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What is Lava? - Definition, Types & Temperature

Instructor: Sergey Segal

Sergey has a Masters in Biomedical Engineering and has taught science and mathematics courses at the University of Wisconsin-Madison.

Lava is a substance that has fascinated many people throughout the ages. Learn more about its different types, subsequently testing your knowledge with a quiz.

Lava Defined

You may have seen lava on TV or even traveled to see it in person. There have also been famous accounts of its destructive power since ancient times, including the Roman city of Pompeii, which was consumed by lava in 79 B.C.E. What is this mysterious substance? Lava is molten rock ejected by volcanoes in the form of a liquid. Once it emerges on the Earth's surface, it flows and gradually cools down, consuming objects along its path. Before starting to solidify, its temperature may range from roughly 700 to 1200 degrees Celsius.

Lava can be classified based on its chemical composition, which we shall now discuss.

Types of Lava Based On Chemical Composition

Felsic lava, also referred to as silicic lava, is rich in silica content. It can erupt at relatively low temperatures of around 700 degrees Celsius. The volcanic rocks that it forms include rhyolite and dacite, which contain substantial amounts of aluminium, calcium, potassium, silica, and sodium.

Andesitic lava is rich in iron and magnesium, with an intermediate silica content. It tends to erupt at higher temperatures than felsic lava.

Basaltic lava is also rich in iron and magnesium, but with a lower silica content than felsic and andesitic lavas. Its eruption temperature is usually greater than that of andesitic lava.

In addition to varying chemical composition, there are different types of lava based on flow. Let's proceed to discuss them.

Types Of Lava Based On Flow

A'a lava, pronounced ah-ah, is a slow-flowing lava that is characterized by its sharp and spiny surface after cooling down. Its eruption temperature is often between 1000 and 1100 degrees Celsius.

Pahoehoe lava, pronounced pa-ho-ho, is lava that flows more readily than a'a and is also characterized by a smoother surface after hardening. Its typical eruption temperature is between 1100 and 1200 degrees Celsius.

A a lava (still hot, spiky appearance) on top of pahoehoe lava (cooling, smoother appearance)
Aa and pahoehoe lava

Pillow lava is formed during underwater eruptions and characterized by the large pillow-like structures that it forms after hardening.

Pillow lava underwater near the Galapagos Islands
Pillow lava

Misconceptions About Lava

Certain movies may give the impression that a person dropped into lava would simply sink into it. In fact, this is very unlikely to happen.

Lava is about three times more dense than water. The average density of humans is slightly greater than that of water, but we can still stay afloat with proper breathing and body movements. If we were to increase the density of water by adding a lot of salt into it, it would be much easier for us to stay afloat. One real-world example of this is the Dead Sea in Israel, where people float naturally without exerting any effort.

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