Tuesday, March 31, 2015

Jan 4, 2005; a post on andamanicobar@yahoogroups.co.in - mud volcanoes

Jan 4, 2005
(Mud volcanoes)

 There are reports of mud volcanoes erupting on the Andamans. One of the mud volcanoes is on North Sentinel Island! This is bad news. 
I'm a geologist, I downloaded topography for all of the Andamans. I'm trying to find the altitude of the islands to work out the survivability. The topography was measured by the Space Shuttle in 1999, its SRTM data. I guess that mud is erupting from a fault line I seen in SRTM data that trends SSE to NNW on North Sentinel. I'm not sure of the altitude of the island, SRTM is measured at tree the level.
The coast of North Sentinel Island seems to be 30-40 metres a.s.l. the interior is 60 to 80 metres a.s.l. but this could be due to the tree effect. Car Nicobar is the same altitude, 30 to 40 metres at the coast and 60 to 80 metres inland, but I heard that its highest point is in fact just 16 metres. The situation appears poor for North Sentinel Island.
The Andamans are part of an accretionary wedge, this occurs where two plates collide. Here wet sediment is squeezed, much like a sponge the water contained in the sediment is forced to the surface along faults. The fact that mud is erupting in a number of sites along faults indicates that the Indian-Australian plate moved west or NW at the Andamans, and squeezed the wet sedimentary wedge and water contained is now erupting to the surface. This in accordance with tsunami simulations by NOAA. The fault on North Sentinel Island is offset to the left, sinistral, this is in accordance with the expected plate movement.

Also the channels that cut the Islands were likely caused by past major tsunamis events, waves washed over the islands splitting them in two. There are reports that islands have been split in two by the latest tsunami. The fact that there were very few channels cutting the islands in the first place indicates that the phenomena of major island splitting tsunamis is very rare, perhaps once per 10,000 years or more. It could explain the language groups, that Great Andaman Island was once contiguous and populated by one group that was later split up by a major tsunami calamity.

Diamond Dave

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