RESULTS FROM FOUR CASCADE VOLCANOES
Mount Hood rises to 11,245 ft and is approximately 50 miles east of Portland, Oreg. (fig. 12). All the Mount Hood drainage systems (White, Zigzag, Sandy, and Hood Rivers) empty into the Columbia River. Figure 13 illustrates that 60 percent of the total area covered by snow and ice is in the Hood watershed. Figures 14 and 15 show ice volumes for radar-measured glaciers, and ice areas by drainage as a function of altitude.
Ice-volume measurements were made on all nine major glaciers of Mount Hood. The total volume of ice and snow on Mount Hood is 12.3 billion ft3. Glacier and snow-patch dimensions are listed by drainage area and by elevation in table 3. The Eliot Glacier has the largest volume, 3.2 billion ft3, and thickest measured ice, 361 ft. The Coe-Ladd Glacier system has the largest surface area, 23.1 million ft2.
TABLE 3.Areas and volumes of glacier ice and snow on Mount Hood
[Methods of determination: A, volume estimated by using area correlation; M, glacier thickness measured by ice radar. Because total glacier areas are required in the application of the volume estimation method, volumes are available by total glacier. Area measured in ft2 (x 106); volume measured in ft3 (x 109).in the area column means no ice or snow present for glaciers at that elevation, and in the volume column it means volume by elevation not determined for that glacier]
The ice and snow boundaries on Mount Hood and basal contours for the measured glaciers in 1981 are shown on plate 3. The isopach maps derived from the surface-basal contours are shown on plate 5.
Mount Hood's composite cone was built during late Pleistocene time (Wise, 1969, p. 969). Its earliest known major eruptive period after the glacial maximum occurred 12,000 to 15,000 years B.P., which, along with two other major eruptive periods (1,500-1,800 and 200-300 years B.P.) produced much of the mountain visible today (Crandell, 1980, p. 1). Much of the topography on the lower slopes of Mount Hood is the result of mudflows and pyroclastic flows, which were formed during the Polallie eruptive period of 12,000 to 15,000 years B.P. and may have been aided by eruption-related icemelt. The absence of these deposits in some valleys indicates the extent of former glaciers (Crandell, 1980, p. 11).
As on Mount Rainier, the river valleys radiating from Mount Hood contain valuable timber and recreational property. The geologically recent eruptive history and hazards of Mount Hood were more comprehensively described in Crandell (1980).
At Mount Hood flooding and lahars are the principal eruptive hazard to these resources. Crandell (1980, p. 56) stated that they represent a hazard in the valleysup to several tens of feet high on the valley walls and higher where the valley is constricted. Interpretations of the hazard map developed by Crandell indicate that a dome-building eruption in the present Crater Rock region might deposit debris on the White River, Palmer, Zigzag, and Reid Glaciers and affect about 2 billion ft3 of ice and snow. The volume of ice above 10,000 ft in the vicinity of Crater Rock is about 47 million ft3. About 80 percent of the total area of snow and ice cover is above 7,000 feet in altitude.
An eruption outside the debris fan region, but near the summit, might cause eruptive deposits on the remainder of the Mount Hood glaciers, which have an ice and snow volume of 10.5 million ft3.
Last Updated: 28-Mar-2006