The Bonneville flood was a catastrophic flooding event in the last ice age, which involved massive amounts of water inundating parts of southern Idaho and eastern Washington along the course of the Snake River. Unlike the Missoula Floods, which also occurred during the same period in the Pacific Northwest, the Bonneville flood happened only once. It is believed to be the second-largest flood in known geologic history. [1] [ clarification needed ]
About 14,500 years ago (radiocarbon dating, 17,400 years ago calendar, "calibrated" dating), pluvial Lake Bonneville in northern Utah reached its highest water level since its formation. [2] The lake occupied the present-day basin of the Great Salt Lake, and was far larger, covering about 32,000 square miles (83,000 km2). As it rose the lake level caused seepage at, then breached, the ancient level of Red Rock Pass, a mountain pass at the headwaters of the Portneuf River, a tributary of the Snake River above present-day American Falls Reservoir. Ancient Red Rock Pass was the site of two alluvial fans descending from opposite sides of the notch, forming a natural dam. [3] When the dam collapsed, it released a 410-foot-high (120 m) [4] flood crest down the Portneuf River valley, also spilling into the neighboring Bear River valley. When it reached the Snake River, it eroded away a lava dam that had been at the site of the present-day American Falls, releasing a 40-mile-long (64 km) lake, American Falls Lake, that had formed behind the natural dam. [5] [6] [7]
At the peak of the flood, approximately 33,000,000 cubic feet per second (930,000 m3/s) poured over the Snake River Plain at speeds of up to 70 miles per hour (110 km/h) and deposited hundreds of square miles of sediments eroded from upstream. [8] The flood scoured the 600-foot-deep (180 m) Snake River Canyon through the underlying basalt and loess soil, creating Shoshone Falls and several other waterfalls along the Snake River. It also carved and increased in size many other tributary canyons, including those of the Bruneau River and Salmon Falls Creek. The flood then entered Hells Canyon, significantly widening the gorge. Its waters eventually reached the Pacific Ocean via the Columbia River. [9]
A 2020 theory presented evidence that Lake Bonneville achieved a stable outflow for possibly a thousand years leading up to the Bonneville Flood and then a massive, multi-segment earthquake on the Wasatch Fault caused surging and tsunami in Lake Bonneville with a surge wave over 140 feet (43 m) high. This surge carried up into the Cache Valley and resulted in the failure of the natural dam at the Zenda threshold just north of Red Rock Pass. [10]
Although the peak of the flood lasted a few weeks at most, erosion at Red Rock Pass continued for a few years before water ceased to spill over. The flood drained the top 351 feet (107 m) of Lake Bonneville, which constituted about 1,200 cubic miles (5,000 km3) of water, and lowered the lake level to a stage known as the Provo shoreline. The flood transformed the Snake River Plain into a series of channeled scablands resembling the Columbia Plateau. Also left by the flood were the many "melon" boulders distributed throughout the canyons in the Snake River Plain. According to some geologists, the total volume of the Bonneville flood was actually greater than any individual one of the Missoula Floods, although the Missoula floods released more water as a whole, [3] and at least one had a much higher peak flow rate. [11]
Much of the sediment scoured by the flood was deposited near the mouth of the Snake River. It now lies beneath about 20 layers of Missoula Floods deposits. [12] [13]
The Snake River is a major river of the greater Pacific Northwest region in the United States. At 1,078 miles (1,735 km) long, it is the largest tributary of the Columbia River, in turn, the largest North American river that empties into the Pacific Ocean. The Snake River rises in western Wyoming, then flows through the Snake River Plain of southern Idaho, the rugged Hells Canyon on the Oregon–Idaho border and the rolling Palouse Hills of Washington, emptying into the Columbia River at the Tri-Cities in the Columbia Basin of Eastern Washington.
Lake Bonneville was the largest Late Pleistocene paleolake in the Great Basin of western North America. It was a pluvial lake that formed in response to an increase in precipitation and a decrease in evaporation as a result of cooler temperatures. The lake covered much of what is now western Utah and at its highest level extended into present-day Idaho and Nevada. Many other hydrographically closed basins in the Great Basin contained expanded lakes during the Late Pleistocene, including Lake Lahontan in northwestern Nevada.
The Missoula floods were cataclysmic glacial lake outburst floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. These floods were the result of periodic sudden ruptures of the ice dam on the Clark Fork River that created Glacial Lake Missoula. After each ice dam rupture, the waters of the lake would rush down the Clark Fork and the Columbia River, flooding much of eastern Washington and the Willamette Valley in western Oregon. After the lake drained, the ice would reform, creating Glacial Lake Missoula again.
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.
Lake breakout is the collapse of a lake, usually of high-altitude. High-altitude lakes tend to form in volcanic craters – where they are called crater lakes – or in valleys dammed as the result of earthquakes or glacial or volcanic deposition. Lake breakouts are most common a few weeks or months after a volcanic eruption as a river becomes blocked by volcanic debris.
The Bear River is the largest tributary of the Great Salt Lake, draining a mountainous area and farming valleys northeast of the lake and southeast of the Snake River Plain. It flows through northeastern Utah, southwestern Wyoming, southeastern Idaho, and back into northern Utah, in the United States. Approximately 350 miles (560 km) long it is the longest river in North America that does not ultimately reach the sea.
