by Sandra Eldredge

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

Selected volcanoes/volcanic areas in Utah mentioned in text.

Utah Volcanoes

Utah contains 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.

Stratovolcano - Mount Rainer and Mt. St. Helens (left background) rise above the surrounding landscape in Washington. These are a few of the active volcanoes in the Cascade Range.  Mt. St. Helens boasts the most recent eruption (1980).
Photo credit: Marli Miller, Earth Science World Image Bank.

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

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.

Shield Volcano - Cedar Hill, located north of Great Salt Lake, bears a resemblance to several Hawaiian shield volcanoes.  The volcano is approximately 1,150,000 years old.	Cinder Cone - Diamond Cinder Cone is one of several cinder cones near St. George in Washington County, Utah. The cone is approximately 27,000 years old.

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