Volcanoes are one of the most fascinating phenomena that grace Earth’s surface; they are the windows into the nether region, a brief glimpse into the underlying processes governing our world. A glimpse offered into the fiery subterranean processes that has inspired awe and fear throughout the span of the human race. Hawaiians worshiped volcano gods; Pliny the Younger reverently documented the destruction of Pompeii. Humankind has been diligently documenting and studying volcanoes for millennia in an attempts to understand volcanoes.
The cliche imagery of volcanoes involve lava: majestic, cardinal red geysers spurting a viscous glowing fluid into a river of oozing, crusting, newly forming rock. The main component determining the heat produced by a volcano is the composition of the lava being erupted. Lava contained within the Earth’s crust is known as magma; rock that has been liquefied due to the intense pressure and heat within the mantle. Just as different solids such as ice or chocolate have different melting points, so do different rock types.
Each different type of lava flow has its own unique mineral composition, viscosity (degree of fluidity & thickness), and normal temperature range. The main determination of lava classes is the amount of silica content in the lava. Silicon dioxide, or silica, is a mineral most commonly known as quartz. Quartz has a relatively low melting temperature, so magma with a higher silica content can form at much cooler temperatures relative to magma that contains denser elements such as iron or magnesium.
Felsic – 1202 – 1472 degrees Fahrenheit
The term “felsic” refers to the high content of quartz laden feldspar minerals in the lava. There are two types of felsic lava: rhyolite and dacite. These low temperature lava flows have a high viscosity, which clogs the inner workings of volcanoes trapping and compounding gases. In turn, felsic magma is associated with the volatile stratovolcano characterized by Plinian eruptions (mushroom cloud) followed by a deadly pyroclastic flow of hot ash, gas, and lava.
Intermediate – 1472 – 1832 degrees Fahrenheit
Intermediate lava has a lower silica content than felsic lava, but not as high magnesium or iron levels as found in mafic lava. The lava flow has a medium viscosity as well, and once cooled, the resulting rock is known as Andesite. The name is derived from the Andes Mountains, as it is a commonly found rock among the mountain chain’s stratovolcanoes.
Mafic – 1832 – 2192 degrees Fahrenheit
“Mafic” is a term used to describe the densest lava flows. The word derives from a composite of the chemical symbols for Magnesium (Ma) and Iron (Fe). This magma has a low viscosity, which allows for gases to escape the volcano, and for the lava flows to erupt calmly and predictably. Mafic lava forms basalt and is associated with the lava flows seen on the Hawaiian Islands and similar shield volcanoes.
The type of lava emitted in an eruption can reveal intimate details of the inner workings of not only the volcano, but also the underlying geological processes governing Earth’s surface. As geologists have classified different lava flows and volcanic eruptions over the centuries, the mechanics of the Earth has become clearer. The theory of plate tectonics, Pangea, and the geothermal energy industry all owe their start to the primal urge of ancient scientists to study and revere Nature’s most fearsome phenomena.
