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Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and metamorphic rocks and constitute an important element of some sediments and sedimentary rocks .
Most examples come from areas of active continental rifting such as the Basin and Range Province. Bimodal volcanism has also been described from areas of transtension , [ 2 ] the early phases of back-arc basin formation [ 3 ] and in the products of both continental and oceanic hotspots (e.g. Yellowstone , Anahim and the Canary Islands ).
On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example, a mid-ocean ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has ...
Cinder Hill, a feature of Mount Bird on Ross Island, Antarctica, is a prominent example of a dissected volcano. Volcanoes that were, on a geological timescale, recently active, such as for example Mount Kaimon in southern Kyūshū, Japan, tend to be undissected. Devils Tower in Wyoming is a famous example of exposed volcanic plug.
They form when lava accumulates within cracks in lava, superheats and explodes in a steam explosion, breaking the rock apart and depositing it on the volcano's flank. Consecutive explosions of this type eventually generate the cone. [50] Volcanoes known to have Surtseyan activity include: Surtsey, Iceland.
Osorno volcano in Chile is an example of a well-developed stratocone.. Stratocones are large cone-shaped volcanoes made up of lava flows, explosively erupted pyroclastic rocks, and igneous intrusives that are typically centered around a cylindrical vent.
Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting or forecasting eruptions, like ...
An example is the massive Level Mountain shield volcano in northern British Columbia, Canada, which covers an area of 1,800 km 2 (690 sq mi) and a volume of 860 km 3 (210 cu mi). [ 1 ] Perhaps the most extensive of all the subaerial basaltic plateaus existed during the Paleogene [ 2 ] and possibly extended over 1,800,000 km 2 (690,000 sq mi) of ...