- 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.
- For the most part, the North American Plate moves in roughly a southwest direction away from the Mid-Atlantic Ridge at a rate of about 2.3 centimeters (~1 inch) per year. At the same time, the Pacific Plate is moving to the northwest at a speed of between 7 and 11 centimeters (~3-4 inches) a year.
- 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).
- On its western edge, the Farallon Plate has been subducting under the North American Plate since the Jurassic Period.
- 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.
- 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.
clockwise around the African Plate
