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Encyclopedia > La Garita Caldera

La Garita Caldera is a large volcanic caldera located in the San Juan Mountains in southwestern Colorado. It is one of a number of calderas that formed during a massive ignimbrite flare-up in Colorado, Utah and Nevada from 40–25 million years ago. La Garita was the site of truly enormous eruptions about 26–28 million years ago, during the Oligocene Epoch. This was the Fish Canyon Tuff, which has a volume of approximately 5,000 cubic kilometers. The scale is unimaginable — for comparison, the May 18, 1980 eruption of Mt. St. Helens (doing an estimated 2 to 3 billion USD in damages) was only 1.2 cubic kilometers in volume. The area devastated by the eruption must have covered a significant portion of what is now Colorado, and ash could have fallen as far as the east coast of North America and the Caribbean. Volcano 1. ... Satellite image of Santorini. ... The San Juan Mountains are a rugged mountain range in the Rocky Mountains in southwestern Colorado. ... Ignimbrite is a compact volcanic pyroclastic rock typically of rhyolitic composition. ... Official language(s) English Capital Denver Largest city Denver Area  Ranked 8th  - Total 104,185 sq mi (269,837 km²)  - Width 280 miles (451 km)  - Length 380 miles (612 km)  - % water 0. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... This article does not cite its references or sources. ... This article is about volcanoes in geology. ... The Oligocene epoch is a geologic period of time that extends from about 34 million to 23 million years before the present. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo and pronounced tuf) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... May 18 is the 138th day of the year in the Gregorian Calendar (139th in leap years). ... 1980 (MCMLXXX) was a leap year starting on Tuesday. ... Mount St. ... The United States dollar is the official currency of the United States. ... World map showing North America A satellite composite image of North America. ... World map depicting Caribbean : West Indies redirects here. ...


The Fish Canyon Tuff, made of dacite, is known to be remarkably uniform in its petrological composition and forms a single cooling unit despite the huge volume. Dacite is a silicic volcanic rock common in explosive eruptions, lava domes and short thick lava flows. La Garita Caldera also has erupted large intracaldera lavas composed of andesite, a volcanic rock compositionally intermediate between basalt (poor in silica content) and dacite (higher silica content). Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Basalt Columnar basalt at Sheepeater Cliff in Yellowstone Basalt (IPA: ) is a common gray to black volcanic rock. ...


The caldera, like the eruption of Fish Canyon Tuff, is also quite large in scale. It is 35 by 75 kilometers (approximately 22 by 47 miles), an unusually oblong shape. Most calderas of explosive origin are roughly circular or slightly ovoid in shape. Because of the vast scale and erosion, it took scientists over 30 years to fully determine the size of the caldera. La Garita can be considered a "supervolcano", albeit an extinct one. A supervolcano refers to a volcano that produces the largest and most voluminous kinds of eruption on Earth. ...


La Garita Caldera is also the source of at least 7 major eruptions of welded tuff deposits over a time span of 1.5 million years since the Fish Canyon Tuff eruption. The caldera is also known to have extensive outcrops of a very unusual lava-like rock made of dacite very similar to that of the Fish Canyon Tuff. This rock has characteristics of both lava and welded tuff and was erupted probably shortly before the Fish Canyon Tuff. The lava-like rock has been interpreted as having erupted as thick spatter during low-energy lava fountaining. The lava-like rock is also rather voluminous -- up to 200-300 cubic kilometers. Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo and pronounced tuf) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ...


Sources

  • The Mid-Tertiary Ignimbrite Flare-Up

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