Yellowstone Lake

Early visitors to Yellowstone Lake discovered that at Fishing Cone, a hot-spring cone poking out of the water at West Thumb, a trout could be caught and boiled without ever leaving the hook. Walter Trumbull of the 1870 Washburn expedition described one that fell into the spring and came up “dead, and literally boiled,” and the stunt became popular enough that anglers scalded themselves straddling the vent. The lake makes a habit of this: the hottest hydrothermal vent temperature ever measured anywhere in the park, 345 degrees Fahrenheit, was recorded not in a geyser basin but on the bottom of this ice-cold, 361-foot-deep lake, in the Deep Hole vent field east of Stevenson Island.

The depth contours reveal a lake built by volcanism and ice together. The map shows the broad main body shelving into a deep central basin, the rounded bowl of West Thumb pressed into the western shore, and the long fingers of the South and Southeast Arms trailing off into shallow, glacially carved water. It is a strange and beautiful outline, half caldera and half fjord.