Why don't volcanoes run out of lava or molten rock after erupting so many
times?
Adam, Isaac, and John
Dear Adam, Isaac, and John,
The main thing to remember is that the magma that eventually erupts at
a volcano as lava or ash comes from beneath the volcano - it isn't
generated within the volcano itself. For example, the magma that
feeds Hawaiian eruptions probably comes from at least 50-60 kilometers
below the surface. The magma may be stored within a volcano for a
while prior to an eruption in what is called a magma chamber. The
magma chamber may become empty, resulting in deflation of the volcano
or perhaps even collapse that generates a caldera, but there is always
more magma to come along some days, months, or years later to re-fill
the magma chamber and generate new eruptions. The reason that the
source of magma down in the Earth's mantle doesn't run out is that
there is plenty of heat down there and plenty of rock that can be
melted to form the magma.
Scott Rowland, University of Hawaii
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