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Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava. As a result, eruptions of volcanoes made of mafic lavas are less explosively violent than felsic-lava eruptions. [10]
Bimodal volcanism is the eruption of both mafic and felsic lavas from a single volcanic centre with little or no lavas of intermediate composition. This type of volcanism is normally associated with areas of extensional tectonics , particularly rifts .
Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic volcanoes. Although they are usually associated with felsic magma, Plinian eruptions can occur at basaltic volcanoes, if the magma chamber differentiates with upper portions rich in silicon dioxide , [ 40 ] or if magma ascends rapidly.
In some cases, felsic volcanic rocks may contain phenocrysts of mafic minerals, usually hornblende, pyroxene or a feldspar mineral, and may need to be named after their phenocryst mineral, such as 'hornblende-bearing felsite'. The chemical name of a felsic rock is given according to the TAS classification of Le Maitre (1975). However, this only ...
The Devil's Inkpot lava flows formed from a fissure around the same time as the Sister's Peak region 829,000 years ago. Benmoreite scoria cones record evidence of mafic volcanism, although older rhyolite and trachyte flows, domes and pyroclastic deposits point to felsic eruptions as well.
Known as a super eruption for its magnitude, the event emptied out enough volcanic material to produce the 30-by-40-mile-wide caldera. The National Park Service said the eruption covered an area ...
The inclusion of mafic and felsic rock indicates multiple other eruptions that occurred and coincided with the one-million-year-long set of eruptions that created the majority of the basaltic layers. The traps are divided into sections based on their chemical, stratigraphical, and petrographical composition. [6]
A volcanic eruption is essentially the only natural way for short-lived – less than a few years – gases like sulfur dioxide and water vapor to make it into the stratosphere.