June – July 2014- Ascension Fieldwork

Following lots of organisational meetings and planning, ten of us (Katie, Rich, Barry, Jon, Jenni, Anna, Charlotte, Ben, Fin, Katy) headed over to Ascension Island in June to carry out fieldwork for ~3 weeks. Although not everyone could be out for the entire time, we managed to collectively cover a lot of ground on the island!

Our main aims on the field trip were:

  • To characterise the range in eruptive deposits present on the island, and begin to establish an eruptive stratigraphy (or timeline) for various parts of the island.
  • To sample the wide range in compositional types of lava flows already identified by previous workers and use these to investigate the eruption ages, and the nature of the magmatic plumbing system.
  • To sample the two youngest lava flows on the island to date both using Ar-Ar and cosmogenic techniques- as well as sampling the pyroclastic units for Ar-Ar eruption age dating.
  • To understand the range of volcanic hazards present on the island.
  • To hold meetings and interviews with island stakeholders to discuss the project, to identify local infrastructure available in the event of a natural hazard on the island and to understand what information would be useful to locals from the project.

Although we were all expecting a wide range in lava and pyroclastic deposits on the island, we were still all surprised by quite how much variation there was in the style and volume of various deposits on the island!

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A range in eruptive deposits found on Ascension Island, from the Green Moutain scoria (left), to the layered fall/breccia deposits on NASA road (middle), to stratified fall deposits and multiple unconformities in Goat Hole Ravine(right). Photos courtesy of Ben Cohen, Charlotte Vye-Brown and Katie Preece

Having identified such a wide range in volcanic deposits, we then set about sampling both lavas and pyroclastic units to take back to the UK with us for dating and geochemical analyses. This sometimes meant a long time searching for the freshest looking section of lava to make sure all our analyses work- but it was time well spent!

By the time we finished our 10-day sampling campaign we had managed to collect 7 full crates of rocks, which were sent by ship back to the UK- which will then be used for analyses of the timing and style of volcanism throughout the island’s subaerial history.image29
Clockwise from top left: An adult and chick masked booby; Pausing on the way to Crystal Cove to take in the view; Group picture after the 4th July Runway Fun Runimage27Katie and Finn sampling lava on English Bay Road; Fin sieving a pyroclastic fall unit on the pyroclastic plain near Two Boats

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The rocks ready to be picked up and sent on the ship to the UK

While our time on Ascension passed all too quickly, we still managed to collect a lot of samples, and get a good handle on the eruptive deposits on the island- now we can’t wait to come back for a second field season to conduct much more detailed stratigraphic logging, to iron out the fine details in Ascension eruptive history!

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