Week 4 - Volcanoes

Dotsero Crater, Photo Credit Big-g at restlessadventure, courtesy of outtherecolorado.com

My family and I traveled to the Dotsero Volcano this week. The view was spectacular! Dotsero is the only Holocene era volcano in Colorado. It is a small scoria cone and maar complex (Venske, 2018). When groundwater meets hot lava, it causes an explosion, called a phreatomagmatic eruption, leaving a maar (crater) in its wake. The scoria mentioned are volcanic rock types with several open spaces (vesicles) and light in weight (Dotsero Volcano & Uniformitarianism, 2014). The foreground quarry is chopped into basaltic tephra deposits on the brim of the maar. One of the least known volcanic centers in the western United States, Dotsero’s most prominent aspect is a 400-meter-deep and 700-meter-wide maar that erupted approximately 4150 radiocarbon years ago (2200 BC +/- 300 years) along a Pennsylvanian ridge with reddish oxidized sandstones and evaporites. Small scoria cones formed on both sides of the maar. Small lahars, followed by a basaltic lava flow traversed three kilometers down twin narrow V-shaped valleys and spread on the Eagle River floodplain, diverting the river on a different course (Venske, 2018).

Topographic map from mapcard.com, courtesy of csmsgeologypost.com

Dotsero Volcano, Photo by Lee Siebert, 1999, courtesy of Smithsonian Institution.

When the magma struck the water, it exploded and left the maar and destroyed a fragment of the scoria-cone chain, showering the landscape with tephra consisting of mostly red sandstone bedrock. This made it an explosive volcano (Yellowstone Volcano Observatory, 2017).

The crater of the Dotsero Volcano, courtesy of Denver Museum of Nature & Science, 2015

The volcano has been dormant since its original eruption and the crater fills in as erosion transports the debris in and around it. Black basalt as well as red and black scoria can be observed hiking around the crater. The black typically signifies oxidation of magnesium minerals, while red usually suggests the oxidation of iron minerals. Although the magma still exists, it is what heats the Glenwood Springs hot springs, it has shown no signs of activity or eruption (Busch, 2015).

Edge of lava flow south of I-70 along frontage road, courtesy of csmsgeologypost.com

It is interesting to me that Interstate 70 was paved right over the basalt field and lava flow that the eruption created (Dotsero Volcano & Uniformitarianism, 2014). The experts do not have Dotsero on the active volcano list, in fact there is a hiking trail that leads to the crater that was used by the Ute Indians, then the silver ore prospectors.

 

Samples of black (left) and red (right) scoria from Dotsero, courtesy of Denver Museum of Nature & Science

References

Busch, R. (2015). The Dotsero Volcano. Denver Museum of Nature & Science. Retrieved from http://www.dmns.org/museum-blog/the-dotsero-volcano/the-dotsero-volcano/

Dotsero Volcano & Uniformitarianism (2014). Colorado Springs Mineralogical Society. Retrieved from https://csmsgeologypost.blogspot.com/2014/04/dotsero-volcano-uniformitarianism.html 

Yellowstone Volcano Observatory (2017). United States Geological Survey. Retrieved from https://volcanoes.usgs.gov/volcanoes/dotsero/

Venzke, E. (2018). Dotsero. Smithsonian Institution. Retrieved from https://volcano.si.edu/volcano.cfm?vn=328010