DESCRIPTION:
Mount Hood Glaciers and Glaciations

[Graphic,12K,GIF]
Simplified Map - Glaciers of Mount Hood, Oregon
-- Modified from: Swanson, et.al., 1989, AGU T106

Twelve glaciers and named snowfields cover approximately 80 percent of the cone above the 2,100-meter level and contain about 0.35 cubic kilometers of ice (Driedger and Kennard, 1986). Most of the glaciers have remained roughly constant in size over the last few decades, after retreating from a neo-glacial maximum early in the 18th century (Lawrence, 1948).

Modern glacier termini are at about 2,100 meters, but in the last major alpine glaciation ( Fraser, about 29-10 thousand years ago) glaciers reached the 700-800 meter level. During this time, ice spread 15 kilometers from the summit area (Crandell, 1980).

Lacustrine siltstone from near-terminus periglacial lakes plaster valley walls just upstream from the mouth of Polallie Creek on the east side of the mountain. Highway 35 crosses White River near the maximum extent of Fraser ice, and the left-lateral moraine is prominent just upstream from the bridge. The full extent of the Fraser-age glaciers has not been accurately mapped.

Glacier retreat released large volumes of outwash, some of which filled the ancestral Hood River Valley near Parkdale, forming the flat surfaces of Upper Hood River Valley and Dee Flat. Outwash also formed a debris fan in the upper East Fork Hood River.

Evidence of older glaciation is seen in roadcuts on the southeast side of the volcano and in rolling morainal landscape near Brightwood west of the volcano. The deposits are not dated but may be coeval with the Hayden Creek Drift near Mount Rainier (Crandell, 1980), probably about 0.14 million years ago (Colman and Pierce, 1981). ...

Jökulhlaups (glacial-outburst floods) have been recorded from the Zigzag, Ladd, Coe, and White River Glaciers.

[Image,54K,JPG]
Mount Hood and White River Drainage, with 1998 Flow Deposits
-- USGS Photo by Cynthia Gardner, September 4, 1998

Jökulhlaups (glacial-outburst floods) have been recorded from the Zigzag, Ladd, Coe, and White River Glaciers. In 1922, a dark debris flow issued from a crevasse high on Zigzag Glacier and moved 650 meters over the ice before entering another crevasse; this event initiated a scare that Mount Hood was erupting (Conway, 1921). The Ladd Glacier jökulhlaup in 1961 destroyed sections of the road around the west side of the mountain and partly undermined a tower of a major powerline (Birch, 1961). The Coe Glacier outburst occurred around 1963, causing a section of trail to be abandoned and the "round-the-mountain" trail to be rerouted farther from the glacier. Jökulhlaups from White River Glacier were reported in 1926, 1931, 1946, 1949, 1959, and 1968; the Highway 35 bridge over the White River was destroyed during each episode. The more frequent outbursts from White River Glacier may be due in part to an increase in size of the fumarole field at the head of the glacier at Crater Rock (Cameron, 1988).

Outburst floods from White River Glacier have taken out numerous, lesser versions of the highway bridge. The aggrading valley floor downstream displays several surfaces formed during this century that can be differentiated by the size (age) of the trees growing on them. The sediment sources for the aggradation are White River Glacier and the canyons that are being cut into diamicts of Polallie and Old Maid age downstream from White River Glacier

During noneruptive periods, relatively small lahars present a hazard along channels and on floodplains on the flanks of Mount Hood. Although of modest size compared to lahars generated by eruptions or large debris avalanches, they occur much more frequently. Twenty-one lahars, including single flows as large as several hundred thousand cubic meters (cubic yards), whose effects were chiefly limited to areas within 15 kilometers (9 miles) of Mount Hoods summit, are reported in the historical record. Most occurred during autumn and early winter rains. Glacial outburst floods caused at least two and probably as many as seven others.

The extent of glaciers during the last major glaciation is pertinent to the eruptive history of Mount Hood because the presence of glacier ice was partly responsible for the distribution of volcanic deposits formed during the first eruptive period ...

The last major advance of glaciers in Washington and British Columbia occurred during the Fraser Glaciation. This glaciation began some time before about 29,000 years ago and ended about 10,000 years ago (Armstrong and others, 1965; Armstrong and Clague, 1977). By comparison with glaciers in western Washington and British Columbia, those at Mount Hood probably reached their maximum downvalley extents by 18,000 years ago and then generally retreated until about 11,000 years ago. Glaciers in the mountains probably were not significantly larger by that time than they are today.

