Megatsunami

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Megatsunamis , actually impact tsunamis, are called tsunamis with a wave height that is significantly higher than that of tsunamis triggered by earthquakes. According to a proposal by geologist and tsunami researcher James Goff, tsunamis are tsunamis with a wave height of more than 100 meters at the point of origin.

The wave height or the amplitude (the height from the calm water level to the high point of the wave crest) of a Megatsunami is higher, the closer the wave is to the place of origin. Since earthquakes, as far as we know today, are not able to generate waves of more than 20 m high, only very rare, catastrophic events such as the impact of a large meteorite or landslides directly on the sea can cause such megatsunami.

Several meteorite impacts are known from recent geological history, which very likely resulted in megatsunamis with global effects. The term megatsunami was probably first used in such a context : in a geological work from 1990 that described tsunami deposits on the Cretaceous-Paleogene border . This tsunami was likely caused by the Chicxulub impact 66 million years ago. In simulations of the impact in the Gulf of Mexico and the water displacement, the wave was up to 1500 m high at the point of origin. At that time there was no land connection between North and South America, a wave about 14 m high in the open sea spread rapidly across the world. The heights on land were not simulated, but were certainly considerably higher than 14 m. The Chesapeake Bay impact in the Eocene 35.5 million years ago probably triggered a megatsunami.

Landslides cause tsunamis of very short wavelength that cannot propagate for thousands of kilometers without losing their energy. Only such locally limited megatsunamis are known for certain from historical times. After the landslides in Hawaii (1868 on Mauna Loa and 1975 on Kīlauea ) large local tsunamis occurred without endangering the American or Asian coast. There is controversial debate as to whether the Mahuika crater in the sea off New Zealand , formed by a meteorite impact, is a possible megatsunami in the 15th century, which is held responsible for deposits up to 220 meters above sea level on Stewart Island . With a run-up height - the height above sea level that the tsunami reached after it landed - of 520 meters, the largest tsunami in at least the last 100 years was triggered on July 9, 1958 by a landslide in Lituya Bay ( Alaska ).

A possible future trigger is z. B. the Cumbre Vieja on the Canary Island of La Palma . Some geologists fear that a flank of the Cumbre Vieja could slide into the Atlantic in the event of further volcanic eruptions. According to studies by the Technical University of Delft , such a landslide is unlikely in the next 10,000 years, since the Cumbre is not yet high and not steep enough. A flank slide would only be possible at all when extremes collide, such as very heavy rain with an extraordinarily strong volcanic eruption at the same time. Calculations by the university state that forces of up to 28 trillion Newtons would have to act.

At high latitudes, the thawing of permafrost and the loss of glacial ice can destabilize slopes, increasing the risk of landslides and megatsunamis.

The following list shows the largest tsunamis of the past 100 years measured by their incidence heights:

Megatsunamis of the last 100 years
year place Waters trigger Max. Run-up height (m) please refer
1958 Lituya Bay, Alaska, USA Fjord subaeric landslide 524
1980 Spirit Lake , Washington, USA lake Landslide as a result of a volcanic eruption 250 → Mount St. Helens erupted in 1980
1963 Casso , Italy reservoir subaeric landslide 235 → Vajont dam
2015 Taan Fjord , Alaska, USA Fjord subaeric landslide 193 → Tyndall Glacier
1936 Lituya Bay, Alaska, USA Fjord subaeric landslide 149
2017 Nuugaatsiaq , Greenland Fjord subaeric landslide 90 → Tsunami in Greenland 2017

Individual evidence

  1. ↑ a b c James Goff, James P. Terry, Catherine Chagué-Goff, Kazuhisa Goto: What is a mega-tsunami? . (PDF) In: Marine Geology (Elsevier) . No. 358, December 2014, pp. 12-17. doi : 10.1016 / j.margeo.2014.03.013 . (accessed on October 7, 2015)
  2. ↑ Katherine Kornei: Huge global tsunami followed dinosaur-killing asteroid impact . In: Eos . December 20, 2018, doi : 10.1029 / 2018EO112419 .
  3. ↑ Linda Maria Koldau: Tsunamis . CH Beck, 2013, ISBN 978-3-406-64656-0 , pp. 19-20 .
  4. ^ Mahuika crater discussion
  5. ↑ Geology.com Lituya Bay Megatsunami
  6. ↑ a b c Bretwood Higman u. a .: The 2015 landslide and tsunami in Taan Fiord, Alaska . In: Scientific Reports . No. 12993 , September 6, 2018, Table 1, doi : 10.1038 / s41598-018-30475-w .
  7. ↑ Document from the University of California Santa Cruz on a possible landslide on the Cumbre Vieja with tsunami simulation (English) (PDF file; 750 kB)
  8. ^ The day the world ended. Delft University of Technology, archived from the original on March 10, 2014 ; accessed on August 5, 2012 .
  9. ^ B. McGuire: Potential for a hazardous geospheric response to projected future climate changes . In: Philosophical Transactions of the Royal Society A . March 2010, doi : 10.1098 / rsta.2010.0080 .

Web links

Commons : Megatsunami  - collection of pictures, videos and audio files