Mount Rainier!   Well, there is only one 14'er in Washington...Mount Rainier! 14,410 ft!
Mount Rainier from McClure Rock, Photo courtesy of U.S.G.S.

Glaciers on Mount Rainier
Glaciers are among the most conspicuous and dynamic geologic features on Mount Rainier in
Washington state. They erode the volcanic cone and are important sources of streamflow for
several rivers, including some that provide water for hydroelectric power and irrigation.
Together with perennial snow patches, glaciers cover about 36 square miles of the mountain's
surface, about nine percent of the total park area, and have a volume of about 1 cubic mile..

Glacier flow on the Mountain
To the casual observer, glaciers may seem to be rigid and unchanging, but in fact, they
deform and flow continuously. Glaciers flow under the influence of gravity by the combined
action of sliding over the rock on which they lie and by deformation, the gradual
displacement between and within individual ice crystals. Maximum speeds occur near the
surface and along the centerline of the glacier. During May, 1970, Nisqually Glacier was
measured moving as fast as 29 inches per day. Flow rates are generally greater in summer
than in winter, probably due to the presence of large quantities of meltwater at the
glacier base.

Glaciers and climate
Climatic conditions in large part regulate the size of a glacier because they control the
quantities of snowfall and melt. The position of the snout, or terminus, of a glacier may
change as the relative quantities of snowfall and glacier melt change. If summer melt
exceeds winter snowfall, the terminus retreats, whereas if snowfall exceeds summer melt,
the terminus advances. These changes in terminus position do not occur instantaneously,
but typically take several years or more to become apparent. Glaciers are therefore
sensitive indicators of climate changes.
Scientists measure winter snow accumulation and summer melt of snow and ice to analyze the
response of glaciers to climate; however, it is very time-consuming and potentially a
hazardous task. Consequently, alternative data, which are obtained by mapping of terminus
positions and surveying of glacier surface elevations, are commonly used. At Mount Rainier,
annual measurements of Nisqually Glacier's terminus position were begun in 1918 by National
Park Service.

Changes in terminus position may actually be forecast by precise surveys of a glacier's
surface elevation. For example, a rise in surface elevation, which reflects an increase in
ice thickness, is typically followed within a few years or decades by terminus advance.
The surface-elevation record at Nisqually Glacier is the lengthiest of any made in North
America. The record, which was started in 1931, shows the glacier's dramatic responses to
about half a century of small but significant climatic variations.

History of Glacier fluctuations
The size of glaciers on Mount Rainier has fluctuated significantly in the past. For example,
during the last ice age, from about 25,000 to about 15,000 years ago, glaciers covered most
of the area now within the boundaries of Mount Rainier National Park and extended to the
perimeter of the present Puget Sound Basin. Geologists can determine the former extent of
glaciers on Mount Rainier by mapping the outline of glacial deposits and by noting the position
of trimlines, the distinct boundaries between older and younger forests or between forests
and pioneering vegetation. Geologists determine the age of some of the deposits by noting the
age of the oldest trees and lichens growing on them and the degree of weathering on boulders.

Between the 14th century and A.D. 1850, many of the glaciers on Mount Rainier advanced to
their farthest extent downvalley since the last ice age. Many advances of this sort occurred
worldwide during this time period known to geologists as the Little Ice Age. During the
Little Ice Age, the Nisqually Glacier advanced to a position 650 feet to 800 feet downvalley
from the site of the Glacier Bridge, Tahoma and South Tahoma Glaciers merged at the base of
Glacier Island, and the terminus of Emmons Glacier reached within 1.2 miles of the White River
Campground.

Retreat of the Little Ice Age glaciers was slow until about 1920 when retreat became more rapid.
Between the height of the Little Ice Age and 1950, Mount Rainier's glaciers lost about one-quarter
of their length. Beginning in 1950 and continuing through the early 1980's, however, many of the
major glaciers advanced in response to relatively cooler temperatures of the mid-century. The Carbon,
Cowlitz, Emmons, and Nisqually Glaciers advanced during the late 1970's and early 1980's as a result
of high snowfalls during the 1960's and 1970's. Since the early-1980's and through 1992, however,
many glaciers have been thinning and retreating and some advances have slowed, perhaps in response
to drier conditions that have prevailed at Mount Rainier since 1977.

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