Lava is a very interesting substance, but most people don't realize that it can come in many very interesting varieties, differing in chemistry and in temperature.

Learning more about the science of lava doesn't necessarily make it any less dangerous, but it reveals that the subject truly can be rather fascinating.

This hot, molten rock which originates within the mantle (the very thick “middle” section between the thin crust and the core) of the planet and is pushed toward the surface by way of plate tectonics usually exists in its liquid form somewhere between 650 and 1600 degrees Celsius (that is, between 1202 and 2912 degrees Fahrenheit, which by any measurement is very, very hot).

The actual temperature of a given sample depends on several variables, such as the geological makeup of the lava and the type of eruption from which it... well... erupts.

(A Brief aside: The terms lava and magma are not to be used interchangeably. Magma only occurs beneath the surface of the Earth. Once it erupts from a volcano, it is called lava. If someone calls the glowing liquid hurtling from an active volcano magma, their mistake should be pointed out to them)

Felsic and Intermediate

The coolest (that is, least frightening) types of lava are known as Felsic and Intermediate lavas, which usually occur in Strombolian eruptions (named for the Italian volcano Stromboli).

Strombolian eruptions are usually long lasting eruptions, known mostly for oozing highly viscous (that is, thick) lava flows, which harden and cool quickly, so as not to cause too much damage, and the occasional burst of ash and lava bombs (Mauna Loa in Hawaii, the largest active volcano on the planet falls under this category).

Felsic and Intermediate lavas exist at temperatures between 650 and 950 degrees Celsius, with the Intermediate being on the upper end of that, which flows much quicker and hotter than the Felsic, due to the slight chemical differences betwen the two types.

Mafic Lava

The next hottest type of lava, Mafic lava, exists in its liquid state at temperatures of more than 950 degrees Celsius. At this temperature, and because of high levels of basalt in its composition, Mafic lava is much less viscous than the Felsic and Intermiate types, while remaining considerably thicker than water. As a result, much of the Felsic lava on the Earth exists in what are known as Shield Volcanos, which are relatively low-lying faults in the Earth, as the lava is too liquid and flows too freely to really form any substantial volcanic height. As far as volcanoes which still exist today go, Mafic lava is pretty much as hot as it gets.

Ultramafic Lava

Of course, historically, another type of lava, Ultramafic (a lava rich in magnesium content) has been known to exist in the past history of Earth, and in temperatures reaching a scalding 1600 degrees Celsius (or so scientists have estimated). Today such flows are very much non-existent, supposedly due to the cooling of the Earth's mantle sometime during the past several thousand years; enough so that it has become impossible for lava with high contents of magnesium to form.

Lava and Culture

The existence of lava, and the fears that people naturally possess about flows of hot, liquid rock, have served authors and filmmakers very well over the years. Countless films have been made which revolve around volcanic explosions or which use lava as, essentially, a “character” (usually the villain).

More positively, however, lava has proven to be a remarkable tourist attraction in places such as Hawaii (which, consequently, would not exist in the first place if it weren’t for the lava built up on the sea floor), where the money coming in from tourists almost makes up for the property which has been damaged by runaway lava flows.

So, love it or hate it, lava has become a part of pop-culture (just as it surely has throughout history). It is truly a very diverse substance – love, hate, fascination, interest, enthusiasm, fear, disdain – these are all feelings that one might feel if confronted with a flow of lava.

References:

“Questions about Lava.” Volcano World.

U.S. Geological Survey.