Variations of Blue, Hoh, and White Glaciers During Recent Centuries

Аннотация

Glaciers in the Olympic Mountains of western Washington, as elsewhere in North America, enlarged in late-postglacial time and attained positions from which they have receded conspicuously. Former locations of the ice are marked by moraines and overridden surfaces which the regional vegetation is slowly invading. An examination of aerial photographs of glaciers on Mt. Olympus taken in 1939 and 1952 clearly reveals the progress of recession. In 1952 Blue and Hoh glaciers appear rather inactive whereas a photograph of Blue Glacier taken about the turn of the century shows an actively discharging tongue, well in advance of its position in the early 1950's. About 1900 glacier termini were nevertheless well behind positions reached when the ice stood farther down the valleys in past centuries. No written accounts or measurements are available from this pre-1900 period, although the ages of trees growing on moraines and outwash offer the means for fixing positions of the glaciers during the time before the earliest observations. The minimum periods elapsed since glaciers may have been even farther advanced are established by the ages of the oldest trees in the forests beyond the recent outermost limits of the ice. A reconnaissance of Blue and Hoh glaciers and the vicinity of White Glacier was made during the 1955 summer, and the former limits of the ice were determined and dated. The purpose was to record the variations of Mt. Olympus glaciers so that the climate of this region during the last several centuries might be interpreted from these changes and compared with other localities where similar studies have been made. ...