Red Lodge, Montana

Glacial Change in the Beartooths

By Dan Seifert, Assistant Forest Geologist, Custer National Forest

Glacial Change in the Beartooths

Glaciers erode landscapes ten to twenty times faster than liquid water and are one of many ever-changing geologic features in the Beartooth Mountains. Glaciers are large flowing masses of ice formed by the compaction and recrystallization of snow. Glaciers survive from year to year and creep downslope due to the stress of their own weight. The flat plateaus, alpine cirques, u-shaped valleys, and lakes of the Beartooths were sculpted by glaciers. Glacial debris deposits visible in the Beartooths include rounded boulders, stream terraces, terminal moraines, and lateral moraines.

Castle Rock Glacier 1961 and 2001

Castle Rock Glacier 1961 (top) and 2001 (bottom).
(photos courtesy of Dr. Ed Chatelain, Valdosta State University)

Evidence of eight glacial advances and retreats in the past 300,000 years is found in the Beartooths. This includes one period in which a thick ice sheet stretched across much of the Yellowstone region, from Jackson Hole north to Paradise Valley and east almost to Red Lodge. Today’s Beartooth glaciers are mostly remnants of the latest glacial advance, which ended approximately 19,000 years ago. There are currently two types of glaciers in the Beartooths. Cirque glaciers occupy bowl-shaped basins against the headwalls of cirques. Rock glaciers are tongue-shaped flowing masses of ice, rock and debris often found just downslope of glaciers. Dependent upon the mapping and identification method, there are an estimated 21 to 107 cirque glaciers and 390 rock glaciers in the Beartooths, which is more than the total reported for Glacier National Park. Currently, approximately 15 percent of Northern Rockies glaciers are in the Beartooths.

Since the early 1900′s, scientists have documented rapid glacial retreat in the Yellowstone region. While most Forest visitors do not notice annual melting of ice, other evidence of glacial decline is readily observable. In 2003, an ice-dammed lake at the head of a glacier in Wyoming’s Wind River Range burst and released an estimated 3.2 million cubic meters of water into valley below. While nothing this dramatic has been observed in the Beartooths, glacial landscape changes are occurring and observable. One researcher estimated Grasshopper glacier has lost about 50% of area and as much as 90% of volume between 1898 and 1981. A 2009 study revealed that Castle Rock Glacier, the largest glacier in the Beartooths, lost 1.2 meters of ice elevation per year, or 60 meters of ice thickness from 1952 to 2003. Photo imagery shows that a melting rock glacier in the Timberline Creek drainage collapsed between 1998 and 2005 to form a 500-foot diameter crater.

Glacier-Pika

Various researchers are working on predictive models of future climate and generally agree that temperatures in the Beartooths will, on the average, rise. Accurate precipitation predictions remain unknown. Overall, it is assumed that glacial decline will continue. This will likely change water storage and runoff patterns in the Beartooths. Recent research has demonstrated that such changes water quality and quantity in lakes and streams could affect aquatic invertebrates and trout spawning patterns. Alpine vegetation, particularly whitebark pine, and wildlife species like pika are predicted to move up in elevation and possibly vanish as alpine vegetation and glacial elevations rise. Glaciers are very dynamic in terms of geologic time and the latest observed changes are one more force affecting the flora and fauna and shaping the landscapes of the Beartooths.

Timberline Creek Cirque

A crater formed by glacial collapse in the Timberline Creek drainage.

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