Beth Pisano, age 13, of Utica, N.Y., for her question:
JUST WHAT IS LAVA?
Lava is the molten rock that comes out of volcanoes when they erupt. It comes from deep within the earth where the heat is great. The lava is a solution of silicate and is similar to the liquid that would result if granite or basalt were melted.
When lava cools quite rapidly, only a few crystals can form. The lava then hardens into a rock that contains large amounts of natural glass.
When lava first comes out of a volcano or from a crack in the earth, it is red hot and reaches temperatures from seven to 10 times hotter than boiling water.
Volcanoes containing lava are sometimes explosive. From time to time they blow out large amounts 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 contains 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 the glassy one called perlite, are heated in furnaces, where they expand into a frothy material used to manufacture lightweight concrete.
There are two kinds of lava: one that is viscous or sticky and moves slowly like thick molasses, and a second kind that is so fluid that it flows faster than a person can run. Both types form a rock crust.
At times the liquid lava inside the crust cracks the hardening surface into many rough blocks that drag and tumble along as the lava creeps down the side of a volcano.
Other times the lava breaks a hole through the rocky crust and flows through, leaving a huge lava cave or tunnel.
The islands of Hawaii are a chain of volcanoes built mostly of lava. The mountain belt of southern Mexico, with its hundreds of volcanoes, also has a great lava pile.
In Idaho, in an area called Craters of the Moon, a person can walk into many lava caves that were formed only a few thousand years ago. The surface is covered with many wrinkles.
Many parts of the earth consist of piled up sheets of lava. In the northwestern United States, the Columbia plateau is a great lava pile more than 5,000 feet thick in places.
Igneous rock is formed by the cooling of melted material called magma, which is lava. Magma is created as a result of great temperature and pressure deep in the earth.
Magma that cools quickly may form a glassy type of rock that includes obsidian. Magma that cools more slowly may form "extrusive" rock consisting of large crystals of such material as quartz, feldspar or pyroxene.
The temperature of extruded magma has been measured as high as 2,500 degrees Fahrenheit.