A massive terminal moraine that lies athwart the White River valley is the prominent hill about one half mile west of White River Campground (map and fig. 8 on pl. 7). The earliest date when Emmons Glacier extended this far is not known, but it had receded sufficiently by 1660 for trees to begin growing at area 27 (map and fig 9 on pl. 7). Later readvances left other ridges, the most prominent moraine being a steeply sloping one (dated 1745) that crosses the valley bottom (between areas 2 to 26, map and fig. 9 on pl. 7, table 8). In this complex of ridges and troughs, as well as in the remainder of Emmons Glacier's moraines, stand scores of mounds, gullies, and ridges as monuments to the ice front and to shifts in the landscape caused by changes in melt water channels.
Ice started to recede about 1745 (fig. 9 on pl. 7) after leaving the prominent moraine trending across the valley, and until the last few years, the glacier has generally been shrinking; however, in the last 150 years at least two additional minor readvances left moraines. Trees started to grow on one of these between 1835 and 1850 and on another about 1900. The moraine from which the glacier started to recede between 1835 and 1850 is best seen where it is cut by Inter Fork and by the Glacier Basin Trail (fig. 1 on pl. 7) near area 31 (map and fig. 9 on pl. 7). A climb 15 feet up the bank and into the woods provides one with a view of the prominent morainic ridge (area 31, fig 2 on pl. 7). When this moraine was being formed, the margin of Emmons Glacier paralleled the present axis of Inter Fork for about one-quarter mile westward. Just upstream from the trail bridge crossing (fig. 3 on pl. 7), a moraine is present in the forest north of the trail (area 63). The glacier margin curved sharply southwestward to area 56 and thence westerly along the present channel of Inter Fork to area 34. One tree (area 56, map and figs. 6 and 9 on pl. 7) was 16 inches tall in 1866: so the glacier margin was not north of this point at that time.
Marking the last readvance of the glacier is the prominent, nearly bare inner ridge visible from the trail along Inter Fork through openings in the trees and from the promontory (area 54) about 100 feet south of the trail bridge (map and fig. 5 on pl. 7). This ridge supports only scattered small trees, but the oldest are more than 60 years old. This was probably the gravelly ridge that Willis, Russell, and Smith saw in 1896 and reported as bare (Russell, 1898, p. 407).
TABLE 8.Emmons Glacier: ages of trees sampled from periglacial features
[Periglacial feature: OS, old surface; M, moraine; MWC, melt water channel within moraine; FP flood plain]
Ice started to recede from lateral moraines (fig. 7 on pl. 7) about A.D. 1530, whereas only a fragment (area 27, fig. 9 on pl. 7) of an old terminal moraine was recognized. Later advances overran most of the terminal moraine dating from before 1550, or outwash from the receding glacier destroyed or buried it before 1661, as indicated by melt-water channels in the old moraine near area 27.
The older lateral moraine is prominent at area 48 about 0.8 miles from the trail bridge across Inter Fork, or about 1-3/4 miles from White River Campground. The trail upvalley from a point about 100 yards north of area 43 is walled in by two prominent lateral moraines before the trail turns westward across one and then another moraine and into the dense forest at areas 43 and 44. The innermost lateral moraine (area 62), toward the valley to the east and not visible from the trail, was formed be fore 1910; the moraine (area 46) above the trail on the east side was formed before 1815; the first moraine that the trail crosses to the west, which also has small trees on it, was formed before 1745; and the second lateral moraine (area 18) which supports large trees 1-1/2 to more than 2 feet in trunk diameter was formed before 1600 and probably corresponds to the lateral moraine at areas 33, 36, 37, and 40 (fig. 7 on pl. 7).
The trees on the slope (area 44, map and fig. 7 on pl. 7) west of the old lateral moraine (area 43) are younger than those on the moraine, but evidence suggests that snow avalanches and fire destroyed an earlier forest. Here a moraine corresponding to the lowest one above the campground is seen 200 feet higher than the A.D. 1590-1600 moraine (area 43) (Crandell, 1965, p. 32).
Glacier Basin Trail leaves the Inter Fork flood plain just east of area 33, angles north, and steepens abruptly onto a sharp terrace at the end of an old lateral moraine. The moraine is banked against and deposited partly on top of a premoraine terrace. It continues almost uninterrupted from area 33 to area 36 and forms a high bank of Inter Fork for another quarter mile. At each end the moraine was destroyed by snow avalanches. The oldest tree (area 40) found on this section of the moraine was 2 feet high in A.D. 1552.
