Definitions and images to illustrate geological terms, links to images and website articles


diagram of stratovolcanobasaltic lava flowThe term 'volcanism' refers to volcanoes and volcanic processes.

Magma is molten (igneous) rock formed when Earth's radioactivity heats rocks to high temperatures – the deeper in the Earth, the greater the temperature.

When melted rock flows at the surface it is called lavaHawaii's and Iceland's basalt lavas fountain (below center) or flow (above right) freely, while other lavas are sticky and explosive, producing deadly pyroclastic flows (nuee ardentes, such as that which killed victims at Pompeii) and towering clouds (below right, below left; pyroclastic flow, Mount St. Helens, 2, Vesuvius, Pinatubo, Soufrière Hills Volcano on Montserrat, Ischia deposits). .


..Plinian eruption of Klyuchsvskaya in Russiapyroclastic cloud above erupting andesitic stratovolcanolava fountain and lava flow, Kilauea, Hawaii

[links: images: webpages: Vesuvius victims 'died instantly' ]

Video The Ring of Fire

images : USGS : top right, schematic of stratovolcano; top left, basaltic lava; bottom right, Plinian eruption of Mt. Klyuchsvskaya in Russia; lava fountain and lava flow, Kilauea, Hawaii; pyroclastic cloud above erupting andesitic stratovolcano.

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