Ancient mega tsunamis discovered

Waw (Dr. Kruawun Jankaew) from Chulalongkorn University has been working on Phra Thong Island for the past seven years to study the extension and impact of the 2004 tsunami. By digging extensive trenches in many parts of the island, she has also been able to find layers of several ancient tsunamis, dating to about 600 and 2000 years back in time. Each of these layers is covered by a distinct soil layer, which helps to distinguish and date the different tsunami events. Her results were published in an article in Nature in 2008 (Jankaew et al. Medieval forewarning of the 2004 Indian Ocean tsunami in Thailand, Nature Vol 455|30 October 2008| doi:10.1038/nature07373).

Waw is Linda Löwhagen’s co-supervisor and the reason why we came to Phra Thong in the first place. Thanks to Waw and thanks to our collaboration with Chulalongkorn University, we were at all able to offer a tsunami research project as part of the teacher’s research school on Natural Hazards (see details about the research school at http://www.geo.su.se).

On our first day on the island, Waw introduced us to her different sections, showed us how the dark soil and light tsunami layers look like, and how tsunami layers can be distinguished from storm deposits. We also visited a village and a temple that had been completely destroyed by the 2004 tsunami and which are now covered by several meters of sand.

To being able to follow the same tsunami layer over a longer distance it is important to dig long and deep trenches perpendicular to the shore. But digging trenches in dense vegetation is not an easy task, especially when these quickly fill up with water, when the water is full of eels and the ground full of snakes, when mosquitos are all around ones head, and the sun is burning hot.

Waw’s explanations in front of the different sections gave us an excellent background for discussing Linda’s research project in more detail. We agreed that Linda should look closer at the elemental composition of the tsunami layers using the Itrax XRF equipment, and that she would compare results from three or four different localities, where all four tsunami layers are present. In addition, she would study a storm deposit using the same analytical techniques and then compare these results with those obtained from the tsunami layers. More radiocarbon dates for the soils bracketing the ancient tsunami layers would also be useful, as these would help narrowing the chronology of the events. Waw’s student Aim, on the other hand, will work with the heavy minerals in the storm and tsunami deposits and will compare these to offshore sediments from different depths.

Thanks to Waw’s earlier excavations, Linda can make use of existing sections. But these need to be cleaned and water has to be pumped out from the trenches to being able to see and sample the sediments. Aim’s project on the other hand requires a boat trip and collection of sediment samples from the ocean bottom at different depths. Clearly, there is a lot of work ahead of us!

Introducing Phra Thong's geology

Introducing Phra Thong’s geology

Where exactly are the trenches?

Where exactly are the trenches?

The water is far too high!

The water is far too high!

Tsunami work means having the feet and legs under water

Tsunami work means having the feet and legs under water

Grass needs cutting and the water needs to be drained

Grass needs cutting and the water needs to be drained

Off to the next section in Mr. Wa's orchard

Off to the next section in Mr. Wa’s orchard

The 2004 tsunami sands covered a whole village

The 2004 tsunami sands covered a whole village

Only the roof of the temple remains

Only the roof of the temple remains

Waw is explaining the extent of the 2004 tsunami

Waw is explaining the extent of the 2004 tsunami

Normal transport on the island

Normal transport on the island

Storm deposits look very different from tsunami deposits

Storm deposits look very different from tsunami deposits

Cham is inspecting the storm deposits

Cham is inspecting the storm deposits

Waw and Svante discussing the storm deposits

Waw and Svante discussing the storm deposits

This entry was posted in Thailand fieldwork and travels, Thoughts and Tales, Travels and tagged , , , , , , , , . Bookmark the permalink.

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