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!

New type of volcanic bomb uncovered on Ascension Island

Geological mapping uncovered some unusual volcanic rocks to the west of White Horse. These dense glassy basaltic bombs are very unusual and so far are only known here on Ascension. Normally basaltic bombs are full of bubbles (trapped magmatic gas), but these are almost entirely free of bubbles. They landed hot as a sticky liquid (like tar) (top photo) and dribbled down into the gaps between the bubbly bombs beneath them (middle photo). The dribbles have beautiful droplet shapes (bottom photo). Work is underway to understand how they form.

Why are these interesting?

These new bombs can be analysed to provide information on processes that happen during volcanic eruptions. This may tell us how the magma behaved under the ground or at the surface and how changes in magma properties affected the nature of an eruption.

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Unusual glassy volcanic bombs found on Ascension

New geological map of Ascension Island being prepared

Work has started on a new geological map of Ascension Island by staff at the British Geological Survey and Durham University. Mapping is being achieved using satellite imagery and ground-truthing fieldwork. It requires the scientists to pore over every rock on the island and is providing many new insights into Ascension Island’s volcanic past. So far fieldwork has focused on Upper Valley Crater, Northeast Bay, Cricket Valley, Weatherpost, and Devil’s Inkpot. Work will continue next year around the south and west sides of Green Mountain. The map will be published digitally by the British Geological Survey.

Why do we need a geological map?

Geological maps provide information on the distribution of volcanic deposits, such as lavas, layers of ash and pumice, and on the location of the vents and craters for individual eruptions. This can help when considering the nature and location of future eruptions on the island. Geological maps also act as starting points for geological research and scientific studies by providing researchers with accurate spatial information on volcanic rocks. Geological maps are dynamic sources of information and as new research happens they can be updated and modified.

printout of satelite photo used in the field for geological mapping

Printout of satelite photo used in the field for geological mapping.

August 2017 – Goldschmidt 2017 Conference

In August 2017, Darren, Katie and Ben attended Goldschmidt 2017 in Paris. Goldschmidt is one of the foremost annual, international conferences on geochemistry and related subjects. Each year, the week-long conference brings together thousands of scientists from throughout the world to talk about subjects including the origin of the Earth and planets, the chemical processes that have shaped Earth over time, the search for new resources, and the environmental challenges facing today’s world. At the conference, Darren convened a session about timescales of crustal processes, and Katie presented a talk about the team’s research and findings entitled “1 million years of volcanism on Ascension Island: insights from stratigraphy, 40Ar/39Ar dating and petrology”. Both the session and the talk were well attended and interest in Ascension geology was strong. After the conference the team even managed to find a bit of time to do some sightseeing and sample the delights of French patisserie.

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December 2016 – Successful NERC Facilities grant!

We are excited to have been awarded a NERC Isotope Geosciences Facilities Steering Committee grant to enable us to date some extra Ascension samples! The grant was awarded to Jenni, Darren and Katie so that they can investigate, in more detail, the timing and frequency of explosive eruptions on Ascension, using the 40Ar/39Ar dating method, linked to the detailed fieldwork that has already been carried out.

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