DESCRIPTION:
Ice Sheets and Glaciations

• Volcanoes and Ice Sheets, Glacial Lakes, Etc.
  • Antarctic Ice Sheet
  • Canada Volcanoes and Ice Sheets
  • Iceland Volcanoes
  • Lake Bonneville
  • Lake Columbia
  • Lake Missoula
  • Lassen Peak
  • Mount Baker
  • Mount Hood
  • Mount Rainier
  • Mount St. Helens
  • Olympic Mountains
  • Snake River Canyon
  • Spokane Floods
  • Wallula Gap
  • Tuyas

For at least the last two million years, the earth's climate has fluctuated between ice ages. These cycles are largely driven by slight changes in the way the earth orbits around the sun -- just small changes in the various wobbles of the earth's motion are sufficient to fundamentally shift the earth from an "ice-house" to a "hot-house".

During the Pleistocene Epoch Ice Age, beginning about 2.5 million years ago, virtually all of southwestern Canada was repeatedly glaciated by ice sheets that also covered much of Alaska, northern Washington, Idaho, Montana, and the rest of northern United States. In North America, the most recent glacial event is the Wisconsin glaciation, which began about 80,000 years ago and ended around 10,000 years ago.

During the Great Ice Age, or Pleistocene Epoch, which began about 2 million years ago, large portions of Canada and the Northern United States were blanketed by the continental ice sheet. ... Much of the rich soil of the Midwest is glacial in origin, and the drainage patterns of the Ohio River and the position of the Great Lakes were influenced by the ice. The effects of the glaciers can be seen in the stony soil of some areas, the hilly land surfaces dotted with lakes, the scratched and grooved bedrock surfaces, and the long, low ridges composed of sand and gravel which formed at the front of the ice sheet.

Increased rainfall in the area south of the continental ice sheet formed large lakes in Utah, Nevada, and California. Remnants of these ancient lakes still exist today as the Great Salt Lake, Pyramid Lake, Winnemucca, and many others. Ancient shorelines for these old lakes can be found along the sides of mountains, as for example, near Provo, Utah.

The tremendous size of the ice sheet further influenced paleogeography by lowering sea level about 450 feet below the present level; the water contained in the ice and snow came from the oceans. The continental shelves around our continent, as well as the other continents of the world, were above water and, as a result, some States such as Florida were much larger than they are today. The shoreline deposits and shells at the edge of the Continental Shelf, in waters to 450 feet deep, are evidence of this marked drop in sea level during the Pleistocene.

During the Pleistocene Epoch Ice Age, beginning about 2.5 million years ago, virtually all of southwestern Canada was repeatedly glaciated by ice sheets that also covered much of Alaska, northern Washington, Idaho, Montana, and the rest of northern United States. In North America, the most recent glacial event is the Wisconsin glaciation, which began about 80,000 years ago and ended around 10,000 years ago.

During the Fraser (Late Wisconsin) Glaciation, the Cordilleran ice sheet advanced southward from source areas in British Columbia and terminated in the United States between the Pacific Ocean and the Continental Divide. The ice sheet extended farthest along major south-trending valleys and lowlands that traverse the international boundary; it formed several composite lobes segregated by highlands and mountain ranges. Each lobe dammed sizable lakes that drained generally southward or westward along ice margins and across divides.

During the Fraser Glaciation the Cordilleran ice sheet occupied parts of the Fraser and Puget lowland and Strait of Juan de Fuca between about 18,000 and 13,000 B.P., after the maximum stand of nearby alpine glaciers. At its maximum extent about 14,500 to 14,000 years B.P., the ice-sheet surface sloped from about altitude 1,000 meters at the international boundary to between 0 and 300 meters at the ice terminus on the continental shelf and in the southern Puget lowland. Drainage from deglaciated alpine valleys in the Cascade Range and Olympic Mountains flowed southward along both ice margins and coalesced into meltwater streams that built broad outwash trains southward and westward to the Pacific Ocean. In the North Cascades Range, Cordilleran ice overrode high divides and inundated major drainage basins. The ice-sheet surface descended from above 2,600 meters near the international boundary to 270 meters in the Columbia River valley.

East of the Cascade Range, the Okanogan lobe extended southward as a broad lobe that dammed the Columbia River valley to form glacial Lake Columbia. The lake discharged along the course of the Grand Coulee, whose tandem gorges developed by recession of great cataracts beneath catastrophic floods from glacial Lake Missoula.

The Columbia River lobe dammed the Spokane valley to form a shallow glacial Lake Spokane. The Pend Oreille River sublobe, and eastern appendage of the Columbia River lobe, was less extensive than formerly inferred. The Priest River valley remained unglaciated except for a distributary of the Purcell Trench lobe that dammed the valley mouth.

The Purcell Trench lobe dammed the 2,000-cubic-kilometer glacial Lake Missoula, which successively discharged as huge jökulhlaups that flowed to Spokane along the Rathdrum valley and from upper Pend Oreille River valley. From Spokane the great floods swept across the Channeled Scabland and down the Columbia River valley.

The West Kootenai and East Kootenai glaciers flowed across a high-relief landscape, terminating within a general upland. The Flathead lobe was more extensive than formerly inferred. Both the Flathead lobe and nearby alpine glaciers reached near-maximum positions during high stands of Lake Missoula and thus during the maximum stand of the Purcell Trench lobe.

