Visit the Shore of Yellowstone Lake：
Geologists indicate that large volcanic eruptionshave occurred in Yellowstone on an approximate interval of 600,000 years. The most recent of these (600,000 years ago) erupted from two large vents, one near Old Faithful, the Mallard Lake Dome, and one just north of Fishing Bridge, the Sour Creek Dome. Ash from this huge explosion, 1,000 times the size of Mt. St. Helens, has been found all across the continent. The magma chamber then collapsed, forming a large caldera filled partially by subsequent lava flows. Part of this caldera is the 136-square mile basin of Yellowstone Lake. The original lake was 200 ft. higher than the present-day lake, extending northward across Hayden Valley to the base of Mt. Washburn.