RECONNAISSANCE STUDY OF MORAINES OF EMMONS AND TAHOMA GLACIERS
Reconnaissance studies were made in the vicinity of Emmons and Tahoma Glaciers in the summer of 1959. These glaciers had histories somewhat different from each other and different from Nisqually Glacier, so a brief summary of them is presented in this report. A more complete study of the age of the modern morainic surfaces here as well as those in the vicinity of some other glaciers at Mount Rainier is in progress.
Emmons Glacier is located on the northeast side of Mount Rainier at the head of White River (fig. 1). The terminus in 1958 (R. K. Fahnestock, written communication) was approximately 6,000 feet upstream from its location in 191013 as shown on the quadrangle map of Mount Rainier National Park. Down valley from the 191013 location for about a quarter of a mile, three prominent moraines extend across a neck of land between White River and Inter Fork (fig. 9). The area and approximate location of the line along which the trees were cored are shown on figure 10.
A prominent terminal moraine that extends across the neck of land approximately half a mile upstream from the confluence of Inter Fork and White River marks the maximunm advance of Emmons Glacier in at least a thousand years. Ages of the trees in the forest on the slope downvalley from the moraine cover a considerable range. Because a complete core could not be obtained from the oldest trees, the maximum age of these trees was not determined. Two old trees were determined to be 411 and 419 years old (fig. 13). The largest count, 694 annual rings, was obtained from a 15-inch core from a tree having a 16-inch radius. This tree is more than 700 years old. A count of 408 rings was obtained from a 7.9-inch core of a trunk having a 38-inch diameter exclusive of the bark. These trees are located about 300 feet downvalley from the toe of the moraine and signify that Emmons Glacier could not have occupied their present sites within at least the last 700 years. They are located in areas 3, 4a, and 5 (figs. 9, 10, and 14). The presence of fallen logs of the same diameter as the 400- to 700-year-old living trees and humus layers composed of rotten wood of ancestral trees indicates that the surface is at least 300 years older than the oldest tree.
The time interval between the start of recession and the establishment of seedlings on the moraines of Emmons Glacier is believed to average about 5 years. This estimate is based on a study of the ages of trees that grow in the transect across surfaces that were known to have been recently covered by Emmons Glacier and that have been previously discussed on pages A12 and 13.
The oldest tree found growing on the terminal moraine is a 210-year-old Douglas-fir at the north end near Inter Fork (area 2, figs. 9 and 10). In the center of the moraine and at the south end, the oldest trees cored are 175 years old (areas 6 and 7, figs. 9, 10, and 14). These trees started to grow in 1749 and 1784. The terminus probably started to recede about 1745, but the surfaces at the south end of the moraine may have remained unstable for almost 30 years. Melt water from the receding glacier may have flowed over this part of the moraine and destroyed any seedlings that were temporarily established. After a period of 35 to 40 years, however, the front probably had receded to a point sufficiently removed from the moraine so that melt water no longer flowed over it and the trees now 175 years old started to grow.
A small ridge (area 8, figs. 9, 10, and 14) was formed inside the terminal moraine during the recession of Emmons Glacier. The oldest trees on it started to grow in 1802 suggesting that ice receded from here in 1797. Another prominent morainic ridge is located about halfway between the 1745 moraine and the approximate location of the ice front in 191013 (area 9, figs. 9, 10, and 14). The oldest trees on it started to grow in 1854, suggesting that recession started from here about 1849. This moraine may have been formed by an advance which was virtually contemporaneous with the maximum advance of Nisqually Glacier.