Topographic lows trending south from southern British Columbia fed each of the major lobes of the Cordilleran ice sheet east and west of the Cascade Range, but the secondary lobation of the ice margins was determined by the configuration of local valleys.

As the Puget lobe retreated northward, ice-marginal streams and proglacial lakes progressively expanded northward. Glacial Lake Russell drained southward during initial retreat; glacial Lake Bretz later drained northward. Calving into seawater, the Juan de Fuca lobe retreated rapidly and perhaps thereby caused the northwestern part of the Puget lobe to stagnate. Continued ice retreat permitted the sea to enter Puget Sound, and a glaciomarine interval ensued from 13,500 to 11,500 years B.P. Stillstands or readvances of the ice margin occurred during and near the end of the glaciomarine interval. In the northeastern Cascade Range and Waterville Plateau, deglaciation occurred by progressive downwasting and backwasting of ice whose margins frequently stagnated. Most lobes east of the Cascade Range built one or more small recessional moraines. As ice tongues retreated, glacial Lakes Columbia and Missoula fell to successively lower levels as they grew northward behind retreating ice. At length the early lakes were succeeded by glacial Lakes Brewster, Clark, and Kootenay.

The apparent absence of the Glacier Peak layer-G tephra within the northern part of its projected fallout area along with the occurrence of several jökulhlaups from glacial Lake Missoula after the Mount St. Helens set-S airfall suggest that much of the glaciated terrain east of the Cascade Range remained glaciated until about 13,000 years ago. In the North Cascade Range, erratics transported by the ice sheet up valleys to cirque floors indicate that, as the ice sheet disappeared, alpine glaciers did not rejuvenate much below the limits of modern glaciers. Although ice lobes both east and west of the Cascade Range generally retreated from terminal positions to the international boundary during the interval 14,000 to 11,000 years B.P., the lobes were not exactly in phase with each other. Particular stillstands and retreats were influenced by local conditions such as topography or seawater that did not affect all lobes equally.

During the Pleistocene Epoch Ice Age, beginning about 2.5 million years ago, virtually all of southwestern Canada was repeatedly glaciated by ice sheets that also covered much of Alaska, northern Washington, Idaho, Montana, and the rest of northern United States. In North America, the most recent glacial event is the Wisconsin glaciation, which began about 80,000 years ago and ended around 10,000 years ago.

A mere 15,000 years ago, during the Ice Age, most of northern America lay under the grip of colossal ice sheets. The effects of the advancing and retreating glaciers can be seen in the headlands of Cape Cod, the Finger Lakes of New York, and the hills of Michigan, but nowhere is the glacier's mark upon the land more impressive than in Wisconsin. Indeed, the state has lent its name to the most recent series of glacial advances and retreats -- the Wisconsin Glaciation lasting from about 100,000 to 10,000 years ago.

Grand Coulee and Moses Coulee to the west largely were formed by the Missoula Floods. A lobe of the Cordilleran Ice Sheet descended into the Okanogan Valley, blocked the Columbia River, and covered 500 square miles of the Waterville Plateau west of Grand Coulee. The south terminus of the Okanogan lobe is clearly marked by an abrupt south limit of lumpy, rocky moraines. The ice-dammed Columbia River backed up to form Glacial Lake Columbia, a huge version of the lake now ponded by Grand Coulee Dam. Lake Columbia's overflow -- the diverted Columbia River -- occupied Grand Coulee between Ice Age Floods events.

Several times during at least the last two million years the climate has cooled for distinct periods, resulting in Pleistocene glaciations. During these periods ice sheets spread over the northern half of the continent. The most recent of these Pleistocene glaciations ended about 10,000 years ago. Geologists tell us the Puget Lobe of the Cordilleran ice sheet scoured, then buried the Puget Sound lowlands in a veneer of drift.

A several-thousand-year period of warmer weather ensued followed by a renewed period of minor glaciation about 6,600 years ago. This renewed glaciation (Neoglaciation) has resulted in numerous glacial advances smaller than those of the Pleistocene. Minor renewed glaciations are still occurring today.

The Puget lobe, the southwesternmost extension of the Cordilleran ice sheet, last advanced into the Puget Lowland of western Washington about 15,000 years ago. It left behind a varied record of both depositional and erosional landforms, which together still dominate the landscape of the region. ... Most prominently, the advancing ice sheet deposited voluminous sediment on a proglacial outwash plain that extended from the Olympic Mountains to the Cascade Range, herein recognized as the "great lowland fill". Subsequent overrunning by the ice sheet modified this surface in several ways: most pervasively, by the deposition of basil till, which was commonly shaped into drumlins, and most notably, by the excavation of deep linear troughs now occupied by large lakes and the marine waters of Puget Sound. Excavation of the troughs and valleys of the Puget Lowland required the transport of about 1,000 cubic kilometers of sediment, almost entirely during ice occupation and primarily by subglacial water.

