Mechanisms of Crater Lake Breaching Eruptions

In this chapter we review physical models on phreatomagmatic, phreatic,
hydrothermal, and geyser-like eruptions and, for the first time, place them
in a crater lake context. Examples of known crater lake systems for the
different eruption types are provided. Besides the direct injection of a fresh
magma into a crater lake, leading to phreatomagmatic activity, a crater
lake is a strong condensing medium, sensitive to sudden pressure changes
when injected by gas-vapor batches, which can lead to non-magmatic,
though violent eruptions. The implosive nature, the role of the heat pipe
and molten sulfur pool at the lake bottom are central in the phreatic
eruption model. Contrary to phreatic eruptions, hydrothermal eruptions are
instigated by a sudden pressure drop, causing boiling and vapor release,
rather than by the input of a gas-vapor phase of magmatic origin. Geyserlike
activity beneath or near crater lakes is analog to classic geysering, and
becomes more obvious when lake water level is low. Although not
explosive, the peculiar lake drainage and refill cycles of two lakes are
discussed. The first outcomes of numerical simulation approaches help to
better quantify injection pressure and vapor/liquid proportions of the input
fluid. We stress that the various manifestations of eruptive activity at crater
lakes is not necessarily linked to changes in magmatic activity, which
could lead to misleading interpretations regarding volcano monitoring.