LR’s Intrusion Mountain Book

Intrusion Magma Mountains


Intrusion mountains are formed when magma slowly moves into cracks and crevices under the Earth. The magma pushes the ground above it upward. This magma cools into rock and becomes part of the mountain. The magma turns into crystals. They kinds of crystals can vary because there are different gasses that are trapped in the cooling rock. This can change the magma’s chemical structure.

The Batholith it is a large body of magma and is the source of the magma for the intrusion mountain. A stock is a miniature batholith. A dike is a narrow tube. Most are vertical and usually connected to a feeder pipe. A sill is cooled magma between two layers of rock. Laccoliths are a larger sills but move the rock above and form the mountains. Pegmatites are a large deposit of crystals. Sometimes intrusion mountain suffer from erosion and show a line of hardened magma that is going straight though a layer of rock.

The 1,167 foot tall Devil’s Tower in Wyoming is an intrusion magma mountain. It was once made of molten igneous rock. After the hot magma cooled inside Devil’s mountain, it shrank in volume and made the small cracks along it’s distinctive vertical lines. The tower was once hidden in surrounding rock but as the rock eroded, it exposed this beautiful tower. Also in 1909, Devil’s tower was the first US National Monument. Here are some other well known intrusion mountains: the Navajo, La Sal, and Abajo.

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