Book Excerpt : Yellowstone Lake

Yellowstone Lake is North America's largest high altitude lake (7732 ft/2376 m) at about 14 by 20 miles (23 by 32 km) in width and length and with more than 110 miles (177 km) of shoreline. The lake has an average depth of 139 feet (42 m); its deepest spot is 387 feet (118 m).

Tributaries

Approximately 125 tributary streams feed into Yellowstone Lake, mostly from the south and east. One of the streams is the Yellowstone River's source, which enters the southeast arm of the lake from the mountains in Bridger-Teton National Forest. Thus, the lake's outlet at Fishing Bridge is not really the headwaters of the Yellowstone River.

Islands

The seven named islands in Yellowstone Lake are, from largest to smallest: Frank, Stevenson, Dot, Peale, Molly (actually two islands named Sandy and Rocky), Carrington, and Pelican Roost. Frank, Peale, and Molly were named by or for members of the 1871 and 1878 Hayden surveys of the Yellowstone area. The names of the other four are explained in the road logs when they come into view.

Winter and the Lake

In winter, ice nearly 3 feet (1 m) deep covers much of the lake, except where shallow water covers hot springs. The lake freezes over by early January, and the ice doesn't break up until late May or early June. Rangers on ski patrol used to shorten their long trek to the southeast area of the park (the Thorofare) by skiing across the ice from Lake Ranger Station to Park Point on the east shore.

Science and the Lake Bottom

In recent years, scientists have explored some of the lake's bottom using a submersible robot called a Remotely Operated Vehicle (ROV). They've learned that the hottest spot in the lake is Mary Bay at the north end, where temperatures up to 212°F (100°C) have been measured—that's above the boiling point at this altitude. They've also found deep pits that may be old hydrothermal explosion craters.

At least two other hot spots in the lake are being studied. West Thumb Bay is another active area with huge hot gas eruptions that stir up food for enterprising trout. Northeast of Stevenson Island, the ROV found a deep underwater canyon containing several hydrothermal springs. Five years later, the scientists returned, just after a major earthquake had shaken the area. The canyon had disappeared!

Spires as much as 100 feet (30 m) high grow in clusters on the lake bottom at some or all of the lake's hot spots. These pinnacles are made of the siliceous shells of diatoms, microscopic algae that live and die near the lake bottom. Exactly how these hydrothermal features form is as yet unknown.

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 This is an excerpt from Yellowstone Treasures, pages 137–8.

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