clockwise around the African Plate
- Columbia River Basalt Group Stretches from Oregon to Idaho (usgs.gov)
The thick, layered lava flows of the CRBG erupted as flood basalts, which originate as some of the most highly effusive eruptions in the world. The CRBG sequence a classic example of flood basalt activity that erupted more than 350 lava flows from about 16.7 Ma to 5.5 Ma. The eruptions originated from a series of generally north-northwest-trending linear fissures, ranging from tens to hundreds of kilometers in length, located along the Washington/Oregon/Idaho border. The magma that fed these massive eruptions may have come from a plume-like upwelling from the mantle called a hot spot. Since the time of the CRBG eruptions, the North American plate has moved in a west-southwestwardly motion, and that hot spot is now believed to reside beneath Yellowstone volcano in northwest Wyoming.
- Millions of years ago, vents and fissures opened under the Pacific Ocean and lava flowed forth, creating huge underwater volcanic mountains and ranges called seamounts. The Farallon tectonic plate that formed a part of the Pacific Ocean floor (separate from the Pacific plate) inched eastward toward North America about 35 million years ago and most of the sea floor subducted beneath the continental land mass of the North America plate. Some of the sea floor, however, was scraped off and jammed against the mainland, creating the dome that was the forerunner of today’s Olympics.
- The remains of the Farallon Plate are the Explorer, Gorda, and Juan de Fuca plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate.
- North American Plate (Wikipedia)
The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76 million km2 (29 million sq mi), it is the Earth’s second largest tectonic plate, behind the Pacific Plate (which borders the plate to the west).
