maandag 20 mei 2013

Today's Atlantis: the Thai Buddist temple Wat Khun Samut Trawat

My last post was criticized about the doomsday prophecies I made about the Fennoscandian area (I think dear Annie missed the non-seriousness in my text, but heck, he/she got a point). The mentioned process of land uplift takes a lot of time and the dramatic geological change will not affect our way of life in a long time. So I decided to write about a geological change that does affect the way of life already today and dramatically in the future. The research I write about is from a couple of my colleagues working a lot with people from Thailand. They are part of a research project called GEO2TECDI-2, which uses GNSS, InSAR and tide gauges to see the movement of the surface of Thailand with respect to the sea level. 

When you look at the topography of Thailand, you will notice that the country is very flat. The difference in height between coastal areas and 500 km inland is only a few meters. This means that if sea level would rise, or the land would collapse (which is already going on very rapidly), most of Thailand will be under water. This means that a lot of the 66 million population will get wet feet. To get an idea of what will happen, the GEO2TECDI-2 research group is examining every source of land and sea motion.

There is one particular area where the effect of this land collapse can be seen very clearly. This is the area around the Thai Buddhist temple Wat Khun Samut Trawat. In 1950, this was still an inland temple surrounded by Thai settlements. Today we can find the current state on Google Earth

Coordinates: 13º  30' 25.42'' N, 100º 31' 53.47'' E, copy the link and post it in google maps

We can clearly see that the temple is surrounded by water and that people have built protective structures to ensure the temples present state. Comparing the current sea shore lines with that of the 1950's tells us that the sea has already taken 1 km of the Thailand mainland. 

The GEO2TECDI-2 research team has accurately measured the sea level rise in the area (tide gauges) for the past 60 years and they found a 25 cm rise in mean sea level. However, this alone could not represent the large land erosion seen today. With InSAR and GNSS measurements they observed a land collapse of 1 meter!!! over the last 60 years. This explains the dramatic geological and social changes in the coastal areas quite well. However, this land subsidence could not be explained by any natural tectonic motion (1-3 mm/yr tectonic uplift and 10-15 mm/yr subsidence after the Sumatra-Andaman earthquake) of the crust. What could it be?

They had an excursion to the Wat Khun Samut Trawat temple. Traveling mostly by boat and they hiked the last bit. During this travel they encountered a lot of shrimp farms (yes, the kind from "My momma always said..."). To grow shrimps you need fresh water (because fresh water shrimps taste better). This fresh water could have be taken from the Bangkok river, east of that area, but industry and population have polluted the river water, making it unusable for shrimp farming. Still, the shrimp farming business in that area is booming. Despite of the law forbidding it, the fresh water is pumped from the groundwater. This is especially clearly visible in InSar images, which show large subsidence in areas where newly build shrimp farms are located. Due to the groundwater pumping, the ground is settled more firmly causing the ground to subside.

It is impossible to ban shrimp farming, because it is the economic driving factor in that area. But it will cause major flooding in the near future. Thanks to the GEO2TECDI-2 research the issue is made visible and they can inform the people of the possible dangers. It is now up to all of us to find out what to do with this information and hopefully find an answer to this complicated question.

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