Coffee Pot Springs

Coffee Pot Springs is a hot spring in Yellowstone National Park.

Coffee Pot Springs in Supervolcano
Approximately two years before the Yellowstone Supervolcano erupted, a new lava dome formed under Coffee Pot Springs. It, along with the one at Sour Creek caused a series of magnitude 5.0 to 5.5 earthquakes.

By a year and a half before eruption, the magma dome under Coffee Pot Springs had been growing at a rate a dozen times faster than any previously recorded causing significant bulging. This had disrupted the geyser displays (especially Old Faithful) causing upset among tourists. Also, the earthquakes had continued. Scientists, having never observed a Supervolcano eruption, were divided whether this signaled a eruption or not.

Yellowstone continued to be studied by a team of geologists led by Larry Skrtel of the US Geological Survey. About year before eruption, this team discovered that Coffee Pot Springs had "gone nuts": a brand new geyser threw water a hundred feet into the air and springs were no longer just pools but blorping boiling water 8-10 feet high along with new, agitated springs forming.

Literary Note
In the Author's Note at the end of Supervolcano: Eruption, Harry Turtledove indicates that while Coffee Pot Springs are real, the lava dome is fictitious.