Mount Redoubt

W.M. White/Alaska Volcano Observatory/U.S. Geological Survey

When an ominous mushroom cloud of ash erupted from Mount Redoubt 31 years ago today, it was anyone’s guess how long the volcanic event would last.

“The rule of thumb for looking at volcanoes like Redoubt is you typically look at how it’s erupted in the past and that often gives you good guidelines in the future," said John Power, a research geophysicist at the Alaska Volcano Observatory.