact included.
- These estimates assume that impacts are randomly distributed in time. It is possible the Earth may be subjected to a barrage of asteroids (or comet fragments) from time to time. This may have happened over the past few thousand years and could be a source of some of the tsunami that appear to have struck Australia during this period.
- May 1999: This page listed in a UK Parliament report on the NEO hazard as "a particularly useful web site" (PDF format).
- May 1999: Scientists know of no asteroid or comet that is on a collision course with Earth, at least for the next thousand years or so. The point of the current publicity is that, with limited funding, the search efforts to date have only found about 10% of the large (1 kilometre or bigger) objects orbiting the Sun near the Earth. Amongst the estimated 1,800 or so undiscovered large objects there could be one on a collision course with Earth in the next few decades. This is very unlikely but it is simply crazy for mankind not to look for them with a program like Spaceguard, just in case something needs to be done to avoid a collision. Please don't worry about the hazard or lose sleep but, by all means, if you agree with these comments please write to your local Federal Member of Parliament seeking support for "Spaceguard" from the Australian Government.
- April 1999: Risk analysis has been extensively revised, based on recent papers by Crawford & Mader and Ward & Asphaug. Note that risk estimates have been substantially reduced from previous values - the risk of a typical coast dweller dying from an asteroid generated tsunami is probably similar to that of dying from the indirect effects of a large asteroid impact (not necessarily impacting the ocean). For some coastal locations which are particularly vulnerable to tsunami the risk is two or three times greater.
- The Tsunami Society held a Symposium May 25-27 1999 in Honolulu. Topics covered (temporary link to abstracts) include: "MEGA-TSUNAMIS FROM ASTEROIDS AND SLIDES", "Eltanin Asteroid Impact Tsunami" and papers on the tsunami risk to numerous coastlines, including Australia. Dr George Pararas-Carayannis's Tsunami Page has more details about the Symposium.
- For flexibility in circulating the document non-ASCII characters have been avoided and Fortran style formulae have been used:* means multiply, ^ means"to the power of", Ey means "10 to the power y".
- Risk calculations should be regarded as "ballpark" estimates, pending further research on the frequency of impacts and the vulnerability of coastlines to tsunami.
- All asteroid sizes refer to diameter. All tsunami wave sizes refer to maximum height above sea level (see diagram).
- the initial size of the wave - based on analysis of the size and shape of the "crater" and the manner in which it collapses, and
- the rate at which a tsunami from an asteroid impact dissipates as it travels.
Asteroid Tsunami - News and updates
An interactive map of the New South Wales tsunami features, with many new photographs, is now available at: Uni of Wollongong. (no longer available)
Much more information about the Washington Scablands is available from the library of the University of Georgia (requires DjVu plug-in).
Publication notes
This page is intended to provide a brief introduction to the effects of an asteroid or comet striking the Earth above an ocean. A method of estimating the risk to coastal regions from tsunami generated by such impacts is presented.
Nature of Tsunami
The waves created by a sudden disturbance in the ocean are known as
tsunami*. Typical causes are earthquakes and underwater landslides
(sometimes
tripped by small earthquakes).
Tsunami generally travel very fast across the ocean (typically 500km/h or more). In deep water the tsunami height might not be great but the height can increase dramatically when they reach the shoreline because the wave slows in shallow water and the energy becomes more concentrated. In addition to the inherent increase in the height of the wave from this shoaling effect, the momentum of the wave might cause it to reach a considerable height as it travels up sloping land. It is typical for multiple waves to result from one tsunami-generating event and these could be several hours apart when they reach a distant shore.
-
*Tsunami is Japanese for "harbour
wave"
which is misleading to the Japanese because tsunami don't just
occur
in harbours. Scientists dislike the term "tidal wave" as used by
the Press but there is a little logic in the term - some tsunamis do
not break when they reach land but surge like a massive, fast
moving high tide to flood low-lying areas. Much of the damage comes as
they recede
back into the ocean.
Illustration of Tsunami Terms (Magnified Vertical Scale)
Amplitude is approximately the maximum height
of
the
wave above sea level when in deep water - see diagram. Note that this
is
not the same as the "double amplitude" which is the vertical distance
between the crest and the trough and is often used to describe the
height of a wave).
Run-up height is the vertical height above sea level of
the
tsunami at its furthest point inland.
