How do volcanos work? From explosive eruptions to creeping lava flows, this NYT video explains the anatomy of a volcano, and how the unseen underground variables can make it difficult to know how a volcano might behave:

“Volcanoes are really difficult to predict because they are so nonlinear,” said Pall Einarsson, a geophysicist at the University of Iceland. “They can suddenly decide to do something very different.”

Dr. Einarsson studies the earthquakes that usually accompany volcanic activity, caused by hot rock, or magma, rising within the earth and creating stresses and fractures. Seismic monitoring is essential for helping to determine if and when an eruption will occur and how it will proceed, but scientists also study the deformation of a volcano’s surface — a sign of increasing pressure within — using G.P.S. units and satellite-based radar, and they also monitor gases and other indicators like the melting of snow or ice.

“Ideally it’s a nice combination of data from many disciplines,” said Stephanie Prejean, a research geophysicist with the United States Geological Survey at the Alaska Volcano Observatory. “And it’s easiest if the things are all escalating together, and escalating dramatically.”

For a variation on this lesson, check out Twig World Films’ What is a Volcano?

Watch more stunning volcano videos: When a volcano erupts underwater, Eruption at Iceland’s Bardabunga Volcano, and After Royal Gardens: molten lava heads 2-miles to the ocean.

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