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How do volcanic eruptions generate tsunamis?


Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area. According to this mechanism, waves may be generated by the sudden displacement of water caused by a volcanic explosion, by a volcano's slope failure, or more likely by a phreatomagmatic explosion and collapse/engulfment of the volcanic magmatic chambers. One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36,417 people. It is also believed that the destruction of the Minoan civilization in Greece was caused in 1490 B.C. by the explosion/collapse of the volcano of Santorin in the Aegean Sea.

 

Diagram of how a volcanic eruption can generate a tsunami.

Diagram of how a volcanic eruption can generate a tsunami. Geoscience Australia.

Diagram source: Geoscience Australia.

 

When you look at the risk of a tsunami in your community, you need to consider the different sources in your area/region that can generate a tsunami. Volcanoes are one source that can produce tsunamis as high as those produced by the largest earthquake. They can be caused by mechanisms such as volcanic earthquakes, undersea eruptions, pyroclastic flows, caldera collapse, landslides, lahars, phreatomagmatic eruptions, lava bench collapse, and airwaves from large explosions. There have been 110 eruptions that caused tsunamis' (NGDC/WDS). Below are a few examples of volcanic eruptions that have caused a tsunami:

  • In 1792, the eruption of Mount Unzen in Japan produced a destructive landslide generating a 
        165-foot tsunami. The death toll from the disaster is estimated at over 15,000 people, 
        making it the most deadly volcanic eruption in Japan's history.
  • The 1883 eruption of Krakatoa in Indonesia caused by *pyroclastic flows entering the water 
        (A base surge resulting from collapse of the eruption column) that produced run-up 
        heights of 120 feet and killed over 26,000 people and many costal villages destroyed.
  • The 1980 Eruption of Mount St. Helens in Washington (USA) caused partial collapse of the 
         volcano's flank and an avalanche into Spirit Lake producing a 780-foot tsunami.


Citations:
 
National Geophysical Data Center / World Data Service (NGDC/WDS): Significant Volcanic Eruptions Database. National Geophysical Data Center, NOAA. doi:10.7289/V5JW8BSH

*1883 eruption of Krakatoa: Volcanologists Self & Rampino had the correct source sorted out in 1981 (Science), though a convincing numerical model confirming that source was not published until Maeno & Imamura in 2011 (JGR).

 mount st helens 1982 2007

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