October 2016 – Excited to be back on island for Field Season 3!

On 16th – 28th October, Katie Rich and Charlotte (with little Sebastian and baby bump Arianna) were on island for the 3rd field season of the project. The aim of the field season was to put into place the remaining pieces of the geology jigsaw, mainly focussing on the rocks in the centre and east of the island, formed during past explosive eruptions. We explored remote nooks and crannies on the island (including a scramble down the infamous Spire Beach track and an acrophobia-inducing walk out to Boatswain Bird View!) and found evidence for even more eruptions than we previously knew about! We were also happy to be able to correlate some volcanic deposits to eruptions that we have documented in previous field seasons. We took even more rock samples to do further 40Ar/39Ar dating, particularly focused on better resolving the timings of young explosive eruptions.  The team also had several meetings with decision makers on the island to discuss how our scientific data will be useful to islanders. We’d like to say a big thank you to everyone on Ascension Island for your amazing hospitality and for making our visit run smoothly and enjoyable as always!

DSCF8607

Rich contemplating a beautiful ignimbrite underlying a lava flow near the Ariane site on the NE coast

DSCF8808

Katie ‘sampling’ the spectacular Little White Hill, her new favourite lava dome

DSCF9002

Happy to have made it to the Spire Beach Letterbox and discover some new eruptions along the way…now just to walk back up again…

DSCF8801

Spectacular views on the Letterbox peninsula, looking out over the Devil’s Inkpot lava flow and Little White Hill

 

April-May 2015: A successful field season!

The dust has settled, and Katie, Katy, Rich and Charlotte are now all safely back in the UK and getting back into ‘normality’ following a very successful field campaign in April/May, which saw Katie and Katy spend more than a month on the island carrying out detailed volcanological field work and collecting the final few samples for dating and chemical analysis.

The main aims of our field work this season were:

  • To correlate eruptions identified in different parts of the island, across the whole island
  • To develop an eruptive stratigraphy for all the explosive eruptions on the island, so that we know how each eruption relates in time relative to others
  • To describe in detail, sample and trace out any zoned eruptive units
  • To sample olivine-rich lavas for geochemical analysis from multiple localities

Aside from undertaking our fieldwork we were also able to hold a public meeting at the Saints Club to share some our understanding of the volcanic history of Ascension and to describe our research, thanks to all who attended. Meetings with decision makers on island were also an important outcome of this visit, so that we can understand how our data will be most useful to the community. As well as the more formal meetings,

Katie and Katy also very much enjoyed taking the cubs out for a small field trip one evening!

Thank you to everyone on the island who made our time on Ascension so successful and enjoyable. We hope to be able to come back and deliver the results of our research next year at the conclusion to this project.

2015_9

Fissure on the North East coast – the vent for the zoned fall deposits

2015_10

Compositionally zoned fall at Upper Valley Crater

2015_11

Looking down on one of the youngest lava flows from Sisters Peak

March 2015 – The Geological Society Supports Second Field Season

Back in January we applied for a Geological Society Grant to support fieldwork on the extra-ordinary range in zoned fall deposits on Ascension, and we’re excited to announce that they have awarded us significant funds to help us spend time on island mapping our their extent, and quantifying the number and range of textures found in the zoned fall units.

2015_6 zoned + EMPA

Zoned fall unit at North Bay and its glass compositions from EMPA showing the change in compositions.

These units are particularly exciting for us as they provide a snapshot into magmatic processes and timescales that are not preserved (or found) in single-composition fall units. By understanding how these zoned fall units were produced we will not only understand more about the controlling processes for Ascension Island volcanism, but also yield insights into how mixed-magma eruptions are produced globally.

Print

February 2015 – Isotope preparation

In order to understand the source of magma under Ascension, and how much interaction the magma has with surrounding rock as it ascends to the surface can be understood by measuring the isotopic composition of the rocks erupted. In this first round of isotope work, Katy has powdered up whole samples of both lava flows and pyroclastic material, and then dissolved them to liquids, in order to isolate the two elements on interest for us: lead (Pb) and strontium (Sr). While a lot of whole rock (WR) isotope work has been carried out on Ascension previously, we have new samples which haven’t been examined in detail before, so we are aiming to fill in a few gaps in our understanding of the source of volcanism on Ascension Island.

Once Katy has cuts of Pb and Sr from each sample, the cuts are taken up into a dilute acid solution, and analysed using a multi-collector (MC) inductively coupled plasma mass spectrometer (ICPMS) at Durham University. Data to come soon!

2015_5 MC-ICP_MS dur

MC-ICP-MS at Durham University.