Volcanoes are built by successive eruptions over many decades, centuries, or hundreds of years. Volcanoes come in different sizes and shapes.


The in its entirety size that a volcano is figured out by the full volume that lava that has actually erupted.


The shape of a volcano is largely established by the type of lava that has erupted, and also importantly, that viscosity. Viscosity is a fluid"s resistance to flow.

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Water, because that example, is a low viscosity fluid. It is thin and also runny. Cold syrup, on the various other hand, has a higher viscosity. That is thick and also goopy. But when syrup is heated, that is viscosity go down. Hot syrup becomes thinner, runnier, much more like water.

Temperature, composition, and also volatile (gas) content largely recognize the viscosity of lava.

Temperature: The hot the lava, the lower the viscosity (the diluent it is). The cooler the lava, the higher the viscosity (the thicker that is).

Composition: he much more felsic the lava (the an ext silica in the lava), the higher the viscosity since silica develops chains in the cooling lava even prior to it crystallizes. The much more mafic the lava (the less silica in it), the lower the viscosity. It turns out the mafic lava is high temperature lava due to the fact that high temperature are compelled to melt mafic mineral in the first place. Felsic lavas space low temperature lavas because lower temperature are required to save felsic mineral molten (and if it was hotter it would have actually incorporated much more iron and magnesium in comparison to silica).

Volatile content describes gases dissolved in the lava, favor carbon dioxide in soft drinks. Lavas may contain as much as 6% or much more of their mass as gases. The two most abundant gases in lava room water vapor and carbon dioxide. Over there is commonly additionally nitrogen, sulfur dioxide, and little amounts that chlorine, hydrogen, argon, and a few other gases. As soon as lava approaches the surface, the press on the is significantly reduced and also the dissolved gases come out of solution; they form bubbles and rise. The to escape of gases may produces tremendous force in a volcano, creating explosive eruptions. In general, the more felsic the magma the higher the volatile content. For this reason mafic/basaltic volcanoes are relatively quiescent, intermediate/andesitic volcanic eruptions are moderately explosive, and felsic/rhyolitic volcanoes may be very explosive.

So, mafic lavas are hot , low in silica and volatiles, and also have reasonably low viscosity. They flow conveniently outward indigenous the vent (where that comes out of the ground), and may travel an excellent distances before totally solidifying.

Felsic lavas are not together hot, high in silica and also volatiles, and have a high viscosity. They room thick and also gooey and resist flowing. Your high volatile content makes them potentially extremely explosive.

Shield Volcanoes

Because mafic lava is low viscosity, as soon as it erupts from a volcano it operation downslope away from the vent, gradually cooling and also crystallizing. Since of the relative ease the flow, basaltic volcanoes space broad, v gentle slopes. Lock don"t have the stereotypical steep volcanic cone shape. Rather, they room shaped much more like a shield set on the ground.

Even though your slopes room gentle (typically 6° - 12°) they might be rather large. The largest mountain top top the planet is the island that Hawaii, i m sorry rises up 30,000 ft indigenous the seafloor. In comparison, the peak of Mt Everest is 29,035 ft above sea level, however the basic of Everest is well over sea level. Hawaii has actually grown come its good size by regular eruptions the basaltic lava for about 700,000 years. Many shield volcanoes are lot smaller. In fact, the island of Hawaii itself is written of numerous volcanoes, not one, though every is itself an extremely large.


Basaltic lava flows on Hawaii and elsewhere develop may have two kinds of surface. One kind has a smooth surface with ridges the look choose coiled ropes. This form of volcanic flow is called by the Hawaiian name pahoehoe. Special lava flows may remain molten in the interior and also continue come move even while the surface ar solidifies. Yet continued activity breaks up the surface into jagged rock fragments. These broken, jagged volcanic operation are dubbed aa.

Flood Basalts

Sometimes basaltic lava erupts from a series of fissures, or crack in the Earth and spreads extensively over the landscape, fairly than erupting from a singe volcanic vent. These type of eruptions produce flood basalts.

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Cinder Cones


Sometimes, in the late stage of basaltic volcanic activity, small cinder cones become active. As soon as its it is provided of magma from deep in the planet slows or stops, the magma chamber beneath a volcano will certainly cool and begin crystallizing. The first-formed minerals will be high-temperature, mafic minerals choose olivine which room rich in iron and magnesium and poor in silica. The result is the the continuing to be magma becomes depleted in iron and magnesium and enriched in silica. Consequently, the viscosity rises in the continuing to be magma and it walk not flow out of the ground together easily. Rather, it builds up enough back-pressure to eject a spray the lava right into the air. The lava droplets cool and also crystallize swiftly (or at the very least the surface of big blobs the lava crystallizes rapidly) and also then they loss as volcano cinders, or pyroclasts, on the flanks of the volcano and also tumble under its side. This procedure forms small volcanic cones v slopes in ~ the angle of repose (the maximum steep angle that loose, unconsolidated materials deserve to lie on), commonly 30° or much more (the angle of repose). Many are much less than 1,000 ft high. Castle usually have actually a huge crater where the pyroclastics were ejected. Sunset Crater in Arizona is an example of a cinder cone.