Utah is known for a lot of geological marvels, however one of them that isn't often talked about, or even realized that we have, are volcanoes. And active ones at that, with the most recent volcanic eruption dating around 660 years ago. Utah's history is deep and varied, and although there is evidence for numerous volcanic eruptions through time with volcanoes buried deep in our geological past, I am only going to focus on some of the most prominent and recent volcanic eruptions that you can visit and see the evidence of today.
The reason that Utah has so many active volcanoes is because of Plate Tectonics, the process that produces mountains, earthquakes, islands, volcanoes, among many other features across the globe. It all started many millions of years ago (at least 40) as the plate off the western coast of North America, the Farallon Plate, was subducting (going beneath) the North American Plate. This subduction was due to the Farallon Plate moving towards the North American Plate, and since the oceanic plate was denser, it got forced downward. As the plates pushed against each other, besides just riding on top of the Farallon Plate, the North American plate also ended up being compressed, or squeezed, like a sponge.
|Illustration of the plate tectonics of the west coast of North America with the Farallon Plate subducting beneath North America. Image courtesy of the NPS.
Over the course of the last 40 million years, or so, the Farallon Plate was eventually subducted almost entirely beneath the North American plate. This rather hot plate, forced the area known as the Colorado Plateau vertically upwards, creating features such as the Grand Canyon, and Zion National Park. However, once the subduction zone on the west coast was no longer present, the compressive force was no longer present either. This resulted in the western part of the North American plate being now allowed to expand, and like a released sponge, it did expand. This expansion is what produced the Basin & Range Province, which is a series of alternating linear mountain ranges and valleys.
|Evolution of the western coast of North America going from a subduction zone to a transform plate boundary causing the formation of the extensional Basin & Range Province. Images courtesy of the NPS.
|The thinning of the crust causes the upper mantle (asthenosphere) to rise up and melt the overlying rocks producing volcanoes. Image courtesy of the NPS and Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest, by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015.
|Photo of Fumarole Butte I took while flying over it from Salt Lake City to Las Vegas.
Fumarole Butte is located just to the northwest of Delta, Utah. It is considered on of the five "subfields" of the Black Rock Desert volcanic field, and it is the oldest of the five subfields. Fumarole Butte was active sporadically from 6.1 to 0.3 million years ago. The most obvious feature of Fumarole Butte is the shield volcano seen above that dates to about 0.9 million years old. A shield volcano is a volcano made up of mostly basaltic rocks, which forms from thin and runny lava that has a low silica (quartz) content. They are also very dark grey to black in color. The most common shield volcanoes in the US are the Hawaiian Islands. Another famous feature of the region is Topaz Mountain, a rhyolite dome with abundant topaz deposits. Rhyolite is on the opposite end of the viscosity spectrum from basalt, where the lava is thick, with a high silica content, and is usually very light in color.
|Pahvant Butte. Image courtesy of Desert Survivor.
Moving our way south, our next volcanic feature is the Pahvant Butte, which is a type of volcano known as a tuff cone. Per National Geographic:
"When heated rapidly by lava, water flashes to steam and expands violently, fragmenting huge amounts of lava into plumes of very fine grains of ash. This ash falls around the volcanic vent, creating an ash cone. Over time, the ash weathers into a rock known as tuff."
|The sign here led me to believe that the volcano was called Red Dome, however that is just the mining operation that uses the scoria from the cinder cone.
|View of the cinder cone (left) and the lava flow driving up.
|Closer up view of the lava flow
|Close up of the cinder cone.
|Inside the cinder cone.
|A piece of scoria from the Ice Springs volcanic eruption.
|The Tabernacle Hill Lava Tubes. Image courtesy of Utah's Adventure Family.
|Lava flows of the Markagunt plateau (Makagunt means "highland of trees" in the Paiute language). Image courtesy of the USRA.
|The Santa Clara cinder cone volcano. Image courtesy of Mapio.