The southwest part of the Cordilleran ice sheet occupied a distinctive geographic region. A broad topographic basin in British Columbia, the Georgia Depression, extends southward into Washington state. The depression splits at the northeast corner of the Olympic Peninsula. One branch, the Strait of Juan de Fuca, trends west between the Olympic Mountains and Vancouver Island. The other branch continues south, forming the Puget Lowland between the Olympic Mountains and Cascade Range. Although low hills at about latitude 46^o45^' define the southern limit of ice advance in the Puget Lowland, the lowland province itself continues south for an additional several hundred kilometers.

The southern Cordilleran ice sheet expanded into the Puget Lowland during several episodes of Pleistocene glaciation (Crandell and others, 1958; Easterbrook and others, 1967; Easterbrook, 1986). Products of the most recent advance, the Vashon Stade of the Fraser glaciation of Armstrong and others (1965), provide the best picture of ice-sheet growth and decay. Ice caps on the mountains of Vancouver Island and the British Columbia mainland expanded and coalesced, gradually extending into the lowland valleys and the Georgia Depression (Clague, 1981). However, as the ice tongue moved southward into the Puget Lowland, it probably received no additional lateral input because glaciers in the Olympic Mountains and Cascade Range had already retreated from their late Pleistocene maximum limits (Porter, 1976; Booth, 1987).

During the Fraser glaciation, the advancing and retreating Puget lobe was among the more rapidly moving North American ice sheets. Only a few thousand years span the advance of the lobe across the Canadian border, attainment of maximum southern position, and retreat back to the foothills of the British Columbia mountains. A movement of the terminus of more than 200 kilometers in each direction was therefore accomplished in this period, resulting in an average velocity of the terminus of at least 100 meters per year. Yet the geomorphic record in the Puget Lowland is primarily that of an ice sheet at maximum stage (see also Sugden, 1979), with well-defined ice limits and may indicators of ice-flow direction that are consistent with a sustained ice-maximum position (Thorson, 1980; Booth, 1990). Thus the lobe undoubtedly maintained its maximum position for at least some fraction of its total history, with limiting radio-carbon dates permitting 500-1,000 years of maximum or near-maximum conditions. Advance and retreat rates were therefore even higher than their minimum, averaged value of 100 meters per year.

During the Fraser (Late Wisconsin) Glaciation, the Cordilleran ice sheet advanced southward from source areas in British Columbia and terminated in the United States between the Pacific Ocean and the Continental Divide. The ice sheet extended farthest along major south-trending valleys and lowlands that traverse the international boundary; it formed several composite lobes segregated by highlands and mountain ranges. Each lobe dammed sizable lakes that drained generally southward or westward along ice margins and across divides. ...

During the Fraser Glaciation, alpine glaciers in western Washington and southeaster British Columbia reached maximum positions between 22,000 and 18,000 years B.P. and had greatly diminished before Cordilleran ice occupied the Puget lowland between 17,000 and 13,000 years B.P. (Mackin, 1941; Crandell, 1963; Armstrong et.al., 1965; Mullineaux, et.al., 1965; Halstead, 1968; Heusser, 1974; Hibbert, 1979; Clague, 1980; Clague et.al., 1980; Barnosky, 1981). Just north of the international boundary east of the Cascade Range, limiting ages on ice-sheet glaciation (about 17,500 years B.P.) and on deglaciation (about 11,000 years B.P.) are broadly similar to limiting ages on the western lobes of Cordilleran ice near the international boundary (Fulton and Smith, 1978; Clague, 1980; Clague et.al., 1980). The invasion and maximal stand of ice-sheet lobes east of the Cascade Range therefore were broadly synchronous with the ice-sheet glaciation of the Puget lowland. ...

Pre-Fraser glaciations influenced the region. Stratigraphy indicates at least three pre-Fraser ice-sheet glaciations in the Puget lowland (Crandell et.al., 1958; Armstrong et.al., 1965; Easterbrook, 1976) and at least two glaciations east of the Cascade Range in British Columbia (Fulton and Smith, 1978). Stratigraphy of loess and paleosols in eastern Washington suggests episodes of glaciation preceding the last interglaciation (Richmond et.al., 1965). Caliche-capped catastrophic-flood deposits indicate that at least one pre-Fraser ice sheet dammed glacial Lake Missoula (Bretz, et.al., 1956; Bretz, 1969; Baker, 1973, 1978b; Patton and Baker, 1978; Waitt, 1982b). The mountains of the Pacific Northwest south of the ice-sheet margin display nested moraines that reveal as many as two pre-Fraser alpine glaciations; each followed by a long nonglacial interval (Page, 1939; Alden, 1953; Richmond, 1960; Crandell, 1967; Schmidt and Mackin, 1970; Weber, 1971; Crandell and Miller, 1974; Porter, 1976; Waitt, 1979a, 1982b). South of the limit of the Fraser-age Cordilleran and Lauentide ice sheets in Montana, stratigraphic sections and eroded moraines give evidence of early ice-sheet glaciations (Alden, 1932, 1953; Richmond, 1960). Pre-Fraser ice-sheet glaciations thus clearly influenced topographic development in the region. Some previously inferred pre-Fraser drift, however, is of Fraser age, and some such "drift" in northern Idaho and northeastern Washington is the deposit of catastrophic floods. ...

