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Wallula Gap, as seen from Juniper Canyon, Oregon.
The waters of the Missoula Floods poured through the Wallula Gap thousands of years ago.
Image taken September 25, 2005.
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Glacial Lake Missoula and the Missoula Floods ...
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Between 80,000 years ago and 10,000 years ago ice sheets called the "Wisconsin Glaciation" covered much of North America, including Northern Washington, Idaho, and Montana. Towards the end of this glaciation a large ice dam blocked the Clark Fork River in the Idaho Panhandle, creating "Glacial Lake Missoula". This lake was a massive lake 2,000 feet deep filling the valleys of western Montana. It stretched eastward more than 200 miles and, at its maximum height and extent, contained more than 500 cubic miles of water - more water than Lake Erie and Lake Ontario combined.
Periodically, the ice dam would fail, resulting in a large catastrophic flood of ice- and dirt-filled water which rushed across northern Idaho and eastern and central Washington, down the Columbia River, through the Columbia River Gorge, and finally poured into the Pacific Ocean at the mouth of the Columbia River. Flood waters filled the Willamette River Valley, reaching Eugene, Oregon, more than 100 miles away.
When 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.
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"...
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.
..."
[U.S. National Park Service, Ice Age Institute website, 2005]
Along the floodwaters’ path, more than 50 cubic miles of earth and rock were removed, transported, and much was deposited as new landforms. The floods built gravel bars as tall as 400 feet and moved boulders weighing many tons and deposited them high on the valley walls. Most of the eroded material was carried out onto the floor of the Pacific Ocean, where extensive deposits of flood sediment have been identified hundreds of miles from the current mouth of the Columbia River. According to Geologist Richard Waitt of the U.S. Geological Survey (1985),
the various limits on the ice sheet and the floods suggests that Glacial Lake Missoula existed for 2,000 to 2,500 years between 15,300 and 12,700 years ago, creating more than 40 and maybe up towards 60 separate flood events.
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The Floods ...
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The Missoula Flood waters passing Wallula Gap reached an elevation of about 1,200 feet, as evidenced by glacial erratics that were left stranded on the slopes of the Horse Heaven Hills and other nearby ridges. At The Dalles the waters reached 1,000 feet and by the time the flood waters reached Crown Point the surface had dropped to 600 to 700 feet.
The area between Portland and the restriction at Kalama was under 400 feet of water. Clatskanie, Oregon, was buried under 275 feet of water. By the time the flood waters reached Astoria they were near sea level.
Missoula Flood heights (measured and estimated) as listed in Allen and Burns (1986) were
- 1,250 feet estimated at Pasco, Washington, located over 200 miles from the Lake Missoula Dam,
- 1,250 feet at the Wallula Gap,
- 1,210 feet estimated at Umatilla, Oregon,
- 1,180 feet estimated at Arlington, Oregon,
- 1,140 feet at the John Day River,
- 1,130 feet at the John Day Dam Gap,
- 1,070 feet at the Deschutes River,
- 1,000 feet at the Ortley Gap (today's Columbia Hills),
- 1,000 feet estimated at The Dalles, Oregon,
- 950 feet at the Bingen Gap,
- 925 feet estimated at Hood River,
- 875 feet at the Dog Mountain Gap,
- 830 feet estimated at Bonneville,
- 700 feet at the Crown Point Gap,
- 540 feet estimated at Troutdale, Oregon,
- 400 feet at Portland, Oregon, nearly 400 miles away,
- 400 feet at Kalama, Washington,
- 400 feet estimated at St. Helens, Oregon,
- 400 feet estimated at Woodland, Oregon,
- 375 feet estimated at Longview and Kelso, Washington,
- 275 feet at Clatskanie, Oregon, and
- sea level at Astoria, Oregon, at 485 miles from the Lake Missoula dam.
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Lake Lewis, Lake Condon, and Lake Allison ...
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The restriction of Missoula Flood waters at the Wallula Gap created a backwater lake called "Lake Lewis". Lake Lewis covered more than 2,000 square miles of the Pasco and Quincy Basins, the Walla Walla River Basin, and the Lower Snake River.
