San Juan volcanic field

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San Juan volcanic field
San Juan volcanic field is located in Colorado
San Juan volcanic field
San Juan volcanic field
Location in Colorado
Highest point
Coordinates 37°53′36″N 106°46′28″W / 37.89333°N 106.77444°W / 37.89333; -106.77444Coordinates: 37°53′36″N 106°46′28″W / 37.89333°N 106.77444°W / 37.89333; -106.77444
Location Colorado, United States
Mountain type Volcanic field

The San Juan Mountains, in southwestern Colorado, consist mainly of volcanic rocks that form the largest remnant of a major composite volcanic field that covered most of the southern Rocky Mountains in middle Tertiary time.[1] Within the region, lies an abundance of caldera volcanoes which comprise the San Juan Volcanic Fields. There are approximately 15 calderas known in the San Juan Volcanic Fields, however it is possible that there are 2, or even 3 more, that exist in the region.[1] The region began with many composite volcanoes that became active between 35 and 40 million years ago were particularly eruptive in the time period around 35-30 million years ago.[1] Around this time the activity changed to explosive ash-flow eruptions.[2] Many of these volcanoes experienced caldera collapse, resulting in the 15-18 caldera volcanoes in the region today.[1]

Phases of Volcanism[edit]

The San Juan volcanic field contains two phases of volcanism.

The earlier volcanism is Oligocene in age, and consists of largely intermediate composition lavas and breccias. A few ash flow tuffs also constitute this phase of volcanism.[citation needed]

The later volcanism is MiocenePliocene in age, and is basaltic in composition. It is best interpreted as a partial melt of the lower crust that was erupted onto the surface.[3]

Notable calderas[edit]

Name Elevation Coordinates Age
Cochetopa Caldera - 38°12′N 106°45′W / 38.2°N 106.75°W / 38.2; -106.75[4]
Nelson Mountain Caldera - 37°58′N 106°56′W / 37.96°N 106.93°W / 37.96; -106.93[4]
Bachelor Caldera - 37°49′03″N 106°54′46″W / 37.817378°N 106.912766°W / 37.817378; -106.912766[4]
Creede Caldera - 37°45′34″N 106°56′20″W / 37.759316°N 106.938858°W / 37.759316; -106.938858[4]
Lake City calderas - 38°01′31″N 107°23′04″W / 38.025377°N 107.384491°W / 38.025377; -107.384491[3]
Platoro calderas - 37°21′08″N 106°31′52″W / 37.352147°N 106.530991°W / 37.352147; -106.530991[3]

See also[edit]


  1. ^ a b c d Steven, Thomas A.; Lipman, Peter W. (1976). "Calderas of the San Juan Volcanic Field, Southwestern Colorado". U.S. Geological Survey Professional Papers. Washington, DC: U.S. Government Printing Office. 958: 1–35. Retrieved 2012-05-16.
  2. ^ Lipman, Peter W.; Steven, Thomas A.; Mehnert, Harald H. (1970-08-01). "Volcanic History of the San Juan Mountains, Colorado, as Indicated by Potassium–Argon Dating". Geological Society of America Bulletin. 81 (8): 2329–2352. doi:10.1130/0016-7606(1970)81[2329:VHOTSJ]2.0.CO;2. ISSN 0016-7606. 
  3. ^ a b c Lipman, P.W.; Doe, B.R.; Hedge, C.E.; Steven, T.A. (1978). "Petrologic evolution of the San Juan volcanic field, southwestern Colorado: Pb and Sr isotope evidence". Geological Society of America Bulletin. 89: 59–82. doi:10.1130/0016-7606(1978)89<59:PEOTSJ>2.0.CO;2. ISSN 0016-7606. 
  4. ^ a b c d e Robinson, Joel E.; Dillon R. Dutton; David W. Ramsey; Peter W. Lipman; Tracey J. Felger (2006). Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado: Geologic Investigations Series. I-2799. U.S. Geological Survey. Retrieved 2010-05-03. 
  5. ^ a b "What's the Biggest Volcanic Eruption Ever?". Live Science. Retrieved 2016-10-23.