In regions where one
tectonic plate descends beneath another,
volcanoes form.
80 km (50 miles) below the surface, the
subducting
plate gets hot enough to release fluids. The rising fluids interact
with the rock above to form
magma.
The
magma is
so thick and gooey that it traps gases beneath the
volcano.
The pressure builds and builds until one day...
it erupts!