Yellowstone: Monitoring the Fire Below

Yellowstone National Park is a Volcano

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What Dangers Await?

“If a lava flow were to occur here today, it certainly would have an effect,” says Lowenstern. “But it wouldn’t cause many, if any, deaths.” Lava is what magma is called after it breaches Earth’s surface. About 80 lava flows since Yellowstone’s last big eruption 640,000 years ago have filled in much of the three calderas, so that their entire circumferences are only detectable with careful fieldwork. Lava erupting from existing or new cracks at Yellowstone would likely be thick and viscous and have little gas left in it. Thus, it would ooze, not explode, and be unable to flow long distances easily. “Tourists just wouldn’t be allowed in certain areas,” says Lowenstern.

Mud pot, Lower Geyser Basin

Image

David Rasmussen

The remaining molten rock in Yellowstone’s collapsed magma chamber is now cooling. It donates heat to the water table above it, which creates Yellowstone’s more than 10,000 hydrothermal features. The hot groundwater can flash as steam in geysers like Old Faithful or belch through cauldronlike mud pots. The water also collects in pools, some of which are acidic, near boiling, blue-green with minerals and microbes, and reeking of rotten-eggy hydrogen sulfide. (“The smell of life,” Lowenstern calls it.) An unanticipated hydrothermal explosion could scald or severely injure park visitors and staff.

Still, a lava flow or a hydrothermal explosion does not herald a new catastrophic eruption. A surer sign would be a dramatic shift in the ground level at Yellowstone, a hint that the magma chamber was moving upward or significantly refilling. Scientists would also look for serious “swarms” of earthquake activity, which would suggest the malleable magma chamber was rupturing the brittle rock above it. Recent monitoring has detected both ground level rises (8 to 10 cm in the past 19 months) and seismic signals, but they’re not dramatic enough to warrant worry. They simply remind geologists that Yellowstone is naturally a place of change.

“Thermal features can change over one day,” says Heasler. “Yellowstone is an interesting place where we can see geologic processes changing on a day-to-day basis rather than a million-year-by-million-year basis.” Monitoring this change is the essence of the geologic work ongoing at Yellowstone. It is the key to predicting the park’s next big moment.