Dwight R. Crandell

“ Crevasses are a glacier’s most awesome features and are a constant hazard for climbers. They form where adjacent parts of a glacier are moving at different speeds. Some of Mount Rainier’s glaciers may be flowing at a speed of several thousand feet per year along their centers but at a much slower rate along their margins. This unequal rate of flow produces stresses in the ice that cause it to break. Groups of crevasses often form where the glacier flows over a steep place in its bed. The ice moves faster here, and pulls apart, and a crevasse is formed. ”

“ A glacier deposits most rock debris at its terminus. The steep snout of any major glacier is a dangerous place to approach closely because rock debris almost constantly falls, rolls, and slides down the melting ice faces. Much of this debris collects at the ice margin, and if the margin stays in one place long enough a ridge-shaped end moraine of rock debris forms along the ice front (fig. 14) . If such a moraine 26 forms across the front of a glacier at its farthest advance it is called a terminal moraine. ”

“ A far more spectacular variety of landslide occurs when a mass of rock drops from a cliff to form a rockfall. The largest rockfalls on Mount Rainier in historic time occurred in December 1963 on the east flank. Masses of rock hundreds of feet across fell repeatedly from the steep north face of Little Tahoma Peak onto Emmons Glacier. The rock masses shattered into dust and countless fragments, fanned out across the glacier, then avalanched down the steep ice surface at tremendous speed. When the avalanches reached the end of the glacier they shot out into space as sheets 36 of rock debris. ”

“ Ice-clad Mount Rainier, towering over the landscape of western Washington, ranks with Fuji-yama in Japan, Popocatepetl in Mexico, and Vesuvius in Italy among the great volcanoes of the world. At Mount Rainier, as at other inactive volcanoes, the ever-present possibility of renewed eruptions gives viewers a sense of anticipation, excitement, and apprehension not equaled by most other mountains. Even so, many of us cannot imagine the cataclysmic scale of the eruptions that were responsible for building the giant 2 cone which now stands in silence. ”

“ An active volcano changes continually. Repeated eruptions build the cone by piling one lava flow on top of others, or on top of other volcanic formations. Simultaneously, the combined processes of erosion wear the volcano down. The relative importance of the two processes—one building, the other destroying—is reflected in the volcano’s shape. The scarred and deeply gouged sides of Rainier’s cone show that erosion has been dominant here for a long time. Is Mount Rainier now doomed to continued piecemeal destruction until the lofty cone is reduced to a featureless mound? ”

“ Mount Rainier probably started to grow during the middle part of the Pleistocene Epoch, or Ice Age, which began more than 1 million years ago, but glaciers had covered this part of the mountains even before the volcano appeared. Masses of rock debris formed by ancient glaciers occur beneath lava flows from Mount Rainier on the west side of Mazama Ridge just upslope from Narada Falls, on the north side of Glacier Basin, and at a few other places in the park. ”

“ Those of one group originate at the volcano’s summit and flow far down the valleys that radiate from the cone. Most of the snow that nourishes these glaciers probably falls on them at altitudes 25 well below the summit. The largest examples of the group are the Emmons, Nisqually, and Tahoma Glaciers.
Glaciers of the second group originate on the flanks of the volcano, mostly at altitudes between 7,000 and 10,000 feet. This group is represented by the South Tahoma, Carbon, and Inter Glaciers. Glaciers of the third group are on north-facing slopes in the mountains around Mount Rainier. ”

“ In some places the orientation or altitude of the cirque did not permit enough snow to accumulate to form a glacier but just enough to create a permanent snowbank. Rock debris that fell from the surrounding cliffs rolled down these snowbanks and formed low ridges at their toes. Such a ridge is called a protalus rampart because it is found just in front of the apron of rock fragments, called talus, that lies beneath cliffs. A trail at Sunrise Point leads to protalus ramparts along the north side of Sunrise Ridge. ”

“ Glaciers transport not only the rocks that they quarry and scrape from their beds but also, more conspicuously, those that fall onto their surfaces from nearby cliffs. These falling rocks range in size from tiny particles to individual masses that weigh tens of thousands of tons, like those that fell onto Emmons Glacier from Little Tahoma Peak in 1963. ”

“ You can sense the carrying power of this swiftly moving water on warm summer days, when large cobbles 28 and boulders are bumping along in a stream swollen by rapid glacier melting. Although you can rarely see these boulders, you can hear their constant low thunder. Their repeated impacts on other boulders in the streambed will vibrate the nearby streambanks beneath your feet. Hikers often find that a melt-water stream safe to cross in the early morning of a warm summer day is an impassable torrent at the same spot by early afternoon. ”

