Swansea Heads base surge deposit

3D Model

This outcrop is the lower section of the cliff at Swansea Heads near Newcastle, Australia. Most of the section shown is the thick (~10 metres) tuff unit of the Reids Mistake Member of the Newcastle Coal Measures - a coal seam can be seen toward the top of the section. Coal also underlies the tuff, and the preserved remains of dozens of Glossopteris trees are present in the lower parts of the tuff on the rock platform.

In this part of the section, a layer about two metres thick shows distinctive wavy bedding that is characteristic of base surge deposits of volcanic ash. Base surge deposits result from proximal ash flow deposits near the base of the volcano they are erupted from. The change in slope near the base causes a sudden slowing of ash flows, which can travel faster than 100 kilometres per hour on steeper secions of the volcanic flank. This observation also indicates that this location was very close to the volcanic edifice.