The interior of the Earth is hot enough to melt rock, and that’s just what happens. Melted rock squeezes together into vast pools of magma beneath the ground. Since it’s less dense than the surrounding rock, it makes its way upward to the surface. If the magma reaches the surface you get a volcano; with the ash, and the lava and the explosions. But if the magma pushes up but doesn’t actually crack through the surface, you can get a dome mountain.
Dome mountains don’t usually get as high as folded mountains because the force of the magma underneath doesn’t push hard enough. Over a long period, the magma cools to become cold, hard rock. The result is a dome-shaped mountain.
Over long periods of time, erosion wipes away the outer layers of the mountain, exposing the dome-shaped cooled magma of harder rock.
An example of a dome-shaped mountain is Half Dome in the Sierra Nevada range in California. It’s made of granite, and was once a large blob of magma pushed up through the Earth. Granite is much harder than other rock, and so it doesn’t erode as easily as the rest of the mountain. The softer layers of sedimentary rock were washed away, leaving the hard granite dome.
Other dome mountains aren’t so easy to spot. You need satellite images to see the circular shape in the Earth’s surface.
We have written many articles about the Earth for Universe Today. Here’s an article about how satellites can measure the movement of the Earth after an earthquake.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.