LaccolithThis mound shaped hill in Montana is the remains of a laccolith, a lens-shaped blob of magm
LaccolithThis mound shaped hill in Montana is the remains of a laccolith, a lens-shaped blob of magma that once intruded the crust. Laccoliths form when magma rises upwards in a dike without making it the whole way to the surface. If the rocks above the dike are too low in density, the magma will not be buoyant enough to reach the surface, and will instead settle at a level of neutral buoyancy. As more molten rock rises upwards, it can push the surrounding layers out of the way, bending the sedimentary layers above into a round shape. The magma blob is shaped into a lens as it bends the surrounding rocks.To expose this laccolith as a hill, the surrounding sediments have been almost completely eroded away. However, the igneous rock of the laccolith was more resistant against erosion and the general shape has been preserved.-JBBImage credit: http://bit.ly/1Np9mM0 -- source link
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