Everything about La Garita Caldera totally explained
La Garita Caldera is a large
volcanic caldera located in the
San Juan volcanic field in the
San Juan Mountains in southwestern
Colorado,
United States, to the west of the town of
La Garita, 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, and was the site of truly enormous
eruptions about 26–28 million years ago, during the
Oligocene Epoch. The scale of volcanism was far beyond anything known in human history. The resulting deposit, known as the Fish Canyon
Tuff, has a volume of approximately
5,000 cubic kilometers, enough material to fill
Lake Erie (in comparison, the
May 18,
1980 eruption of
Mt. St. Helens was only 1.2 cubic kilometers in volume). The area devastated by the La Garita eruption is thought to 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.
The eruption that created the La Garita Caldera was one of the largest known eruptions, if not the largest, to have occurred in Earth's history. By contrast, the most powerful man-made explosive device ever detonated, the
Tsar Bomba or Emperor Bomb, had a yield of only 50 megatons, whereas the eruption at La Garita released approximately 10 zettajoules. It is possibly only the second most energetic event to have ocurred on Earth besides the
Chicxulub impact, which released an estimated 500 zettajoules (5×10
23 joules) of energy, equivalent to 100 teratons of TNT (10
14 tons), making it 2 million times more powerful.
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).
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.
La Garita 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 that's very similar to that of the Fish Canyon Tuff. This rock, which has characteristics of both lava and welded tuff, 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 voluminous — up to
200-300 cubic kilometers.
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