The Fraser Glaciation in western Washington consisted of an alpine phase followed in the lowlands by an advance and retreat of an ice-sheet lobe, a glaciomarine phase, and an ice-sheet readvance. Before 18,000 years B.P. and before ice-sheet glaciation of the lowlands, mountain glaciers in the western Cascade Range, Olympic Mountains, and Vancouver Island advanced to valley mouths, built moraines, and retreated far into the mountains (Mackin, 1941; Crandell, 1963; Halstead, 1968; Carson, 1970; Williams, 1971; Heusser, 1974; Heller, 1980). Cordilleran ice advanced southward into the Puget lowland and across southeastern Vancouver Island about 18,000 years B.P. (Fulton, 1971; Alley and Chatwin, 1979; Clague et.al., 1980). Bifurcating around the Olympic Mountains, the ice sheet advanced to the western Strait of Juan de Fuca by about 17,000 years B.P. and to the Seattle area after 15,000 years B.P. (Anderson, 1968; Mullineaux, et.al., 1965). (Anderson (1968) contended that the Juan de Fuca lobe terminated in the eastern part of the strait. Subsequent analyses (Heusser, 1973; Alley and Chatwin, 1979; Thorson, 1981) suggest that Anderson's radiocarbon dates of about 17,200 years B.P. represent the maximum stand of a lobe that terminated far to the west.) ...

During its maximum stand the Cordilleran ice sheet buried much of the northeastern North Cascade Range (Barksdale, 1941; Waitt, 1972, 1977, and unpublished report). It crossed a high-relief landscape and converged into thick ice streams along the Skagit, Chelan, Methow, Okanogan, and Columbia valleys. As reconstructed from the upper limit of ice-beveled divides and erratics, the ice surface descended from above altitude 2,600 meters at the international boundary to 250 meters in the Columbia valley (Waitt, 1972, and unpublished report). ...

Holocene

• Winthrop Creek Glaciation
• "Hypsithermal interval

Pleistocene

• Fraser Glaciation
• Olympia Interglaciation
• Salmon Springs Glaciation
• Puyallup Interglaciation
• Stuck Glaciation
• Alderton Interglaciation
• Orting Glaciation

The Quaternary history of the Puget Lowland is marked by three early Pleistocene glaciations (the Orting, Stuck, and Salmon Springs, separated by interglacial periods represented by the Alderton and Puyallup Formations) and two pre-late Wisconsin glaciations (the Double Bluff and Possession, separated by an interglacial period represented by the Whidbey Formation). Laser-argon, fission-track, thermoluminescence (TL), amino-acid, and paleomagnetic dating techniques now allow the beginning of a firm chronology for sediments of these glacial and interglacial periods.

Orting Drift

The Orting Drift is reversely magnetized and lies beneath sediments laser-argon dated at about 1.6 million years ago. Considering that the beginning of the Matuyama Reversed Polarity Chron occurred at 2.4 million years ago, the age of the Orting Drift is considered to be between 1.6 and 2.4 million years.

Alderton Formation

The Alderton Formation is reversely magnetized, and laser-argon dating of volcanic ash interbedded with mudflows and fluvial and lacustrine sediments gave an age of about 1.6 million years.

Stuck Glaciation

Drift of the Stuck Glaciation has so far yielded no datable material.

Puyallup Formation

The Puyallup Formation is reversely magnetized, and laser-argon dates of 1.69 +/- 0.11 million years on plagioclase and 1.64 +/- 0.13 million years from hornblende have been obtained from pumice in fluvial sediments.

Salmon Springs Glaciation

The Lake Tapps tephra, interbedded between two drifts of the Salmon Springs Glaciation, has been fission-tracked dated at 1.06 +/- 0.11 million years and associated silt is reversely magnetized.

Double Bluff Drift

Clay beneath Double Bluff Drift at its type section on Whidbey Island was dated at 289 +/- 74 thousand years by TL analysis, and Double Bluff glaciomarine drift there was dated at 177 +/- 38 thousand years. Clay beneath Double Bluff till near Pebble Beach on Camano Island was TL-dated at 291 +/- 86 thousand years, and laminated (varved?) clay overlying Double Bluff till at Lagoon Point on Whidbey Island was dated at 320 +/- 100 thousand years. These ages correspond reasonably well with amino-acid ages from mollusk shells in Double Bluff glaciomarine drift that range from 111 to 178 thousand years at the type locality and 150 to 250 thousand years elsewhere in the central Puget Lowland.

Whidbey Formation

Four TL dates from clay in Whidbey Formation interglacial fluvial sediments range from 102 +/- 38 to 151 +/- 43 thousand years: 102 +/- 38 thousand years at Lagoon Point; 106 +/- 17 thousand years at Blowers Bluff; 142 +/- 10 thousand years north of West Beach; and 151 +/- 43 thousand years at Point Wilson. These ages compare favorably with amino-acid ages of 97 +/- 35 thousand years, 96 +/- 35 thousand years, and 107 +/- 9 thousand years from shells in marine sediments correlated with Whidbey Formation on Whidbey Island.

Possession Glaciation

Amino-acid analyses of marine shells in glaciomarine drift at three localities suggest a mean age of 80 +/- 22 thousand years for the Possession Glaciation.

