Colorado’s one and only active volcano!
No physical cache at this location, you must visit the site and make observations prior to logging. Download or print this page ahead of time - cell service is spotty.
Getting There
Land ownership is by the US Dept of Interior, Bureau of Land Management. The Dotsero Crater Rec Site is listed for public access (reference below). From I-70 exit 133, head east towards the mobile home park.
The terrain rating is based on the hike from the parking to the crater: 1.5 miles one-way and 840 ft elevation gain. If you choose to drive (4WD/high-clearance required), please be aware of spur roads and potential truck traffic. We encountered a bulldozer pushing a boulder downhill when we visited.
Note: No-Snow attribute indicates that you need to see the road surface at the coordinates. You may or may not get up the road if it is snowed in,
Formation of the Dotsero Crater
Aproximately 4200 years ago, a phreatomagmatic eruption occurred when magma encountered groundwater. The resulting explosion excavated a crater in the surrounding Maroon Formation rock and blasted basaltic tephra and sandstone into the air. The resulting lapilli tuff covers the surface as far as four miles away. Not a good day to be hiking in the area.
The resulting crater type is called a maar. Underneath the crater floor is a diatreme filled with volcanic debris and fragmented sedimentary rock. There are numerous scoria cones in the area that formed after the explosive event creating the maar. A lava flow preceeded the eruption and reached as far south as the Eagle River floodplain. In geological terms, this Holocene eruption was an extremely recent event.
Modern Times
Interstate 70 crosses the lava flow, and an industrial park is located on the lava field adjacent to the Eagle River. A former industry in the area was the production of cinder blocks.
Dotsero is in the middle of the yellow (moderate) volcano threat ranking at #82 with an overall score of 49. It is the only Colorado entry on that list. See the 2018 Update to the U.S. Geological Survey National Volcanic Threat Assessment linked from the USGS site in the references for more info on threat assessments.
Definitions
- Diatreme: Funnel-shaped fracture in the crust rock resulting from a gaseous explosion
- Holocene: The current geologic time period, beginning approximately 12,000 years ago
- Lapilli: Tephra in the size range of 2 to 64 mm (0.08 to 2.52 in) in diameter
- Maar: Low, broad volcanic crater, often with flat floor or a lake
- Phreatomagmatic: Volcanic eruptions resulting from interaction between magma and water
- Scoria: Volcanic ejecta, pitted with cavities from gas bubble. Synonym: Cinder.
- Tephra: Rock fragments ejected by a volcanic eruption
- Tuff: A type of rock made of volcanic ash and scoria that has deposited and consolidated into a solid
References
- https://www.blm.gov/visit/dotsero-crater-rec-site
- https://www.usgs.gov/volcanoes/dotsero-volcanic-center
- https://en.wikipedia.org/wiki/Dotsero
- https://www.nps.gov/articles/000/maars-and-tuff-rings.htm
Logging Tasks
Either message or email answers to the following questions before posting your log. Include the GC code and cache name if using email. Do not post photos showing the answers to tasks 1-3.
1. At the posted coordinates, look at the rocks embedded in the road surface.
a) What type of rock is here?
b) Describe the color and surface texture.
c) How do you think this rock got here?
2. About 15 feet farther along the road to the NW there are some different rocks in the road surface.
a) What type of rock is here?
b) Describe the color and surface texture.
c) How do you think this rock got here?
3. Now look at the terrain on the east side of the road.
a) Describe the surface characteristics on the left and right sides of your view.
b) What do you think caused this terrain?
4. Photo required – You made a trek to see this photogenic geological feature, now take a selfie to remember it by. Post a photo of yourself or a personal item with the crater in the background. Stay outside the safety fence!