I need to explain to my son the formation, growth and eruption of volcanoes.
He has a school project and he needs to explain something about volcanoes.
Armando Romero Mariscal Guasp
Dear Armando,
The Earth has volcanoes because it is hot inside. In some places it is
hot enough to turn solid rock into liquid rock. Geologists call the
liquid rock magma. The magma rises towards the surface because it is
less dense than the surrounding rock (like a hot air balloon rising
through the cooler air). If the magma reaches the surface it is called
lava and lava accumulates to make a volcano.
Volcanoes grow by intrusion and extrusion. An intrusion is magma that
moves up into a volcano and then it stops, never erupting. This way the
volcano grows on the inside. An extrusion is an eruption. It can add
layers of lava or ash. This way the volcano grows on the outside.
Volcanoes erupt because of density and pressure. The lower density of
the magma causes it to rise (like air bubbles in syrup). It will rise to
the surface or to a depth that is determined by the density of the magma
and the weight of the rocks above it. As the magma rises, bubbles start
to form from the gas dissolved in the magma. The gas bubbles exert
tremendous pressure. This pressure helps to bring the magma to the
surface and forces it in the air, sometimes to great heights.
You might also look through some of the other questions in Ask a
Volcanologist.
Steve Mattox, University of North Dakota
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