Saturday, 2 March 2013

19 - Crossing the Caribbean

Pete Talling points out the island of Montserrat.  The hazy cloud is ash blowing off the flank of the volcano behind which is the slowly inflating volcanic dome and the devastated town of Plymouth.
After four days we are now just off the volcanic island of Montserrat for voyage JC083. This island is one of the Lesser Antilles island arc, a chain of volcanic islands that marks the western edge of the Caribbean.

Island arc volcanoes form where the ocean crust is consumed back into the Earth’s interior at deep-ocean trenches. The best known of these are the trenches surrounding the Pacific Ocean, and the island arcs are popularly known as the ‘Pacific Ring of Fire’.

In the Caribbean, the Lesser Antilles arc is also a fiery phenomenon. No more so than at Montserrat, which over the past 20 years has been devastated by a series of volcanic eruptions. The capital city of Plymouth is just a ruin now, barely visible below the thick carpet of ash and debris erupted from the volcano. Our task here will be to trace the trail of devastation out to sea.

Surge deposits, dumped by hot clouds of ash and gas at temperatures of hundreds of degrees Celsius and travelling at many tens of kilometres per hour scour the land over which they travel and rush out over the sea where they eventually dump millions of tonnes of debris onto the seafloor.

No one knows what these deposits look like, or what effect they have had on the seabed below. Using the ROV Isis, we will make highly detailed maps of the deposits on the seafloor. Then, with a new piece of equipment called a vibro-corer attached to the ROV, we will take cores from these deposits to examine the physical and chemical effects of these highly destructive volcanic eruptions.

Pete Talling is leading this part of the expedition and hopes to be the first to make a study of an underwater volcanic surge deposit. To get the shallow part of the deposit, Captain Peter Sarjeant has special permission from the volcano observatory to take our ship, the RRS James Cook, inside the exclusion zone and to within a kilometre and a half of the coast just off the devastated town of Plymouth.

Already, we can see and smell the ash cloud blowing off the side of the volcano.

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