Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river forms in the Rocky Mountains of British Columbia, Canada. It flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean. The river is long, and its largest tributary is the Snake River. Its drainage basin is roughly the size of France and extends into seven states of the United States and one Canadian province. The fourth-largest river in the United States by flow, the Columbia has the greatest flow of any river into the eastern Pacific.
The Columbia and its tributaries have been central to the region's culture and economy for thousands of years. They have been used for transportation since ancient times, linking the region's many cultural groups. The river system hosts many species of anadromous fish, which migrate between freshwater habitats and the saline waters of the Pacific Ocean. These fish—especially the salmon species—provided the core subsistence for native peoples.
The first documented European discovery of the Columbia River occurred when Spanish explorer Bruno de Heceta sighted the river's mouth in 1775. On May 11, 1792, a private American ship, Columbia Rediviva, under Captain Robert Gray from Boston became the first non-indigenous vessel to enter the river. Later that same year William Robert Broughton of the British Royal Navy commanding HMS Chatham as part of the Vancouver Expedition, navigated past the Oregon Coast Range and upriver to what is now Vancouver, Washington. In the following decades, fur-trading companies used the Columbia as a key transportation route. Overland explorers entered the Willamette Valley through the scenic but treacherous Columbia River Gorge, and pioneers began to settle the valley in increasing numbers. Steamships along the river linked communities and facilitated trade; the arrival of railroads in the late 19th century, many running along the river, supplemented these links.
Since the late 19th century, public and private sectors have extensively developed the river. To aid ship and barge navigation, locks have been built along the lower Columbia and its tributaries, and dredging has opened, maintained, and enlarged shipping channels. Since the early 20th century, dams have been built across the river for power generation, navigation, irrigation, and flood control. The 14 hydroelectric dams on the Columbia's main stem and many more on its tributaries produce more than 44 percent of total U.S. hydroelectric generation. Production of nuclear power has taken place at two sites along the river. Plutonium for nuclear weapons was produced for decades at the Hanford Site, which is now the most contaminated nuclear site in the United States. These developments have greatly altered river environments in the watershed, mainly through industrial pollution and barriers to fish migration.
Course
The Columbia begins its journey in the southern Rocky Mountain Trench in British Columbia. Columbia Lake above sea level and the adjoining Columbia Wetlands form the river's headwaters. The trench is a broad, deep, and long glacial valley between the Canadian Rockies and the Columbia Mountains in BC. For its first, the Columbia flows northwest along the trench through Windermere Lake and the town of Invermere, a region known in BC as the Columbia Valley, then northwest to Golden and into Kinbasket Lake. Rounding the northern end of the Selkirk Mountains, the river turns sharply south through a region known as the Big Bend Country, passing through Revelstoke Lake and the Arrow Lakes. Revelstoke, the Big Bend, and the Columbia Valley combined are referred to in BC parlance as the Columbia Country. Below the Arrow Lakes, the Columbia passes the cities of Castlegar, located at the Columbia's confluence with the Kootenay River, and Trail, two major population centers of the West Kootenay region. The Pend Oreille River joins the Columbia about north of the United States–Canada border.File:Columbia River route on satellite image.jpg|left|thumb|alt=Modified satellite view of the Columbia River watershed showing the course of the river in red from Columbia Lake in British Columbia, Canada, to Astoria, Oregon, in the United States. The maps show that the river, although flowing on average in a southwesterly direction from source to mouth, changes direction sharply from northwest to south at Big Bend in Canada, from south to west near Grand Coulee Dam in Washington, from west to south near Wenatchee, Washington, and from south to west near the Tri-Cities area in Washington.|Course of the Columbia River
The Columbia enters eastern Washington flowing south and turning to the west at the Spokane River confluence. It marks the southern and eastern borders of the Colville Indian Reservation and the western border of the Spokane Indian Reservation. The river turns south after the Okanogan River confluence, then southeasterly near the confluence with the Wenatchee River in central Washington. This C-shaped segment of the river is also known as the "Big Bend". During the Missoula Floods 1015,000 years ago, much of the floodwater took a more direct route south, forming the ancient river bed known as the Grand Coulee. After the floods, the river found its present course, and the Grand Coulee was left dry. The construction of the Grand Coulee Dam in the mid-20th century impounded the river, forming Lake Roosevelt, from which water was pumped into the dry coulee, forming the reservoir of Banks Lake.
The river flows past The Gorge Amphitheatre, a prominent concert venue in the Northwest, then through Priest Rapids Dam, and then through the Hanford Nuclear Reservation. Entirely within the reservation is Hanford Reach, the only U.S. stretch of the river that is completely free-flowing, unimpeded by dams, and not a tidal estuary. The Snake River and Yakima River join the Columbia in the Tri-Cities population center. The Columbia makes a sharp bend to the west at the Washington–Oregon border. The river defines that border for the final of its journey.
File:ColumbiaGorge CapeHorn.jpg|thumb|The Columbia River Gorge facing east toward Beacon Rock
The Deschutes River joins the Columbia near The Dalles. Between The Dalles and Portland, the river cuts through the Cascade Range, forming the dramatic Columbia River Gorge. Via the gorge, the Columbia crosses the Cascades at a lower elevation than any other river. The gorge is known for its strong and steady winds, scenery, and its role as a transportation link. The river continues west, bending sharply to the north-northwest near Portland and Vancouver, Washington, at the Willamette River confluence. Here the river slows considerably, dropping sediment that might otherwise form a river delta at the Columbia's mouth. Near Longview, Washington and the Cowlitz River confluence, the river turns west again. The Columbia River empties into the Pacific Ocean just west of Astoria, Oregon, over the Columbia Bar, a shifting sandbar that makes the river's mouth one of the most hazardous stretches of water to navigate in the world. Because of the danger and the many shipwrecks near the mouth, it acquired a reputation as the "Graveyard of Ships".