Run-up factor is the run-up height divided by the
deepwater
wave amplitude
The run-up factor can vary considerably, depending on local topography and the direction of travel of the wave. Hills and Goda (1998) note that earthquake-generated tsunami in Japan have an average run-up factor of 10 but sometimes reach 25. In Hawaii run-up factors of 40 have been observed for earthquake-generated tsunami. There is a particular danger to seaports from tsunami because the approach channel to the port can support a much more energetic tsunami (there is less energy dissipated or reflected as it travels over the continental shelf). On the other hand, based on recent assessments of tsunami risks for various locations, Crawford and Mader (1998) estimate the typical run-up factor is only 2 to 3.
Contrary to popular notions, the Australian coastline is vulnerable to tsunami (Nott & Bryant 1999 and Rynn & Davidson 1999). There is also evidence of substantial variations in run-up factor for tsunami along the Australian coast . Along a 40km stretch of coastline the run-up height from one (ancient) tsunami event varied by more than 40 (based on Young et al 1996). The effects are complicated by features such as estuaries, harbours, cliffs and reefs. The topography and features of the continental shelf, the shoreline, an estuary/harbour and the land are all very important is considering the damaging effects of tsunami. Some coastal areas could be vulnerable to relatively small tsunami. Until recently there appears to have very little assessment of this risk except in areas prone to earthquake-generated tsunami such as Japan and Hawaii.
The urgency for increased research on tsunami is reinforced by the devastating tsunami which struck northern New Guinea in July 1998. Scientists are still trying to understand mechanisms of that earthquake-related tsunami.
Asteroid impacts with
the
Earth
Stony asteroids with a diameter less than about 100 metres generally do
not reach the Earth's surface. These objects usually explode several
kilometres above the surface (an "airburst"). This was probably the
case with the
"Tunguska" Siberian event in 1908. The kinetic energy involved is
substantial
- a typical impact by a 50m object releases about 10 megatons of TNT
and
that of a 100m object releases about 75 Mt (the actual kinetic energy
depends
on several factors such as speed and density and can vary by a factor
of
more than 10). These explosions are equivalent in energy to large
thermonuclear
explosions and they can cause devastation over thousands of square
kilometres
- in the case of Tunguska the area of destruction was about 2,000 sq km
or a circle of radius 25km.. Fortunately the region was sparsely
populated
and had little effect on humans (unlike now when it could not have been
mistaken for a hostile nuclear explosion).
Estimates of risk based on asteroid/comet impact frequency
may
vary by a factor of ten - "Events like Tunguska occur with uncertain
frequency, possibly once every 50 years, if the interpretation of the
Spacewatch data is correct, or at most once every 300 to 500 years"
(Steel 1995). Subject to this uncertainty, the probability of an
impact at a given location can be estimated from
P = P(D) * AD
/ AE
(1)
where
P(D) is the probability of an impact by an
asteroid
of diameter D somewhere on the Earth
AD is the area of destruction
due
to the impact
AE is the total area of the
Earth's surface (including ocean).
Applying this to the Tunguska event, and assuming an average interval between Earth impacts of one century, the annual probability of a given location being within the devastation area is P(annual) = 0.01 * 2000 / 5.1E8 = 4E-8 or about 1 in 25 million. .
Steel (1995) provides the
following
formula for estimating the area of destruction, based on nuclear
weapons tests:
A = 400 (Energy)0.67
(2)
Using this formula the following table sets out the typical values for
stony asteroid up to 200m diameter (assuming velocity=20km/s, density=3
g/cc). Again the values are subject to considerable uncertainty and may
vary
by a factor of ten or more. The area of devastation for 500m and 1km
asteroids is derived from the range of values presented by Morrison & Chapman (1995).
Table 1 - Risk of direct impact for a given location
| Diameter | Kinetic Energy | Area Devastated |
|
||
| (m) | Mt TNT | sq km | Earth | "City" | Inhabited Region & Expected Death toll |
|
50
|
10
|
1900
|
100 yr
|
30 million yr
|
900 yr
1 million
|
|
100
|
75
|
7200
|
1000 yr
|
70 million yr
|
8000 yr
3 million
|
|
200
|
600
|
29 000
|
5000 yr
|
90 million yr
|
30 000 yr
14 million
|
|
500
|
10 000
|
70 000
|
40 000 yr
|
290 million yr
|
180 000 yr
30 million
|
|
1 km
|
75 000
|
200 000
|
100 000 yr
|
260 million yr
|
290 000 yr
60 million
|
|
2 km
|
1 million MT
|
-
|
1 million yr
|
-
|
1 million yr
1.5 billion
|
|
All*
|
90 yr
|
14 million yr
|
800 yr
|
||
-
*All = 1/ ( 1/T50+ 1/T100
+ 1/T200 + 1/T500 + 1/T1000) on
the basis that probabilities are independent and span the range
of asteroid sizes.
