Glaciers in Grand Teton National Park are shrinking, as they are around the planet. Meanwhile tourism is growing: In 2015 record numbers visited both Grand Teton and Yellowstone, its neighbor to the north. The parks attract an increasingly diverse array of international travelers. PHOTO: CHARLIE HAMILTON JAMES
A WORK IN PROGRESS
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he park lies atop what geologists call the Yellowstone Plateau, with an average elevation of 8,000 feet. Dense stands of lodgepole pine cover this great uplift, and high meadows of grass and sage, as well as some lesser bulges such as Blacktail Deer Plateau and a network of gently undulant roads, all across ground that appears cold and static. Don’t be fooled. There’s a dramatic geological reason for the height of the Yellowstone Plateau. Directly beneath it lies a vast volcanic hot spot, a gigantic channel in Earth’s mantle and crust, through which magma rises, releasing heat that further melts the rocks, creating a massive plume. That thermal torrent comprises two magma chambers of partly molten rock, one atop the other, bulging the land surface into an enormous pustule. Around the bulge, like disorderly ramparts, loom mountains that are older and higher—most notably the Tetons, the Absarokas, the Gallatins. On the plateau itself, geologists have traced the evidence of three huge calderas, representing the scars left by three stupendous explosions over the past 2.1 million years. Those explosions, and the volcanic forces that powered them, have earned Yellowstone’s hot spot the label “supervolcano.” Ordinary volcanoes generally occur along the edges of tectonic plates; supervolcanoes blaze directly through those plates, like a stationary torch burning blisters through a sliding sheet of steel. And the Yellowstone torch, feeding heat toward preposterous eruptions, is likely the largest beneath any continent on Earth. “It all starts with heat,” according to Robert B. Smith of the University of Utah, who has studied Yellowstone’s geology for more than five decades. While the North American plate has drifted southwestward T h e Pa r a d ox o f t h e Pa r k 59