The evidence indicates that it existed at least 600,000 years ago. Other spectacular examples of Bonneville Flood features are the Snake River Canyon, alcoves, and waterfalls (e.g. The shorelines of this ancient lake can be seen on the higher slopes of the Wasatch Mountains, more than 984 feet above the present level of the Great Salt Lake. With less rainfall and glacial melting to sustain Lake Bonneville, coupled with increased evaporation, the vast lake began to retreat. At ~50 ka, the Bear River cut through the Oneida Narrows , near the town of Thatcher (Figure 3) and diverted to the Bonneville basin. Over a period of weeks and months, nearly 1,000 cubic miles of water were released, and Lake Bonneville dropped more than 350 feet.The flood scoured the walls and bed of the Snake's existing canyons from Pocatello to Pasco and also inundated a wide swath on the adjacent Snake River Plain across southern Idaho. The current Great Salt Lake's drainage area is roughly that of ancient Lake Bonneville. The flood drained the top 351 feet (107 m) of Lake Bonneville, which constituted about 1,200 cubic miles (5,000 km ) of water, and lowered the lake level to a stage known as the Provo shoreline. Also imagine that same ice-age lake releasing a surge of floodwater whose volume was six times the flood flow of the Mississippi River. The highest buildings in the valley would have been submerged by 700 feet of water if Lake Bonneville were still in existence. The maximum extent of erosion (stripped basalt surfaces) by the flood is shown fairly precisely by the limits of cultivation on the uplands. Once captured, water from rainfall, stream flows, and glacial melting remained in the lake, except for those amounts lost through evaporation. Bonneville was the precursor of the Great Salt Lake. Other prominent remnants include Utah Lake, Sevier Lake, and the Great Salt Lake Desert. ( Public Domain ) First, it is stated that “[the Great Salt Lake] is salty because it does not have an outlet.” I will not dispute that the second part of this statement, namel… The flood emptied the top 107 meters of water from Lake Bonneville , an estimated volume of 4,750 cubic km of water (Link and Phoenix, 1996). After the Lake Bonneville Flood, the lake fell to the Provo shoreline level. ISS/NASA imagery of the Great Salt Lake. The flood transformed the Snake River Plain into a series of channeled scablands resembling the Columbia Plateau.
The floodwaters followed the route of the Snake River and its existing canyons across southern Idaho, then veered north through Hell's Canyon, and finally poured into the Columbia River near Pasco, Washington. Lake Bonneville was the largest stage of the ancient lake that is now the Great Salt Lake. At 14.5000 ybp (radiocarbon years before present), Lake Bonneville overfilled and formed a body of water that broke through the rock at Red Rock Pass and flooded much of southern Idaho.
At the beginning of the colossal prehistoric flood from Lake Bonneville through Red Rock Pass, the spillway first formed as the water level in the lake on the south side reached the 5,100 feet level of the dam. It also was relatively fresh. After the Lake Bonneville Flood, the lake fell to the Provo shoreline level. [The flood is described more fully in David Alt and Donald W. Hyndman, Scoured and fluted basalt surface near Portneuf Narrows. Deposits of sand and gravel also partially blocked Hell's Canyon's side valleys. Animals such as bears, camels, deer, mammoths, horses and musk oxen roamed its shores.In addition to being confined by higher ground at the basin rim, a "natural dam" at Lake Bonneville's northern limit at Red Rock Pass prevented outflows. The Bonneville Flood, which occurred about 15,000 years ago, dropped the level of Lake Bonneville more than 300 feet to the Provo Level (4,740 feet above sea level). The large set of falls in the middle foreground is Cauldron Linn* which stopped the Impressive deposits of melon gravels can be found near Hagerman; in Malad Gorge; in Melon Valley south of Wendell; at Swan Falls south of Melba; and near the towns of Hammett, Glenn's Ferry and King Hill.May 2010 hike to view Bonneville Flood features in Hells Canyon:At Tammany Bar south of Lewiston, Idaho - Bonneville Flood gravels (B) are capped Geologists know … At Tammany Bar south of Lewiston, Idaho - Bonneville Flood gravels are capped with Lake Missoula Floods rhythmites 2-20 feet thick.