Lake Missoula facts for kids
Quick facts for kids Lake Missoula |
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 Lake Missoula
Location in Montana
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| Location | Western Montana |
| Area | 7,770 km2 (3,000 sq mi) |
| Designated: | 1966 |
| Lake Missoula | |
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Wave-cut strandlines cut into the slope at left in photo. These cuts record former high-water lines, or shorelines. Gullies above the highway are the result of modern-day erosion. (NPS Photo)
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 Lake Missoula
Location in Montana
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| Location | North America |
| Coordinates | 46°56′20″N 114°08′37″W / 46.93889°N 114.14361°W |
| Lake type | former lake |
| Primary inflows | Channeled Scablands |
| Primary outflows | Wallula Gap of the Columbia River |
| Basin countries | United States |
| Max. length | 200 mi (320 km) |
| Max. width | 57 mi (92 km) |
| Surface area | 7,700 km2 (2,973 sq mi) |
| Max. depth | 2,000 ft (610 m) |
| Water volume | 2,100 km3 (500 cu mi) |
| Residence time | 20 incidents |
| Surface elevation | 4,206 ft (1,282 m) |
Lake Missoula was a huge prehistoric lake in western Montana. It existed many times at the end of the last ice age, between 15,000 and 13,000 years ago. This ancient lake was about 7,770 square kilometres (3,000 sq mi) in size. It held a massive 2,100 cubic kilometres (500 cu mi) of water. That's half the amount of water in Lake Michigan!
The Glacial Lake Missoula National Natural Landmark is a special place. It is about 110 kilometres (68 mi) northwest of Missoula, Montana. This landmark was named in 1966. It has giant ripples in the land. These ripples are 25 to 50 feet (7.6 to 15.2 m) high and 300 feet (91 m) long. They helped scientists like J Harlen Bretz prove a big idea. He showed that the Channeled Scablands in Washington State were made by huge floods. These floods happened many times over only 2,000 years. Before, people thought it took millions of years of slow erosion.
Lake Missoula formed because of an ice dam. This dam was on the Clark Fork River. It was created by a large finger of the Cordilleran Ice Sheet. This ice sheet pushed into the Idaho Panhandle. The ice dam was usually about 610 metres (2,000 ft) tall. It flooded the valleys of western Montana for about 320 kilometres (200 mi) to the east. It was the biggest ice-dammed lake ever known.
The ice dam broke many times. This caused the Missoula Floods. These were giant floods that rushed across eastern Washington. They also flowed down the Columbia River Gorge. This happened about 40 times over 2,000 years. The floods moved a huge amount of loess (silt), sediment, and basalt. They carved out 210 cubic kilometres (50 cu mi) of material from the Channeled Scablands. These floods are important because they created large canyons and other geologic features very quickly. This is different from how most landforms are made, which is usually through slow, gradual processes.
Contents
How Lake Missoula Formed
The Ice Dam on the Clark Fork River
A huge sheet of ice, called the Cordilleran ice sheet, grew from British Columbia. It spread southwards. A part of this ice sheet, called the Purcell Lobe, moved down the Purcell Valley. It went past Lake Pend Oreille in Idaho. This ice blocked the natural path of the Clark Fork River. The Clark Fork River and its smaller rivers were the most important water system in western Montana.
The ice dam was about 2,000 feet (610 m) deep. It stretched for at least 10 miles (16 km), and some say up to 30 miles (48 km). This ice dam reached east up the Clark Fork to Cabinet, Montana. It also went south around the mountain to Bayview, Idaho. This is on the south tip of Lake Pend Oreille. Here, the ice sheet was over 2,000 feet (610 m) thick. It was also 25 miles (40 km) south of where Lake Missoula formed.
How Big Was Lake Missoula?
The Clark Fork River flows through many valleys and high mountain ranges. Lake Missoula filled this area in western Montana. It is named after the city of Missoula. The mountains around Missoula still show lines from the lake's old shorelines. These lines formed nearly 20,000 years ago.
