How was the Columbia gorge formed?

Answer 1

The rifting of Pangea pushed North America away from Europe and Africa and into the Panthalassic Ocean (Pacific Ocean.) As the North American continent moved westward, theFarrallonPlate subducted under its western margin. As the plate subducted, it carried along island arcs which were accreted to the North American continent. 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 40 and 20 million years ago, in the Eocene and 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 2-mile (3.2 km) 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 flodd basalt lava covered theColumbia River Plateau and forced the lower Columbia into its present course.