Part 3

1 A hypothetical block of the Earth’s crust in the region of Glacier National Park as it existed more than 60 million years ago. The two layers shown actually represent many strata of sedimentary rocks.

2 Lateral pressure begins to force the rock layers to buckle.

3 A large fold has been created, forcing the rock strata to double over and overturning some layers. A break, or fault, is forming at the plane of greatest stress.

4 The break has been completed and the strata west of the fault have slid eastward, up and over the rocks east of the fault.

5 The Glacier landscape today. Throughout the millions of years during which the folding, faulting, and overthrusting have been taking place, the process of erosion has continued; a thousand meters of stratified rocks have been worn away, so that only a remnant of the overthrust layers can be seen today. Because Glacier’s eastern slope represents the eroded face of the overthrust block, the mountain range rises precipitously from the prairie, with no foothills breaking the abrupt transition from open prairie to mountain valley.]

1 This is how the landscape in this region might have appeared before the onset of the Pleistocene, millions of years ago. Note the stream-eroded, V-shaped valleys. The climate at that time was dry.

2 Glaciers began to form high on the peaks, crept downward, and joined to form larger glaciers.

3 After many centuries of glaciation, tributary glaciers have cut back into the peaks, forming basins called cirques. Thick glaciers, moving rapidly and carrying rock fragments, have abraded the main valleys’ floors and sides, widening and deepening the valleys into characteristic U-shapes.]

V-shaped Valley Tributary Glacier Unglaciated Peak Headwall Meltwater Stream Nose of Glacier Crevasse

During all this time, all parts of the terrain not buried under ice and snow have been weathered and eroded by nonglacial forces. Thus the contours of the jagged peaks and sheer cliffs have been softened.]

Unglaciated V-shaped Valley U-shaped Valley Hanging Valley Cirque Tarn Alluvial Cone Moraine Morainal Lake

Because of an eastward flow of cool, moist Pacific air masses, the climate of northwestern Montana, including the western portion of Glacier National Park, differs from that of other portions of Montana. As a result of increased precipitation, Glacier’s western valleys support a rich flora, more typical of the Pacific Northwest.

West

Moist Pacific air

As the moisture-laden Pacific winds are pushed up the windward slopes of Glacier’s mountains, the air cools and water vapor condenses, forming fog or clouds. Rain or snow begins to fall as the air continues to rise and cool. By the time the air mass reaches the crest and flows down the leeward slopes, most of the moisture has been lost.

Western slopes average about 70 cm. of precipitation at elevations between 900 and 1,100 m. Upper elevations average 200 to 250 cm., mostly in the form of snow; and 300 to 500 cm. is common.

East

Dry chinook winds

Eastern slopes, under the influence of Continental air masses, receive less annual precipitation. West Glacier’s annual average is 66.5 cm. Babb, a small town east of the park, averages 49.3 cm. Frequent high winds east of the Divide further reduce moisture through evaporation.

Exposed to Arctic air masses flowing down from Canada, locations east of the Divide also suffer more severe winter conditions than do protected western valleys. Average January temperature is -5°C at West Glacier, -8° at Babb.

Moreover, 80 percent of the winter days in the western portion of the park are overcast, a condition almost identical to that of Seattle, Wash. This serves to moderate winter temperatures and to minimize evaporation.]

Two species of hummingbirds—the rufous and the calliope—are found in Glacier. Pictured is a female rufous (which weighs about the same as a dime) landing on its lichen decorated nest to feed its two young on a protein-rich mixture of nectar and small insects.]

Reaching the mountain wall, the goats scramble upward to a ledge, sending scree streams pouring from several clefts. Encountering a narrow, steep snowbank, they do not hesitate but continue across the slope. Above the rock fingers of this peak the gathering clouds grow black. A sudden crack of thunder hurries me down the trail.

Although geologically young, the Rocky Mountains in Glacier are composed of soft sedimentary rocks that are easily assailed by the many agents of weathering and erosion. If not rejuvenated by continual uplift, these magnificent peaks will glimmer but briefly in the long memory of the planet.

Already the sharp countenance of this land is being softened by the ongoing forces of erosion. Chief among these is water, which attacks the mountains everywhere. In addition, frost action continually exploits rock fractures, breaking down blocks of rock into talus and scree. Avalanche and rockfall sweep down the slopes. Layers of softer rock erode quickly, undercutting more resistant rock and creating overhangs which gravity, in time, will collapse.

The lashing rain catches me on this sun-and-storm-contested pass. Ice, gravity, wind, and especially water—all attack a land that dares the clouds.

The Rising of the Sun and the Running of the Deer: A Glacier Year

As if to make up for the days-long darkness of this last blizzard, the peaks today wear snow plumes—long, graceful trails of white, curving up into an ice-blue sky. Yesterday the snow-mad wind raced through the forest. Today the motionless trees are cloaked in heavy, glistening robes, the leafless aspen and young larch bent down.