David Harvie, age 11, of Allentown, Penn., for his question:

WHAT IS LAVA?

Lava is molten rock that comes out of some volcanoes or from cracks in the earth. It comes from deep within the earth where the heat is great.

When lava first comes to the surface, it is red hot and reaches a temperature that is from seven to 10 times hotter than boiling water.

Lava is actually a solution of silicate materials. It is similar to the hot liquid that would result if granite or basalt were melted.

When lava cools quite rapidly, only a few crystals can form. The lava hardens into a rock that contains large amounts of natural glass.

There are two kinds of lava. One is viscous or sticky, and it moves slowly like thick molasses. The other is so fluid that, when it first erupts, it flows down the side of a volcano very fast. Both types form a crust of rock.