34 Eighth Ann. Rept. U. S. Geol. Surv., 1889, part I, pp. 360–366.
The most important ice-streams about Mount St. Elias and Mount Cook are indicated on the map forming plate 8. The Tindall, Guyot, and Libbey glaciers and the lower part of the Agassiz glacier there represented are taken from a map published by H. W. Topham.35 All of the other glaciers indicated on the map were hastily surveyed during the present expedition and are described to some extent in the accompanying narrative. By far the most important of these is the one named the Seward Glacier.
35 Alpine Journal, London, vol. XIV, 1887, pl. op. p. 359.
The Seward Glacier is of the Alpine type, and is the largest tributary of the Malaspina glacier. Its length is approximately 40 miles, and its width in the narrowest part, opposite Camp fourteen, is about 3 miles. The main amphitheatre from which its drainage is derived is north of Mount Owen and between Mount Irving and Mount Logan. The general surface of the broad level floor of this névé field has an elevation of approximately 5,000 feet. The snow from the northern and western sides of Mount Irving, from the northern slope of Mount Owen, and from numerous valleys and cañons in the vast semicircle of towering peaks joining these two mountains, unite to form the great glacier. There is another amphitheatre between Mount Owen and the Pinnacle pass cliffs supplied principally by snows from the northwestern slope of Mount Cook, which sends a vast flood of ice and snow into the main drainage channel. Other tributary glaciers descend the steep slopes of Mount Augusta and Mount Malaspina, and a lesser tributary flows eastward from Dome pass. All of these ice-drainage lines converge toward the narrow outlet of Camp 14 (plate 8) and discharge southward down a moderately steep descent several miles in length. Below Camp 14 there are other névé fields bordering the glacier, which contribute no insignificant amount of ice and snow to its mass. Between the extremity of the Hitchcock range and the Samovar hills the path of the glacier is again contracted and greatly broken as it descends to the plateau below.
The Seward glacier, like all ice rivers of its class, has its névé region above, and its ice region below. The limit between the two is the lower margin of the summer snow, and occurs just above the ice-fall between the southern extremity of the Hitchcock range and the Samovar hills. All the névé region is pure white and without moraines, except at the immediate bases of the most precipitous cliffs. At the bases of the Corwin cliffs, which rise fully 2,000 feet above its border, no débris can be distinguished even in midsummer. An absence of moraines along the base of Pinnacle pass cliffs was also noticed during our first visit, but when we returned over the same route in September the melting of the snow had revealed many large patches of dirt and disintegrated rock. In several places near the bases of steep cliffs, strata of dirty ice, containing many stones, were observed in deep crevasses. It was evident that vast quantities of débris were sealed up in the ice along the borders of the glacier, only to appear at the surface far down the stream where summer melting exceeds the winter accumulation.
The surface of the glacier below the lower fall is composed of solid ice with blue and white bands, and has broad moraines along its borders. The course of the glacier, after entering the great plateau of ice to which it is tributary, may be traced for many miles by the bands of débris along its sides. These moraines belong to the Malaspina glacier, and have already been referred to.
At the outlet of the upper amphitheatre, about 6 miles above Mount Owen, there is an ice-fall which extends completely across the glacier. Below the pinnacles and crevasses formed by this fall the ice is recemented and flows on with a broad, gently descending surface, gashed, however, by thousands of crevasses, as shown in plate 20, to the end of the Pinnacle pass cliffs. It there finds a more rapid descent, and becomes crevassed in an interesting way. The slope is not sufficient to be termed a fall, but causes a rapid in the ice-stream.
The change of grade in the bed of the glacier is first felt about a mile above Camp 14. A series of crevasses there begins, which extends four or five miles down-stream. At first the cracks are narrow, and trend upstream in the manner usual with marginal crevasses. Soon the cracks from the opposite sides meet in the center and form a single crevasse, bending upstream in the middle. A little lower down, the crevasse becomes straight, showing that the ice in the center of the current flows more rapidly than at the sides. The more rapid movement of the center is indicated by the form of the crevasses all the way down the rapid. After becoming straight they bow in the center and form semi-lunar gashes, widest in the center and curving up-stream at each extremity. Still farther down they become more and more bent in the center and at the same time greatly increased in breadth. Still lower the curve becomes an angle and the crevasses are V-shaped, the arrow-like point directed down-stream. These parallel V-shaped gashes set in order, one in front of the other, are what gives the glacier the appearance of "watered" ribbon when seen from a distance.
With the change in direction and curvature of the crevasses, there is an accompanying change in color. The cracks in the upper part of the rapid are in a white surface and run down into ice that looks dark and blue by contrast. Lower down, as the cracks increase in width, broad white tables are left between them. Cross-fractures are formed, and the sides of the table begin to crumble in and fill up the gaps between. As the surface melts the tables lose their pure whiteness and become dust-covered and yellow; but the blocks falling into the crevasses expose fresh surfaces, and fill the gulfs with pure white ice. In this way the color of the sides of the crevasses changes from deep blue to white, while the general surface loses its purity and becomes dust-covered. Far down the rapid where the V-shaped crevasses are most pointed, the tables have crumbled away and filled up the gulfs between, so that the watered-ribbon pattern is distinguished by color alone. The scars of the crevasses formed above are shown by white bands on a dark dust-covered surface. Before the lower fall is reached nearly all traces of the thousands of fissures formed in the rapids above have disappeared.
On looking down on the rapids from any commanding point, the definite arrangement of the crevasses along the center of the ice-stream at once attracts attention, and their order suggests a rapid central current in the stream.