GEOLOGIC HAZARDS

Volcanic Hazards

Volcanic hazards are typically those associated with active volcanoes and include volcanic eruptions of lava, ash, steam, and pyroclastics (rock material ejected during an explosive eruption); lava and pyroclastic flows; lahars (volcanic debris flows); glacier outburst floods; rock, debris, and ice avalanches; lateral blasts; tsunamis; and dome growth and collapse. While Utah does not have any active volcanoes, several basalt flows in the West Desert area are only several hundred years old. In addition, eruptions of volcanoes in the western United States, including the Yellowstone caldera, could result in volcanic ash clouds and significant deposition in Utah.

Lava Flow

A flow of molten rock on the Earth’s surface flowing out of a volcano.

Volcanic Eruption

An eruption of molten rock from within the Earth and may be accompanied by lava, ash, steam, and pyroclastics. Can be violently explosive, such as the 1980 Mount St. Helens eruption, relatively benign as some Hawaiian volcanoes with slow moving lava flows, or somewhere in between.

Three Main Types of Volcanoes
The three main types of volcanoes differ in shape, size, and make-up; the differences partly result from the different types of eruptions.
Volcano Type Volcano Shape Volcano Size Volcano Materials Eruption Type Utah Example
Cinder Cone

Steep conical hill with straight sides
Small
less than 300m high
cinders
Explosive
Diamond Cinder Cone,
Washington County
Shield Volcano

Very gentle slopes; convex upward (shaped like a warrior’s shield)
Large
over 10s of kms across
fluid lava flows (basalt)
Quiet
Cedar Hill,
Box Elder County
Stratovolcano

Gentle lower slopes, but steep upper slopes; concave upward
Large
1-10 km in diameter
numerous layers of lava and pyroclastics
Explosive
Mount Belknap,
Tushar Mountains, and
Monroe Peak, Sevier Plateau

Utah’s Volcanic Hazards

GeoSights - Castle Rock Campground

The two white layers within the Sevier River Formation, near the bottom and the top, are airfall volcanic ash deposits.

Stratovolcanoes erupted in western Utah between about 40 and 25 million years ago. At this time, Utah was closer to a continental-oceanic plate boundary where an oceanic plate (Farallon) was subducting underneath the North American continental plate. Stratovolcanoes are found at these types of plate boundaries. Today’s active stratovolcanoes include those in the Cascade Range in Washington, Oregon, and California where an oceanic plate (Juan de Fuca) is subducting underneath the North American continental plate.

Two examples of Utah’s stratovolcanoes are Mount Belknap in the Tushar Mountains and Monroe Peak on the Sevier Plateau. Because these volcanoes are old and have been extensively eroded, it is difficult to distinguish the original volcano shapes.

Shield volcanoes and cinder cones started to erupt about 12 million years ago after plate motions and resulting crustal forces changed. Compressional forces had eased, and the crust started to stretch between the Wasatch Range in Utah and the Sierra Nevadas in California. This extension created splintered zones in the Earth’s crust where magma rose to the surface creating shield volcanoes and cinder cones.

The most recent volcanic activity in Utah occurred about 600 years ago in the Black Rock Desert (Millard County).

Related Information:
Geologic Hazards and Insurance – Are You Covered?

Quaternary Volcanic Rocks of Utah

Volcano Publications and Maps

Open File Report 166

A Re-Evaluation of the Volcanic History and Mineral Potential of the Central East Tintic Mounts, Utah

Special Study 61

Geologic Excursions in Volcanology: Eastern Snake River Plain (Idaho) and Southwestern Utah, Geological Society of America Guidebook. part III

GeoSights

Volcanic Features in the Black Rock Desert, Millard County

View All Hazard Publications


Volcano Articles

Search:
TitleTopicPublished
GeoSights: Pine Park and the Ancient Supervolcanoes of Southwestern Utah Volcanoes 2019
Ancient Volcanoes of the Central Wasatch Range Volcanoes 2018
Crystal Geyser, Grand County Water 2018
Alhambra Rock, San Juan County, Utah Volcanoes 2015
Volcanic Features in the Black Rock Desert, Millard County Volcanoes 2014
Roosevelt Hot Springs Geothermal Area, Beaver County Water 2014
The Honeycombs, Juab County Volcanoes 2012
Fremont Indian State Park, Sevier County Volcanoes 2010
G.K. Gilbert Geologic View Park, Salt Lake County Landforms 2008
Spectacular Towering Cliffs at Castle Rock Campground, Sevier County Volcanoes 2006
Granite Peak Mountain Mountains 2006
Devils Playground, Box Elder County Landforms 2006
New Age for the Santa Clara Basalt Flow Volcanoes 2006
“Bubblin’ Crude” at Rozel Point, Box Elder County Great Salt Lake 2005
The Midway hot pots – natural hot springs, Wasatch County Water 2004
Big Rock Candy Mountain – a colorful reminder of Utah’s volcanic past Volcanoes 2003
Inverted Topography in the St. George Area of Washington County Volcanoes 2002
Pahvant Butte in the Black Rock Desert Volcanoes 2002
Paul Bunyans Woodpile, Juab County, Utah Volcanoes 2001
Utah’s Sevier Thrust System Geologic History 2000
How was Utah’s topography formed? (major physiographic provinces) Landforms 2000
Volcanoes (Activity for 3rd grade) Volcanoes 1999
Obsidian in the Black Rock Desert, Millard County Rocks and Minerals 1995
The Earth’s Surface, the only Constant is Change. Landforms 1994
Generalized Geology of Snow Canyon State Park Washington County, Utah Maps 1992
The geology of Snow Canyon State Park, Washington County, Utah (pdf) Volcanoes 1992
Landforms Presentation (PowerPoint) Landforms

Volcano Articles: 27