Composite volcanoes are built by layers of ash and cinders sandwiched between layers of hardened lava. The shape on one side of the cone formed by composite volcano usually looks the same as the shape on the opposite side.

: Mt. Fuji in Japan Example: Mt. Fuji in Japan

Mt. Rainier

Cinder-cone volcanoes are built by thick lava that is thrown high into the air and falls as chunks or cinders. These mountains form as a cone shape with a narrow base and steep sides.

Shield volcanoes are built by thinner fluid lava that spreads over a large area. These mountains have a broad base and gently sloping sides.

Shield volcano on Mars; Taken from space The Mauna Loa volcano in Hawaii— the largest volcano on Earth—has the broad expanse characteristic of shield volcanoes. It spreads across half the island of Hawaii.

The Hawaiian Islands are an island chain, or a line of volcanic mountains. They rest on a slowly moving tectonic plate. As it moves, the plate passes over a stationary pool of magma called a hot spot. Over millions of years, lava erupting from the hot spot formed a mountain. Eventually the mountain grew taller than the ocean’s surface and became a volcanic island. l/101/lectures/media/Lecture04/HotSpot.swf

In areas where an ocean-floor plate is pushed under another ocean-floor plate an island arc forms. As the plate is pushed down, it melts. Magma forms, rises upward, and erupts through the ocean floor. The eruptions form a series of volcanic island along the plate boundary. The Aleutian Islands in Alaska form an island arc.