Lava is molten rock that spews from an erupting volcano. It is extremely hot, reaching temperatures as high as 1,300 to 2,000 degrees Fahrenheit (704 to 1093 degrees Celsius). In a volcanic eruption, lava is in liquid form. When it solidifies, it forms igneous rock. However, it can take quite a long time to cool, traveling great distances before becomes solid.
Molten rock is not always called lava. Before a volcano erupts and molten rock is still underground, it is called magma. Besides being a little cooler, molten rock is not dramatically different once it's above ground. The distinction between magma and lava is basically made to make geological occurrences easier to understand and explain.
Eruptions of lava are no accident. Underground, magma contains gas bubbles. These gas bubbles are usually kept from expanding by pressure from layers of overlying rocks. Sometimes, however, gas pressure can increase enough that the bubbles begin to expand and rise, carry magma with them. When the pressure increases to high enough levels, the volcano can fracture, allowing magma to escape, enabling the bubbles to expand rapidly, and causing an eruption of lava.
Lava can be propelled to amazing heights; a lava fountain can shoot up to 2,000 feet (609.6 meters) above a volcano. As with the eruption itself, it is gas that sets such explosive propulsions in motion. As gas bubbles expand and burst in magma, it climbs toward the surface and is forced up and out of the volcano. Lava flows at various speeds, ranging from very slow to relatively fast. One of the fastest measured flows reached about 37 miles (59.5 kilometers) per hour.
Many individuals are unaware that lava isn’t always red. It can be bright orange, bright red, dark red, or brownish red, depending on its temperature. At its hottest, above about 1832 degrees Fahrenheit (1,000 degrees Celsius), it is bright orange, while it is dark red at temperatures between 1472 and 1,832 degrees Fahrenheit (800-1000 degrees Celsius). Lava is dark red at temperatures between 1202and 1472 degrees Fahrenheit (650-800 degrees Celsius), and brownish red at temperatures ranging from 932 to 1202 degrees Fahrenheit(500 to 650 degrees Celsius). In its solid form, lava is black.
There are a few different types of lava. Each is classified by its silica content. The types of lava are basalt, andesite, dacite, and rhyolite. Basalt has the lowest silica content, while rhyolite has the highest. The silica content affects how lavas flow. For example, basaltic lavas are given to widespread, thin flows; rhyolite is stiffer and flows at a slower pace.