Misplaced Pages

#953046

42-405: Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about 7,770 square kilometres (3,000 sq mi) and contained about 2,100 cubic kilometres (500 cu mi) of water, half the volume of Lake Michigan . The Glacial Lake Missoula National Natural Landmark

84-418: A moraine during the retreat of a melting glacier , a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice. At the end of the last ice age about 10,000 years ago, large proglacial lakes were a widespread feature in the northern hemisphere. The receding glaciers of the tropical Andes have formed a number of proglacial lakes, especially in

126-550: A glacial overspill channel created when the water of a proglacial lake rose high enough to breach the lowest point in the containing watershed. Cordilleran ice sheet The ice extent covered almost all of the continental shelf north of the Strait of Juan de Fuca and south from approximately the southwestern third of the Yukon Territory . This included all of mainland British Columbia , South Central Alaska ,

168-470: A land or seafloor margin, as scientists believe the western marine-terminating margin retreated much faster than its southern, land-terminating front. This rapid retreat resulted in noticeably fewer glacial landforms in the west of the Cordilleran's maximum extent compared to the south and east, though the exact mechanisms behind this disparity are unknown. Some glacial landforms are still present though:

210-550: Is 8 miles (13 km) wide east–west and 10 miles (16 km) north-south. The basin is bordered by Rattlesnake Ridge on the north and Petty Mountain on the south(west). Features: strandlines along the valleys east flank. The basin extends from south of Conner to Lolo , 57 miles (92 km) to the north. The Bitterroot Mountains form the west shore and the Sapphire Mountains the east. The valleys of Potomac , Greenough, and Ovando - Helmville are linked by

252-847: Is a partial list of rivers that had glacial ice dams. The retreating glaciers of the last ice age, both depressed the terrain with their mass and provided a source of meltwater that was confined against the ice mass. Lake Algonquin is an example of a proglacial lake that existed in east-central North America at the time of the last ice age . Parts of the former lake are now Lake Huron , Georgian Bay , Lake Superior , Lake Michigan and inland portions of northern Michigan. Examples in Great Britain include Lake Lapworth , Lake Harrison and Lake Pickering . Ironbridge Gorge in Shropshire and Hubbard's Hills in Lincolnshire are examples of

294-654: Is located about 110 kilometers (68 mi) northwest of Missoula, Montana , at the north end of the Camas Prairie Valley, just east of Montana Highway 382 and Macfarlane Ranch. It was designated as a National Natural Landmark in 1966 because it contains the great ripples (often measuring 25 to 50 feet (7.6 to 15.2 m) high and 300 feet (91 m) long) that served as a strong supporting element for J Harlen Bretz 's contention that Washington State's Channeled Scablands were formed by repeated cataclysmic floods over only about 2,000 years, rather than through

336-498: Is named for the city of Missoula in the upper reaches of the Clark Fork watershed. The mountains surrounding the city show the strandlines from the lake nearly 20,000 years ago. At its largest extent, Lake Missoula's depth exceeded 2,000 feet (610 m) and may have held 600 cu mi (2,500 km) of water, as much as Lake Erie and Lake Ontario combined. The surface area covered 3,000 sq mi (7,770 km) and

378-534: Is probable, though, that its northern margin also migrated south due to the influence of starvation caused by very low levels of precipitation. At its western end it is currently understood that several small glacial refugia existed during the last glacial maximum below present sea level in the now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island . However, evidence of ice-free refugia above present sea level north of

420-693: The Alaska Panhandle , and peninsula . The southern glacial maximums extended south to Washington state near Olympia in the west and to Spokane , the Idaho Panhandle , and much of Western Montana at the eastern glacial edge. At its eastern end the Cordilleran ice sheet merged with the Laurentide Ice Sheet at the Continental Divide , forming an area of ice that contained one and a half times as much water as

462-722: The Antarctic ice sheet does today. The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers . The ice sheet covered up to 2,500,000 km (970,000 sq mi) at the Last Glacial Maximum and probably more than that in some previous periods, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho. It

