I was living in eastern Washington State in May 1980 when Mount St. Helens erupted after a massive landslide triggered by a magnitude 5.1 quake. Vast amounts of molten rock were violently released to the surface of the Earth, erupting not only as sizeable rocks but as fine-grained volcanic ash that floated on the breeze. Us “down-winders” were enveloped in conditions that were dark as night until the ash finally fell to the ground.
Volcanic ash isn’t the same material as the ash in your fireplace — it’s fine-grained volcanic rock. The St. Helens’ ash was a mess all summer long for those of us in eastern Washington State. It blew around and clogged the air filters of cars, as well as making us cough and hack. But thanks to early warnings from the U.S. Geological Survey and actions taken by Washington’s governor to exclude people from the area immediately around the volcano, only 57 people died in the massive eruption St. Helens experienced. Their loss was a tragedy, but the death toll could have been much higher — and would have been without the good work of geologists giving timely warnings to government leaders.
A number of other volcanoes in the mountains of western Washington, western Oregon, and northern California pose similar potential hazards. One of the most beautiful volcanic peaks is Oregon’s Mount Hood. Two researchers have recently published results from their study of Mount Hood in the journal Nature.
Molten rock underground is called magma (it’s termed lava once it gets to the surface). The Nature article by Kari Cooper and Adam Kent explains that there are components of magma under volcanoes that are stored stably deep within the crust for long periods of time — meaning, in this case, tens of thousands to hundreds of thousands of years. An important question is how and when this stable magma can become mobilized and move upwards to start the events that lead to an eruption.