Yellowstone – Just the Tip of the Volcano

By Dr. Robert Thorson

‘Where are we going to go when the volcano blows?”

That lyric by singer Jim Croce was playing in the background when I was being introduced on WTIC radio during last week’s morning commute. I was being interviewed about the recent swarm of about 900 small earthquakes beneath Yellowstone National Park and the potential threat of a colossal eruption.

I had no answer for the question of where to go when the volcano blows. But I did have an answer to the main question of whether this was news at all. My talking-head answer was yes and no.

The “no” part of my answer dealt with the fact that the swarm of earthquakes generated little more than a swarm of news stories. They are common geophysical events, comparable to squalls on the surface of a still lake. Things become ruffled and then return to normal.

The “yes” part of my answer involved the old adage that no news is usually good news. Knowing that the monster volcano beneath Yellowstone National Park hasn’t uncorked in the past 600,000 years is comfortably like knowing that a giant asteroid will miss us by a few hundred thousand miles. But such events do remind us that our safety and security depends on powers far greater than ours. Hence, the big story from Yellowstone last month is that of thankfulness for being alive.

Where’s the volcano at Yellowstone? There’s no cone-shaped summit like Mount Rainier in Washington. There’s no broad shield like those of the Hawaiian Islands, which light up with fountains of orange lava every decade or so.

To find the volcano at Yellowstone, start by looking at the bizarre collection of geothermal springs, geysers, fumaroles, briny ponds and travertine. What keeps this weirdness going is “fire down below.” Second, look at the layers of yellow stone for which the national park is named.

They didn’t form peacefully like strata of chalky mud transformed into yellow limestone beneath a shallow sea. Rather, they are sheets of ignimbrite formed by incandescent clouds of ash so thick and hot that the particles fused into solid rock. The yellow color is rust from tiny specks of iron-rich minerals that crystallized before each ancient eruption.

Third, start looking for a hole rather than a hill, because a volcano, by definition, is less an eminence above the surface of the Earth than the vent through which materials arise from below. Liquid magma isn’t the only thing that comes up. Also important is carbon dioxide, the gas that makes soda fizzy, trees grow and climates warm.

Finally, to actually see the volcano at Yellowstone, go up in an aircraft. Only from well above the Earth’s surface is the caldera – big enough to hold all of Yellowstone Lake – visible. A caldera is a circular depression created by collapse following the loss of magma at depth.

The bad news about Yellowstone is that it’s a super-volcano, arguably the most dangerous one in the United States, capable of destroying everything within hundreds of miles. Besides blowing a hole in the crust the size of Connecticut, the most recent caldera-forming eruption left a thick layer of ash as far east as the Mississippi River, depositing a thousand times more material than the eruption of Mount St. Helens in 1980. The good news is that it only blows up every few hundred thousand years.

Yellowstone’s pattern of high-magnitude, low-frequency eruptions is the polar opposite of Hawaii. There, the lava is chemically simple because it comes straight up from the mantle and flows easily because it’s hot and iron-rich. In contrast, the magma beneath Yellowstone contains an abundance of re-melted continental crust, making it chemically complex, rich in silica, much cooler, and loaded with explosive gas.

The December earthquake swarm reminded us that terra firma is an illusion. Beneath Earth’s eggshell crust everywhere is a caldron of hot liquids and soft solids above which our familiar geography floats.

Every day, I give thanks to Planet Earth for allowing my presence.