Evidence Of Tsunamis On Indian Ocean Shores Long Before 2004

Kruawun Jankaew led a team of geologists who unearthed evidence that tsunamis have repeatedly washed over a Thai island during the last 2,800 years.

A quarter-million people were killed when a tsunami inundated Indian Ocean coastlines the day after Christmas in 2004. Now scientists have found evidence that the event was not a first-time occurrence.

A team working on Phra Thong, a barrier island along the hard-hit west coast of Thailand, unearthed evidence of at least three previous major tsunamis in the preceding 2,800 years, the most recent from about 550 to 700 years ago. That team, led by Kruawun Jankaew of Chulalongkorn University in Thailand, included Brian Atwater, a University of Washington affiliate professor of Earth and space sciences and a U.S. Geological Survey geologist.

A second team found similar evidence of previous tsunamis during the last 1,200 years in Aceh, a province at the northern tip of the Indonesian island of Sumatra where more than half the deaths from the 2004 tsunami occurred.

Sparse knowledge of the region's tsunami history contributed to the loss of life in 2004, the scientists believe. Few people living along the coasts knew to heed the natural tsunami warnings, such as the strong shaking felt in Aceh and the rapid retreat of ocean water from the shoreline that was observed in Thailand.

But on an island just off the coast of Aceh most people safely fled to higher ground in 2004 because the island's oral history includes information about a devastating tsunami in 1907.

"A region's tsunami history can serve as a long-term warning system," Atwater said.

The research will reinforce the importance of tsunami education as an essential part of early warning, said Jankaew, the lead author.

"Many people in Southeast Asia, especially in Thailand, believe, or would like to believe, that it will never happen again," Jankaew said. "This will be a big step towards mitigating the losses from future tsunami events."

The team found evidence for previous tsunamis by digging pits and auguring holes at more than 150 sites on an island about 75 miles north of Phuket, a Thai tourist resort area ravaged by the 2004 tsunami. That tsunami was generated 300 miles to the west when the seafloor was warped during a magnitude 9.2 earthquake.

At 20 sites in marshes, the researchers found layers of white sand about 4 inches thick alternating with layers of black peaty soil. Witnesses confirmed that the top sand layer, just below the surface, was laid down by the 2004 tsunami, which ran 20 to 30 feet deep across much of the island.

Radiocarbon dating of bark fragments in soil below the second sand layer led the scientists to estimate that the most recent predecessor to the 2004 tsunami probably occurred between A.D. 1300 and 1450. They also noted signs of two earlier tsunamis during the last 2,500 to 2,800 years.

There are no known written records describing an Indian Ocean tsunami between A.D. 1300 and 1450, including the accounts of noted Islamic traveler Ibn Battuta and records of the great Ming Dynasty armadas of China, both of which visited the area at different times during that period. Atwater hopes the new geologic evidence might prompt historians to check other Asian documents from that era.

"This research demonstrates that tsunami geology, both recent and past tsunamis, can help extend the tsunami catalogues far beyond historical records," Jankaew said.

The new findings also carry lessons for the northwest coast of North America, where scientists estimate that many centuries typically elapse between catastrophic tsunamis generated by the Cascadia subduction zone.

"Like Aceh, Cascadia has a history of tsunamis that are both infrequent and catastrophic, and that originate during earthquakes that provide a natural tsunami warning," Atwater said. "This history calls for sustained efforts in tsunami education."

Findings from both teams are published in the Oct. 30 edition of Nature.

Other co-authors of the Thai paper are Yuki Sawai of the Geological Survey of Japan, Montri Choowong and Thasinee Charoentitirat of Chulalongkorn University, Maria Martin of the UW and Amy Prendergast of Geoscience Australia.

The research was funded by the U.S. Agency for International Development, Thailand's Ministry of Natural Resources and Environment, the U.S. National Science Foundation, the Japan Society for the Promotion of Science and the Thailand Research Fund.

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The above post is reprinted from materials provided byUniversity of Washington. Note: Materials may be edited for content and length

Advances Since the 2004 Indian Ocean Tragedy | sci-english.blogspot.com

Tsunami File photo in tamilnadu, india | sci-english.blogspot.com

The Indian Ocean tsunami was one of the worst natural disasters in history. Enormous waves struck countries in South Asia and East Africa with little to no warning, killing 243,000 people. The destruction played out on television screens around the world, fed by shaky home videos. The outpouring of aid in response to the devastation in Indonesia, Sri Lanka, Thailand and elsewhere was unprecedented.

The disaster raised awareness of tsunamis and prompted nations to pump money into research and warning systems.  on the 10th anniversary of the deadly tsunami, greatly expanded networks of seismic monitors and ocean buoys are on alert for the next killer wave in the Indian Ocean, the Pacific and the Caribbean. In fact, tsunami experts can now forecast how tsunamis will flood distant coastlines hours before the waves arrive.

But hurdles remain in saving lives for everyone under the threat of tsunamis. No amount of warning will help those who need to seek immediate shelter away from beaches, disaster experts said.


"A lot of times, you're not going to get any warning near these zones where there are large earthquakes, so we have to prepare the public to interpret the signs and survive," said Mike Angove, head of the National Oceanic and Atmospheric Administration's (NOAA) tsunami program. In 2004, the tsunami waves approached coastal Indonesia just nine minutes after the massive magnitude-9.1 earthquake stopped shaking, Angove said.


 On alert

Since 2004, geologists have uncovered evidence of several massive tsunamis in buried sand layers preserved in Sumatran caves. It turns out that the deadly waves aren't as rare in the Indian Ocean as once thought. "We had five fatal tsunamis off the coast of Sumatra prior to 2004," said Paula Dunbar, a scientist at NOAA's National Geophysical Data Center. Over the past 300 years, 69 tsunamis were seen in the Indian Ocean, she said.

Despite the risk, there was no oceanwide tsunami warning system in the region. Now, a $450 million early-alert network is fully operational, though it is plagued with equipment problems. (Even the global monitoring network loses 10 percent of its buoys each year, according to NOAA.) Essentially built from scratch, the $450 million Indian Ocean Tsunami Warning System (IOWTS) includes more than 140 seismometers, about 100 sea-level gauges and several buoys that detect tsunamis. More buoys were installed, but they have been vandalized or accidentally destroyed. The buoys and gauges help detect whether an earthquake triggered a tsunami.

The global network of Deep-Ocean Assessment and Reporting of Tsunami (DART) buoys, which detects passing tsunami waves, has also expanded, from six buoys in 2004 to 60 buoys in 2014, Angove said.

Regional tsunami alert centers have been built in Australia, India and Indonesia. Scientists at the centers decide whether a tsunami is likely based on information from the network of sensors, estimate the probable size, then alert governments to get the warning out through sirens, TV, radio and text alerts.

Getting the warnings down to people living in remote coastal areas is one of the biggest hurdles for the new system. Not all warnings reach the local level. And not every tsunami earthquake is strong enough to scare people away from shorelines. In Sumatra's Mentawai Islands, a 2010 tsunami killed more than 400 people because residents failed to evacuate in the short time between the earthquake and the tsunami's  arrival. The shaking was simply not strong enough to trigger people's fear of tsunamis, even though islanders had self-evacuated after a 2007 earthquake, according to an investigation by the University of Southern California's Tsunami Research Center. There was also no clear-cut warning from the regional tsunami alert system.

"Tsunami earthquakes remain a major challenge," Emile Okal, a seismologist at Northwestern University in Evanston, Illinois, said Dec. 15 at the American Geophysical Union's (AGU) annual meeting in San Francisco.