A larger form of tsunami caused by a truly gigantic landslide, such as a collapsing island, into a body of water, such as an ocean or sea. Such a tsunami can reach hights of 100 meters, can reach jet speed and they can reach up to 12km inland, and possibly more in low-lying regions.

The possibility of such colossal disasters was first observed in Alaska by two geologists searching for oil, when they observed evidence of unusually large waves in the nearby bay. Five years later, landslides were revealed to be the source of the waves. These landslides would hit the water so fast that the displaced water could not settle before the rocks had, which increased the strength of the resulting wave. Subsequently, this was found to pertain to much larger landslides as well, including collapsing island masses.

The geological record shows that events such as mega tsunamis are very rare, but are extremely devastating to anything near the receiving shore when they do occur. The last such event (that we know of) occured approximately 4000 years ago on RĂ©union Island, to the east of Madagascar.

The most likely candidate for the next mega tsunami is the island of La Palma, in the Canary Islands. If the Cumbre Vieja on La Palma were to collapse, the result would be a massive wave headed straight for the eastern coast of the United States, and the aftermath would hold obvious implications for the stability of the government and economy of the world. While potentially not as devastating as a supervolcano, a mega tsunami would be a very tragic disaster in whatever region of the world it occured.
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