Columbia River Basalt Group

The Columbia Plateau basalt is an extensive flood basalt in the U.S., parts of the states of Washington, Oregon and Idaho covered.

During the late Miocene and early Pliocene devoured huge amounts of basalt more than 163,700 km ² of the Pacific Northwest and formed a large magmatic province with an estimated volume of 174,300 km ³. The eruptions were in front 17-14 million years ago, most violent, were promoted as over 99 % of the basalt. The following front 14-6 million years outbreaks were less extensively.,

The lava flows were eroded later in the rushing waters of the Missoula floods often, in the Columbia River Gorge and the Channeled Scablands merely laid on the Wallula Gap, at the lower Palouse River, many layers of basalt flows.

The Columbia Plateau basalt is considered a possible link to the Chilcotin Plateau basalts in south-central British Columbia, Canada.

The formation of the Columbia Plateau basalt

Over a period of perhaps 10 to 15 million years ago, lava flowed over lava, they rallied to a thickness of more than 1,800 m. As the molten rock hence flow at the surface, the earth fell to the deflating magma reservoir slowly. The lowering of the earth's crust known generated a large, slightly bowl-shaped lava plain, now known as the Columbia Basin or Columbia River Plateau. The predecessor of today's Columbia River was forced by the advancing northward Lavaflut in its current run. When the lava is distributed over the territory they dammed in many places a river valleys and produced impoundments and lakes. In the remains of these lakes are found today fossil leaf impressions, petrified wood, fossil insects and the fossilized bones of vertebrates, including those of the Blue Lake Rhino.

The transition to Flutvulkanismus

Until more than 17 million years, the eruptions of volcanoes in the Cascade Range were done already more than 20 million years, with steady regularity, as is the case today. In the middle Miocene was an abrupt transition to the effusion of flood basalts. The eventual reason for this type of volcanism is still being discussed. The most accepted idea is that as in the case of a Hawaii Manteldiapir or a rise of the upper mantle pulled the extensive and voluminous basaltic volcanism after.

The basalt effusions can be divided into three main divisions: the Grande Ronde Basalt, Wanapum Basalt, and the Saddle Mountains Basalt of. The age of the various lava flows were determined by radiometric dating, especially by the potassium - argon method.

Imnaha basalt

The oldest with 17.4 to 17 million years ago, part of the basalts is the Imnaha basalt. The Imnaha lava flows poured over northeastern Oregon. Although they account for 10% of the total amount of flood basalts estimates, they were buried under the follow effusions and are visible only in a few places.

Grande Ronde Basalt

The next oldest of the lava flows is 17 to 15.6 million years of the Grande Ronde Basalt. Subunits or flow zones within the Grande Ronde basalt are the Meyer Ridge Unit and the Sentinel Bluffs unit. Geologists estimate that the lavas of the Grande Ronde Basalt represent up to 85 % of the total volume. The Grande Ronde basalts have a special feature on the Chief Joseph Dike Swarm, a Swarm of Dykes, through which advanced the lava, and their number is estimated at 20,000. Some of these migration pathways were 5 to 10 meters wide columns through which an enormous amount could emerge at Lava. Much of the lava flowed north into what is now Washington in, and through the valley of the Columbia River to the Pacific Ocean. These huge lava flows created the actual Columbia Plateau. , The basalts and transitional swarms of Grande Ronde Basalt 3 can be well observed in the rugged 600 -meter walls of the Joseph Canyon in Oregon route. Parts of the Grande Ronde, Wanapum and Saddle Mountain Basalts are at Wallula Gap digested (pictured from bottom to top ).

Wanapum basalt

The Wanapum Basalt consists of the units of the Eckler Mountain Member ( 15.6 million years old), the Frenchmen Springs Member ( 15.5 million years old), the Roza Member ( 14.9 million years old) and the Priest Rapids Member ( 14.5 million years old). ,

Saddle Mountains Basalt

The Saddle Mountains Basalt, particularly well observed in the Saddle Mountains, consists of several lava flows: Umatilla Member, Wilbur Creek Member, Asotin Members (13 million years old ), Weissenfels Ridge Member, Esquatzel member, Elephant Mountain Member ( 10.5 million years old ), Bujford member, Ice Harbor member (8.5 million years old ) and Lower Monumental member (6 million years old ).

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