Volcanoes are developed by successive eruptions over numerous decades, centuries, or thousands of years. Volcanoes come in different sizes and also shapes.


The in its entirety size the a volcano is identified by the complete volume the lava that has erupted.


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

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Water, because that example, is a short viscosity fluid. The is thin and runny. Cold syrup, ~ above the various other hand, has actually a higher viscosity. The is thick and goopy. But when syrup is heated, its viscosity goes down. Warm syrup i do not care thinner, runnier, an ext like water.

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

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

Composition: he 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 more mafic the lava (the less silica in it), the reduced the viscosity. It turns out the mafic lava is high temperature lava since high temperature are forced to melt mafic minerals in the first place. Felsic lavas space low temperature lavas because lower temperatures are forced to keep felsic mineral molten (and if it to be hotter that would have incorporated more iron and magnesium in comparison come silica).

Volatile content refers to gases dissolved in the lava, prefer carbon dioxide in soft drinks. Lavas might contain as much as 6% or an ext of your mass as gases. The two many abundant gases in lava room water vapor and also carbon dioxide. There is commonly also nitrogen, sulfur dioxide, and little amounts that chlorine, hydrogen, argon, and a couple of other gases. As soon as lava approaches the surface, the push on it is considerably reduced and also the dissolved gases come the end of solution; they form bubbles and rise. The to escape of gases may produces tremendous pressure in a volcano, producing explosive eruptions. In general, the an ext felsic the magma the better the volatile content. Therefore mafic/basaltic volcanoes are relatively quiescent, intermediate/andesitic volcano eruptions are moderately explosive, and felsic/rhyolitic volcanoes may be exceptionally explosive.

So, mafic lavas are warm , short in silica and volatiles, and have relatively low viscosity. They flow quickly outward indigenous the vent (where the comes out of the ground), and may travel great distances before totally solidifying.

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

Shield Volcanoes

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

Even though their slopes space gentle (typically 6° - 12°) they might be fairly large. The largest mountain top top the earth is the island of Hawaii, i beg your pardon rises increase 30,000 ft native the seafloor. In comparison, the peak of Mt Everest is 29,035 ft above sea level, yet the base of Everest is well above sea level. Hawaii has grown to its good size by consistent eruptions the basaltic lava for about 700,000 years. Most shield volcanoes are lot smaller. In fact, the island that Hawaii itself is composed of several volcanoes, no one, though every is itself an extremely large.


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

Flood Basalts

Sometimes basaltic lava erupts indigenous a series of fissures, or crack in the Earth and spreads commonly over the landscape, fairly than erupting indigenous a singe volcanic vent. These kinds of eruptions develop flood basalts.

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Cinder Cones


Sometimes, in the late stage of basaltic volcano activity, small cinder cones come to be active. As soon as its it is provided of magma indigenous deep in the earth 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 like olivine which room rich in iron and magnesium and also poor in silica. The result is the the remaining magma i do not care depleted in iron and also magnesium and enriched in silica. Consequently, the viscosity increases in the remaining magma and also it go not circulation out the the ground together easily. Rather, it build up sufficient back-pressure to eject a spray of lava into the air. The lava droplets cool and also crystallize rapidly (or at least the surface of huge blobs of lava crystallizes rapidly) and then they autumn as volcano cinders, or pyroclasts, ~ above the flanks the the volcano and also tumble under its side. This process forms tiny volcanic cones v slopes at the edge of repose (the maximum slope angle that loose, unconsolidated materials have the right to lie on), generally 30° or more (the angle of repose). Most are much less than 1,000 ft high. Castle usually have actually a large crater whereby the pyroclastics to be ejected. Sunset Crater in Arizona is an example of a cinder cone.