Volcanic Tsunamis
Daily Earth Science Repost

Volcanic tsunamis

Sunday’s news carried reports about ongoing eruptions of the Taal volcano located 45 miles south of Manila in the Philippines. Evacuations are underway due to concerns about a catastrophic eruption within days. One of the concerns is a potential volcanic tsunami on Taal lake. 

Located in the middle of Taal lake, the Taal volcano is one of the world’s smallest. Also, it is a popular tourist destination. The recent events at White Island in New Zealand demonstrate that tourism and volcanos are not always a good mix. But the fact that the Taal volcano is on the small side does not reflect the size of the threat. This volcano erupts every decade on the average and has killed about 6000 people during the past 300 years.

One of the threats posed by the Taal volcano is an eruption which triggers a tsunami in the lake surrounding the island. 

A brief review of volcanic tsunamis

Most of the time, we associate tsunamis with earthquakes, but volcanic eruptions have a long and deadly history of sparking disaster from these devastating waves. The famous 1883 eruption of Krakatoa in Indonesia generated a 120-foot high tsunami that killed 26,000 people.

Earlier in 1792, an eruption of Mount Unzen in Japan generated a 165-foot tsunami, and 15,000 people perished. Most recently, the eruption of Mount St. Helens resulted in a 760-foot tsunami when a collapsed flank of the mountain crashed into Spirit Lake.

Before reliable historical accounts, the ancient Minoan civilization in Greece is believed to have been wiped out by a tsunami from the collapse of the volcano of Santorin in the Aegean Sea.

The mechanics of disaster 

Tsunamis triggered by volcanic eruptions occur because of various reasons. For volcanos submerged beneath the water surface, phreatomagmatic explosions are a source of danger. These explosions result from the release of heat energy from the volcanic magma and its subsequent transfer to the surrounding water. These types of explosions are most likely in water depths of 100 meters or less but can occur as deep as 1 kilometer below the water surface.

Volcanos that tower above oceans or lakes pose different kinds of threats. Sometimes, the violent collapse of mountain flanks, like the Mount St. Helens example, creates an avalanche of rock, ash, pyroclastic flows, and lahars. The massive amount of kinetic energy in these fast-moving flows transfers to the water at the slope’s base in the form of tsunami waves. A tsunami generated from this process spreads outward to inundate all coastal communities in its path.

Volcanic explosions and collapses occurring at sea level employ yet another mechanism. These eruptions result in the displacement of large volumes of water through both explosive and implosive processes. As with earthquakes, this large-scale displacement of water creates a corresponding energy release/transfer in the form of tsunami waves.

So, we can add one more item to the list of why volcanos don’t mix with tourism:

  • Lava Flows
  • Pyroclastic Flows
  • Lahars
  • Poisonous gas release
  • Tsunami

The list is growing.


ArcheanWeb:

Disaster on White island (Source: ArcheanWeb) – https://archeanweb.com/2019/12/10/disaster-on-white-island-dangerous-volcano/ Also:

Washington: home to dangerous volcanoes (Source: ArcheanWeb) – https://archeanweb.com/2019/12/12/washington-home-to-dangerous-volcano/ Also:

Sources:

Philippines warns of ‘explosive eruption’ as volcano spews ash (By Enrico Dela Cruz and Karen Lema – U.S News and World Report) – https://www.usnews.com/news/world/articles/2020-01-12/restive-philippine-volcano-prompts-evacuation-of-thousands-of-residents Also:

How do volcanic eruptions generate tsunamis? (International Tsunami Information Center) – http://itic.ioc-unesco.org/index.php?option=com_content&view=article&id=1159:how-do-volcanic-eruptions-generate-tsunamis&catid=1340&Itemid=2059 Also:

TAAL VOLCANO ERUPTION IN PHILIPPINES SPARKS RARE ‘VOLCANIC LIGHTNING’ AS MANILA AIRPORT FLIGHTS SUSPENDED (Jon Lockett – The Sun) – https://www.thesun.co.uk/news/10720994/taal-volcano-eruption-philippines/ Also:

Phreatomagmatic Explosions in Subaqueous Volcanism (Bernd Zimanowski –  Washington DC American Geophysical Union Geophysical Monograph Series) – https://www.researchgate.net/publication/259619285_Phreatomagmatic_Explosions_in_Subaqueous_Volcanism Also:

Feature Image: The Great Wave off Kanagawa, by Katsushika Hokusa (Modified) – This work is in the public domain in the United States because it was published (or registered with the U.S. Copyright Office) before January 1, 1925.

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.

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