Tsunami left autographs in Indonesia's coastal cave

Scientists exploring a coastal cave in Indonesia have discovered the oldest tsunami report in the world. No, this is not a chronicle or a cave drawing of an ancient diver, but a 5,000-year-old sedimentary section. Studying it, experts understood how little science knows about how exactly earthquakes cause massive waves.

Wave footprint

The recent devastating tsunami in the Indian Ocean in 2004 claimed the lives of millions of coastal residents. And the find suggests that people still cannot predict when the next earthquake will occur. Tsunamis are unevenly distributed in time: long periods can pass between them, but also only a few decades.

The discovery was made in a sea cave on the west coast of Sumatra in Indonesia, south of the city of Banda Aceh, which was destroyed by the tsunami in December 2004. The stratigraphic record shows successive layers of sand, bat droppings, and other debris left by the tsunami that occurred from 7900 to 2900 years ago. Newer layers erased the 2004 tsunami.

Sea worries times

Scientists have found that over the past 5000 years, 11 tsunamis occurred in these places as a result of earthquakes along a large fault in the Indian Ocean off the coast of Sumatra. At the same time, two millennia were “silent” - during this time not a single tsunami occurred. On another occasion, four large waves appeared in these places in just one century.

In general, one can notice a pattern: small tsunamis occur at shorter intervals, and then “sleeping” periods begin, interrupted by strong earthquakes and tsunamis, as in 2004.

Research data says that in the coming decades we can expect some more strong tsunamis after earthquakes in the Indian Ocean.