Information Entries for Wetterhorn Peak and Geology

Geology (Wetterhorn Peak)

Title: Volcanics and Glaciation

Entered by: WSC_Geologist12

Added: 06/11/2010, Last Updated: 06/11/2010

Sources: Krabacher, P.P., Herron, J., Graves, J., Brown, K., 2006, "Reclamation feasibility report: Henson Creek Watershed", Colorado Department of Natural Resources. 171pp. Irving and Bancroft, 1911, "Geology and Ore Deposits Near Lake City, Colorado. Luedke, and Burbank, 1987, "Geologic Map of the Lake City Caldera Area, Western San Juan Mountains, Southwestern Colorado

The geologic history of the Uncompahgre and Wetterhorn areas are not easy to discern. Instead the area is riddled with confusing faulting, mind-twising structures, and to cap it all off, there are several intrusive igneous rocks that have intruded their way into the volcanic rocks of the area.

The majority of the San Juans are made up of collapsed volcanoes called "calderas". Geologist have identified 13 separate calderas across the San Juans. The story here is fairly simple: A large volcano, perhaps a cinder cone erupts all of the magma it has out of its chamber leaving an empty chamber. The weight of the volcano then causes it to collapse in on itself creating a ring-shaped fault. These collapses are associated with violent eruptions that produce ash-flow tuffs and or lava bombs. The rocks of the area reflect the evidence of the calderas because the majority of the rocks are indeed ash-flow tuffs with large clasts representing lava bombs.

However the collapse of all the calderas did not mark the ending of volcanic activity. The magma ended up intruding into the calderas and forming large bodies of intrusive igneous rock underneath the volcanic rocks that are seen. These intrusives are represented in Handies, Redcloud and Sunshine peaks, along with other peaks of that area.

These volcanoes were very high, some were estimated to soar above 18,000 feet at one time. Mountain climbing enthusiasts definately wish that those peaks still existed somewhere in Colorado today, because we might be able to talk some crap about mountains like Denali, Orizaba and Whitney.

Along with the high altitude comes snow, and the snow on the volcanoes often melted with heat and caused mudflows, which are also seen in the San Juans in places.

However, the important part of the snow is glaciation, which has carved the peaks into the shapes we see them today. Uncompahgre and Wetterhorn have simple histories when it comes to rocks, but the shaping of those rocks is what is confusing. All the peaks in the northern San Juans are composed of thick lava flows of silicic composition, the rock type is said to be "porphyritic quartz latite" but for those of you who have amatuer backgrounds in geology, you can refer to this as "rhyolite". As the glaciers in the San Juans melted, they carved Uncompahgre, Wetterhorn, Matterhorn, Coxcomb, and many more into the shapes that we see them as.

If anybody has any questions or comments, even corrections please message me I would love to chat geology, and if you ever decide to climb with me, do know we'll be chatting geology.
James Haag
Hydrologist BLM

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