# See Appendix for calculation of risk to inhabited regions and predicted death toll.
There is uncertainty about the diameter of many asteroids when they are initially discovered. These objects are generally so small and so far away that their diameter has to be inferred from their absolute magnitude. Brightness, in turn, depends on the object's albedo (amount of light reflected from the surface). An object of magnitude 23 might have a diameter between 65m and 108m. Furthermore, with limited observations, the absolute magnitude may vary by +/-0.5 therefore the estimated diameter can range from 50m to 190m.
Iron asteroids are more likely to reach the ground intact. They comprise perhaps 5% of the smaller asteroids and are disregarded in this analysis.
Tsunami generated
by
impacts
Although, for a given location on the Earth's surface, the risk of a
"direct" hit from an asteroid is slight, researchers realized
that an ocean impact had the potential to be much more destructive due
to the effects of tsunami. An airburst explosion is a three dimensional
event and energy decreases according to the square of the distance but
a radiating ocean wave is a two-dimensional phenomenon and, in theory,
energy decreases in proportion to distance. Since the early 1990s some
advanced computer simulations
have been conducted to estimate the effects of asteroid impacts
above
deep oceans. The dramatic picture by Don Davis is a little misleading. When an asteroid hits the ocean at 70 000km/h there is a gigantic explosion. The asteroid and water vaporize and leave a huge crater - typically 20 times the diameter of the asteroid (that is, a 100m asteroid will create a 2 kilometre diameter crater). The water rushes back in, overshoots to create a mountain of water at the middle and this spreads out as a massive wave - a tsunami. The centre of the "crater" oscillates up and down several times and a series of waves radiate out. An idea of the mechanism can be obtained by bursting a balloon in a bathtub.
At this stage there are considerable differences in asteroid/tsunami predictions between the researchers. For a review of the methods see Ward & Asphaug (1999). After presenting their predictions of risk to coastal areas these authors note that "Being about ten times less than Hills et al. (1994) and perhaps ten times greater than Crawford and Mader (1998), our predictions split the field".
The main items of contention appears to be:
Crawford & Mader (1998) explain that, for an impact to produce a coherently propagating wave (one that does not dissipate substantial energy when it travels over great distances) the "cavity" must be 3 to 5 times broader than the depth of the ocean. Using a rule-of-thumb (derived from simulations) that the cavity diameter is 20 times the asteroid diameter then, for a typical ocean depth of 4km, the impactor must be at least 1 km in diameter to produce a coherent wave. On this basis, for asteroids smaller than about 1km, the wave will dissipate considerably as it travels over thousands of kilometres of ocean.
|
|
|
Ward & Asphaug (1999) (their Figure 6) |
Crawford & Mader (1998) (their
Table 1)
|
|
200m
|
1m (5m from equation)
|
5m
|
negligible
|
|
500m
|
11m
|
15m
|
<2m
|
|
1 km
|
35m
|
50m
|
6m
|
In the case of asteroids 200m and larger there is likely to be an impact into the ocean. For objects under this diameter there is a reduction in the size of the deepwater wave due to energy dissipation in the atmosphere. Speed, trajectory, density and strength of the object can affect the nature of the explosion. There does not appear to be an empirical formula available to deal with these smaller objects and it is possible that the smaller asteroids produce no appreciable waves. On the other hand, in the case of serious tsunami generated by earthquakes the energy involved is estimated to be equivalent to about 2 Megatons of TNT (Yabushita 1998). The impact by a 100m asteroid typically involves kinetic energy of about 75Mt so it would only involve the conversion of about 3% of this energy to wave energy in order to produce a serious tsunami - albeit, the tsunami could quickly dissipate, compared with an earthquake generated tsunami.