Early Pleistocene (1,700,000 +/- to 800,000 years ago):

Type localities for the Orting Drift, Alderton Formation, Stuck Drift, Puyallup Formation, and Salmon Springs Drift were defined by Crandell and others (1958) near the southernmost extension of the Cordilleran ice sheet. When they were defined, no finite ages were know for any of the sediments, and the maximum extent of pre-Wisconsin glaciations was unknown because older drift units have been buried by younger deposits. Virtually all data about early Pleistocene glaciations of the region come from deposits at the southern extent of the Puget Lobe. No early Pleistocene deposits of the Juan de Fuca lobe or in the northern or central Puget Lowland have been documented, but they may exist below sea level. ...

Middle Pleistocene (800,000 - 300,000 years ago):

The "middle Pleistocene" has been defined as the period between 300 thousand and 800 thousand years ago (Richmond and Fullerton, 1986). No sediments of this age have been recognized in the Puget Lowland. They may be present below sea level in the Puget Lowland, but are not accessible and have not been unequivocally identified in cores. ... Consequently, no deposits spanning the time gap between the Double Bluff Drift and the Salmon Springs Drift have been recognized.

Late Pleistocene (300,000 - 10,000 years ago):

The "late Pleistocene" has been defined as the interval between 10,000 and 300,000 years ago (Richmond and Fullerton, 1986). Pleistocene sediments whose ages range between 100,000 and 300,000 years old are widespread in the central Puget Lowland, but they have not been unequivocally identified and dated elsewhere in the lowland.

The late Pleistocene stratigraphy and chronology of the Puget Lowland may be considered in terms of the pre-late Wisconsin interval and the late Wisconsin. ...

Holocene Epoch: (International Quaternary [IQ] stade 1): the current post-glacial warm period (stade) beginning roughly 11,000 years ago to the present. The current rise in global sea level following the last glaciation cycle is called the Flandrian transgression.

Subdivisions of the Late Pleistocene Epoch:

Wisconsin glaciation (IQ stages 2 and 4): consists of a series of glacial advances and retreats 100,000 to 11,000 years ago (called Pinedale glaciation stage in the central Rocky Mountains);

Sangamon interglaciation (IQ stade 5): a mostly warm period between 100,000 to 250,000 years ago) (associated with the Lenore erosion cycle in the central Rocky Mountains);

Illinoian glaciation (IQ stage 6): - consists of a series of glacial advances and retreats 400,000 to 250,000 years ago (called Bull Lake glaciation stage in the central Rocky Mountains);

Yarmouth interglaciation (IQ stade 7): a mostly warm period between the Illinoian and Kansan stages (associated with the Circle erosion cycle in the central Rocky Mountains).

Subdivisions of the Early Pleistocene Epoch:

Kansan Stage (IQ stage 8+) - consisted of a series of glacial advances and retreats 900,000 to 750,000 years ago (associated with the Buffalo glaciation stage in the central Rocky Mountains);

Aftonian Stade (IQ stade 11+?) - a mostly warm period between the Kansan and Nebraskan stages (associated with the Black Rock and(or) Union Pass erosion cycles in the central Rocky Mountains);

Nebraskan Stage (IQ stage 14+?) - consisted of a series of glacial advances and retreats between 2 million and 1.65 million years ago.

Pliocene Epoch and Late Miocene Epochs:

Early glaciation periods may have occurred in the region prior to 1.65 million years, but no evidence has clearly established in the Western Interior region. The Fremont surface (also called “Summit peneplain”) in the central Rocky Mountains may represent remnants of a late Miocene to early Pliocene pediment surface.

Antarctica represents about 9 percent of Earth's continental crust and has been in a near-polar position for more than 100 million years. It is covered by a continental ice sheet with an average thickness of 3 kilometers. There is unequivocal evidence that for a long period after the continent arrived at its high-latitude position, extensive continental ice sheets did not exist there. The ice sheets, through their interaction with and effect on oceanic and atmospheric circulation, play a key role in modulating global climate.

The Antarctic plate, largely aseismic and immobile, is broken internally by large rift structures which have produced one of the world's largest alkalic volcanic provinces. The 3,200-kilometer-long West Antarctic rift system is comparable in size to the better-known East African rift. Volcanic constructs range from large basaltic shields to small monogenetic vents; the presence of the continental icesheet has resulted in a larger volume of hyaloclastite rocks than perhaps any other subaerial volcanic region. The only subduction-related volcanoes within or adjacent to the Antarctic plate form the South Sandwich and South Shetland Islands.

Antarctica Volcanoes and Volcanics - Menu

Because volcanic activity in western Canada was contemporaneous with the ebb and flow of Cordilleran glaciations, many of the volcanoes display ice contact features. Mount Garibaldi itself is a supraglacial volcano which erupted onto a regional ice sheet. Others, such as Hoodoo Mountain, were contained within basins thawed in the ice and assumed the flat-topped form of tuyas. Still others, such as the subglacial mounds of the Clearwater Field, were erupted under glacial ice to form piles of pillow lava and hyaloclastite.

