Ascension here we come……

In just a few days myself (Bridie) and a team of geologists from UEA, Durham and BGS (Jane, Rich and Charlotte) will land on Ascension for the first (and rather long) field season of my PhD.

With a grand total of ~36 days on Island we will have the chance to look in detail at several aspects of Ascension’s eruptive history, with each member of the team focussing on a slightly different aspect.

I will be visiting some of the outcrops already identified by Katie Preece and Katy Chamberlain during their 2014 and 2015 field seasons to get some really detailed sampling done. One such locality is a pumice fall deposit that shows a transition from pumice to scoria accompanied by a compositional transition from trachyte to trachy-basaltic andesite  (find the link to Katy’s paper here). Other sites of interest include a pumice-scoria breccia from the central felsic complex (see geology of ascension map) and various lava domes and flows located in the central and eastern parts of the island. E.g. White Horse and the Devils Cauldron trachyte lava flow.

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Geological map of Ascension Island – Adapted from Chamberlain et al., (2016)

My research focuses on trying to understand what causes the volcanic activity on Ascension to change from effusive (lava flows and domes) to explosive (pumice and ash falls, pyroclastic density currents etc) and vice versa. To do this I will be sampling the larger pumice fall deposits in detail so that I can carry out in-depth studies on their vesicles (bubbles) and crystals to understand more about the processes leading to their formation. I will also target lava flows and domes that I can tie to explosive eruptions in the same area (e.g. that can be traced back to the same volcanic vent, show a similar chemical signature or erupted around the same time in that region). By sampling both styles of eruption I will be able to compare the processes acting on the magma as it evolves and moves towards the surface.

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Mafic lava flows and scoria cones extending across Ascension island

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Katie Preece examining lava dome at Little White Hill

My project links quite closely with that of Jane Scarrow a fairly new member of the Ascension team who focuses on finding zircon crystals in igneous rocks so that she can date them and provide timescales for magmatic processes occurring deeper in the volcanic plumbing system. As Jane focuses on the deeper processes and I on the shallow ones, combining our research should provide some interesting insights into magmatic evolution and volcanism on Ascension.

Getting my hands on lots of amazing samples is the first step of my PhD research, the overall aim of which is to to improve our understanding of the volcanic system on Ascension in order to better mitigate and prepare for potential volcanic hazards in the future.

Other objectives of this field season include:

  • Completion of the Ascension geological map (Charlotte Vye-Brown, BGS, and Rich Brown – Durham)
  • Ongoing interaction and communication with Ascension Island Government regarding volcanic hazards (Charlotte Vye-Brown)
  • Mapping of lava flows in the North of the island (Charlotte Vye-Brown)
  • Collection of plutonic rocks to use for zircon dating (Jane Scarrow – UEA)

We are all very excited to get our feet on the ground and start hunting for rocks that will help us to unlock more of Ascension’s volcanic secrets!

Watch this space for updates from our field season!

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