Dome mountains form when large globs of magma float up from beneath the crust and push up surface rocks, creating a rounded swelling in the crust. Once the magma cools, it creates a large dome of harder rock under the surface, which erosion sometimes reveals.
Processes within the Earth melt rock, which gathers into large pools. This molten rock is lighter than the solid rock around it, so the pressure at those depths gradually forces it upward. Once it encounters sedimentary rocks near the surface, it begins to push it up ahead of itself. If the molten rock breaks through, it forms a volcano, but if not, it forms a dome mountain.
Dome mountains are generally smaller than mountains formed by folds in the crust, and have a different shape. Well-known dome mountains include Half Dome in California, which is a fully exposed granite dome formed by cooled magma. Despite the name, most of the dome actually remains, and it was originally formed as a narrow, wedge-shaped dome. The whole side is almost as steep as the cleaved one. While it is very visible, many dome mountains are not. Some dome mountains are only detected by satellite imaging, which shows a circular bulge in the ground.