Lava is molten rock that pours out of volcanoes or from cracks in the earth. It comes from deep in the earth where the heat is great. There, lava is called magma. When lava first comes to the surface it is red-hot, reaching temperatures from 7 to 12 times hotter than boiling water.
Loading the player...Lava
Properties of lava.
Lava is a solution of silicate minerals (see Silica). It is similar to the hot liquid that would result if granite or basalt were melted. When lava cools rapidly, only a few crystals can form. The lava hardens into a rock that contains large amounts of natural glass.
The volcanoes or earth fissures (cracks) that contain the lava are sometimes explosive. From time to time, they blow out quantities of dust and rock fragments that form layers between lava flows. Some types of lava contain large amounts of dissolved gases. As the gases expand, they are trapped in the lava and form many bubbles. Pumice is a type of lava that has many bubbles.
Lands that were once covered with lava often become quite fertile after weathering has broken the lava into fine soil. Some lavas, such as a glassy lava called perlite, are heated in furnaces. They expand into a frothy material used to manufacture lightweight concrete.
Kinds of lava.
The two most common forms of lava are called aa and pahoehoe. Aa is viscous (sticky) and moves slowly. Pahoehoe is so fluid that when it first erupts it flows down the side of a volcano faster than a person can run. Both kinds cool at the surface first, forming a solid crust over a liquid core.
Sometimes the liquid lava inside the crust cracks the hardened lava surface into many rough blocks that drag and tumble along as the lava creeps down the side of the volcano. At other times, the lava breaks a hole through the rocky crust and flows through, leaving a huge lava cave or tunnel. In Idaho, in the area of the Craters of the Moon, a person can walk into many lava caves that were formed only a few thousand years ago. The surface of such lava is covered with many wrinkles.
Location of lava beds.
Many regions of the earth consist of piled-up sheets of lava. In the Northwestern United States, the Columbia lava plateau is made up of a great lava pile more than 5,000 feet (1,500 meters) thick in places. The islands of Hawaii are a chain of volcanoes built mostly of lava. The mountain belt of southern Mexico also has a great lava pile. Loading the player...
Volcano
See also Igneous rock; Pumice; Rock (Igneous rock); Volcano.
