What type of lava does the Poas volcano have? Pahoehoe, Aa, or Pillow?

Expert Answers
jgregerson eNotes educator| Certified Educator

The Poas volcano is in Costa Rica and is an active stratovolcano made up of a variety of rock types, namely andesite, basalt, and dacite. The types of lava you mention (pahoehoe, aa, and pillow) refer to types of lava flows that result from basaltic lava that is very low in silica content. An excellent example of basaltic lava flows can be seen in Hawaiian volcanoes. This is very different from what happens at the Poas volcano.

Since the Poas volcano contains rocks other than basalt with different silica contents, this results in different types of eruptions than what occur in Hawaiian volcanoes. Many of the eruptions recorded at Poas have been the result of groundwater interacting with magma. These are called phreatic and phreatomagmatic eruptions. These eruptions release superheated steam, gasses and, in the case of phreatomagmatic eruptions, ash and small rock. 

So, to answer your question, none of those types of lava flows applies to the Poas volcano. Instead, it is better to describe the Poas volcano as having phreatic and phreatomagmatic eruptions.

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