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What Is Lava?


3–5, 6–8, 9–12

Expert volcanologist Dr. Stanley Williams answered the following questions for Scholastic Network.


What is lava made of?
Lava is mostly made of two elements — Si (the symbol for silicon) and O (the symbol for oxygen). Together, they make a very strong bond and then get together with other elements, like Fe (iron), Mg (magnesium), K (potassium), Ca (calcium), and more. They make crystals of minerals like olivine, which are beautiful yellow-green crystals that people call peridot. When you see a lava rock, it is usually kind of dark gray and there are no crystals easy to see. The volcano erupted it before the elements could become crystals.

How hot is lava?
Lava is extremely hot. Lava can reach temperatures of about 1,250° Celsius. The lava of the Hawaiian volcanoes reach these temperatures. Normal lava temperatures reach 750° Celsius. That is still much hotter than your oven is capable of reaching.

Why does the lava get so hot?
It is very difficult to melt rocks, because they are so strong. The temperature of lava flow is usually about 700° to 1,250° Celsius, which is 2,000° Fahrenheit. Deep inside the earth, usually at about 150 kilometers, the temperature is hot enough that some small part of the rocks begins to melt. Once that happens, the magma (molten rock) will rise toward the surface (it floats). Deeper inside the earth, the temperatures are so hot that the entire outer core is molten. The inner core is made of different chemicals, so they are not molten.

How do you measure heat in lava?
We measure the temperature of lava by putting a probe of metal into it. Our thermocouple tells us the temperature, in degrees Celsius.

How fast does lava move?
Lava is not fast; you can outrun it. It is pretty common that people are most afraid of lava when it is really in the last and slowest steps of an eruption, after the gases have been given off by the volcano and the magma is cooling off. The hot Hawaiian lava moves at about a few meters per minute. The cool lavas move only a few meters in a day.

How does lava become white?
No lava is actually white. They might look white because they are so hot that they give off a white color, but that is almost impossible for us to see.

Are there lava flows under the earth?
Lava does not flow inside the earth. Magma is moving around, as it rises beneath volcanoes. That happens because it is so light.

If the oxygen is cut off from the lava, will it immediately turn to solid rock?
Oxygen is an important element because it, along with silica, are the most important elements of the minerals. However, it is not important for making a lava harden. Maybe, what you are thinking about is the air that can circulate around in a lava and help it to cool off and become solid.

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Susan Cheyney

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