Mechanisms of Cauldron Subsidence

Abstract

WIKLIAMS'S subdivision of calderas into ‘Krakatoan’ and ‘Glen Coe’ types¹ has been the subject of recent discussion^2–4. Williams's concept of the ‘Krakatoan’ mechanism is that explosive eruption of pumiceous volcanic products from the vents of a central-type volcano produces a void in the underlying magma chamber; the unsupported chamber roof then collapses, producing a caldera at surface level bounded by a ring-fault escarpment. The ‘Glen Coe’ type, on the other hand, is said to involve the stoping of magma up ring fractures and the coeval descent of the enclosed cylindrical block.