Iceland and Hawaii are great modern examples of the shield volcanoes which have periodically erupted in Utah over the last 15 million years.

Utah’s Three Types of Volcanoes

Perhaps because it is covered in detail in Grade School and Middle School curriculum, one of the most asked geologic questions I hear from youth has to do with differentiating between the three types of volcanoes.

 

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, Paiute County

In the State of Utah there are many examples of the three main types of volcanoes. The following is a brief introduction to Utah’s volcanoes; only several of numerous volcanoes are mentioned.

Stratovolcanoes

Stratovolcanoes erupted in western Utah between about 40 to 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 most recent stratovolcanoes are Mount Belknap in the Tushar Mountains and Monroe Peak on the Sevier Plateau. These stratovolcanoes exists on the tail end of a line of explosive volcanism that extended from near Richfield, southwestward to the Nevada border. Like ancient Yellowstone National Park, many of these volcanoes were among the largest volcanoes to ever erupt in North America.

Because these volcanoes are old and have been extensively eroded, it is difficult to distinguish the original volcano shapes.

The Mount Saint Helens eruption in 1980, is one of the best known examples of a strato-volcano in the U.S. Utah has a long history of similar type volcanoes.

The Mount Saint Helens eruption in 1980, is one of the best known examples of a strato-volcano in the U.S. Utah has a long history of similar type volcanoes.

 

Shield Volcanoes and Cinder Cones

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 Nevada Range in California. This extension created splintered zones in the Earth’s crust where magma rose to the surface creating shield volcanoes and cinder cones. These types of volcanoes are far less explosive than stratovolcanoes and tend to create smaller deposits.  Because the lava from shield volcanoes comes from a deeper source and contains more iron and less silica than stratovolcanoes, they tend to leave darker and thinner magma deposits.

The most recent volcanic activity in Utah occurred about 600 years ago in the Black Rock Desert (Millard County). The only place in the United States were these types of volcanoes are currently active is Hawaii.

 

Iceland and Hawaii are great modern examples of the shield volcanoes which have periodically erupted in Utah over the last 15 million years.

Iceland and Hawaii are great modern examples of the shield volcanoes which have periodically erupted in Utah over the last 15 million years.

 

Science Language

Volcano – a vent (opening) at the Earth’s crust through which magma (molten rock) and associated gases erupt.
Magma – molten rock beneath the surface of the Earth.
Lava – magma that has reached the surface.
Cinders – lava fragments about 1 centimeter in diameter.
Pyroclastics (“fire fragments”) – ash, cinders, angular blocks, and rounded bombs (block and bomb fragments can be over 1 meter in diameter).
Explosive eruptions – eject lava and pyroclastics.
Quiet eruptions – fluid lava flows out of a volcano’s vent.

Utah Volcano Map

Use this map to zoom in and explore Utah’s various volcanic deposits. Each element can be clicked for more details.  The top arrow opens a Legend which explains the meaning of the maps various features.

“The Pit of Despair” in Poe Canyon, also known as "smiling cricket,” is a difficult to traverse keeper pothole in the Waterpocket Fold south of Capitol Reef National Park.

Keeper Potholes & How They Are Formed

Keeper potholes are found in slot canyons. In the recent decades “slot” canyoneering has become a major sport, and very few areas of the world have nearly the number or diversity of slot canyons as southern Utah. People come from all over the world to descend slot canyons of varying difficulty in places such as Zion National Park, Grand Staircase–Escalante National Monument, Capitol Reef National Park, the San Rafael Swell, and Glen Canyon National Recreation Area.

Cascade Falls just below the cave opening, forming the headwaters of the North Fork of the Virgin River.

CASCADE FALLS, KANE COUNTY, UTAH

Nestled in the northwestern corner of Kane County is a geologically unique feature that receives relatively few visitors. Although most people in Utah have seen caves and waterfalls, it is peculiar for a waterfall to emerge from a cave system. Cascade Falls does just that, as an underground river emerges from a deep cave system and cascades down a steep cliff face.