Scientists studying volcanoes have long thought that rising magma rich in gas bubbles should quickly zip to the top of a volcano and cause an eruption.
But famous eruptions, like Chile’s Quizapu and Mount St. Helens in Washington state, haven’t fit this mold. Between 1846 and 1847, Quizapu gently unloaded one of South America’s largest lava flows ever documented, leaving behind piles of rock spanning some 20 square miles.
And months before Mount St. Helens erupted for nine hours in 1980, something strange happened: Lava chock-full of gas and seemingly primed to explode instead leisurely flowed inside the volcano’s cone. A massive blast was only triggered when an earthquake and resulting avalanche struck, causing the north face of the mountain to crumble. (This freed pressured gases within the volcano, prompting magma from below the surface to surge upward and spew into the air.)
Now, researchers say they have identified a pressure release valve of sorts, which enables a sluggish escape of thick, gas-rich lava.
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