“ This was the remarkable Osceola Mudflow, which streamed down the valleys of the White River and West Fork about 5,800 years ago. When these great rivers of mud joined in the White River valley, they formed an even larger mudflow which swiftly flowed downvalley for a distance of 15 miles and then spread beyond the Cascade mountain front into the Puget Sound lowland. There the mudflow submerged a total area of more than 100 square miles to depths as great as 70 feet and buried the sites of the present towns of Enumclaw and Buckley. ”

“ The face of the mountain also varies from day to day as its broad snowfields melt during the summer. The melting of these frozen reservoirs makes Mount Rainier a natural resource in a practical as well as in an esthetic sense, for it ensures steady flows of water for hydroelectric power in the region, regardless of season. ”

“ These turbulent streams flow from tunnels beneath every glacier, and their degree of muddiness roughly shows how active the glacier is. Glaciers that move very slowly, or that are stagnant, produce relatively clear melt water because they are not actively eroding bedrock. In contrast, streams of muddy water that look like chocolate milk often come from very active or “live” glaciers. These streams carry rock debris ranging from flour-size particles to large boulders. ”

“ Although any one rock fragment might scrape away only 1 millimeter of rock along a single groove, the total effect is great when multiplied by countless thousands of similar fragments rasping a bedrock surface for hundreds or thousands of years. Glacier ice may also break chunks of rock loose as it overrides them and may even plow up sections of softer rocks. ”

“ Glaciers representing this group are the Unicorn and Pinnacle Glaciers in the Tatoosh Range, a small unnamed glacier near the west end of Burroughs Mountain, and the somewhat larger Sarvent Glaciers east of Mount Rainier.
Work Habits of Glaciers
Glaciers are extremely capable workers. Their work includes erosion, transportation, and deposition. The smoothed and grooved bedrock at Box Canyon and at many points along the trail to the ice caves near Paradise Park shows erosion of rock by glacier ice. ”

“ Pumice layer X probably was erupted during one or more of these times, but we do not know exactly when.
And will Mount Rainier erupt again? We think that it will, but we now have no sure way of predicting the time, the kind, or the scale of future eruptions.
23 Why Glaciers?
We frequently hear the question: “Why are there glaciers on Mount Rainier?” A glacier forms wherever snowfall repeatedly exceeds melting over a period of years. Above 6,500-7,000 feet on Mount Rainier, more than 50 feet of snow falls each winter, and not all of it melts before the next winter. ”

“ It is mostly white, but it contains large dark mineral grains that give it a “salt-and-pepper” appearance (fig. 3) . 10 The large size of the grains is a result of the molten rock cooling slowly at a considerable depth below the land surface—the individual minerals had a long time to grow before the “melt” solidified into rock. In contrast, the rocks formed from lavas that flowed onto the ground surface are generally fine grained because the lavas cooled too quickly for the mineral grains to grow appreciably. ”

“ Only a flood may move the boulders farther downstream. However, the current carries fine material far downstream to deposit it in lakes, in Puget Sound, or in the Pacific Ocean. 29 The Puyallup River, for example, is still very muddy where it enters Puget Sound at Tacoma, more than 40 miles from its source in the glaciers on Mount Rainier. ”

“ The snow-covered lava cone lies in a depression 11⁄4 miles wide at the summit of the volcano. The cone was probably built about 2,000 years ago. Liberty Cap is to the left and Point Success is to the right. The cliffs below and to the right of Liberty Cap enclose Sunset Amphitheater. (Fig. 11)
Even though the lava flows that formed the summit cone were relatively short, their eruption greatly affected some valleys at the base of the volcano. ”

“ The hummocky end moraine at the left still had blocks of ice buried in it when this picture was taken in 1954. The front of Emmons Glacier was near the left edge of the bare moraine in about 1900. Now the glacier ends 1 mile farther upvalley at the upper right. The valley floor and moraine were buried by an avalanche of rock debris from Little Tahoma Peak in 1963. (Fig. 19)
Nearly all the glaciers gradually decreased in size after the mid-18th century. ”

“ A muddy grayish-blue lake several hundred feet long lies behind a small horseshoe-shaped end moraine of Flett Glacier, on the northwest side of Mount Rainier. The glacier is mostly out of view to the left. (Fig. 14)
Glaciers erode, transport, and deposit huge quantities of rock debris. ”

“ An old lava flow from Mount Rainier which forms Rampart Ridge west of the meadow at Longmire. The thick lava flowed down an old valley floor and cooled and solidified. Rivers then eroded new valleys along both sides of the flow. These new valleys, subsequently glaciated, are today followed by the Nisqually River and Kautz Creek. Thus, the area of a former valley floor is now a ridge. (Fig. 5)
Columns of dark-gray andesite at the east end of an old lava flow from Mount Rainier. ”