Mount Rainier, a Record of Exploration

by Unknown

The Columbia River afforded to the first people who came to Washington and Oregon the easiest and most feasible route across the Cascade Mountains. It was through this gateway that travel passed from one side of the range to the other until the advent of the railways in comparatively recent years. The early travelers along the river who were of an observing or scientific bent, noted that the rocks were, in general, dark, heavy and massive and of the class commonly known as basalt. Here and there a sort of pudding stone or agglomerate was observed, which in some instances might represent a sedimentary deposit, but which here had clearly an igneous origin.

The observations of the early travelers were supplemented later by the further studies of geologists; and from the facts noted along the Columbia River, the generalization holds good to a great extent on the Oregon side, but it is by no means true on the Washington side, as has been shown by later studies. Granite rocks are encountered within a few miles of the Columbia River as one travels north along the Cascade Range. Associated with these granite rocks are found rocks of a metamorphic type, such as gneiss, schists, quartzites, crystalline limestone, slate, etc. Such rocks exist south of Mount Rainier, but are not conspicuous. North of this point, however, and throughout all of the northern Cascades they form the great bulk of the rock.

In other words, in the Cascades of Washington, igneous activity has been much more common in the region south of Rainier than in that north of the mountain. When the first observations were made upon the great lava flows of southeastern Washington, which form a part of the greatest lava plain in the world, it was supposed that the lava had its origin in the volcanoes of the Cascades. Later investigations have shown this view to be erroneous. The lava of the plain has come directly from below through great longitudinal fissures instead of through circular openings such as one finds in volcanoes.

It is probable that the Cascades, like most other mountains, have had several different periods of uplift. We have several notable examples of mountains which have had an initial uplift and then have been reduced to base by erosion. By a second upheaval the plain has been converted into a plateau, and this in time assumes a very rugged, mountainous character as a result of the combined forces of air and water. Eventually these same forces would reduce the region to a plain again. Just how many times this thing has happened in the Cascades we do not know. Bailey Willis has shown that in the northern Cascades, at least, the whole country was reduced to a plain prior to the last uplift, which took place in comparatively recent times. Out of this plateau, formed by the uplifting of the plain, has arisen through the active attack of erosive forces the truly mountainous character of the district. Erosion has been at the maximum in the mountains because of the heavy precipitation. Precipitation in the high mountains being chiefly in the form of snow has led to the formation of glaciers, producing thereby a rapidity of erosion of the first order. The active work of ice and running water has given to the mountains an extremely rugged appearance, characterized by valleys of great depth extending into the very heart of the mountains and with precipitous divides.

It must be understood that the time consumed in the uplifting of the Cascades, and the conversion from plain to plateau, was of considerable duration. With the beginning of the uplift, the sluggish streams of the plain became rejuvenated, and took up actively once more the work of erosion. By the time the maximum uplift was reached, the plateau had lost to a certain degree its character of extreme levelness. The streams had already entrenched themselves in rather conspicuous valleys. It is believed that the great volcanoes of Washington—Rainier and its associates—began their activities about the time the uplift described above reached its maximum height. In the vicinity of Rainier the rock of the old plateau is granite; and the volcano may be said to be built upon a platform of that material. On the north side of the mountain granite appears conspicuously at a height of about 7,000 feet; while on the south side it appears at points varying from 5,000 to 6,000 feet above the sea.

That the surface of the granite platform was irregular and uneven may be seen in the walls of the Nisqually canyon, near the lower terminus of the glacier. As one ascends the canyon to the glacier, the contact between the lava rock and the granite shows quite plainly on both the right and the left side. On the left the contact is at least 1,000 feet above that on the right side. A little way above the lower end of the glacier, on each side of the canyon, a good opportunity presents itself to study the contact of the lava and granite. The granite at this place shows clearly that it was once a land surface; and one may note weathering for a distance downward of seventy-five or one hundred feet. The upper portion of the granite shows the usual characteristics of weathering, namely, the conversion of feldspar into kaolin, the oxidation of iron, etc. At this point the lava overlying the granite is quite basic and massive. The first flow reached a thickness here of fully three hundred feet, and exhibits a fine development of basaltic structure.

In following up the canyon walls one observes that the activity of the volcano for some time was characterized almost exclusively by lava flows. In the main the lava is an andesite, and is very generally of a porphyritic structure. Some of the lava flows were of great extent, and reached points many miles distant from the center of the mountain. While the earlier stages of the activity of the volcano were characterized by lava flows of great thickness, by and by explosive products began to appear, and interbedded with the sheets of lava one finds bombs, lapilli, cinders, etc.

It may be said in general that as the volcano grew in years it changed more and more from eruptions of the quiet type to those of the explosive character. It is plain that a long period of time was consumed in the making of that great volcanic pile, and that the eruptions were by no means continuous. It is clearly shown that after certain outflows of lava, quietude reigned for a time; that at last the surface of the rock became cool and that erosive agents broke it up into great masses of loose stones. In later flows of lava these stones were picked up and cemented into layers of pudding stone, which are styled agglomerates.

Rocks of an agglomerate type are well shown in the walls of Gibraltar. This massive pile is largely made up of boulders, great and small, rather loosely held together by a lava cement. The work of frost and ice, expansion and contraction, loosens the boulders readily, and their constant falling from the cliffs gives to this part of the mountain's ascent its dangerous character. While this volcano belongs to a very late period in the history of the earth, it is very clear that there has been no marked activity for many thousands of years. The presence of steam, which is emitted from the hundreds of small openings about the crater, undoubtedly shows the presence of heated rock at no great distance below the surface. Rock is a poor conductor, however, and cooling takes place with very great slowness after a depth of comparatively few feet is reached.

Like most volcanoes, the composite character of the cone is shown on Mount Rainier. After a certain height is reached in the building up of a cone, the rising lava in the throat, or the explosive activities within, sometimes produce an opening through the walls of the cone, and a new outlet to the surface is formed. This often gives the volcano a sort of hummocky or warty appearance, and produces a departure from the symmetrical character. In the case of Rainier it seems to the writer that upon the summit four distinct craters, or outlets, are distinguishable. The first crater reached by the usual route of ascent is the largest one, and may be styled the East crater. It is nearly circular in outline, with a diameter of about one-half mile. Its walls are bare of snow for nearly the whole of its circumference, but the pit is filled with snow and ice. Going across the crater to the westward, one passes over what is really the highest point on the mountain, and then goes down into a smaller crater, or the West crater. This is similar in character and outline to its neighbor, but here the many jets of issuing steam are much more prominent. At a point a few hundred feet lower on the mountain-side there is a peak known as Liberty Cap. A cross-section of the cap is in plain view and shows very clearly that this is a minor cone or local point of eruption. It is made up of rock very similar to the main mass of the mountain; and it is likely that the volcanic activity of the mountain was centered here for some time. Looking directly south from the West crater one sees at a distance of less than a mile another peak which is entirely snow-covered; but which may represent an instance parallel with that of the peak on the north side.