Teacher’s Corner: Dome Mountains
Geological Features and Processes in Utah
By Sandy Eldredge
Navajo Mountain in San Juan County is a dome mountain that was probably formed by a laccolith.
Geological features constitute anything from major landforms such as mountains or plateaus, to ripple marks or glacial striations on a rock. The geological processes, such as volcanic eruptions, earthquakes, erosion, and deposition are what create or change geological features.
Mountains are major geological features on the surface of the Earth. Depending on what geological processes created these landforms, mountains can be classified as different types: volcanic, dome, fold, and fault block. Utah has all four types.
Dome Mountains are formed from hot molten material (magma) rising from the Earth’s mantle into the crust that pushes overlying sedimentary rock layers upward to form a “dome” shape. Unlike a volcano, the magma typically does not reach the Earth’s surface. Instead, the magma cools underneath the surface and forms the core of the mountains.
Dome mountains in Utah include Navajo Mountain and the La Sal, Abajo, and Henry Mountains in the southeastern part of the state.
Activity (for 3rd grade)
Materials for pairs of students:
- tube of toothpaste
- one large index card
- dried grass
- Punch a small, pencil size hole in the index card.
- Cover the surface of the card with finely cut dried grass to represent rock layers and the surface of the earth.
- Have one student hold the index card while the other student places the tube of toothpaste under the hole and slowly squeezes until the grass is pushed up into a small dome over the squeezed toothpaste
(alternate method – take the cap off the tube of toothpaste, drill a hole in the cap, place the index card hole over the neck of the toothpaste tube, and place the cap back on so the card is fastened between the cap and the tube).
What does the toothpaste represent? Magma.
What could happen inside the earth that would create the same effect? Magma can squeeze and move like the toothpaste.
What does the grass represent? Rock layers and the surface of the Earth.
How is this landform different from a volcano? The magma does not erupt onto the surface of the earth.
Some of this information was taken from a 3rd-grade Utah Core teaching packet called Investigate Geological Processes that Shape Landforms – Earthquakes, Volcanoes, Erosion, Deposition.
Survey Notes, v. 32 no. 1, January 2000