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Blue Lake crater is made up of basalt and picrite basalt, or picrobasalt (representative sample pictured) Blue Lake Crater is part of the Oregon branch of the Cascade volcanic arc in western North America, [4] though it lies about 3 miles (4.8 km) to the east of the major crest. [13]
The world's thickest basalt flow may be the Greenstone flow of the Keweenaw Peninsula of Michigan, US, which is 600 meters (2,000 ft) thick. This flow may have been part of a lava lake the size of Lake Superior. [13] Deep erosion of flood basalts exposes vast numbers of parallel dikes that fed the eruptions. [17]
Basalt columns seen on Porto Santo Island, Portugal. Columnar jointing of volcanic rocks exists in many places on Earth. Perhaps the most famous basalt lava flow in the world is the Giant's Causeway in Northern Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed.
Columnar jointing in Giant's Causeway in Northern Ireland Columnar jointing in the Alcantara Gorge, Sicily. Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms (basalt prisms), or columns.
Flood basalts on Vancouver Island form a geologic formation called the Karmutsen Formation, which is perhaps the thickest accreted section of an oceanic plateau worldwide, exposing up to 6,000 m (20,000 ft) of basal sediment-sill complexes, basaltic to picritic pillow lavas, pillow breccia, and thick, massive basalt flows.
During late Miocene and early Pliocene times, a flood basalt engulfed about 63,000 square miles (160,000 km 2) of the Pacific Northwest, forming a large igneous province. [2] Over a period of perhaps 10 to 15 million years, lava flow after lava flow poured out, ultimately accumulating to a thickness of more than 6,000 feet (1.8 km). [ 2 ]
Grand Coulee is a large coulee on the Columbia River Plateau.This area has underlying granite bedrock, formed deep in the Earth's crust 40 to 60 million years ago. The land periodically uplifted and subsided over millions of years giving rise to some small mountains and, eventually, an inland sea.
Most of the south of the island consists of sub oceanic basalt layered between Globigerina ooze. The part north of Langdon Point and Ballast Bay consists of serpentinite derived from gabbro, troctolite, and peridotite (dunite, wehrlite, and harzburgite). This was formed in the deep crust and mantle. [17]