We are now nearing the end of the research cruise and it feels as if it is all over before it really began. All the aims of the cruise have been met and it has thus far been a great success. I say thus far, as we wont know how successful the OBS (Ocean Bottom Seismometers) that we deployed have been until we recover them (hopefully!) next year, and then retrieve the 15 months worth of seismic data. This isn’t a trivial task as the OBS will have been sat on the seabed between ~4500 and 1000m for this time, so fingers crossed we can communicate with them and get them all back! We have also had the chance to carry out a series of magnetic surveys. We do this by towing a magnetometer around 300m at 5-10m depth, out the back of the boat. These will give us insights into the relative ages and spreading directions on the subducting and overriding plates.
In the last couple of days we have been treated to some great views of the islands, particularly Montserrat. Here we could see the pyroclastic flows from Soufrière Hills which began a devastating eruptive episode in 1995, destroying the capital of Plymouth, and later, the airport on the eastern side. I was lucky enough to visit Montserrat last year and take a trip into the exclusion zone to see the flows close up (picture below). Today, we passed to the east of the volcanic islands of St. Kitts and Nevis, and then went very close to Redonda, the remnant of an extinct volcano. It is an impressive island as you can see the guts of the old volcano, with dipping lava and pyroclastic flows either side, and a dense plug in the centre which was once part of the conduit that fed the eruptions. It has been great to see the islands as it gives you a sense of place, as whilst further out at sea, you really could be anywhere (well anywhere with a hot climate at least).
We now sail to the northeast of Antigua to deploy the final 4 OBS and carry out another Magnetic survey. We are expecting the sea to get rougher again as we pass back over to the Atlantic side of the arc and into deeper waters. It will be interesting to test whether the body has now adapted or not! Finally, we will then head into St. Johns, Antigua to disembark on the 17th. Next year, there will be a second cruise on which the OBS will recovered and more will be used for active source experiments, these will be done further to the east, on the incoming plate. The incoming Atlantic plate has many fracture zones running perpendicular to the subduction zone and the aim is to see if these are linked to variations in the extent of hydration and what effect this may have on the volcanism along the arc.