Mount Garibaldi is one of the larger volcanoes (6.5 cubic kilometers) in a chain of small Quaternary volcanic piles -- the Garibaldi Belt -- which trend N25degrees W within the southern Coast Mountains of British Columbia. Mount Garibaldi is noteworthy both for the excellent exposures of its internal structure and for its striking topographic anomalies, which can be attributed to the growth of the volcano onto a major glacial stream, part of the Cordilleran Ice Sheet, and the subsequent collapse of the flanks of the volcano with the melting of the ice.

Hoodoo Mountain lies west of the main axis of the Stikine Volcanic Belt. It consists of a symmetrical lava dome, approximately 6 kilometers in diameter, surrounded on three sides by alpine glaciers. Only its southern slope, which extends down to the floodplain of Iskut River is ice free. Hoodoo's steep sides and nearly flat 900-meter summit suggest it formed as a subglacial tuya when regional ice sheets covered all but the highest peaks of the northern Coast Mountains. Subaerial lava flows which rest on glacial till along Iskut River indicate that volcanic activity continued after retreat of the ice. Radiometric dates of 0.11 and 0.09 million years are consistent with the age of other ice-contact features in the Stikine Volcanic Belt.

The Wells Gray - Clearwater Volcanic Field is a tight cluster of basaltic volcanoes, and includes the Quesnel Cone Group. The origin of this volcanism is not yet clear, but appears to be a result of local crustal thinning. Many of these eruptions occurred during periods of glaciation, so the eruptions interacted with the ice sheets in complex ways, forming distinctive volcanic forms. A number of these eruptions have occurred in the last 10,000 years. The volcanoes included in this field are Pyramid Mountain and Kostal Cone.

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Grimsvötn, together with Mardarbunga and Kverkfjöll, lie beneath the vast Vatnajökull icecap in east-central Iceland.

The Vatnajökull glacier in Europe is a temperate glacier covering about 8,300 square kilometers in the SE part of Iceland. Volcanic fissure systems of the Mid-Atlantic Ridge plate boundary are partly covered by the western part of the ice sheet. Two major volcanic centers lie beneath the ice, the Bardarbunga volcanic centre and the Grimsvötn volcanic centre both with large subglacial caldera depressions. The Bardarbunga centre is a part of a fissure system extending over 100 kilometers to the south and some 50 kilometers to the north of the glacier. The last eruption within the Bardarbunga centre occurred in 1910, but eruptions on the fissure system have occurred in 871 AD, 1477 AD and 1862 AD, all producing substantial amounts of lava. The Grimsvötn centre is the more active of the two with an eruption frequency during past centuries close to one eruption per decade. The last eruption occurred in 1983. As Bardarbunga the Grimsvotn centre is a part of a fissure system which includes the Laki fissure, which in 1783 produced about 12-14 cubic kilometers of basaltic lava. Within the ice filled Grimsvötn caldera intense geothermal activity continuously melts the ice to form a subglacial lake, which at intervals of 5 to 10 years is emptied along subglacial channels to create large floods (jökulhlaup) on the sandur plain, Skeidararsandur, on the Icelandic south coast. The lake was last emptied in 1996 and the water level is presently low.

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Ice Age Lake Bonneville, which existed around 14,500 years ago, covered more than 20,000 square miles in Utah and parts of Idaho and Nevada. For hundreds of years, the water level of Lake Bonneville maintained a fairly constant level. The water level dropped almost 400 feet when part of Red Rock Pass, which was holding back the water, eroded. The floodwaters flowed down the Snake River and joined the Columbia River near the Tri-Cities. For a short period of time, the resulting floodwaters from Lake Bonneville increased the size of the Snake River and the Columbia River by more than 20 times their normal flow. After the flood occurred, the water levels of the Great Salt Lake eventually subsided close to what they are now. Lake Bonneville drained only once, with catastrophic results.

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Grand Coulee and Moses Coulee to the west largely were formed by the Missoula Floods. A lobe of the Cordilleran Ice Sheet descended into the Okanogan Valley, blocked the Columbia River, and covered 500 square miles of the Waterville Plateau west of Grand Coulee. The south terminus of the Okanogan lobe is clearly marked by an abrupt south limit of lumpy, rocky moraines. The ice-dammed Columbia River backed up to form Glacial Lake Columbia, a huge version of the lake now ponded by Grand Coulee Dam. Lake Columbia's overflow -- the diverted Columbia River -- occupied Grand Coulee between Ice Age Floods events.

During the last Ice Age, a finger of the Cordilleran ice sheet crept southward into the Idaho Panhandle, blocking the Clark Fork River and creating Glacial Lake Missoula. As the waters rose behind this 2,000-foot ice dam, they flooded the valleys of western Montana. At its greatest extent, Glacial Lake Missoula stretched eastward a distance of some 200 miles, essentially creating an inland sea.

Periodically, the ice dam would fail. These failures were often catastrophic, resulting in a large flood of ice- and dirt-filled water that would rush down the Columbia River drainage, across northern Idaho and eastern and central Washington, through the Columbia River Gorge, back up into Oregon's Willamette Valley, and finally pour into the Pacific Ocean at the mouth of the Columbia River.

