Volcanic Activity in the “Age of Discovery” – New dates for Ascension lavas

The team has published a new paper in ‘Geology’ journal revealing when Ascension last erupted and proving that Ascension should be classed as an ‘active’ volcanic system.

The team targeted the youngest-looking lava flows for dating via the 40Ar/39Ar technique to determine when they erupted. The 40Ar/39Ar analyses, carried out by team members in the Argon Isotope Facility (SUERC), revealed that the youngest eruptions occurred just over 500 years ago, and were lava flows erupted near to Comfortless Cove and Sisters Peak. These ages coincide with the increase of chronicled observations of travel associated with the early modern European ‘Age of Discovery’ (early 15th to 17th centuries). Throughout this period, Ascension was frequently used by sailors as a stopping place to take on provisions, and during this time the sailors wrote many accounts of the island. The team therefore searched these historical records for eye-witness accounts of an eruption. Although the fresh nature of the lava is frequently detailed, as well as a description of fumarolic activity, no mention of an eruption was found in the records, supporting the 40Ar/39Ar data in the conclusion that the last eruption took place not long before the island’s discovery.

Results show that the Davidson Flow (named after our late colleague Jon Davidson) erupted about 1600 years ago (plus or minus 370 years), the Comfortless Cove lava is 550 years old (plus or minus 120 years) and the South Sisters Flow is a similar age and erupted 510 years ago (plus or minus 180 years). There are currently no signs of volcanic activity occurring on the island, but volcanologists class an ‘active’ volcano as one which erupted within approximately the last 10,000 years.

The team are very excited by the results as young lavas are very difficult to date and these ages are the youngest ever produced using the 40Ar/39Ar technique. The results therefore offer new prospects for dating young volcanic rocks worldwide; crucial for volcanic hazard assessment.

If you’d like to read this paper you can access it here or contact the team for copy.

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Images showing location of youngest dated flows on Ascension Island, courtesy of Katie Preece

2 thoughts on “Volcanic Activity in the “Age of Discovery” – New dates for Ascension lavas

  1. This is fascinating – I made two visits to Ascension Island in 2007 and 2008, walking extensively around the Island, climbing Sisters and staying on Green Mountain.
    At the time there was barely anyinformation about the vulcanology of the islands, and whether the volcanoes were still active – which I found surprising bearing in mind the communication and defence-related facilities on the island.
    My gut reaction was that Sisters looked as if it may have erupted c 500 years ago – so I’m thrilled that I appear to have been pretty close!
    Has anyone done any survey work or research at the Devil’s Riding School? What is the origin of the devil’s eyeballs?
    I’d be really interested to hear about any recent research.

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    • Hi Karin,

      Yes, a lot of people on Ascension had the same feeling about Sister’s so it was great to be able to confirm it with Katie’s work! Over the last several years our group has done a fair bit of work on Ascension, talking about the different volcanic features and potential hazards associated so hopefully if you were to visit now there would be a bit more information around, even just via word of mouth.

      The Devil’s eyeballs haven’t been a key focus of our work and the process of formation seems to be a little disputed/uncertain. Our best guess is that they are something called accretionary lapilli. These are pellets that form due to the interaction with erupted ash and water. But as I say, this is not definite!

      Our most recent published work is all found on our publications page so do take a look. There are other projects still underway e.g. an updated geological map and an investigation of the Devil’s Inkpot lava and eruptions on Letterbox, we will provide updates from them as soon as we can.

      all the best,

      Team Ascension

      Like

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