Seeing the grand sweep of the mountains of Yellowstone, or the vast waters of Yellowstone Lake, it is hard to remember that you are standing on a thin crust over one of the largest magma chambers of one of the largest super volcanos in the world. Two active magma domes under the park inflate and deflate on a long cycle, actually tipping the landscape in real time…changes that can be, and are being, measured. Then you come up on one the hydrothermal areas beside the road: bubbling hot springs and travertine domes and terraces, geysers blowing superheated water high into the air, or as here, steam rising from super heated, boiling mud…and the volcanic nature of Yellowstone becomes that much more real. The thickness of the crust of rock over the magma domes still is measured in miles…as little as 3 or as much as 12…but there are few areas in the world where the crust is so thin. Old Faithful may be impressive, and justly well known because it is, but it the sheer number of hydrothermal features in Yellowstone that is the most impressive. Sony a5100 with the Sony E 10-18 f4 zoom at various focal equivalents for framing. Superior Auto with Landscape scene mode selection. Processed in Photomator.