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 | |||||
|---|---|---|---|---|---|
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The three main types of volcanoes differ in shape, size, and make-up; the differences partly result from the different types of eruptions.
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| 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
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?
Highlighted Scientific Publications
Open File Report 166
A Re-Evaluation of the Volcanic History and Mineral Potential of the Central East Tintic Mounts, Utah
Report of Investigation 154
Mount St. Helens, a Report to Governor Scott M. Matheson
Special Study 61
Geologic Excursions in Volcanology: Eastern Snake River Plain (Idaho) and Southwestern Utah, Geological Society of America Guidebook. part III
Survey Notes
Ancient Volcanoes of the Central Wasatch Range
GeoSights
Volcanic Features in the Black Rock Desert, Millard County
GeoSights
Crystal Geyser, Grand County
Public Interest Articles
Volcano Articles: 29
