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.

Unusual glassy volcanic bombs found on Ascension