SECTION 10

#1732776327954

504-818: The Blackfoot River east of Missoula. A second reach, up the Clearwater River , joins the Blackfoot River at Clearwater. This basin joins the Clark Fork at Bonner . Upper valleys of the Clearwater-Blackfoot River basins run 394 miles (634 km) from Seeley Lake , eastward to Browns Lake along Montana Route 83 and Montana Route 200. The Clark Fork of the Columbia River has its headwater near Butte , 130 miles (210 km) east of Missoula. Lake Missoula reached up

546-521: The Cordillera Blanca of Peru, where 70% of all tropical glaciers are. Several such lakes have formed rapidly during the 20th century. These lakes may burst, creating a hazard for zones below. Many natural dams (usually moraines ) containing the lake water have been reinforced with safety dams. Some 34 such dams have been built in the Cordillera Blanca to contain proglacial lakes. Several proglacial lakes have also formed in recent decades at

588-464: The Haida Gwaii , the lower thickness of the ice sheet meant that sea levels were as much as 170 m (560 ft) lower than they are today, forming a lake in the deepest parts of the strait. This was because the much greater thickness of the center of the ice sheet served to push upwards areas at the edge of the continental shelf in a glacial forebulge . The effect of this during deglaciation

630-604: The Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s. Unlike the Laurentide Ice Sheet, which may have taken as many as eleven thousand years to fully melt, the Cordilleran ice sheet melted very quickly, probably in four thousand years or less. This rapid melting caused floods such as the overflow of Lake Missoula and shaped the topography of the fertile Inland Empire of Eastern Washington . Further north,

672-778: The glaciofluvial deposits , informally known as the Hanford formation that are found in parts of the Othello Channels, Columbia River Gorge, Channeled Scabland , Quincy Basin, Pasco Basin, and the Walla Walla Valley . The age of these deposits is demonstrated by the presence of multiple interglacial calcretes interbedded in these glaciofluvial deposits, sequences of sediments with normal and reverse magnetostratigraphy , optically stimulated luminescence dating, and unconformity truncated clastic dikes . Based upon these criteria, Quaternary geologists estimated that

714-530: The Clark's Fork to Cabinet, Montana, and southward around the mountain to Bayview, Idaho on the south tip of Lake Pend Oreille in Farragut State Park . Here, the ice sheet stood over 2,000 feet (610 m) and 25 miles (40 km) south of Lake Missoula. The Clark Fork's drainage is a network of valleys among high mountain ranges. Lake Missoula formed through this region of western Montana . It

756-587: The Cordilleran is responsible for a large number of glacial landforms scattered across the west of Canada . The rate of thawing has also played a significant role in research surrounding early human migration into the American continents. The rapid retreat of the Cordilleran ice sheet is a focus of study by glaciologists seeking to understand the difference in patterns of melting in marine-terminating glaciers, glaciers whose margin extends into open water without seafloor contact, and land-terminating glaciers, with

798-593: The Ice Free Corridor previously posited to have allowed for migration amid the retreat of the eastern front of the Cordilleran ice sheet and the western front of the Laurentide ice sheet. The Ice Free Corridor is a subject of debate among anthropologists in recent years. Recent studies have provoked skepticism, with areas of discussion including the lack of evidence of sufficient flora in the area to support megafaunal migration, to radiometric dating placing

840-717: The Pleistocene cannot be estimated with any confidence. Although Lake Missoula likely was the source of many of the Ancient Cataclysmic Floods, the fragmentary nature of the older deposits within the Hanford formation makes precise determination of the precise origin of the floods that deposited them very difficult. The Cordilleran ice sheet originating in British Columbia expanded out of the mountains and southward. A tongue of ice pushed down

882-575: The Purcell Valley or Purcell Trench , reaching south beyond Lake Pend Oreille . This Purcell Lobe blocked the natural outlet of the Clark Fork River . Including its tributaries, Clark Fork represented western Montana's most important river system. The ice mass that effectively dammed Clark Fork was about 2,000 feet (610 m) deep and extended for at least 10 miles; some say it extended as much as 30 miles. The ice dam reached east up

