Some kinds of lava are almost as runny as water, and other kinds are very thick. There are several types of volcanoes. Shield volcanoes have gentle slopes like a shield, because they are made of many layers of a kind of volcanic rock that flows easily when melted. This kind of rock is called basalt. When it flows out of a vent in the earth's surface it forms thin layers sloping away from the crater.
Some shield volcanoes get to be very large.
The volcanoes that make up the Hawaiian Islands are shield volcanoes. Kahoolawe, Hawaii Cinder cones are made of bits of a kind of volcanic rock called andesite. Sometimes there are bits of basalt too. These bits of rock are called cinders. They may be tiny, like ash, or larger like gravel.