On balance the following conservative values have been used for risk assessment. These are based on extrapolation of Crawford and Mader data. Note that compared with Table 2, the range has been reduced to 100km to obtain reasonable values for the smaller asteroids.
Table 3. Estimated deepwater wave
height
(above sea level)
at a point 100km from asteroid
impact
(based on extrapolation of Crawford & Mader)
| Asteroid Diameter (m) |
|
|
50
|
0.12
|
|
100
|
0.7
|
|
200
|
3
|
|
500
|
22
|
|
1 km
|
70
|
|
2 km
|
230
|
Estimated risk to
coastal
locations
Taking the New Guinea experience as a reference level, it is assumed
that a tsunami with a 10m run-up will be
of concern to low-lying coastal areas. This risk is estimated in the
following steps: 
-
a) Determine the run-up factor W for the location in question.
b) Determine the critical deepwater wave height that will produce a tsunami with a run-up height of 10m (H = 10 / W).
c) For each size of asteroid, determine the distance over which a deepwater wave will need to travel before it has reduced in size to the critical height determined in step (b). This will be the "danger radius" for this combination of run-up factor and asteroid size.
d) Determine the area of a semi-circular area of ocean with a radius equal to the distance derived in step (c).
e) Calculate the probability of an impact within the area derived in step (d).
Using a log-log plot of the Crawford and Mader data (see Appendix), the following estimates of danger radius have been derived by (gross) extrapolation.
"Danger radius": Estimated radius from impact
for a tsunami 10m or higher at the shore
| Stony Asteroid |
|
||||||
| Diameter | 5 | 10 | 20 | 40 | |||
| (m) |
|
||||||
|
50
|
10
|
20
|
40
|
60
|
|||
|
100
|
40
|
70
|
130
|
230
|
|||
|
200
|
140
|
250
|
460
|
820
|
|||
|
500
|
800
|
1400
|
2500
|
4400
|
|||
|
1000
|
2800
|
5000
|
9000
|
16 000
|
|||
Impacts by asteroids 2km and larger exceed the global catastrophe threshold and are disregarded for the purpose of analysing tsunami effects.
For most coastal locations the surface area of ocean which poses a tsunami threat is a semi-circle with a radius R equivalent to the distances derived in the above table. This radius is, however, limited by the size of the ocean. An area corresponding to 30% of the surface area of the Earth has been used for this limit (the approximate size of the Pacific Ocean). Applying equation (1) to the resulting semi-circular areas provides the following estimates of average intervals between events:
(tsunami height 10m or more)
| Stony Asteroid |
|
||||||
| Diameter | 5 | 10 | 20 | 40 | |||
| (m) |
for a single location ("city") on the shore of a deep ocean. |
||||||
|
50
|
-
|
81 million
|
20 million
|
9 million
|
|||
|
100
|
-
|
66 million
|
19 million
|
6 million
|
|||
|
200
|
83 million
|
26 million
|
8 million
|
2 million
|
|||
|
500
|
20 million
|
7 million
|
2 million
|
670 000
|
|||
|
1,000
|
4 million
|
1.3 million
|
400 000
|
330 000
|
|||
|
All*
|
3 million
|
1 million
|
300 000
|
190 000
|
|||
In all cases it appears that risk of serious tsunami from asteroids 200m diameter and smaller is much less than for larger objects.
For a given coastal location the predicted average interval between 10m tsunami events (bottom row from Table 5) can be compared with the average interval between "direct" impacts (Table 1) to derive the relative risk for that location compared with an inland location (that is, a location which is not vulnerable to a 10m tsunami). Note that this is independent of the actual rate of impacts.
Table 6 - Relative risk of coastal
location compared to inland location
| Tsunami Run-up factor |
Relative risk due to all types of
impact
|
|
0 (inland)
|
1
|
|
5
|
4
|
|
10
|
14
|
|
20
|
46
|
|
40
|
74
|
This tentative analysis suggests that the risk to a
low-lying
coastal area from tsunami generated by asteroids is significantly
greater than the risk from a "direct" impact by such objects. The
average interval between such tsunami events is estimated to range from
about 190,000 years for a location with a run-up
factor of 40 to about 3 million years for a location with a
run-up factor of 5. These compare with an average interval of 14
million years for a "direct hit".
