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Mount ST Helens post 1980 eruption Dacite Dome USGS

Dacite lava is a viscous lava which is squeezed out of volcanoes and commonly forms lava domes. If this collapses then pyroclastic flows can occur. It erupts at a temperature between 800 and 1000 C.If the magma is gaseous then Plinian style eruptions can occur when low in gases dacite is extruded as a lava dome.

It forms a light grey rock which contains 63% to 68% silica and the minerals plagioclase, pyroxene and amphibole / hornblende. Dacite is found above subduction zones particularly on ocean/continent boundaries. Mt.St Helens.Mt Pinatubo and Mt.Unzen have all erupted Dacite.