The Teton fault cracks the Earth’s crust for forty miles along the base of the range. Motion on the fault generates large earthquakes that hinge the mountain block skyward and tilt the valley block downward.
Motion on the Teton fault lifted the range while erosion due to water, wind and ice carved the skyline. Most of today’s mountain terrain reflects a glacial past, but before glaciers, water carved the landscape.
One of the park’s black diabase dikes protrudes from Mount Moran since it is harder than the surrounding gneiss. Another dike forms a slot on the Middle Teton since it is softer than the surrounding granite.
A number of small alpine glaciers cling to the high peaks. These formed during a cool period called the Little Ice Age. A glacier is a flowing body of ice marked by crevasses and flanked by moraines.
Glaciers act as conveyor belts to transport debris – rock flour, gravel and boulders. Glaciers deposit debris as they melt leaving behind ridges called moraines. Many moraines form natural dams around lakes.
Rivers are critical to the valley providing water and habitat for many species. Rivers also carve the valley floor leaving behind terraces, grind rocks into smaller particles, and transport sediment downstream.
Lakes dot the landscape from the valley to the alpine. Alpine lakes form in glacial cirques. Glacial moraines dam valley lakes at the mouths of canyons and at the southern extent of the Yellowstone ice sheet.
Surprisingly, the park has few waterfalls. The best-known waterfall, Hidden Falls, is actually a cascade because the water bounces off rocks as it drops. Cascade Creek feeds the falls and flows into Jenny Lake.
Steep topography, loose rocky material, heavy snowpack, spring rain and occasionally earthquakes may trigger landslides. The valley’s largest landslide is the Gros Ventre slide just east of the park.