Discussion
Comparison with the risk analysis by others
In a paper titled "Asteroid impact hazard: a probabilistic hazard assessment" to be published in Icarus (and findings presented at the Tsunami Symposium in May 1999), Ward and Asphaug (1999) set out a comprehensive method of determining the impact tsunami risk. This analysis is based on methods they have developed for assessing earthquake risk. Probabilities are derived for a range of tsunami sizes striking a given coastline within a 1,000 year period. Note that in that paper tsunami height is measured just before the wave reaches the shore rather than run-up height. They assess the tsunami risk for a generic coastline and for the coastal cities San Francisco, New York, Tokyo, Hilo Harbour (Hawaii), Perth and Sydney.
The estimates derived above indicate considerably less risk from an asteroid-generated tsunami than that derived by Ward and Asphaug. For example, they estimate the risk of a 10m tsunami inundating a generic coastline (with a semi-circular "target area" of ocean having is radius of 6,000km) is 1.1% in 1,000 years, equivalent to one event every 91,000 years and about one tenth of the risk estimated above.
The main differences are likely to arise from assumptions about initial wave size and dispersion.
Comparison with other asteroid impact risks
In effect, the above analysis refers to risk of being caught in a region of direct devastation (being within the "blast area") compared with being within an area inundated by a tsunami. In the case of an impact by a large asteroid (diameter 2km or more) it has been estimated that 25% of the human population would die - mainly from indirect effects, such as starvation. This type of event is thought to occur with an average interval of 1 million years. The annual risk of dying in such an event is therefore about 1 in 4 million, which is similar to the tsunami risk for a location with a run-up factor of 5 (1 in 3 million).
In some circumstances an ocean impact might even be less hazardous to mankind than a land impact because less debris will be thrown into the atmosphere and indirect effects might be reduced. For example, it has been noted by Mader (1998) that the Eltanin impact by a large asteroid (estimates range from 1km to 4km) into the ocean near Chile some 2 million years ago did not create a crater on the seabed and apparently did not result in mass extinction. Contemplate what could have happened if the object had struck a slightly more northerly latitude and a few hours earlier - perhaps continental Africa would have been the target. Would Australopithecus, such as "Lucy", have survived? (Update: maybe it wasn't so benign - see this ABC News item about primate extinctions)
Update 15 Feb 02: Steve Ward provided this dramatic graphic of the Eltanin impact (right click and View for a higher resolution).
Conclusion
This tentative analysis suggests that the risk from asteroid tsunami has been substantially overstated - particularly in popular books about asteroid impacts with Earth. For typical coastal regions the risk of dying from an asteroid-generated tsunami is probably no greater than that of dying from the indirect effects of a large asteroid striking the Earth.For some coastal regions with unusual vulnerability to tsunami the risk of dying from asteroid-generated tsunami may be several times greater than that of dying from other asteroid-related causes. For these highly vulnerable areas the typical interval between asteroid tsunami events is likely to be about 200,000 years - assuming that impacts are randomly distributed in time.
There is considerable uncertainty about most of the "input values" used in these estimates. Also it is possible that impacts are not randomly distributed in time (Steel et al, 1995) and the Earth may be subjected to a barrage of small asteroids (or comet fragments) from time to time. This may have happened over the past few thousand years and could be a source of some of the tsunami that appear to have struck Australia during this period. Until we better understand the impact threat, there is no cause for complacency over the long intervals derived above. Finally, it is stressed that the run-up factor is not the sole issue in determining the destruction caused by a tsunami.
References
Crawford D.A. and Mader C.L. (1998) "Modeling asteroid impact and
tsunami", Science of
Tsunami Hazards, Vol 16, No.1.
Hills J.G. and Goda M.P (1998a) "Tsunami from asteroid and comet impacts: the vulnerability of Europe",Science of Tsunami Hazards, Vol 16, No.1.
Hills J.G. and Goda M.P (1998b) "Damage from the impacts of small asteroids", J Planetary and Space Science, Elsevier Science,( available in PDF format )
Mader C.L. (1998) "Modeling the Eltanin asteroid impact", Science of Tsunami Hazards, Vol 16, No.1.
Morrison D. and Chapman C. 1995 "The Biospheric Hazard of Large Impact". Proceedings of Planetary Defense Workshop.
Nott J. and Bryant E. (1999) "PALEOTSUNAMIS ALONG THE AUSTRALIAN COAST", Proceedings of the Tsunami Symposium,(temporary link), The Tsunami Society, May 1999.
