Volcanoes are constructed by successive eruptions over plenty of decades, centuries, or thousands of years. Volcanoes come in various sizes and also shapes.


The all at once size that a volcano is determined by the total volume the lava that has erupted.


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

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Water, because that example, is a low viscosity fluid. That is thin and also runny. Cold syrup, top top the various other hand, has a greater viscosity. The is thick and also goopy. However when syrup is heated, that viscosity go down. Warm syrup i do not care thinner, runnier, an ext like water.

Temperature, composition, and volatile (gas) contents largely determine the viscosity of lava.

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

Composition: he more felsic the lava (the much more silica in the lava), the higher the viscosity because silica develops chains in the cooling lava even before it crystallizes. The much more mafic the lava (the much less silica in it), the lower the viscosity. It transforms out the mafic lava is high temperature lava since high temperature are forced to melt mafic mineral in the very first place. Felsic lavas are low temperature lavas since lower temperature are forced to store felsic mineral molten (and if it was hotter the would have actually incorporated an ext iron and magnesium in comparison come silica).

Volatile content refers to gases liquified in the lava, like carbon dioxide in soft drinks. Lavas might contain approximately 6% or an ext of your mass together gases. The two most abundant gases in lava room water vapor and also carbon dioxide. Over there is commonly also nitrogen, sulfur dioxide, and small amounts that chlorine, hydrogen, argon, and also a few other gases. Once lava approaches the surface, the push on that is substantially reduced and the dissolved gases come out of solution; they kind bubbles and also rise. The escape of gases might produces tremendous pressure in a volcano, developing explosive eruptions. In general, the much more felsic the magma the better the volatile content. For this reason mafic/basaltic volcanoes are fairly quiescent, intermediate/andesitic volcano eruptions space moderately explosive, and felsic/rhyolitic volcanoes might be extremely explosive.

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

Felsic lavas space not as hot, high in silica and volatiles, and also have a high viscosity. They room thick and also gooey and also resist flowing. Their high volatile content provides them potentially very explosive.

Shield Volcanoes

Because mafic lava is low viscosity, when it erupts indigenous a volcano it operation downslope far from the vent, progressively cooling and crystallizing. Due to the fact that of the relative ease that flow, basaltic volcanoes are broad, v gentle slopes. They don"t have actually the stereotypical steep volcano cone shape. Rather, they are shaped more like a shield to adjust on the ground.

Even though your slopes are gentle (typically 6° - 12°) they might be quite large. The biggest mountain ~ above the planet is the island of Hawaii, which rises up 30,000 ft native the seafloor. In comparison, the top of Mt Everest is 29,035 ft over sea level, however the basic of Everest is well over sea level. Hawaii has actually grown to its good size by continual eruptions that basaltic lava for around 700,000 years. Many shield volcanoes are much smaller. In fact, the island that Hawaii itself is written of numerous volcanoes, not one, though each is itself very large.


Basaltic lava operation on Hawaii and also elsewhere produce may have two type of surface. One form has a smooth surface with ridges that look choose coiled ropes. This form of volcanic flow is called by the Hawaiian name pahoehoe. Thick lava flows might remain molten in the interior and also continue come move even while the surface ar solidifies. Yet continued motion breaks increase the surface into jagged absent fragments. This broken, jagged volcanic flows are dubbed aa.

Flood Basalts

Sometimes basaltic lava erupts indigenous a series of fissures, or cracks in the Earth and spreads widely over the landscape, fairly than erupting indigenous a singe volcanic vent. These type of eruptions create flood basalts.

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Cinder Cones


Sometimes, in the late stage of basaltic volcano activity, small cinder cones come to be active. When its it is provided of magma from deep in the earth slows or stops, the magma room beneath a volcano will certainly cool and begin crystallizing. The first-formed minerals will be high-temperature, mafic minerals favor olivine which are rich in iron and magnesium and also poor in silica. The result is the the staying magma i do not care depleted in iron and magnesium and enriched in silica. Consequently, the viscosity boosts in the remaining magma and it does not circulation out that the ground together easily. Rather, it build up enough back-pressure to eject a spray that lava into the air. The lava droplets cool and also crystallize rapidly (or at least the surface ar of big blobs the lava crystallizes rapidly) and then they autumn as volcanic cinders, or pyroclasts, ~ above the flanks the the volcano and also tumble under its side. This procedure forms tiny volcanic cones with slopes at the angle of repose (the maximum slope angle the loose, unconsolidated materials deserve to lie on), frequently 30° or much more (the angle the repose). Many are less than 1,000 ft high. They usually have a big crater whereby the pyroclastics to be ejected. Sunset Crater in Arizona is an instance of a cinder cone.