Deposits of the Fraser Glaciation at Mount Hood can be recognized by yellowish-brown soil oxidation and by a lack of appreciable weathering of stones in soil profiles. The tickness of the oxidized zone on till measured at 17 localities ranged from 35 to 80 centimeters and averaged 63 centimeters. These characteristics are similar to those of deposits of the first eruptive period (Polallie) ... Some Polallie deposits, in fact, resemble those of glacial origin because of their coarse, poorly sorted, or unsorted texture. For example, deposits in roadcuts along U.S.Highway 26 about 3 kilometers west of Government Camp resemble till, but they were formed by volcanic mudflows. Similar mudflow deposits on the northeast side of Mount Hood have obscured the extent of glacial deposits of Fraser age, thus, the extent of glaciers is not known in that area.

The average altitude of north-facing cirques near Mount Hood is about 1,030 meter (3,400 feet) in the areas north and northwest of the volcano, about 1,250 meters (4,100 feet) south of the volcano, and about 1,370 meters (4,500 feet) to the east. These cirque floors provide a crude measure of the altitude of areas of ice accumulation during the last glaciation; however, the lower limits of accumulation in areas outside cirques must have been higher because ice was not as protected from the sun there as in the cirques.

When Fraser glaciers were at their maximum extents, the northern slopes of Mount Hood probably were largely covered by ice at altitudes about 1,370 meters (4,500 feet), and the southern slopes above perhaps 1,525-1,675 meters (5,000-5,500 feet). Most north-facing glaciers today terminate at altitudes of 1,830-1,980 meters (6,000-6,500 feet), and the lower limits of perennial snow on the south slope of the volcano seem to be at about 2,150 meters (7,000 feet).

Deposits of one or more older glaciations have also been recognized at scattered localities in the Mount Hood area. One such deposit is till that forms a terminal moraine in the Sandy river valley near Brightwood; this moraine probably represents the farthest downvalley extent of a glacier during the glaciation that immediately preceded the Fraser Glaciation. Yellowish-brown soil oxidation extends to a depth of 1.5-2 meters in the till, and stones in the soil profile have weathered rinds 1-2 millimeters thick. Glacial deposits in the Mount Rainier area of Washington that have similar weathering characteristics were assigned to the Hayden Creek Drift of the Salmon Springs Glaciation (Crandell and Miller, 1974).

Till thought to be of Hayden Creek age elsewhere in the Sandy River valley underlies a deposit of distinctive pumice that was erupted at Mount St. Helens in southern Washington between about 35,000 and 40,000 years ago (D.R.Mullineaux, oral commun., 1976). The best outcrop at which the relation of the till to the pumice can be seen is along a road to a rock quarry south of U.S.Highway 26.

At Bennett Pass, on the southeast side of Mount Hood, a large cut along State Highway 35 exposes three tills separated by yellowish-brown oxidized zones that constitute buried soils. The uppermost till forms a lateral moraine of Fraser age; the ages of the underlying tills are not known.

[Graphic,12K,GIF]
Simplified Map - Glaciers of Mount Hood, Oregon
-- Modified from: Swanson, et.al., 1989, AGU T106

North side of Mount Hood

Jökulhlaups (glacial-outburst floods) have been recorded from the Zigzag, Ladd, Coe, and White River Glaciers. ... The Coe Glacier outburst occurred around 1963, causing a section of trail to be abandoned and the "round-the-mountain" trail to be rerouted farther from the glacier.

Summit Glacier

Northeast side of Mount Hood

Northwest side of Mount Hood

Jökulhlaups (glacial-outburst floods) have been recorded from the Zigzag, Ladd, Coe, and White River Glaciers. ... The Ladd Glacier jökulhlaup in 1961 destroyed sections of the road around the west side of the mountain and partly undermined a tower of a major powerline (Birch, 1961).

North-northeast side of Mount Hood

East side Mount Hood

South side of Mount Hood

West side of Mount Hood

West side of Mount Hood

South side of Mount Hood

Jökulhlaups (glacial-outburst floods) have been recorded from the Zigzag, Ladd, Coe, and White River Glaciers. ... Jökulhlaups from White River Glacier were reported in 1926, 1931, 1946, 1949, 1959, and 1968; the Highway 35 bridge over the White River was destroyed during each episode. The more frequent outbursts from White River Glacier may be due in part to an increase in size of the fumarole field at the head of the glacier at Crater Rock (Cameron, 1988).

Southwest side of Mount Hood

Jökulhlaups (glacial-outburst floods) have been recorded from the Zigzag, Ladd, Coe, and White River Glaciers. In 1922, a dark debris flow issued from a crevasse high on Zigzag Glacier and moved 650 meters over the ice before entering another crevasse; this event initiated a scare that Mount Hood was erupting (Conway, 1921).

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