How Volcanoes Can Trigger Tsunamis

How Volcanoes Can Trigger Tsunamis
Nobody had any clue. There was certainly no warning. It's part of the picture that now suggests a sudden failure in the west-southwest flank of the Anak Krakatau volcano was a significant cause of Saturday's devastating tsunami in the Sunda Strait.

Of course everyone in the region will have been aware of Anak Krakatau, the volcano that emerged in the sea channel just less than 100 years ago. But its rumblings and eruptions have been described by local experts as relatively low-scale and semi-continuous. In other words, it's been part of the background.

And yet it is well known that volcanoes have the capacity to generate big waves. The mechanism as ever is the displacement of a large volume of water. The first satellite imagery returned after the event on Saturday points strongly to a collapse in the west-southwest flank of the volcano during an eruption. This would have sent millions of tonnes of rocky debris into the sea, pushing out waves in all directions.

Prof Andy Hooper from Leeds University, UK, is a specialist in the study of volcanoes from orbit. He had little doubt in the interpretation when examining the pictures from Europe's Sentinel-1 radar spacecraft.

"As well as an increase in the size of the crater, there are new dark features on the west side indicating steep-sided scarps in shadow, presumably due to collapse; as well as changes in the coastline."

The comparison between Saturday's imagery and Sentinel pictures acquired before the tsunami are telling.  But the precise anatomy of this event will not be known until teams can get into the area of the volcano to do a proper survey, and at the moment that is too dangerous. Further collapse could kick off more tsunamis.

Scientists have had concerns for some time about Anak Krakatau, the edifice that has grown in place of the infamous Krakatau mountain that blew itself apart on the same spot in 1883. Continue...

James Koroma

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