Erupted material Volcano

pāhoehoe lava flow on hawaii. picture shows overflows of main lava channel.



the stromboli stratovolcano off coast of sicily has erupted continuously thousands of years, giving rise term strombolian eruption.



san miguel (volcano), el salvador. on december 29, 2013, san miguel volcano, known chaparrastique , erupted @ 10:30 local time, spewing large column of ash , smoke sky; eruption, first in 11 years, seen space , prompted evacuation of thousands of people living in 3 km radius around volcano.



ash plume san miguel (volcano) chaparrastique , seen satellite, heads towards pacific ocean el salvador central america coast, december 29, 2013


lava composition

another way of classifying volcanoes composition of material erupted (lava), since affects shape of volcano. lava can broadly classified 4 different compositions (cas & wright, 1987):

if erupted magma contains high percentage (>63%) of silica, lava called felsic.

felsic lavas (dacites or rhyolites) tend highly viscous (not fluid) , erupted domes or short, stubby flows. viscous lavas tend form stratovolcanoes or lava domes. lassen peak in california example of volcano formed felsic lava , large lava dome.
because siliceous magmas viscous, tend trap volatiles (gases) present, cause magma erupt catastrophically, forming stratovolcanoes. pyroclastic flows (ignimbrites) highly hazardous products of such volcanoes, since composed of molten volcanic ash heavy go atmosphere, hug volcano s slopes , travel far vents during large eruptions. temperatures high 1,200 °c known occur in pyroclastic flows, incinerate flammable in path , thick layers of hot pyroclastic flow deposits can laid down, many meters thick. alaska s valley of ten thousand smokes, formed eruption of novarupta near katmai in 1912, example of thick pyroclastic flow or ignimbrite deposit. volcanic ash light enough erupted high earth s atmosphere may travel many kilometres before falls ground tuff.


if erupted magma contains 52–63% silica, lava of intermediate composition.

these andesitic volcanoes occur above subduction zones (e.g. mount merapi in indonesia).
andesitic lava typically formed @ convergent boundary margins of tectonic plates, several processes:

hydration melting of peridotite , fractional crystallization


sarychev peak eruption, matua island, oblique satellite view



melting of subducted slab containing sediments
magma mixing between felsic rhyolitic , mafic basaltic magmas in intermediate reservoir prior emplacement or lava flow.




if erupted magma contains <52% , >45% silica, lava called mafic (because contains higher percentages of magnesium (mg) , iron (fe)) or basaltic. these lavas less viscous rhyolitic lavas, depending on eruption temperature; tend hotter felsic lavas. mafic lavas occur in wide range of settings:

at mid-ocean ridges, 2 oceanic plates pulling apart, basaltic lava erupts pillows fill gap;
shield volcanoes (e.g. hawaiian islands, including mauna loa , kilauea), on both oceanic , continental crust;
as continental flood basalts.


some erupted magmas contain <=45% silica , produce ultramafic lava. ultramafic flows, known komatiites, rare; indeed, few have been erupted @ earth s surface since proterozoic, when planet s heat flow higher. (or were) hottest lavas, , more fluid common mafic lavas.

lava texture

two types of lava named according surface texture: ʻaʻa (pronounced [ˈʔaʔa]) , pāhoehoe ([paːˈho.eˈho.e]), both hawaiian words. ʻaʻa characterized rough, clinkery surface , typical texture of viscous lava flows. however, basaltic or mafic flows can erupted ʻaʻa flows, particularly if eruption rate high , slope steep.

pāhoehoe characterized smooth , ropey or wrinkly surface , formed more fluid lava flows. usually, mafic flows erupt pāhoehoe, since erupt @ higher temperatures or have proper chemical make-up allow them flow greater fluidity.