Geology of the Pacific Northwest debris. Rising above this volcanic platform are a few strikingly large volcanoes that dominate the landscape. The Cascade volcanoes define the Pacific Northwest section of the Ring of Fire, an array of volcanoes that rim the Pacific Ocean. The Ring of Fire is also known for its frequent earthquakes. The volcanoes and earthquakes arise from a common source: subduction. Beneath the Cascade Volcanic Arc, a dense oceanic plate plunges beneath the North American Plate; a process known as subduction. As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules
Circum-Superior Belt has been suggested for magmatism of the 2,215 million-year-old Nipissing sills as well, which the Ungava dike swarm could have transported magma to the Nipissing sills area. Before 2003, all magmatism of the Circum-Superior Belt was thought to only occur along the outer margin of the Superior craton. However, the Pickle Crow dike was discovered in 2003 in the interior of the Superior craton and it has since been recognized as a magmatic event related to the Circum-Superior Belt. The dike is dated to 1,880 million years old and associated dikes are traced for at least . These dikes likely