What is meant by phreatic?
Mary DeLaTorre
Hi Mary,
A phreatic eruption is when ground water contacts hot magma and explodes into
steam. Phreatic eruptions can include just
steam or steam plus pre-existing rocks, but none of the hot magma. There are
eruptions where steam and the hot magma both get erupted but these are called
"phreato-magmatic" eruptions.
A phreatic eruption can occur if a body of magma moves upward and comes into
contact with groundwater. The resulting explosions may rip through to the
surface and leave a hole called a maar. Because none of the magma gets erupted
in a phreatic eruption there is no ash around the maar, but there may be some
debris from the material that was ripped out by the explosions. Maars often get
filled in with rain water or groundwater, and their name means "sea" in German.
I hope this helps answer your question.
Sincerely,
Scott Rowland, University of Hawaii
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