Maars and Phreatic Eruptions
A maar is a volcanic crater that forms when magma contacts groundwater to produce a steam explosion.
What is a Maar?
A maar is a shallow volcanic crater with steep sides that is surrounded by tephra deposits. The tephra deposits are thickest near the crater and decrease with distance from the crater.
A maar is formed by one or more underground explosions that occur when hot magma comes into contact with shallow ground water to produce a violent steam explosion. These explosions crush the overlying rocks and launch them into the air along with steam, water, ash and magmatic material. The materials usually travel straight up into the air and fall back to Earth to form the tephra deposits that surround the crater. If the tephra lithifies, it will become an igneous rock known as tuff.
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