SECTION 20

#1732776327954

924-610: The United States, the sudden rupturing of the supporting dam caused glacial lake outburst floods , the rapid and catastrophic release of dammed water resulting in the formation of gorges and other structures downstream from the former lake. Good examples of these structures can be found in the Channeled Scablands of eastern Washington, an area heavily eroded by the Missoula Floods . The following table

966-506: The canyon opens out and continues to the east 49 miles (79 km) with the river paralleled by Interstate 90 to as far as Ninemile, where it opens out into the Missoula basin. A western branch of this basin runs up the St. Regis River another 32 miles (51 km) along with Interstate 90 to near Riverbend . The Flathead basin abutted the south face of the ice sheet. For most of this period,

1008-614: The coast of Alaska. A similar event takes place after irregular periods in the Perito Moreno Glacier , located in Patagonia . Roughly every four years the glacier forms an ice dam against the rocky coast, causing the waters of the Lago Argentino to rise. When the water pressure is too high, then the giant bridge collapses in what has become a major tourist attraction. This sequence occurred last on 4 March 2012,

1050-411: The emergence of a corridor through the central Canadian Shield too late to account for the earliest known human sites south of the glaciers . Because of the weight of the ice, the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today (measured by the level of bedrock ). However, on the western edge at

1092-459: The end of glaciers on the eastern side of New Zealand's Southern Alps . The most accessible, Lake Tasman , hosts boat trips for tourists. On a smaller scale, a mountain glacier may excavate a depression forming a cirque , which may contain a mountain lake, called a tarn , upon the melting of the glacial ice. The movement of a glacier may flow down a valley to a confluence where the other branch carries an unfrozen river. The glacier blocks

1134-740: The glacial ice reached south to Polson , covering the entirety of Flathead Lake . The basin drains from the Polson Moraine at the south end of Flathead Lake, south to Ravalli , with a major lobe up the Little Bitterroot River and a minor basin on Camas Creek near Perma . The basin extends from Missoula , west to Ninemile and up the Ninemile Creek valley. This 39-mile-long (63 km) valley broadens from 5 miles (8 km) at Ninemile to 10 miles (16 km) at Missoula. The central part of this basin around Missoula

1176-487: The ice dam and exploded downstream, flowing at a rate 10 times the combined flow of all the rivers of the world. Because such ice dams can re-form, these Missoula Floods happened at least 59 times, carving Dry Falls below Grand Coulee . In some cases, such lakes gradually evaporated during the warming period after the Quaternary ice age. In other cases, such as Glacial Lake Missoula and Glacial Lake Wisconsin in

1218-529: The millions of years of erosion that had been previously assumed. The lake was the result of an ice dam on the Clark Fork caused by the southern encroachment of a finger of the Cordilleran ice sheet into the Idaho Panhandle (at the present-day location of Clark Fork, Idaho , at the east end of Lake Pend Oreille ). The height of the ice dam typically approached 610 metres (2,000 ft), flooding

1260-798: The north the Flathead River basin became an expansive body of water, creating an island of Red Sleep Mountain (in the CSKT Bison Range ) and extending north 286 miles (460 km) to Polson at the basin of the Flathead Ice Lobe and 286 miles (460 km) up the Little Bitterroot River to Niarada some 132 miles (212 km) above the Flathead Rivers mouth at the Clarks Fork. The water

1302-529: The oldest of the Pleistocene Missoula floods happened before 1.5 million years ago. The older Pleistocene glaciofluvial deposits within the Hanford formation are fragmentary in nature because they have been repeatedly eroded and largely removed by subsequent Missoula floods. Because of the fragmentary nature of older glaciofluvial deposits, the exact number of older Missoula floods, which are known as Ancient Cataclysmic Floods , that occurred during

Glacial Lake Missoula - Misplaced Pages Continue

1344-612: The previous having taken place four years before, in July 2008. About 13,000 years ago in North America, the Cordilleran Ice Sheet crept southward into the Idaho Panhandle , forming a large ice dam that blocked the mouth of the Clark Fork River , creating a massive lake 2,000 feet (600 m) deep and containing more than 500 cubic miles (2,000 km ) of water. Finally this Glacial Lake Missoula burst through

