Three Main Types of Volcanoes and Utah Volcanoes

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
less than 300m high
Diamond Cinder Cone,
Washington County
Shield Volcano

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

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

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 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 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.

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

*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.