The restriction at The Dalles created "Lake Condon", which covered approximately 1,500 square miles from The Dalles to Umatilla.
The restriction at Kalama created a backwater lake, known as "Lake Allison". This lake filled the Willamette River Valley as far as Eugene, Oregon, over 100 miles away, with a measured height of 400 feet at Oregon City and an estimated height of 380 feet at Eugene. The area covered was approximately 3,000 square miles. The flood waters dumped thick layers of Palouse Silt, making the Willamette Valley one of the most fertile agricultural lands in the country.
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- Wallula Gap ...
- Hat Rock ...
- Maryhill Museum and Stonehenge ...
- Fairbanks Gap ...
- Horsethief Butte ...
- Tom McCall Nature Preserve ...
- Hood River ...
- Beacon Rock ...
- Multnomah Falls and Crown Point ...
- Rocky Butte ...
- Kalama Gap ...
- Nicolai Ridge and Clatsop Crest ...
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Columbia River Mile (RM) 308 ... Wallula Gap ...
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Many features along the Columbia River were impacted or created by the Missoula Floods.
The Wallula Gap near the eastern end of the Columbia River restricted flood waters creating a temporary "Lake Lewis". Lake Lewis stretched back into the Yakima River Valley and covered the today's cities of Richland, Pasco, and Kennewick.
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Wallula Gap, Washington
The flood crest at the Wallula Gap was about 1,200 feet as evidenced by glacial erratics left stranded on the hillsides.
View from downstream from a pullover on Highway 730, just east of Sand Station Recreation Area, Oregon.
Image taken September 29, 2003.
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RM 298 ... Hat Rock, Oregon ...
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Downstream from the Wallula Gap is Hat Rock, a basalt remnant created by the eroding waters of the Missoula Floods. Lewis and Clark passed Hat Rock on October 19, 1805.
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Hat Rock, Oregon.
Hat Rock is a remnant of a Columbia River Basalt flow, eroded during the Missoula Floods.
Image taken September 24, 2004.
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"... a rock in a Lard. resembling a hat just below a rapid at the lower Point of an Island in the Midl: of the river ..."
[Clark, October 19, 1805, first draft]
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RM 205 and RM 210 ... Maryhill Museum and Stonehenge, Washington ...
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Maryhill Museum and the Columbia Hills, Washington, as seen from Interstate 84, Oregon.
Maryhill Museum sits on a large bench carved by the Missoula Floods.
Image taken September 24, 2005.
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Stonehenge Memorial, Maryhill, Washington, perched on the banks of the Columbia River.
Image taken April 24, 2004.
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RM 200 ... Fairbanks Water Gap, Oregon ...
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Avery Park, Washington, with Fairbanks Water Gap, Oregon.
Waters from the Missoula Floods flowed through the Fairbanks Water Gap into Fifteenmile Creek, east of The Dalles, Oregon.
Image taken September 28, 2011.
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RM 194 ... Horsethief Butte, Washington ...
The great floods of the last ice age carved the basalts of Horsethief Butte and the surrounding Columbia River channel, creating the features we see today. The basalts themselves were created thousands of years earlier when a series of lava flows emerged from cracks in the earth's crust and blanketed the entire eastern Washington and northern Oregon region. Horsethief Butte is made up of a series of lava flows, visible in the cliffs.
[More]
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Horsethief Butte and Horsethief Lake.
View from Columbia Hills State Park (Horsethief Lake State Park).
Image taken September 28, 2011.
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RM 180 ... Tom McCall Nature Preserve, Oregon ...
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The Tom McCall Nature Preserve and nearby Rowena Crest are located on a high basalt mesa known as the "Rowena Plateau". During the end of the last ice age over 200 feet of raging flood waters (today known as the Missoula Floods) ripped across this plateau stripping it clean. Over the next ten thousand years this surface was covered by 3 to 4 feet of loess (wind blown ash, most likely from nearby Mount St. Helens volcano) which eventually eroded into the mounds. These mounds, wildflower-covered in the spring, dot the surface of the basalt flow. They are commonly referred to as "biscuit mounds" or "biscuit scabland".
