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.