Valerie Helman, age 13, of Monroe, La., for her question:
WHAT IS IN LAVA?
Lava is molten rock that comes out of volcanoes or some cracks in the earth. Lava is a solution of silicate minerals, similar to the hot liquid that would result if granite or basalt were melted.
There are two kinds of lava. One is viscous or sticky and it moves slowly like thick molasses. The other kind is so fluid that when it first erupts, it flows down the side of a volcano faster than a man can run. Both the viscous and the fluid types form crusts of rock as the lava cools.
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 a 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.
Some volcanoes or "earth fissures," as cracks are called, are explosive. From time to time they blow out large quantities of dust and rock fragments that form layers between lava flows.
Some types of lava contain large amounts of dissolved gas. As the gases expand, they are trapped in the lava and form many bubbles. Pumice is a type of lava that contains 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 lava called perlite, are heated in furnaces. They expand into a frothy material used to manufacture light weight concrete.
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 thick in places.
The Hawaiian islands are a chain of volcanoes built mostly of lava. The mountain belt of Mexico, with its hundreds of volcanoes, also has a great lava pile.
When lava first comes to the surface, it is red hot and has a temperature from seven to 10 times hotter than boiling water. It comes from deep in the earth where the heat is great.
When lava cools quite rapidly, only a few crystals can form. The lava hardens into a rock that contains large amounts of natural glass.
The melted rock material deep within the earth is called "magma." Magma is under great pressure and is extremely hot with underground temperatures ranging from 1380 degrees Fahrenheit to 2000 degrees.
Lava is the name for magma that reaches the surface of the earth, coming up under pressure through a fissure or crack in the earth's surface or in a volcanic eruption.