La Garita Caldera
Coordinates: 37 ° 45 ′ N , 106 ° 56 ′ W
The La Garita Caldera is a large volcanic caldera located in the San Juan Mountains of southwest Colorado , United States . About 26 to 28 million years ago ( Oligocene ) there was a gigantic volcanic eruption of magnitude 8 on the volcanic explosion index ( supervolcano ).
During this eruption, about 5,000 cubic kilometers of material (Fish Canyon Tuff ) were expelled. The eruption was twice as strong as the Toba eruption or 500 times as strong as the 1991 Pinatubo eruption . The Fish Canyon Tuff consists of Dacite and is surprisingly uniform in its composition. Dacite is a silicon-rich volcanic rock that is found in explosive eruptions , in lava domes and in short, thick lava flows .
The caldera is 35 by 75 kilometers in size and has an elongated shape that is unusual for a caldera. In the 1.5 million years after the Fish Canyon Tuff eruption, there have been at least seven major eruptions with different material compositions.
literature
- Peter W. Lipman, Joel E. Robinson, Dillon R. Dutton, David W. Ramsey, and Tracey J. Felger: Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado . USGS Geologic Investigations Series I-2799, 2006. (includes maps, photo collection , and links to on-line abstracts)
- Ben G. Mason, David M. Pyle, and Clive Oppenheimer: The size and frequency of the largest explosive eruptions on Earth . In: Bulletin of Volcanology . 66, No. 8, 2004, pp. 735-748. doi : 10.1007 / s00445-004-0355-9 .
- Daniel R. Askren, Michael F. Rodden, and James A. Whitney: Petrogenesis of Tertiary Andesite Lava Flows Interlayered with Large-Volume FelsicAsh-Flow Tuffs of the Western USA . In: Journal of Petrology . 38, No. 8, 1997, pp. 1021-1046.