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Rowena Plateau, Tom McCall Nature Preserve, Oregon.
Image taken May 13, 2007.
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Loess mounds, Rowena Plateau, Tom McCall Nature Preserve, Oregon.
Image taken May 13, 2007.
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RM 169 ... Hood River, Oregon ...
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The Hood River Valley was inundated by backwater from the Missoula Floods, with flood deposits reaching above 800 feet, with some ice-rafted erratics thought to be Missoula Flood erratics being between 840 and 880 feet. Peak high is estimated at approximately 925 feet.
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RM 142 ... Beacon Rock, Washington ...
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Beacon Rock is a large 840-foot-high basalt plug. The Missoula Floods eroded away the softer outer material.
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Beacon Rock and Hamilton Mountain, Washington.
Beacon Rock is a large 840-foot-high basalt plug. The Missoula Floods eroded away the softer outer material
View from Beacon Rock boat dock. View from left to right is Beacon Rock, Hamilton Mountain, and Aldrich Butte. Pierce National Wildlife Refuge is at the waters edge.
Image taken August 1, 2004.
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RM 136 and RM 129 ... Multnomah Falls and Crown Point, Oregon ...
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The 700-foot-high
Crown Point was inundated during peak floods, and the nearby 620-foot-high cliff at Multnomah Falls was enhanced when
flood waters of the Missoula Floods eroded away softer material, highlighting the spectacular cliff face.
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Multnomah Falls, Oregon, with Benson Bridge.
Multnomah Falls, located near Portland, Oregon, drops 620 feet over Grande Ronde Basalt of the Columbia River Basalt Group. The Missoula Floods enhanced the cliff face, eroding away loose and softer materials. At Multnomah Falls the visitor can view six flows in the cliff face, with pillow flows being visible in the upper sequence near the lip of the Upper Falls.
Image taken March 6, 2005.
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Crown Point, Oregon.
Crown Point as seen from Rooster Rock State Park, Oregon.
Crown Point is a remnant of a massive Priest Rapids intracanyon lava flow. The Priest Rapids is a member of the Wanapum Basalt of the Columbia River Basalt Group (CRBG), and erupted in the middle Miocene. The 700-foot-high feature was covered by waters of the Missoula Floods.
Image taken March 20, 2004.
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RM 113 ... Rocky Butte, Oregon ...
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Rocky Butte stood in the path of the Missoula Floods. The rushing flood waters heading down the Willamette Valley eroded the land on the upstream side of the Butte, similar to how a stream erodes the sediment on the upstream side of a rock in its path. Today on the east side of Rocky Butte, Interstate 205 and Interstate 84 follow the broad channels carved by the floods.
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Rocky Butte, Oregon, and Interstate 205.
View from the south.
Image taken February 19, 2006.
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RM 71 ... Kalama Gap ...
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The constriction between Carrolls Bluff on the Washington side of the Columbia and the bluff on the Oregon side just north of Prescott Beach backed up flood waters from the Missoula Floods into the Willamette Valley. This constriction is known as "Kalama Gap". Flood heights are estimated to have been around 400 feet.
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Carrolls Bluff, Washington.
View heading north on Interstate 5.
Cottonwood Island is visible on the left.
Image taken November 15, 2005.
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Prescott Beach, Oregon, and bluff to the north.
Image taken February 28, 2004.
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RM 40 ... Nicolai Ridge and Clatsop Crest, Oregon ...
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Nicolai Ridge and Clatsop Crest is a long basalt ridge on the Oregon side of the Columbia River which was undercut by Missoula flood erosion, resulting in a steep north face towering over Westport and Wauna, Oregon, and Puget Island, Washington. Bradley State Wayside, downstream of Wauna, sits upon this ridge and provides great views. Bradley State Wayside is at Columbia River Mile (RM) 40.
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Columbia River looking upstream from Bradley State Wayside, Oregon.
Visible are Puget Island (left) and Coffee Pot Island (middle), with Wauna, Oregon, on the right. The ridge in the background is Nicolai Ridge, a basalt ridge undercut and steepened by the Missoula Floods.
Image taken November 20, 2004.
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From the Journals of Lewis and Clark ...
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