one erupting volcano

Lava gushes indigenous a spatter cone at Kilauea, Hawaii, 2004. Hawaii Volcano Observatory (United states Geological Survey) image.

You are watching: Type of magma containing little silica

A volcano is an opening in the earth’s crust with which lava, volcano ash, and gases escape. Volcano eruptions are partially driven by press from liquified gas, lot as escaping gases force the cork the end of a party of champagne. In ~ a volcano, liquid magma containing dissolved gases rises with cracks in the earth crust. As the magma rises, press decreases, permitting the gases to kind bubbles. Just how the magma (lava) behaves once it get the surface depends on both the gas content and chemical composition. Lavas with low silica materials have short viscosities and flow freely, allowing any gas bubbles to escape readily, if lavas with high silica materials are an ext viscous (resistant come flow), for this reason that any kind of trapped gases cannot escape gradually.

mountain Garibaldi

Mount Garibaldi, a potentially energetic volcano in southwest brothers Columbia, located within 30 km of the communities of Whistler and Squamish.

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Nazko cone
photos of volcanic eruptive actions

How the silica and also gas contents of lava impact volcano eruptive behaviour. Pictures courtesy the (a) and also (c) Hawaii Volcano Observatory (HVO), (b) United claims Geological survey (USGS) /Alaska Volcano Observatory (AVO) (Clucas), and also (d) USGS/AVO (McGimsey).

A low viscosity (runny) lava, like basalt that consists of lots the gas, develops fire-fountains, spewing spectacularly right into the air and also breaking right into globs that solidify together they fall to the ground. Tiny fire-fountain eruptions create cinder cones (like night Cone in northern British Columbia). when runny lava includes less gas, however, that erupts in outpouring lava flows. Recurring fire-fountain and also lava flow eruptions over lengthy time periods type gently sloping shield volcanoes choose Anahim optimal in central British Columbia, and also the volcanoes that the Hawaiian Islands. Andesite, dacite, and rhyolite lavas room progressively higher in silica and an ext viscous, therefore gases cannot escape gradually. If high-silica lavas contain little trapped gas, they might ooze progressively onto the surface to heap up together steep-sided lava domes. when high-silica lavas contain many trapped gas, the pressure builds up and also is released in explosive eruptions that develop volcanic ash. Some volcanoes experience both explosive and non-explosive activity, alternating explosive eruptions with periods of dome-building, developing stratovolcanoes choose Mount St. Helens and also Mount Garibaldi.