Rynn J. and Davidson J.(1999) "CONTEMPORARY ASSESSMENT OF TSUNAMI RISK AND IMPLICATIONS FOR EARLY WARNINGS FOR AUSTRALIA AND ITS ISLAND TERRITORIES", Proceedings of the Tsunami Symposium,(temporary link), The Tsunami Society, May 1999.
Steel D. (1995) Rogue Asteroids and Doomsday Comets, John Wiley & Sons
Steel D., Asher D., Napier W. and Clube S. (1995) "Are impacts correlated in time?" Hazards due to comets and asteroids,
Ward S.N. and Asphaug E. (1999) "Asteroid impact tsunami: a probabilistic hazard assessment", Icarus, 1999 (preprint). Summary in PDF format
Yabushita S (1997) "On the possible hazard on the major cities caused by asteroid impact in the Pacific Ocean - II", Earth, Moon and Planets. 76 (1/2):117-121.
R.Young R.W.,Bryant E.,Price D. and Spassov E. (1996) "The
imprint
of tsunami in quaternary coastal sediments of Southeastern Australia"
website http://wwwrses.anu.edu.au/~edelvays/tsunami1.html
Appendices
Vulnerability the East Coast of Australia to a 10m TsunamiIrrespective of the cause, there is a need to assess the risk to coastlines from tsunami. The south east coast of Australia makes an sobering case study. This coastline covers about 1,500 km from the Sunshine Coast in Queensland to Eden in New South Wales. Many low lying coastal areas along the south east coast of Australia have been intensively developed. Excluding the non-coastal suburbs of Sydney and Brisbane, the total population along this coastline is about 1.2 million.
Consider the effects of a 10m tsunami like the one which hit northern New Guinea in July 1998. Based the topography of coastal developments along the south east coast of Australia it is conservatively estimated that about 50,000 dwellings, containing about 140,000 people (about 12% of the population), are in areas which could be inundated by a 10m tsunami. If it is assumed that these people are in or near their dwellings (or similar vulnerable areas) for 50% of the time and that the death rate from people caught in such a tsunami is 50% then it is expected that 25% of the population would be killed#. The predicted death toll from one event which caused a 10m tsunami along the south east coast of Australia is therefore 35,000 (25% of 140,000). This could easily double during peak summer periods.
Based on the above predictions, and assuming a run-up factor of 10, the chances of an asteroid-generated tsunami event occurring in the next fifty years are estmated to be about 1 in 20,000 - a low risk but high consequence event. For comparison, Ward & Asphaug (1999) include a site-specific calculation of tsunami risk for Sydney. They estimate there is a 1.15% risk of a 10m or higher tsunami in the next 1,000 years - this is equivalent to a 1 in 1,700 chance in 50 years.
Research by the University of Wollongong suggests that the New South Wales South Coast has been struck by at least six large tsunami within the last 6,000 years - a typical interval of 1,000 years - perhaps much less ( Young et al 1995). One possible cause is giant underwater "landslides" on the edge of the continental shelf but earthquakes and asteroid impacts may also be causes. Irrespective of the risk of tsunami from asteroid impact we really need to learn more about the risk to our coastlines from major tsunami.
# For comparison, the earthquake-generated 24m tsunami which hit about 300km of the coastline of Honshu, Japan in 1896 killed 27,000 people. In vulnerable fishing villages 80% or more of residents were killed. The tsunami hit at 8pm when most people were at home.
Update Dec 1999: The paper CONTEMPORARY ASSESSMENT OF TSUNAMI RISK AND IMPLICATIONS FOR EARLY WARNINGS FOR AUSTRALIA AND ITS ISLAND TERRITORIES by Rynn and Davidson is now available in PDF format (part of a 7.6Mb file for Vol 17 No. 2). See my review.
Poisson Distribution - events randomly distributed in time
In a Poisson process "events" occur at random points in time. It is possible to work out the probability of a certain number events occurring over a given interval of time. This can be useful for understanding the "uncertainty" about the time between impact events, and why the apparent lack of significant impacts over the past few hundred years (other than Tunguska) does not mean the estimates of impacts, from the known NEO population, are incorrect. This table sets out the probability for a process where the long term average interval between events is 100 years, as is estimated to be the case with the impact of 50m asteroids.Number of events
| Interval (yrs) | Nil | 1 | 2 | 3 | 4 |
| 50 | 61% | 30% | 8% | 1% | 0.2% |
| 100 (mean) | 37% | 37% | 18% | 6% | 2% |
| 200 | 14% | 27% | 27% | 18% | 9% |
| 500 | 1% | 3% | 8% | 14% | 17% |
For example, the probability of exactly one event
during a
100 year interval is 37% which is the same probability as nil events.
