Geological Survey Professional Paper 387—B Recent Activity of Glaciers of Mount Rainier, Washington

Just 130 years ago, in the 1840's, about the time Europeans settled the Puget Sound region (Brockman, 1940, p. 21), it would not have been possible to walk in the small stand of trees between the present parking area and the old road under the Nisqually Glacier bridge at the Nisqually River. Not only did the forest not exist, but ice many tens of feet thick filled the valley bottom at this point and extended about 750 feet downvalley from the present bridge site (figs. 1, 3, and map on pl. 2). The position occupied by Nisqually Glacier in the 1840's is marked by a prominent, bouldery ridge representing the maximum advance in at least 10,000 years (Crandell and Miller, 1964). The moraine, here called the 1840 moraine, is seen, in the photograph, just inside the dense forest (area 24) north of the parking area (fig. 2 on pl. 2) at the west end of Nisqually Glacier bridge, and then it slopes steeply across the road to the bare gravel of the Nisqually River flood plain. The difference in appearance of the forest on opposite sides of the moraine is striking. The forest is open on the east side where trees range from 1 to 2 feet in diameter and only small logs are present on the ground. On the west side the forest is dense; trees are large, ranging from 2 to 5 feet in diameter, and the ground is littered with logs equally large (see table 1).

TABLE 1.—Nisqually Glacier: ages of trees sampled from periglacial features

[Periglacial feature: OS, old surface; M, moraine; OW, outwash]

During the last 10,000 years, when Nisqually River valley below the 1840 moraine was free of ice, at least eight geologic events affected the forested slopes. Four or more of these were debris flows that deposited varying amounts of rock and mud as far as 25 miles downvalley from Nisqually Glacier (Crandell and Mullineaux, 1967, p. 10). The other four events were deposition of layers of pumice from eruptions of Mount Rainier and of other volcanoes.

The most prominent pumice deposit here is yellowish to reddish brown and can be seen at the top of road embankments opposite the parking area west of the 1840 moraine. Excavation in the old forest floor reveals that a thick humus mat of decayed wood overlies the ash layer. This ash erupted from Mount St. Helens 3,000 to 3,500 years ago (Crandell and others, 1962).

Lt. A. V. Kautz, stationed at nearby Fort Steilacoom, first recorded observations of the front of Nisqually Glacier and reported in 1857 that it was at a "rock throat" (Brockman, 1938, p. 769-770; Giles and Colbert, 1955, p. 4; Meany, 1916, p. 82-83). Three trees mark the approximate position of the glacier reported by Kautz (fig. 2 on pl. 2). The older of two trees, area 27, was about a foot tall in 1858 and the oldest of five at area 28 was the same size three years earlier in 1855. The glacier terminus in 1857 was not beyond the location of these trees.

Two other moraines are especially prominent on the open and shrubby slopes above the river upvalley from the bridge; these possibly represent minor readvances of stillstands of the glacier margins in the last 100 years. The end of the older moraine is seen on the bank north of the old bridge site. The other, largely hidden by alders on the slope near Tato Falls, is apparent as a narrow ridge on the nearly bare slope above Tato Falls and upvalley. The assigned dates are arbitrary, as insufficient data are available to define them precisely. The glacier margin probably was at the indicated position within 10 to 15 years of the assigned dates.

Like other glaciers at Mount Rainier, Nisqually Glacier until just a few years ago has, in general, been receding for more than a century. Also like the other glaciers, it has been advancing the past few years. Between July 1960 and September 1966, the front of Nisqually Glacier advanced about 1,250 feet (derived from examination of aerial photographs).