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.
Geologic Background
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.
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| 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.
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| 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. |
Besides just creating the alternating mountains and valleys, the expansion of the Basin & Range Province produced another effect, a thinning of the crust. As the crust thins, the liquid mantle gets closer to the surface. And since it is closer to the surface, there are times when the hot liquid mantle is able to melt the overriding crustal rocks, forming volcanoes.
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| 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. |
And that is what has been produced in Utah, a series of volcanoes that align along the eastern edge of the Basin and Range Province. The Basin & Range province essentially ends with the Wasatch Mountain Range to the east, curving westward down through St. George in southern Utah. This line is paralleled by the line of active, or recently active, volcanoes in Utah, seen in the map below. By definition, an "active" volcano is one that has erupted within the last 10,000 years. We will go through them from north to south.
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| Map of the most recent, active volcanoes in Utah. |
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| 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.
2. Pahvant Butte
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:
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| 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."
Pahvant Butte is located within the youngest of the five Black Rock Desert subfields, Ice Springs. Erupting ~15,500 years ago, Pahvant Butte started erupting during the time of Lake Bonneville, a vast Ice Age lake that covered much of Utah and Nevada. The volcano quickly breached the surface of the lake, rising to a total of 740 feet (about 400 feet above the highest lake levels). Several shorelines were eroded into the volcano at the time including one that called the "Lace Curtain", which is a vertical cut shoreline cliff, which exposes tuff that was cemented by the ground water producing an intricate lacy pattern.
3. Ice Springs Volcano
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| 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. |
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| Google aerial photo of the Ice Springs Lava Flow. |
The Ice Springs volcano and lava flow is easily one of the most recognizable features in Utah on Google Earth. It is a strong black smear on the landscape in an otherwise brown and green landscape located just west of the town of Fillmore. I had visited the volcano on a drive home. I had frequently driven fairly close to this area but never actually stopped before. It was a lot of fun just to check out some of the volcanic debris.
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| View of the cinder cone (left) and the lava flow driving up. |
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| Closer up view of the lava flow |
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| Close up of the cinder cone. |
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| Inside the cinder cone. |
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| A piece of scoria from the Ice Springs volcanic eruption. |
The Ice Springs volcano and lava flow is the youngest of the Black Rock Desert subfields and the youngest of all of the lava flows in all of Utah, dating to about 660 years ago (~1360 CE). The volcano is a cinder cone, which is a volcano formed from the eruption of "cinders", also known as scoria, dark black basaltic rocks full of air holes. The lava erupts out of the crater and solidifies in the air, piling up alongside the vent. Eventually these "cinders" build up into a cone shape. The area also contains a basaltic lava flow.
4. Tabernacle Hill Lava Tubes
Also part of the Ice Springs subfield, since the Tabernacle Hill Lava Tubes were distinct enough and located a little bit further south than the main Ice Springs volcano, I am listing it separately. The Tabernacle Hill Lava Tubes erupted ~14,500 years ago and are located to the west of Meadow, Utah. They consist primarily of basalt.
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| The Tabernacle Hill Lava Tubes. Image courtesy of Utah's Adventure Family. |
A lava tube is formed during a volcanic eruption when you have a flowing river of lava. The surface of that river is in contact with the air and slowly starts to solidify. Eventually the lava river crusts over, insulating the lava in the river. This allows for the lava river to keep flowing and eventually when the volcano peters out, the lava flows out leaving the solidified tube behind. Lava tubes are predominantly made out of basaltic rocks, because the higher viscosity rhyolitic (high silica) lava can't flow fast enough to produce the lava rivers. Within the Tabernacle Hill eruption there is also a central crater still present that once held a lava lake.
5. Markagunt Plateau volcanic field
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| Lava flows of the Markagunt plateau (Makagunt means "highland of trees" in the Paiute language). Image courtesy of the USRA. |
The Markagunt Plateau volcanic field is a vast field with many volcanic eruptions across it primarily composed of basaltic rocks and scoria. It is located east of Cedar City, Utah and butts up against the Cedar Breaks National Monument. The area of the volcanic field exceeds 1,000 square miles and was active from 5.3 million years ago to less than 10,000 years ago. Overall, there were 40 to 50 one-off cinder cone eruptions that formed over three distinct periods of time: 5.3 to 2.8 million years ago, 1 to 0.5 million years ago, and less than 0.5 million years ago. The youngest lava flows are estimated to be around 900 years old, based on the ages of the oldest trees on the flows. This agrees with a Southern Paiute legend, whom arrived in the area around 1,000 years ago, about the ejection of fiery rocks and molten lava flows (Palmer, 1957).
6. Santa Clara Volcano
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| The Santa Clara cinder cone volcano. Image courtesy of Mapio. |
The Santa Clara volcano is a cinder cone located to the north of the city of St. George, Utah, and is one of the southernmost volcanoes within Utah. Within the area are two cinder cones and a lava flow that flowed 16 km south down into Snow Canyon. The associated basaltic lava flow has been dated at ~27,000 years old. This lava flow is often touted as one of the Colorado Plateau's youngest lava flows, however the dates of many in the Black Rock Desert and Markagunt Plateau have been dated to be vastly younger.
References
https://pubs.usgs.gov/gip/dynamic/Farallon.html
https://www.nps.gov/subjects/geology/plate-tectonics-transform-plate-boundaries.htm
Palmer W R, 1957. Why the North Star Stands Still and other Indian legends. Englewood Cliffs, New Jersey: Prentice-Hall, 158 p.
Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest, by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015
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