This may seem counter-intuitive given that the average interval
between
events is 100 years but it simply results from th erandom
distribution.
Notice that the probabilities in this row, (and the row for 50 year
interval)
add up to 100% - the other rows, if extended to larger numbers of
events,
would also add up to 100%.
Since both geological and historical records of a 50m NEO impact are
unlikely to be reliable beyond 200 years the "fact" that just one event
(Tunguska) appears to have occurred in this period is not unusual - it
has a probability of 27% - the same probabilty as 2 events.
Small time intervals
The above table applies where the time interval under consideration (h) is similar to the average time interval between events (T). Where the time interval under consideration is a small proportion of the average interval between events the probability of 1 event during time h is closely approximated by:-
P(one event in time h) = h /T
In a true poisson distribution we are never "overdue for an
event" - the probability of an event occurring in the next year is the
same as
in the previous year and will be the same in the following year. The
time
since the last event has nothing to do with the timing of the next
event.
Are impacts randomly distributed in time?
These calculations are based on the assumption that impacts are randomly distributed in time (Poission distribution). In the paper "Are impacts correlated in time?" by Steel, Asher, Napier and Clube (see the book "Hazards due to comets and asteroids"), it is proposed that impacts of objects in the range 50m to 300m arrive not randomly but in epochs of high activity.
Notes about the
analysis
There are several uncertainties about the values used in the above
calculations. These can only be resolved through more research into the near-earth
asteroid population (i.e. Spaceguard Survey) and tsunami effects on the
coastlines of interest.
Population estimates
Estimates of numbers killed depend on the number of people located in vulnerable areas when the tsunami hit and the circumstances at the time. The above population estimates for the East Coast of Australia were based on the proportion of each coastal town/city considered to be vulnerable to a 10m tsunami (roughly the proportion of dwellings in low-lying coastal areas - this varied from town to town but averaged out to about 12%) and the population of each town. The populations could easily double in peak summer periods. For a typical coastal plain it is estimated that a 10m tsunami would penetrate about 1km inland whereas a 100m tsunami would penetrate about 22km (Based on Hills and Mader 1995).The basis of the estimate of the proportion killed is given
in
the analysis but this is highly dependent of the time of day, the
season and the weather. A popular beach day would obviously be the
worst scenario -
perhaps ten times the estimate. Fortunately the chances of this are
very
slight - the total hours of popular beach days perhaps comprise 2% of
the
total hours in a year (mind you, Warringah's 6 beaches had an estimated
1.7
million visitors last summer!).
Extrapolation of Crawford & Mader data
The following graph is a log-log plot of the extrapolations used to derive Table 4, superimposed on the data from Crawford & Mader (their Table 1 on page 28). It can be seen that the extrapolations are speculative for both smaller asteroid sizes and large distances, since the Crawford and Mader data do not go below an asteroid diameter of 250m and do not go beyond a radius of 1,000km (and then only for the 1km asteroid). Strictly the extrapolations for the 50m and 100m asteroids do not take into account airburst effects but since the contribution of these impacts to overall tsunami risk turns out to be very low this will have negligible effect on the risk estimates. As a consequence of the uncertainties the risk estimates derived above should be regarded as ballpark estmates.The graph shows deepwater wave height (metres above sea level) by distance from impact (kilometres) for a range of asteroid diameters. The horizontal lines show the deepwater wave height which would produce a tsunami with a run-up height of 10m for a range of run-up factors (5, 10, 20 & 40).
An estimate of "danger radius" can be derived from the intercept of these lines with the asteroid lines. For example, the lower, thick horizontal line shows a deepwater wave height of 0.25m which would produce a 10m tsunami at a location with a run-up factor of 40. This intercepts the extrapolated line for a 200m asteroid at a "distance from impact" of about 800km, suggesting that an impact by a 200m diameter asteroid anywhere within a radius of 800km would produce a tsunami 10m or higher at a location with a run-up factor of 40 (this is an unusually high factor).
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