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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]
An erosion surface on the Vishnu Basement Rocks is covered by sedimentary rocks and basalt flows, and these rocks formed in the interval from about 1250 to 750 million years ago: in turn, they were uplifted and split into a range of fault-block mountains.
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.
It flows westward along the county line between Pitkin and Eagle County. Below Meredith, it is dammed to form the Ruedi Reservoir. It joins the Roaring Fork below Basalt. A portion of the river's water is diverted to the east side of the continental divide for irrigation and drinking water via the Fryingpan-Arkansas Project.
Three prominent, columnar jointed, cliff-forming lava flows can be seen on North Table Mountain, one exposed part way up the northwest slope, and two that form its cap. The Ralston Dike, a body of intrusive monzonite located about 2 miles (3.2 km) to the northwest, probably represents the volcanic vent from which the flows erupted. [ 6 ]
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 ( icelandite ).
The mesa is topped by a hard layer of volcanic basalt. This layer formed between about 10.9 and 9.6 million years ago, by the eruption of at least 27 separate lava flows from a vent in the Crag Crest area and probably other vents. This built up a maximum total thickness of more than 93 meters (310 feet) of basalt. [2]