Evidence of ancient tsunamis uncovered at seaside cave in Indonesia
Seaside cave offers material deposits that were used to date ancient tsunamis
Ancient tsunamis occurred at unpredictable times
Dating materials found in a seaside cave in Indonesia leads researchers to find evidence of ancient tsunamis. In 2011, researchers discovered seabed sand deposits layered with bat guano which preserved remains of clamshells and microscopic organisms. By dating these materials using radiocarbon analysis, researchers were able to uncover evidence of ancient tsunamis of massive size.
The cave is located a couple of hundred yards inland from the coast, off the far western tip of Sumatra island in Aceh province. This is the place where 100 foot waves killed 230,000 people in several countries in 2004.
The limestone cave is merely 3 feet above knee-high tide, yet only waves that could engulf the coastal area are able to reach.
Researchers found that 11 ancient tsunamis of massive proportion had occurred, and possibly more.
They admitted the potential inaccuracy due to other ancient tsunamis possibly eroding the evidence of others.
The findings show that the ancient tsunamis were not evenly spaced. The last one occurred approximately 2,800 years ago; however in the preceding 500 years, 4 occurred.
Researchers are still working to determine the size of the waves from the ancient tsunamis.
“The take-home message is perhaps that the 2004 event doesn’t mean it won’t happen for another 500 years,” said Rubin, who added that the cave was discovered by chance and not part of planned field work. “We did see them clustered together closer in time. I wouldn’t put out a warning that we’re going to have an earthquake, but it shows that the timing is really variable.”
“The findings are very significant,” Katrin Monecke, a geosciences professor at Wellesley College in Massachusetts wrote in an email. She worked on tsunami sand deposits discovered in marshes in the area, but was not involved with the cave research on ancient tsunamis, which was presented this month at an American Geophysical Union conference in San Francisco. “The sand sheets in the cave cover a very long time span and give an excellent idea about earthquake frequency.”
“By learning about the type of tsunamis that happened in the past, maybe we can do planning for mitigation for the next tsunami,” said Nazli Ismail, head of the physics and geophysics department at Syiah Kuala University in Banda Aceh who worked on the project.