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Indonesian volcano shrinks after collapse that triggered deadly tsunami

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By Alice Tidey
Anak Krakatau
Anak Krakatau   -   Copyright  Antara Foto/Muhammad Adimaja via REUTERS
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Indonesia's Anak Krakatau volcano shrunk by over two thirds when a flank collapsed last week triggering a deadly tsunami following a series of eruptions, satellite images revealed.

The volcano, which had grown to be 338 metres high since it first appeared above water in 1927, now measures only 110 metres, according to the Centre for Volcanology and Geological Hazard Mitigation.

Its volume is now estimated between 40-70 million cubic metres after about 150-170 million cubic metres tumbled into the sea.

The estimates were made based on pictures from several radar satellites including the European Space Agency's Sentinel-1. Photographic satellite images were not available because of cloud cover.

Japan's Geospatial Information Authority also released before and after pictures and said that "approximately 2 kms square" of the volcano's southwestern flank had collapsed. It added that the deadly December 22 tsunami in the Sunda Strait was likely triggered when a chunk slipped into the ocean.

Geospatial Information Authority of Japan

More than 420 people lost their lives when five-metre-tall waves battered the coastlines of Indonesia's Java and Sumatra islands.

Anak Krakatau, which had spewing lava and ash for weeks prior to the tsunami, continues to do so. Indonesia authorities extended a no-go zone to five kms on Thursday and ordered flights to steer clear of the area.

Authorities also indicated that the eruption pattern had changed from Strombolian — relatively mild blasts of lava — to Surtseyan, which can result in loud explosions as lava comes in contact with shallow sea water producing ash.

But the volcano's reduced size makes it unlikely that another tsunami will be triggered, the head of the country's energy ministry's geology agency, Antonius Ratmomopurbo, said on Saturday.