A fourth moraine (area 11, figs. 9, 10, and 14) is located a short distance downvalley from the 191013 location of the ice front but was formed earlier. The oldest trees on it started to grow in 1901. The ice could have been at this moraine in 1896 at the time Willis, Russell, and Smith made field studies at Mount Rainier (Russell, 1898). Russell (p. 407) observed that Emmons Glacier, as well all others that were visited, showed evidence of recent recession by the presence of nearly bare moraines around the margins of the glaciers upon which young trees were beginning to grow. The oldest trees between this moraine of Emmons Glacier and the next one downvalley, the 1849 moraine, are now 80 to 90 years old. Of 11 trees cored here, 9 range from 70 to 80 years. When Russell saw Emmons Glacier in 1896, the oldest trees between the end of the glacier and the 1849 moraine were 17 to 27 years old. Most of them were between 7 and 17 years. On the 1849 moraine, the oldest trees were 42 years old and half of them were less than 25 years old. Thus the trees upvalley from the 1849 moraine were the young trees that Russell (1896) mentioned. Because a conspicuous moraine is located near the position of the ice front where Russell saw it, a minor readvance of Emmons Glacier probably occurred at about this time; the recent recession which Russell found probably started about 1849 at Emmons.
The moraine marking the maximum modern advance of Emmons Glacier, from which the front started to recede about 1745 is not present in the Nisqually River valley.
Tahoma Glacier is located at the head of South Puyallup River on the west side of Mount Rainier (fig. 1). A brief study was made in a small area on the left side of South Puyallup River valley near the location of the glacier terminus in 1913 and extending downvalley across two moraines into an old forest. A short arc of an outer moraine is present in only one part of the area studied. The remainder of the moraine represented by the outer arc was obliterated by a younger advance of the glacier that extended farther downvalley.
The inner moraine is younger and the trees sampled range in age from 107 to 119 years. The oldest tree started to grow in 1840 and thus the glacier probably started to recede about 1835. The stand has the appearance of a young forest, and these living trees are believed to be the first to grow on the moraine since the ice receded from this position.
The arc of the outer moraine curves more sharply at both ends toward the axis of the valley than does the arc of the younger moraine. The glacial advance that formed the 1835 moraine extended across the older moraine but probably extended only a short distance farther downvalley, as shown in class B2(fig. 5).
Only six trees on the older moraine were cored; the oldest tree is 320 years old, thus it started to grow in 1639. The trees on this moraine range in diameter from 18 to 40 inches, and they, too, appear to be of the first generation to grow since the ice receded. Many trees have fallen across this moraine but all are smaller than the standing trees. The young forest on the inner moraine is sufficiently close that the smaller trees could have grown on it and have fallen across the older moraine. There is no evidence that large trees have fallen on the moraine that are as old or older than the oldest living ones.
These two moraines, the young one and the one from which ice started to recede about 1635, are the only moraines found in the area studied on the left side of South Puyallup River valley (fig. 15). Evidence of the 1635 moraine was not found near either Nisqually or Emmons Glaciers.
The forest downvalley and upslope from both moraines below Tahoma Glacier is old. The largest count obtained was 338 years from a core from part of the radius of a 40-inch noble fir. Many fallen logs in all stages of decay as well as thick humus, composed largely of rotten wood, characterizes the old forest. Two trees, which are growing on fallen logs, are 182 and 198 years old; thus the fallen trees died before 1777 and 1761. The log upon which the 182-year old tree is growing is 13 inches in diameter 10 feet from the roots, and the wood in the center is still sound. Therefore, the presence of humus layers composed of completely decayed wood signifies that the surface has been forested for a long time.
The two moraines represent the maximum advance of Tahoma Glacier in a period that may also prove to be at least one thousand years. Their configuration shows that the ice front during the earlier advance had a shape different from that of the later advance even though both must have reached about the same distance down valley. Furthermore, in the areas studied in the vicinity of three glaciers flowing from Mount Rainier, evidence of a recession in the 17th century was found only at Tahoma Glacier. The possibility that such evidence exists elsewhere, however, is not precluded although it apears doubtful that further work at Nisqually Glacier will uncover it. The examination of the area at Emmons Glacier was too incomplete to justify an early conclusion about a 17th century advance.
Last Updated: 01-Mar-2005