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A flood basalt (or plateau basalt [1]) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reaching the surface of the Earth via a mantle plume . [ 2 ]
The Columbia River Basalt Group (including the Steen and Picture Gorge basalts) extends over portions of four states. The Columbia River Basalt Group (CRBG) is the youngest, smallest and one of the best-preserved continental flood basalt provinces on Earth, covering over 210,000 km 2 (81,000 sq mi) mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. [1]
Basalt is distinguished from andesite by SiO 2 < 52%. Basalt is field B in the TAS classification. Vesicular basalt at Sunset Crater, Arizona. US quarter (24mm) for scale. Columnar basalt flows in Yellowstone National Park, US. Basalt is composed mostly of oxides of silicon, iron, magnesium, potassium, aluminum, titanium, and calcium.
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]
The upper unit of the Cardenas Basalt is a series of cliff-forming basaltic and andesitic lava flows that are interbedded with beds of breccia, sandstone, and lapillite. It is about 200 m (660 ft) thick and contains four to six, prominent lava flows that range in composition from quartz tholeiite to tholeiitic andesite .
Flood waters eroded the loess cover, creating large anastomizing channels that exposed bare basalt and creating butte-and-basin topography. The buttes range in height from 30 to 100 m (98 to 328 ft), while the rock basins range from 10 m (33 ft) in width up to the 11 km (7 mi) long and 30 m deep Rock Lake .
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.
The cliffs come from the earlier Cenozoic Afton basalt flow; the magma that caused the maar explosion was also basalt. [ 1 ] Kilbourne Hole is a maar volcanic crater , located 30 miles (48 km) west of the Franklin Mountains of El Paso, Texas , in the Potrillo volcanic field of Doña Ana County, New Mexico .