At its biggest, Lake Missoula was over 2,000 feet (610 m) deep. It might have held 600 cu mi (2,500 km3) of water. That's as much water as Lake Erie and Lake Ontario combined! The lake covered about 3,000 sq mi (7,770 km2). Its shoreline was at an elevation of 4,200 feet (1,300 m).
The lake spread through the Clark Fork River basin. It reached east of Missoula, 259 miles (417 km) to Gold Creek. It also went northeast up the Blackfoot River 270 miles (430 km) to Lake Alva. Two large parts of the lake formed to the south and north. To the south, the Bitterroot Valley filled as far as Sula, Montana, 286 miles (460 km). To the north, the Flathead River basin became a huge body of water. It made an island of Red Sleep Mountain, which is now the National Bison Range. The lake extended north 286 miles (460 km) to Polson.
The water in the lake was deep, dark, and cloudy with sediment. Scientists think that fine sediment, called rock flour, made the water poor for aquatic life. There is no sign of fish or large mammals like mammoths, mastodons, or bison living in the lake. There is also no evidence of humans living in the area at that time.
Lake Missoula Basins and Features
Clark Fork Canyon Area
This area follows Montana Route 200 along the Clark Fork River canyon. It stretches 92 miles (148 km) to Paradise. Then it continues 49 miles (79 km) through the Paradise-St. Regis Canyon. At St. Regis, the canyon widens. It continues east 49 miles (79 km) with the river next to Interstate 90, until Ninemile. Here, it opens into the Missoula basin.
- Nine Mile Rhythmites: These are layers of light pink sand and silt. They were laid down at the bottom of the lake near Ninemile. These silt deposits formed where the lake basin was wide. When the lake drained, the fast currents did not reach this area. Each layer shows a time when the water was still behind the ice dam. The darker layers are winter deposits, and the lighter layers are from more active summer currents. These layers show about 1000 years of sediment.
Flathead Basin Area
The Flathead basin was next to the south side of the ice sheet. For most of this time, the glacier reached south to Polson. It covered all of Flathead Lake.
- Camas Prairie Giant Ripples: Camas Prairie is a small basin on Camas Creek. You can see multiple long ridges of sediment here. They are 25 feet (7.6 m) high and 100 feet (30 m) apart. These formed when water flowed out during a break in the ice dam.
- Markle Pass Kolks: Markle Pass is between Camas Prairie and the Little Bitterroot Valley. The Kolks are holes carved into the bedrock. They were made by strong underwater vortices (like underwater tornadoes). These formed as Lake Missoula quickly drained during the great floods. When these tornado-like currents hit the bottom, they pulled rocks out. You can find this rock debris downstream.
Missoula Basin Area
This basin stretches from Missoula west to Ninemile. It also goes up the Ninemile Creek valley. This valley is 39 miles (63 km) long. It gets wider from 5 miles (8.0 km) at Ninemile to 10 miles (16 km) at Missoula.
- Glacial Erratic: You can find a large Glacial erratic (a rock moved by a glacier) on the grounds of the University of Montana.
- Strandlines: These old shorelines can be seen on the slopes of Mount Jumbo and Mount Sentinel in the Missoula Valley. These lines show the different levels of the lake as the ice dam broke and reformed.
Other Basins
- Hamilton Basin: This basin is in the Bitterroot Valley. It runs from south of Conner to Lolo, about 57 miles (92 km) to the north. The Bitterroot Mountains form its west side, and the Sapphire Mountains form its east side.
- Blackfoot River Basin: The valleys of Potomac, Greenough, and Ovando-Helmville are connected by the Blackfoot River. This is east of Missoula.
- Upper Clark Fork: The Clark Fork River starts near Butte, 130 miles (210 km) east of Missoula. Lake Missoula reached up this valley for about 55 miles (89 km) to the east, near Gold Creek.
See also
In Spanish: Lago Missoula para niños
