3 Historical Cases of Tsunami Caused by Rockslide, Pyro Clouds

TEMPO.CO, Jakarta - Many people were bewildered by the origins of the recent Sunda Strait tsunami that hit Carita Beach in Banten, West Java and Lampung, as the area’s early warning systems installed specifically to alarm people of an impending tsunami were not triggered.

After the tsunami took place on Saturday night, the Meteorology, Climatology and Geophysics Agency (BMKG) initially issued a public announcement through its Twitter account @infoBMKG stating there its early data suggest there were no seismic activities recorded in the region.

The agency later corrected their statement in the following tweet on December 23 at 02:55 AM stating that the tsunami is believed to be caused by activities from the nearby Mount Anak Krakatau (child of Krakatoa), though further analysis will need to be conducted.

As people await for BMKG’s official investigation report upon the cause of the Sunda Strait tsunami, distant and recent history have shown that a tsunami, which is generally a massive displacement of water, can be caused by major landslides. However, such as the Lituya Bay tsunami in 1958, an earthquake triggered a rockslide which eventually caused a massive tsunami. 

1. 1883 Krakatoa Mega Eruption

Pyroclastic clouds initially causing 46-meter waves

Mandeville, C.W.; Carey, S; Sigurdsson, H. & King, J. (1994) in their Journal of Geophysical Research: Solid Earth mentioned that the town of Merak was destroyed by a tsunami 46-meter high. Some of pyroclastic flows reached the Sumatran coast as much as 40 km away, having apparently moved across the water on a cushion of superheated steam.

The single most powerful eruption set off tremendous tsunamis that overwhelmed hundreds of villages on the coasts of Java and Sumatra.

2. 1958 Lituya Bay, Alaska

An earthquake that triggered rockslides causing a 520-meter wave

The 1958 Lituya Bay earthquake occurred on July 9 at 22:15:58 with a moment magnitude of 7.8 and a maximum Mercalli intensity of XI (Extreme). The earthquake took place on the Fairweather Fault and triggered a rockslide of 30 million cubic meters and about 90 million tons into the narrow inlet of Lituya Bay, Alaska. The impact with the waters beneath caused sudden displacement of water that resulted in a mega-tsunami that washed out high-rising trees to a maximum elevation of 520 meters.

3. 2017 Karrat Fjord, Greenland

Landslide causing a 100-meter wave

A massive 100-meter tsunami suddenly appeared after a landslide that occurred in the evening of June 17, 2017, hit a remote settlement in Karrat Fjord on the west coast of Greenland.

Researchers found that a large volume of rock had plunged from one of the steep sides of the fjord into the water 1,000-meters below, and shattered chunks of a glacier. That disturbance pushed water levels up by more than 90-meters along the coastline.

RICKY M N