By: Kyle James | 12-23-2018 | Science
Photo credit: @Sydney_Uni

How Undersea Landslides Cause Tsunamis

Tsunamis are the focus of many disaster films, but since they are limited to coastal areas, the vast majority of people have never experienced one. It is difficult to imagine the vast power of mother nature and even reading or seeing footage of a tsunamis does not do them justice. They are a powerful and destructive force of nature that can strike at virtually any moment.

What Is A Tsunami?

The National Ocean Service describes a tsunami as "giant waves caused by earthquakes or volcanic eruptions under the sea." It's like taking a kiddie pool, filling it with water, and then kicking the bottom of the pool from underneath, the result is a series of waves that although they do not dramatically increase in height, as they travel inland the depth of the ocean becomes shallower and shallower.

Take, for example, the "Boxing Day Tsunamis" which occurred on December 26, 2004, as the result of an undersea megathrust earthquake that registered a magnitude of 9.1-9.3. The earthquake which started the tsunamis was caused by a rupture along the fault line between the Burma Plate and the Indian Plate. The result was a massive series of tsunamis, some ranging as high as 100 feet, which collectively became known as the Boxing Day Tsunamis. These tsunamis killed around 227,898 people in over 14 countries all stemming from the singe megathrust earthquake at the ocean floor.



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What Causes A Tsunami?

In the case of the 2004 Boxing Day Tsunamis, a submarine earthquake was the cause, but what else can cause a tsunami? They can also form as a result of an eruption or collapse of an island or coastal volcanoes. Interestingly enough, a landslide can also cause a tsunami. Landslides are often the result of earthquakes and can be generated on impact as a rapidly moving landslide mass enters the water. A 7.9 magnitude earthquake on the Fairweather Fault occurred on July 9, 1958, triggering a rock avalanche at the head of Lituya Bay, Alaska. The landslide generated a wave that reached as high as 1,719 feet on the opposite shore.




But did you know a landslide can also occur under the ocean and create a tsunami by causing the water to be displaced behind and ahead of a rapidly moving underwater landslide? U.S. Geological Survey research in the Canary Islands concludes "that there have been at least five massive volcano landslides that occurred in the past, and that similar large events might occur in the future. Giant landslides in the Canary Islands could potentially generate large tsunami waves at both close and very great distances, and could potentially devastate large areas of coastal land as far away as the eastern seaboard of North America."

This animation by Geoscience Australia illustrates how an undersea landslide can generate a tsunami.



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The Most Recent Tsunami

The most recent tsunami was reported to have hit the coast around Indonesia's Sunda Strait on December 22, 2018. At 1:55 p.m. Saturday, Indonesia's disaster management agency confirmed a tsunami left at least 168 dead and another 745 injured. A spokesman from the agency named Sutopo Purwo Nugroho said those numbers are likely to rise as many areas have still not been reached by rescue crews.







How To Recognize The Signs Of A Tsunami

Learning about tsunami's doesn't do you much good if you don't learn how to recognize one in the real world. Let's say you are vacationing in the Caribbean and enjoying a day at the beach. How would you know when a tsunami is about to occur? The Pacific Tsunami Warning Center offers these three signs to be on the lookout for if you want to survive a tsunami.

1. Severe ground shaking from local earthquakes may cause tsunamis.

2. As a tsunami approaches shorelines, water may recede from the coast, exposing the ocean floor, reefs and fish.

3. Abnormal ocean activity, a wall of water, and an approaching tsunami create a loud "roaring" sound similar to that of a train or jet aircraft.

Furthermore, the Pacific Tsunami Warning Center says, "If you experience any of these phenomena, don't wait for official evacuation orders. Immediately leave low-lying coastal areas and move to higher ground."



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Source: https://www.usgs.gov/faqs/how-do-landslides-cause-tsunamis?qt-news_science_products=0#qt-news_science_products

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Thoughts on the above story? Comment below!
2 Comment/s
Anonymous No. 93164 2018-12-23 : 21:31

You think in this day and age of information at your fingertips, when the waters recede for 2 miles back to the ocean, people would know its a massive tsunami coming and not just a curiosity.

Fantasys No. 94627 2019-08-08 : 20:38

The most important cause of tsunamis is not mid-ocean earthquakes but underwater landslides just off shore, according to geophysicists presenting research at the American Geophysical Union Meeting in San Francisco.

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