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Learning from the past: tsunami evidences along our coasts

Articles based on this release apeeared on PTI, NDTV.com, ibnlive.in.com, zeenews.com, Deccan Herald, The Hindu, Free Press Journal, Earnfree.in.

The 2004 tsunami was a devastating and unprecedented experience for countries bordering the Indian Ocean. In the absence of any known tsunami during recent or historic periods, one has to depend on the geologic records. Such data are very critical in evaluating tsunami hazards.

Coastal strips affected by regular sea surges and by anthropogenic activities are unlikely to preserve the tsunami sands, whereas inland lakes and streams have greater potential to preserve these records.

The tsunami from the 2004 Indonesian earthquake made inland traverses of 1-2 km in some parts of the Andaman and Nicobar islands. A team of researchers at the Centre for Earth Sciences (IISc) has been searching along the beaches and banks of inland streams of these islands for evidence for paleotsunami deposits. The paper presents the results of the arduous search along these coastal tracts to unearth findings from what they describe as “sheltered environments” which show higher chances for the preservation of such deposits.

They visited sites in the Andaman group of islands (Hut Bay, Port Blair, Interview Island, and East Island) and Kaveripattinam on the Indian east coast to study how their geomorphic settings make them useful archives of paleo-tsunami deposits.

The authors found that locally extensive occurrence of deposits such as sand, gravel and boulders, and their typically upward and inland occurrence are two important characteristics of tsunami deposits. Due to their greater inland penetration, tsunami deposits tend to occupy higher elevations (>5m) as compared to storm deposits, which are less than 4m typically.

They used evidence from such sheltered locations to reiterate the earlier conclusion by these researchers that the last major tsunami to have visited the Indian shores is about 1000 years old. Across the different regions studied, the authors were able to identify locations of high preservation potential. Co-relation of age data across locations suggested that the deposits were due to a regional event and not a localized sea surge. The authors believe that this spatially consistent chronological evidence opens more opportunities for tsunami geology, a nascent but important research area for India.

Dr. Kusala Rajendran says, “Actually the bottom line is that we need to develop such strategies to succeed in tsunami geology research in tropical countries with very active coastal regions that barely preserve anything beyond a few tens of years at the most. In the high latitudes, the story is different. Thus, identification of potential locations is key to developing the paleotsunami archives, for tunami hazard and recurrence studies.”

About the authors

Kusala Rajendran is an Associate Professor and Vanessa Andrade, a former Ph.D student at the Centre for Earth Sciences (CEaS) at the Indian Institute of Science. C P Rajendran is with the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore.

Contact: 080-2293-2633; kusala@ceas.iisc.ernet.in

Paper link: http://www.sciencedirect.com/science/article/pii/S1367912014003812

Journal: Journal of Asian Earth Sciences. Corrected proof published online on 3rd September 2014.