Utah contains extensive evidence of past volcanic activity, which has shaped much of the landscape in the western and southern parts of the state. While the word “volcano” may suggest explosive, currently erupting mountains, the vast majority of Utah’s volcanic features are ancient or extinct. The geologic record shows that eruptions have occurred here across millions of years, with some of the most recent events happening within the last millennium.
Primary Regions of Past Volcanic Activity
The most geologically recent and visible remnants of volcanism are concentrated in three main areas. West-central Utah hosts the Black Rock Desert Volcanic Field near Fillmore in Millard County, which is the location of the state’s youngest known lava flows.
Further south, the Markagunt Plateau volcanic field is situated near Zion National Park and Cedar Breaks National Monument. Volcanic activity here has been occurring for about five million years, with the youngest flows dating to approximately 1,000 years ago near Panguitch Lake. These fields are part of a broader volcanic belt extending down into Arizona.
The southwest corner of the state, particularly the Santa Clara and St. George area, is characterized by numerous basaltic cinder cones and lava flows. These features are easily visible, with some vents aligning with major fault lines.
Defining Utah’s Volcanic Features
The physical remnants found across the state vary widely depending on the age and composition of the magma that erupted. The younger, more fluid basaltic eruptions created widespread lava flows and numerous cinder cones. Cinder cones are steep, conical hills built from fragments of glassy, gas-filled lava called cinders or scoria.
Older, more silica-rich eruptions produced much larger, more explosive stratovolcanoes, though these features are heavily eroded today. Examples like Mount Belknap in the Tushar Mountains and Monroe Peak on the Sevier Plateau are remnants of these ancient volcanoes. These massive structures erupted between 40 and 25 million years ago and are now difficult to recognize as their original volcanic forms.
Visitors can also find specific features like lava tubes, which are natural conduits formed when flowing lava crusts over and the molten rock drains away beneath the surface. The Duck Creek Lava Tube on the Markagunt Plateau is one of the longest known lava tubes in the United States. Other landforms include shield volcanoes, which have very gentle slopes, and explosion craters called maars.
Current Activity Status and Seismic Context
Despite the abundance of volcanic features, Utah has not experienced a volcanic eruption in historical times. The youngest recorded eruption occurred at the Ice Springs vent within the Black Rock Desert field approximately 600 to 720 years ago. This makes the volcanic fields geologically young, but they are not currently active.
Most of the younger volcanic fields are classified as dormant, meaning they are capable of erupting again. The U.S. Geological Survey monitors areas like the Black Rock Desert, classifying them as moderate-threat volcanoes due to their young age and potential for future activity. While renewed activity is possible, it is likely thousands of years away, and scientists have seismometers in place to detect magma movement.
Volcanism in Utah is linked to the region’s high level of tectonic activity along the Intermountain Seismic Belt. The forces that cause the crust to stretch and break, leading to earthquakes, also create pathways for magma to rise. This ongoing tectonic movement contributes to the state’s geothermal resources, such as hot springs, which result from heat transferred from shallow magma bodies.
Geological Drivers of Utah Volcanism
The underlying cause of Utah’s younger volcanism is the ongoing extension of the continental crust in the Basin and Range Province. Beginning about 17 million years ago, the crust in the western United States began to stretch apart in an east-west direction. This pulling motion causes the crust to thin and fracture along numerous normal faults.
As the crust thins, the pressure on the underlying mantle decreases, a process known as decompression melting. This lowered pressure allows the solid mantle rock to melt, creating magma that rises through the crustal fractures to feed the basaltic volcanoes and cinder cones. This mechanism explains why younger volcanic fields, like the Black Rock Desert, are aligned with the eastern margin of the Basin and Range.
The older, explosive stratovolcanoes were driven by a different, earlier process related to subduction. Between 40 and 25 million years ago, the Farallon oceanic plate was sinking beneath the North American continental plate. This subduction produced a line of arc volcanism, similar to the modern Cascade Range, that stretched across western Utah.