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What Volcanic Crystals Tell Us About the Evolution of Mount St. Helens
One of the major reasons I (Erik Klemetti) am a geologist is that I love history. I majored in both history and geology as an undergraduate because I am fascinated by unraveling what has happened in the past and what was the evidence that we can use to see those events. For me, it is the crystals in volcanic rocks that hold the key to understanding the evolution of magma at volcanoes--they record events in crystalline structure through crystal growth, changing compositions of the crystals or incorporation of radioactive elements that can be used as a stopwatch.
Even after the crystal forms, the elements are redistributed to show how time has passed. Two studies that came out this week examining St. Helens and Long Valley use these tools to unlock the unseen history of the volcanoes. These crystals hold the story of the volcano, in both the long and short term, and reading that history is what fascinates me.
To read the history in crystals, you need to know that "ages" in geology don't all come the same. There are two types of ages when we consider almost any geochronologic information--relative and absolute ages. The latter is straight forward--an absolute age is one where you can assign a specific date to the event in question.
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