The Columbia drains an area of about. Its drainage basin covers nearly all of Idaho, large portions of British Columbia, Oregon, and Washington, all of Montana west of the Continental Divide, and small portions of Wyoming, Utah, and Nevada; the total area is similar to the size of France. Roughly of the river's length and 85 percent of its drainage basin are in the US. The Columbia is the twelfth-longest river and has the sixth-largest drainage basin in the United States. In Canada, where the Columbia flows for and drains, the river ranks 23rd in length, and the Canadian part of its basin ranks 13th in size among Canadian basins.
The Columbia shares its name with nearby places, such as British Columbia, as well as with landforms and bodies of water.
Discharge
With an average flow at the mouth of about, the Columbia is the largest river by discharge flowing into the Pacific from the Americas and is the fourth-largest by volume in the U.S. The average flow where the river crosses the international border between Canada and the United States is from a drainage basin of. This amounts to about 15 percent of the entire Columbia watershed. The Columbia's highest recorded flow, measured at The Dalles, was in June 1894, before the river was dammed. The lowest flow recorded at The Dalles was on April 16, 1968, and was caused by the initial closure of the John Day Dam, upstream. The Dalles is about from the mouth; the river at this point drains about or about 91 percent of the total watershed. Flow rates on the Columbia are affected by many large upstream reservoirs, many diversions for irrigation, and, on the lower stretches, reverse flow from the tides of the Pacific Ocean. The National Ocean Service observes water levels at six tide gauges and issues tide forecasts for twenty-two additional locations along the river between the entrance at the North Jetty and the base of Bonneville Dam, its head of tide.*1858–1899: 6,280 m3/s
Geology
When the rifting of Pangaea, due to the process of plate tectonics, pushed North America away from Europe and Africa and into the Panthalassic Ocean, the Pacific Northwest was not part of the continent. As the North American continent moved westward, the Farallon Plate subducted under its western margin. As the plate subducted, it carried along island arcs which were accreted to the North American continent, resulting in the creation of the Pacific Northwest between 150 and 90 million years ago. The general outline of the Columbia Basin was not complete until between 60 and 40 million years ago, but it lay under a large inland sea later subject to uplift. Between 50 and 20 million years ago, from the Eocene through the Miocene eras, tremendous volcanic eruptions frequently modified much of the landscape traversed by the Columbia. The lower reaches of the ancestral river passed through a valley near where Mount Hood later arose. Carrying sediments from erosion and erupting volcanoes, it built a thick delta that underlies the foothills on the east side of the Coast Range near Vernonia in northwestern Oregon. Between 17 million and 6 million years ago, huge outpourings of flood basalt lava covered the Columbia River Plateau and forced the lower Columbia into its present course. The modern Cascade Range began to uplift 5 to 4 million years ago. Cutting through the uplifting mountains, the Columbia River significantly deepened the Columbia River Gorge.The river and its drainage basin experienced some of the world's greatest known catastrophic floods toward the end of the last ice age. The periodic rupturing of ice dams at Glacial Lake Missoula resulted in the Missoula Floods, with discharges exceeding the combined flow of all the other rivers in the world, dozens of times over thousands of years. The exact number of floods is unknown, but geologists have documented at least 40; evidence suggests that they occurred between about 19,000 and 13,000 years ago.
The floodwaters rushed across eastern Washington, creating the channeled scablands, which are a complex network of dry canyon-like channels, or coulees that are often braided and sharply gouged into the basalt rock underlying the region's deep topsoil. Numerous flat-topped buttes with rich soil stand high above the chaotic scablands. Constrictions at several places caused the floodwaters to pool into large temporary lakes, such as Lake Lewis, in which sediments were deposited. Water depths have been estimated at at Wallula Gap and over modern Portland, Oregon. Sediments were also deposited when the floodwaters slowed in the broad flats of the Quincy, Othello, and Pasco Basins. The floods' periodic inundation of the lower Columbia River Plateau deposited rich sediments; 21st-century farmers in the Willamette Valley "plow fields of fertile Montana soil and clays from Washington's Palouse".
Over the last several thousand years a series of large landslides have occurred on the north side of the Columbia River Gorge, sending massive amounts of debris south from Table Mountain and Greenleaf Peak into the gorge near the present site of Bonneville Dam. The most recent and significant is known as the Bonneville Slide, which formed a massive earthen dam, filling of the river's length. Various studies have placed the date of the Bonneville Slide anywhere between 1060 and 1760 AD; the idea that the landslide debris present today was formed by more than one slide is relatively recent and may explain the large range of estimates. It has been suggested that if the later dates are accurate there may be a link with the 1700 Cascadia earthquake. The pile of debris resulting from the Bonneville Slide blocked the river until rising water finally washed away the sediment. It is not known how long it took the river to break through the barrier; estimates range from several months to several years. Much of the landslide's debris remained, forcing the river about south of its previous channel and forming the Cascade Rapids. In 1938, the construction of Bonneville Dam inundated the rapids as well as the remaining trees that could be used to refine the estimated date of the landslide.
In 1980, the eruption of Mount St. Helens deposited large amounts of sediment in the lower Columbia, temporarily reducing the depth of the shipping channel by.