The glacial lake, at its maximum height and extent, contained more than 500 cubic miles of water. When Glacial Lake Missoula burst through the ice dam and exploded downstream, it did so at a rate 10 times the combined flow of all the rivers of the world. This towering mass of water and ice literally shook the ground as it thundered towards the Pacific Ocean, stripping away thick soils and cutting deep canyons in the underlying bedrock. With flood waters roaring across the landscape at speeds approaching 65 miles per hour, the lake would have drained in as little as 48 hours.

But the Cordilleran ice sheet continued moving south and blocking the Clark Fork River again and again, creating other Glacial Lake Missoulas. Over thousands of years, the lake filling, dam failure, and flooding were repeated dozens of times, leaving a lasting mark on the landscape of the Northwest. Many of the distinguishing features of the Ice Age Floods remain throughout the region today.

Together, these two interwoven stories of the catastrophic floods and the formation of Glacial Lake Missoula are referred to as the "Ice Age Floods."

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Lassen Peak is the largest of a group of more than 30 volcanic domes erupted over the past 300,000 years in Lassen Volcanic National Park in northern California. ... When Lassen Peak formed, it looked much like the nearby 1,100-year-old Chaos Crags Domes, with steep sides covered with angular rock talus. However, from 25,000 to 18,000 years ago, during the last ice age, Lassen's shape was significantly altered by glacial erosion. For example, the bowl-shaped depression on the volcano's northeastern flank, called a cirque, was eroded by a glacier that extended out 7 miles from the dome.

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The present-day (Mount Baker) cone is relatively young, perhaps less than 30,000 years old, but it sits atop a similar older volcanic cone called Black Buttes volcano which was active between 500,000 and 300,000 years ago. Much of Mount Baker's earlier geologic record was eroded away during the last ice age (which culminated 15,000-20,000 years ago), by thick ice sheets that filled the valleys and covered much of the region. In the last 14,000 years, the area around the mountain has been largely ice free, but the mountain itself remains heavily mantled with snow and ice.

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Mount Baker Glacier and Glaciations - Menu

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. 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.

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 to 1,675 meters (5,000 to 5,500 feet). Most north-facing glaciers today terminate at altitudes of 1,830 to 1,980 meters (6,000 to 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).

Mount Hood Glaciation: 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. ...

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). ...

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Mount Hood Glacier and Glaciations - Menu

The old drift, Hayden Creek, Wingate Hill, and McNeeley Drifts originated with glaciers that existed on Mount Rainier during and after the Pleistocene. The oldest drift visible is termed old drift. Although we do not know its age, we know that it was deposited on bedrock and beneath the lava flows of Mount Rainier. During the Hayden Creek glaciation, ice flowed as far down the Cowlitz River valley as below Mayfield Lake, about 65 miles from the mountain. Later glaciations deposited Evans Creek Drift and McNeeley Drift that now form conspicuous features in the park. While the Puget Lobe retreated from the lowlands about 11,000 years ago, the glaciers on Mount Rainier, being smaller and more sensitive to climatic changes, advanced and retreated, probably on many occasions. The McNeeley Drift was deposited at this time.

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.

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Mount Rainier Glacier and Glaciations - Menu

Much of the Swift Creek assemblage accumulated during the last major glacial episode (Fraser Glaciation) in western Washington which occurred between about 25,000 and 10,000 years ago, and glacial drift is interbedded with deposits of volcanic origin in some areas. ...

The glacial drift that is interbedded with the Swift Creek assemblage at Mount St. Helens probably was deposited during the Evans Creek Stade of the Fraser Glaciation. This correlation is based on a comparison of such relative weathering features as depth of oxidation and thickness of weathered rinds on stones in glacial drift in this area with those described in other areas of western Washington. The Evans Creek Stade was originally thought to have occurred between about 25,000 and 15,000 years ago. Subsequent work has suggested that alpine glaciers in southwestern British Columbia began to advance after 20,000 years ago, and alpine glaciers on the west side of the Olympic Peninsula evidently reached their maximum extents before about 18,800 years ago. ...

Exposures of glacial drift in the vicinity of Mount St. Helens and in the Lewis River valley west of the volcano show that the area was glaciated at least three times prior to the Fraser Glaciation and prior to the formation of the Swift Creek assemblage. These earlier alpine glaciers extended at least 50 kilometers down the Lewis River valley than did the glacier of Fraser age. During these earlier glaciations all the area at, and adjacent to, the present site of Mount St. Helens, except perhaps the highest peaks, may have been covered by glaciers.

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Mount St. Helens Glacier and Glaciations - Menu

In the past, a vast continental ice sheet, descended from Alaska, south through British Columbia to the Olympics. The ice split into the Juan de Fuca and Puget ice lobes, as they encountered the resistant Olympic Mountains. A glacial outwash stream surged around the southern end of the peninsula to the Pacific Ocean. This isolated the Olympic Peninsula from the nearby Cascade Mountains and limited species from entering and exiting the peninsula. When the ice sheet reached the Peninsula, large areas of the continental shelf were also exposed by the lower sea levels since so much water was trapped as ice. This created a coastal refuge. The distance from Mount Olympus to the Pacific Ocean may have been double that of today.

