Life in the Cauldron

How many are your works, Lord!
In wisdom you made them all;
the earth is full of your creatures.

All creatures look to you
to give them their food at the proper time.

–Psalm 104:24, 27

Few experiences bring me more joy than my yearly fly-fishing trips to the Northwest Mountain States. In the bitter Illinois winter, I find myself swiping through images on my phone of the region’s many fishable rivers: the rough-and-tumble Box Canyon stretch of Henry’s Fork, the fast-paced runs and slicks of the Madison, the breathtaking mountain views of the Gallatin. But one of my favorite memories is wading in the Firehole River in the western section of Yellowstone National Park, tufts of snow drifting down to disappear on the water’s surface, wisps of steam rising from nearby hot springs. Bison lie in the whitening grass on the opposite bank, uninterested in my casting. The only outlier in this moment of serene beauty is a slight smell of rotten eggs.

This odor, emanating from the hot springs and other hydrothermal features that give the Firehole River its name, provide the tiniest whiff of a startling truth about Yellowstone: the park rests upon a massive supervolcano. “I’ve long believed,” says geophysicist Robert Smith, “that when visitors come into the park they could be greeted with a sign that says, ‘Welcome to Yellowstone—you’re now entering a volcano.’”

The rotten egg smell is the result of bacteria (such as Desulfovibrio vulgaris) that feed off sulfides and create hydrogen sulfide as a byproduct. These anaerobic bacteria thrive without oxygen, living in water deep beneath the earth’s surface. This water is heated by the great cove of magma located ...

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