In
volcanology, a
lava dome or
volcanic dome is a roughly circular mound-shaped protrusion resulting from the slow
extrusion of
viscous lava from a
volcano. The
geochemistry of lava domes can vary from
basalt to
rhyolite although most preserved domes tend to have high
silica content. The characteristic dome shape is attributed to high viscosity that prevents the lava from
flowing very far. This high viscosity can be obtained in two ways: by high levels of
silica in the magma, or by
degassing of fluid
magma. Since viscous
basaltic and
andesitic domes
weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or
dacite.