The Fraser glaciation lasted about 10,000 years and consisted of 3 stades (periods of ice expansion) and 2 interstades (ice recession). The Fraser ice advance in the Olympics began with expansion of alpine glaciers -- the Evans Creek stade. Although poorly dated on the Olympic Peninsula, at maximum advance -- about 21,000-19,000 B.P.(before present) -- glaciers extended down west-side valleys. Glaciers in east-side drainages were smaller and were restricted to upper valley areas or headwalls. The Evans Creek advance coincided with the beginnings of an enormous ice buildup in the mountains of British Columbia.

Alpine glaciers retreated to undetermined positions up valleys following the Evans Creek stade. This brief interstade was followed by advance of Cordilleran ice sheet from British Columbia into the Puget Sound area -- the Vashon stade. The ice reached its maximum extent around 15,000 B.P., splitting into the Juan de Fuca and Puget ice lobes as it encountered the Olympic Mountains. Ice at the northeast corner of the Olympics was at least 3,800 feet thick at maximum advance. The Vashon ice produced glacial lakes behind massive ice dams that formed in the northern and northeastern river valleys. The ice sheet apparently did not contact the remaining alpine glaciers. The spatial and temporal relations between ice sheets and alpine glaciers have important implications for the biogeography of endemic taxa; suitable habitat for alpine plants evidently persisted in or near the Olympic Mountains during both alpine and ice sheet advances of the Fraser glaciation.

The Vashon advance was short-lived; by 13,600 B.P., the two lobes had receded into a single lobe located in the northern Puget lowlands. A minor readvance (the Sumas stade) occurred about 11,500 B.P., but the extent and climate significance of this stade has been questioned. The Fraser glaciation ended about 10,000 B.P. when major climatic changes occurred.

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As you drop into the Snake River Canyon, you can trace some of the geologic history of the area. The canyon cliffs show layer upon layer of lava flows interspersed with sedimentary layers. As you reach the bottom, the canyon floor is scattered with hundreds of house-size boulders left behind from the Bonneville flood. This flood raced through the canyon 15,000 years ago with more than 100 meters (350 feet) of water rushing at 110 kilometers (70 miles) per hour.

MORE about Lake Bonneville and the Bonneville Flood

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In many ways, the story of the Floods is also the story of J Harlen Bretz (1882-1981), who proposed the theory that the Channeled Scablands of eastern Washington, and much of the Northwest as we know it today, were formed by catastrophic flooding. ... Bretz began his field research in the Channeled Scablands of central Washington during the summer of 1922, and it quickly became clear to him that neither glaciation nor ordinary stream erosion explained the Scablands. The following year Bretz made his two presentations to the Geological Society of America on the Scablands.

The first paper provided a detailed physiographic description of the Scablands; the second suggested that it would have taken a massive volume of water to create the degree of channel erosion that had occurred. Bretz's second paper on the Scablands also discussed the mounded gravel deposits that were scattered throughout the area. He proposed the idea of a catastrophic flood and included the first detailed geological map that included all of the Scablands and showed the extent of the floods. Bretz used the name "Spokane Flood" because he assumed the source of the water for this flood was somewhere near Spokane, Washington.

Bretz was confident that a flood had occurred, but was unable to figure out where the water had come from. Originally, he proposed that the water was the result of increased runoff from melting glaciers. But even Bretz had a tough time imagining any significant volume of water melting rapidly enough to have such devastating impact. Not until 1930 did Bretz consider Glacial Lake Missoula as the possible source of water he was searching for. But the geologic evidence was elusive, and he did not fully embrace the idea until 1956. Unable to provide a clear, scientific argument for the source of flood water, Bretz went on to other activities.

MORE about the Columbia Plateau

MORE about Glacial Lake Missoula and the Missoula Floods

A tuya is a volcano that erupts initially beneath a glacier, melts through the ice, and develops an upper, subaerial part, which commonly consists of a flat-topped form capped by a lava flow.

Because volcanic activity in western Canada was contemporaneous with the ebb and flow of Cordilleran glaciations, many of the volcanoes display ice contact features. Mount Garibaldi itself is a supraglacial volcano which erupted onto a regional ice sheet. Others, such as Hoodoo Mountain, were contained within basins thawed in the ice and assumed the flat-topped form of tuyas. Still others, such as the subglacial mounds of the Clearwater Field, were erupted under glacial ice to form piles of pillow lava and hyaloclastite.

Hoodoo Mountain lies west of the main axis of the Stikine Volcanic Belt. It consists of a symmetrical lava dome, approximately 6 kilometers in diameter, surrounded on three sides by alpine glaciers. Only its southern slope, which extends down to the floodplain of Iskut River is ice free. Hoodoo's steep sides and nearly flat 900-meter summit suggest it formed as a subglacial tuya when regional ice sheets covered all but the highest peaks of the northern Coast Mountains. Subaerial lava flows which rest on glacial till along Iskut River indicate that volcanic activity continued after retreat of the ice. Radiometric dates of 0.11 and 0.09 million years are consistent with the age of other ice-contact features in the Stikine Volcanic Belt.

Glacial-outburst waters that crossed the Channeled Scablands during the Spokane floods (Missoula Floods) were channeled through Wallula Gap. For several weeks, as much as 200 cubic miles of water per day were delivered to a gap that could discharge less than 40 cubic miles per day. Ponded water filled the Pasco Basin and the Yakima and Touchet valleys to form temporary Lake Lewis.

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