1386-485: The remains or artifacts of contemporaneous humans have been found associated with Lake Missoula. The Clark Fork River flows into Lake Pend Oreille at 2,062 feet (628 m). This reach follows Montana Route 200 up the Clark Fork River canyon, 92 miles (148 km) to Paradise , then follows the Clark Fork, then 49 miles (79 km) through the Paradise-St. Regis Canyon along Montana Highway 135 . At St. Regis ,

1428-562: The retreat of the Cordilleran bears significance not just to glaciologists, but to anthropologists interested in the migration of early humans into the Americas . In particular, the collapse of the western front of the Cordilleran ice sheet has been proposed as one route through which early humans could have migrated after crossing the Beringian Land Bridge during the Last Glacial Maximum . This serves as an alternative to

1470-543: The river, which backs up into a proglacial lake, which eventually overflows or undermines the ice dam, suddenly releasing the impounded water in a glacial lake outburst flood also known by its Icelandic name a jökulhlaup . Some of the largest glacial floods in North American history were from Lake Agassiz . In modern times, the Hubbard Glacier regularly blocks the mouth of Russell Fjord at 60° north on

1512-547: The shoreline attained an elevation of 4,200 feet (1,300 m). The lake spread through the Clark Fork River basin, reaching east of Missoula, 259 miles (417 km) to Gold Creek ; northeast up the Blackfoot River 270 miles (430 km) to Lake Alva; 253 miles (407 km) and east of Ovando 270 miles (430 km). Two large lobes formed to the south and north. To the south the Bitterroot Valley filled as far as Sula, Montana , 286 miles (460 km). To

1554-416: The valley, about 55 miles (89 km) to the east along I-90 to just east of Gold Creek . Smaller reaches formed along the tributary valleys of Gold Creek, 13.5 miles (21.7 km) up Flint Creek, forming an 8-mile-wide (13 km) basin, up Lower Willow Creek, and 20 miles (32 km) up Rock Creek. Proglacial lake In geology, a proglacial lake is a lake formed either by the damming action of

1596-479: The valleys of western Montana approximately 320 kilometres (200 mi) eastward. It was the largest ice-dammed lake known to have occurred. The periodic rupturing of the ice dam resulted in the Missoula Floods – cataclysmic floods that swept across eastern Washington and down the Columbia River Gorge approximately 40 times during a 2,000 year period. The cumulative effect of the floods

1638-505: The well-characterized landscape of coastal Washington State contains glacial troughs, some glacial lakes, and an extensive outwash plain. Many of the southern and eastern landforms fall near the northern reaches of the American Cordillera , the mountain ranges which geologists believe to be the region from which the Cordilleran first grew, and, after its sudden retreat and ultimate collapse, where it terminated. The timing of

1680-460: Was deep (average - 800 feet (240 m)): maximum - 2,100 feet (640 m)), dark and murky with sediment. Fish fossils have not been found in deposits of Lake Missoula. Possibly, glacial sediment, rock flour , suspended in the turbid lake water which created an hostile aquatic habitat for fish. In addition, fossils of large mammals ( megafauna ), i.e.; mammoths , mastodons and bison which may have roamed nearby, not been found. Similarly, neither

1722-474: Was that sea levels on the edge of the ice sheet, which naturally deglaciated first, initially rose due to an increase in the volume of water, but later fell due to rebound after deglaciation. Some underwater features along the Pacific Northwest were exposed because of the lower sea levels, including Bowie Seamount west of Haida Gwaii which has been interpreted as an active volcanic island throughout

Glacial Lake Missoula - Misplaced Pages Continue

1764-451: Was to excavate 210 cubic kilometres (50 cu mi) of loess , sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream. These floods are noteworthy for producing canyons and other large geologic features through cataclysms rather than through more typical gradual processes . In addition, Middle and Early Pleistocene Missoula flood deposits have been documented to comprise parts of

#953046