The Western United States: A Geographical Reader

by Harold W. Fairbanks

Upon the summit of the Cascade Range the dense forests of the river valley give place to more open woods interspersed with park-like meadows. A few miles away to the south rise the volcanic peaks of the Three Sisters, clear and cold in the mountain air, wrapt about with a mantle of white except where the slopes are too precipitous to hold the snow.

An indistinct trail leads through the tamarack forest and over a field of rugged lava to the base of the peaks. Here we come upon a swiftly flowing stream of a strange milky color. This appearance is due to the presence of fine mud, the product of the work of the glacier at the head of the stream as it slowly and with mighty power grinds away the surface of the rocks over which it moves. Wherever one meets a stream of this kind, he will probably be safe in asserting that it is fed by a glacier upon some distant mountain peak.

This little stream, the course of which we must follow to reach the glacier, is choked with sand and pebbles brought to it by the moving ice. These are not ordinary stream pebbles, for they have strangely flattened sides which often show scratches, and look as if they had been ground off against a grindstone. They are the tools with which the ice does its work. The ice block takes up the rock fragments which fall upon its surface or which it tears from beneath, and carries them along, grinding every surface which it touches. The fragments are dropped at the end of the glacier, and the smaller pebbles are washed away down the stream that flows from the melting ice.

FIG. 17.—GLACIER ON THE THREE SISTERS

We follow up the little glacial creek, past icy snow-banks and through groves of fir trees where the warm sunshine brings out the resinous odors. Upon one side of the cañon there lies a field of black lava which not many hundreds of years ago forced this glacial creek from an earlier channel into its present bed. Now we come upon what appears at first to be a snow-bank lying across the course of the stream, and from beneath which its waters issue. Deep cracks in the outer mass of snow show the clear, pale-green ice below. This is the lower end of the glacier which we have been so long a time in reaching.

A short climb up a steep slope brings us to the top of the glacier. It forms a perfectly even plain, extending back with a gentle slope to the head of a deep notch between the two northern Sisters, while above and beyond rise the steeper snow-fields, from which this ice is continually renewed.

The glacier does not terminate in the usual manner, with a stream flowing from its centre, for the outlet is at one side, while the middle abuts against a low mound of rock. This mound we find most interesting, for upon reaching its top we look down into a volcanic crater. From this crater flowed the great stream of lava to which we have already referred. The lava ran downward, bending this way and that among the hollows, until it spread nearly to the McKenzie River.

During the Glacial period, before the eruption took place, this glacier was much larger. The summit of the Cascade Range was then covered by glaciers. This fact we know from the presence of grooved and polished rocks wherever the surface has not been worn away or covered with newer lava. The Glacial period had passed away and the climate had become much the same as it now is when the volcanic forces broke out at the spot where the crater is situated. The eruption undoubtedly melted the ice in the vicinity, but after it had ceased and the rocks had become cold, the glacier never gained strength enough to push the loose materials of the volcanic cone out of its path. The ice banked up snugly against the obstruction, and as it melted the water found its way out at the side of the lava.

although the surface of the glacier appears at first to offer an easy route to the higher mountain slopes, yet there are numerous hidden crevices into which one may fall. The safest arrangement is to tie a company of people together with a stout rope, so that if one falls into a crevice the rope will save him. Toward the middle of the glacier the ice becomes so badly fissured that it is necessary to turn toward the right margin. There are two sets of these fissures, one parallel to the direction in which the glacier is moving, the other at right angles. They are due to the strain to which the ice is subjected as it moves along at an uneven rate and over a surface composed of hollows and ridges.