Pushing Up Earth's Surface
Earth's features can be pushed up from below as well as built up from above. Not far below Earth's surface, it is very hot. In some places, it is hot enough it melt rock! Melted rock below Earth's surface is called magma. Magma is formed in a layer of Earth just below the crust. Pressure below the surface can cause magma to push up on Earth's crust. This pushing forms round, dome-shaped mountains.
In some places, magma can work its way up through the crust and flow out on Earth's surface. Magma at Earth's surface is called lava. As lava flows, it cools and hardens into rock.
Earth's features can be pushed up from below as well as built up from above. Not far below Earth's surface, it is very hot. In some places, it is hot enough it melt rock! Melted rock below Earth's surface is called magma. Magma is formed in a layer of Earth just below the crust. Pressure below the surface can cause magma to push up on Earth's crust. This pushing forms round, dome-shaped mountains.
In some places, magma can work its way up through the crust and flow out on Earth's surface. Magma at Earth's surface is called lava. As lava flows, it cools and hardens into rock.
In other places, enough lava will build up to form a huge deposit with gently sloping sides. Such deposits are called shield cones. Shield cones often form on the ocean floor. If they rise above the water, they form islands.
The Hawaiian Islands are the tops of several giant shield cones. The base of Mauna Loa, the largest of the cones, is about 4500 m below the surface of the Pacific Ocean. Its peak rises over 4100 m above the ocean's surface.
The Hawaiian Islands are the tops of several giant shield cones. The base of Mauna Loa, the largest of the cones, is about 4500 m below the surface of the Pacific Ocean. Its peak rises over 4100 m above the ocean's surface.
A different constructive force is the movement of huge pieces of Earth's crust. These moving pieces of crust can crash into each other and cause the crust to fold. When this happens, the crust rises to form high mountains. The Himalaya Mountains began forming in this way about 65 million years ago.
Other features of Earth are made from the remains of living things. For example, the chalk cliffs in Dover, England, are made up of shells of tiny sea animals. These shells were deposited on the sea floor millions of years ago. When forces below the crust raised the sea floor, the chalk deposits became chalk cliffs.
Coral reefs are another type of Earth feature made from the remains of living things. In shallow tropical waters, tiny animals called corals gather in colonies. As corals die, their skeletons build up into a bumpy ridge called a reef. In some Pacific Ocean waters, reefs are build around islands. Sometimes an island will sink, but the coral continues to grow. The reef forms a ring shaped island called an atoll.