The Portneuf River is a 124-mile-long (200 km) tributary of the Snake River in southeastern Idaho, United States. It drains a ranching and farming valley in the mountains southeast of the Snake River Plain. The city of Pocatello sits along the river near its emergence from the mountains onto the Snake River Plain.
Grand Coulee is an ancient river bed in the U.S. state of Washington. This National Natural Landmark stretches for about 60 miles (100 km) southwest from Grand Coulee Dam to Soap Lake, being bisected by Dry Falls into the Upper and Lower Grand Coulee.
The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods within the southeastern part of Washington state. The Channeled Scablands were scoured by more than 40 cataclysmic floods during the Last Glacial Maximum and innumerable older cataclysmic floods over the last two million years. These floods were periodically unleashed whenever a large glacial lake broke through its ice dam and swept across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. The last of the cataclysmic floods occurred between 18,200 and 14,000 years ago.
Massacre Rocks State Park is a history-focused public recreation area in the Northwest United States featuring the Massacre Rocks, a famous spot along the Oregon Trail and California Trail during the middle 19th century. The state park is located along the Snake River, ten miles (16 km) southwest of American Falls, in Power County, Idaho.
Red Rock Pass is a low mountain pass in the western United States in southeastern Idaho, located in southern Bannock County, south of Downey. It is geologically significant as the spillway of ancient Lake Bonneville. It is traversed by U.S. Route 91 at an elevation of 4,785 feet (1,458 m) above sea level, bounded by two mountain ranges; the Portneuf to the east and the Bannock to the west.
The Palouse River is a tributary of the Snake River in Washington and Idaho, in the northwest United States. It flows for 167 miles (269 km) southwestwards, primarily through the Palouse region of southeastern Washington. It is part of the Columbia River Basin, as the Snake River is a tributary of the Columbia River.
Dry Falls is a 3.5-mile-long (5.6 km) scalloped precipice with four major alcoves, in central Washington scablands. This cataract complex is on the opposite side of the Upper Grand Coulee from the Columbia River, and at the head of the Lower Grand Coulee, northern end of Lenore Canyon. According to the current geological model, catastrophic flooding channeled water at 65 miles per hour through the Upper Grand Coulee and over this 400-foot (120 m) rock face at the end of the last glaciation. It is estimated that the falls were five times the width of Niagara Falls, with ten times the flow of all the current rivers in the world combined.
Shoshone Falls is a waterfall in the western United States, on the Snake River in south-central Idaho, approximately three miles (5 km) northeast of the city of Twin Falls. Sometimes called the "Niagara of the West," Shoshone Falls is 212 feet (65 m) in height, 45 feet (14 m) higher than Niagara Falls, and flows over a rim nearly one thousand feet (300 m) in width.
The Morley Nelson Snake River Birds of Prey National Conservation Area has one of the densest populations of nesting raptors. The National Conservation Area (NCA) is located 35 miles (56 km) south of Boise, Idaho along 81 miles (130 km) of the Snake River, and is managed by the Bureau of Land Management. The NCA covers 484,873 acres (1,962.21 km2). In descending order of land area it is located in Ada, Elmore, Owyhee, and Canyon counties.
The Touchet Formation or Touchet beds consist of well-bedded, coarse to fine sand and silt which overlays local bedrock composed of Neogene basalt of the Columbia River Basalt Group in south-central Washington and north-central Oregon. The beds consist of more than 40 to 62 distinct rhythmites – horizontal layers of sediment, each clearly demarcated from the layer below. These Touchet beds are often covered by windblown loess which were deposited later; the number of layers varies with location. The beds vary in thickness from 330 ft (100 m) at lower elevations where a number of layers can be found to a few extremely thin layers at the maximum elevation where they are observed.
Lake Lewis was a large transient lake in the Pacific Northwest region of North America, formed by periodic Missoula Floods along the Columbia River paleocourse between 21,000 and 16,000 years ago.
A volcanic dam is a type of natural dam produced directly or indirectly by volcanism, which holds or temporarily restricts the flow of surface water in existing streams, like a man-made dam. There are two main types of volcanic dams, those created by the flow of molten lava, and those created by the primary or secondary deposition of pyroclastic material and debris. This classification generally excludes other, often larger and longer lived dam-type geologic features, separately termed crater lakes, although these volcanic centers may be associated with the source of material for volcanic dams, and the lowest portion of its confining rim may be considered as such a dam, especially if the lake level within the crater is relatively high.
The Ice Age Floods National Geologic Trail is a network of routes connecting natural sites and facilities that provide interpretation of the geological consequences of the Glacial Lake Missoula floods of the last glacial period that occurred about 18,000 to 15,000 years ago. It includes sites in Washington, Oregon, Idaho, and Montana. It was designated as the first National Geologic Trail in the United States in 2009.
Salmon Falls Creek is a tributary of the Snake River, flowing from northern Nevada into Idaho in the United States. Formed in high mountains at the northern edge of the Great Basin, Salmon Falls Creek flows northwards 121 miles (195 km), draining an arid and mountainous basin of 2,103 square miles (5,450 km2). The Salmon Falls Creek valley served as a trade route between the Native American groups of the Snake River Plain and Great Basin. Today, most of its water is used for irrigation.