Mt. St. Helens and the Cascade Volcanic Arc: Iceland in America
Mt. St. Helens erupted 30 years ago. With an Icelandic volcano causing global problems today, the Mt. St. Helens anniversary is a reminder of volcanic activity in America's Lower 48 states.
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Mt. St. Helens struck a nation that – at least in its 48 contiguous states – often sees volcanic eruptions as exotic events on civilization’s fringe, the narratives of Hawaiians and Icelanders and (more recently) Europeans stranded in shuttered airports.
Yet America has its own Iceland, in some respects. It is called the Cascade Volcanic Arc, running from northern California through Washington State, and the eruption of Mt. St. Helens on May 18, 1980, was just a taste of what it can do.
The dynamics of the region’s tectonics make the Cascades and Iceland different. The Cascades, for one, are far less active. But each Cascades eruption has the potential to be far more explosive – as was demonstrated by Mt. St. Helens.
Mt. St. Helens vs. Eyjafjallajökull
The reason is that, geologically speaking, Iceland is set to simmer. New earth is constantly bubbling up through the rift that runs across the island and separates the North American and Eurasian tectonic plates. The function of Iceland’s volcanoes is essential to perpetually replenish the earth’s crust with new magma, which cools into rock.
Beneath the Cascades, however, the opposite is happening. The San Juan de Fuca tectonic plate is actually sliding beneath the North American plate and melting as it is driven into the earth. The melting rock then rises and occasionally explodes with tremendous force through the volcanoes of the Cascade Volcanic Arc.
Mt. St. Helens and its Cascades brethren are, in effect, the release valve for the pent up forces of tectonic cannibalism.
As if to send a small reminder of this fact, a swarm of small earthquakes recently hit Oregon’s Mt. Hood, suggesting the subterranean movement of magma. “These swarms are relatively common, but still worth watching,” writes geologist Erik Klemetti on his Eruptions blog.