The moraine at area 43 probably corresponds to the moraine defined by locations of areas 33, 36, 37, and 40 (fig. 7 on pl. 7) because it is the oldest modern moraine here, and the oldest tree at area 43 is closer to the oldest at area 40 than at area 45, which defines the 1745 moraine. The range in age between the oldest tree sampled at area 43, 351 years, and at area 40, 411 years, may be expected of trees in stands of this age. The number of trees at area 43 is small, and the oldest to grow here evidently was not sampled or had died earlier.
Trees were sampled on the valley floor of White River in 1959 in areas 12 to 22 (map and fig. 9 on pl. 7), but all the sample areas were buried by rock-fall-avalanches in December 1963. The deposits bury the area sampled to depths of 50 to 80 feet and are part of an estimated total volume of 14 million cubic yards of rock debris that roared down the valley (Crandell and Fahnestock, 1965). In the vicinity of area 47 living trees can be seen that had bark and branches torn from the upvalley side by flying rock debris (Crandell and Fahnestock, 1965, p. A10-A11). Many of these trees now alive will continue to survive, and the scars that remain will be datable throughout their lives (Sigafoos, 1964, p. A9-A12).
The forest downvalley from the terminal moraine (map and fig. 9 on pl. 7) appears to be composed of trees of two distinct ages, and no evidence was found of earlier generations of forest that have fallen and partly decayed. Most trees are relatively young; ages of the 30 trees sampled in areas 1, 4, and 26 range from 56 to 265 years, all younger than the oldest trees on the older lateral moraines. In the other areas (3, 4a and 5) eight trees are more than 400 years old, and one is at least 700. The bases of the trunks of the older trees are straight sided and show no root flare (Sigafoos and Hendricks, 1961, fig. 13), suggesting that they were buried and hence are growing on a lower surface. The younger trees, however, are flared at the base, indicating that they began growing on the present surface, which may be outwash deposited when the glacier stood at the terminal moraine. This outwash may have killed most trees in its path but left a few old ones, some of which were sampled. The terminal moraine, however, represents the maximum known advance of Emmons Glacier in the last 10,000 years (Crandell and Miller, 1964, p. D113), because the next older moraines are on the slope 700 feet above White River Campground (Crandell, 1965, p. 32).
The continuity of the terminal and younger lateral moraines is broken by many small valleys cut by melt-water streams from the glacier when it filled the valley bottom. About 350 feet east of the point where the trail to the present glacier terminus climbs from the bridge to the top of the morainal ridge, at least two melt-water channels (areas 49, 50, 51, and 53) cut through the moraine complex and are floored with coarse gravel and boulders. Areas 49, 50, and 51 are successively lower surfaces in one channel (fig. 9), and ages of the trees on these deposits tell us that water flowed through area 49 not later than 1865, through nearby area 50 not later than 1870, and through area 51 not later than 1917. In 1917, water was flowing through another channel about 200 feet to the west (area 53, fig. 4 on pl. 7) and did so until 1920. At least part of the drainage from Emmons Glacier flowed from the north side and down Inter Fork from before 1865 until as recently as 1920. The older drainage ways, now high terraces of the eastern channel (areas 49 and 50), are higher surfaces than that of area 51. It seems probable that continued flow eroded a deeper channel which dried up before 1917 when the terminus melted back from this overflow point. Either or both these two channels could be the one mapped as a stream in 1896 (fig. 10) (Russell, 1898).
Ages of trees growing in the channels between the rounded hills west of area 42 have not been determined; therefore, the periods of runoff through these cannot be related to those to the east. Because the channels cut through the 1835-50 moraine, water drained from the glacier through them into Inter Fork after the 1850's and probably when the water drained through the easternmost channels. These channels are apparent on the aerial photograph as breaks in the line of rounded hills that represent a lateral moraine.
Approximate ages of moraines and melt-water channels for Emmons Glacier are summarized in the following table:
Age of features, A.D.
The dates assigned to these features emphasize the variable behavior of Emmons Glacier and the periglacial features formed during the last 420 years. At certain times Emmons Glacier was broader and formed lateral moraines which were not overridden later, whereas at other times the glacier was narrower and extended farther downvalley, destroying or burying older terminal moraines. The melt-water channels, on the north side of the valley, show that at least some flow from the glacier was into Inter Fork, which was probably a larger stream then than it is now.
Last Updated: 28-Mar-2006