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Because dacite is the main type of lava erupted from Mount Garibaldi, lava flows are a low to moderate hazard. [3] Dacite is felsic [ d ] in composition, containing 62–69% silica content. [ 71 ] [ 72 ] This high percentage in silica content increases the viscosity of dacitic melts relative to that of andesite or basalt , generally resulting ...
The shape of effusive lava flows is governed by the type of lava (i.e. composition), rate and duration of eruption, and topography of the surrounding landscape. [ 3 ] For an effusive eruption to occur, magma must be permeable enough to allow the expulsion of gas bubbles contained within it.
Low viscosity lava can generate massive lava fountains, while lava of thicker viscosity can solidify within the vent, creating a volcanic plug. Volcanic plugs can trap volcanic gas and create pressure in the magma chamber, resulting in violent eruptions. [36] Lava is typically between 700 and 1,200 °C (1,300–2,200 °F). [37]
Dacite and rhyolite lavas are normally too viscous to flow away from a volcanic vent, resulting in the formation of lava domes. [25] An exception is the 15-kilometre-long (9.3-mile) Ring Creek dacite lava flow from Opal Cone on the southeastern flank of Mount Garibaldi, a length that is normally attained by basaltic lava flows. [19]
As a result of this fluidity, the peralkaline felsic lava flows were able to form small-scale folds and 1-to-2-metre-diameter (3.3-to-6.6-foot) lava tubes. The liquidus temperatures of these flows were in excess of 1,200 degrees Celsius (2,190 degrees Fahrenheit) with viscosities as low as 100,000 poise .
The word lava comes from Italian and is probably derived from the Latin word labes, which means a fall or slide. [2] [3] An early use of the word in connection with extrusion of magma from below the surface is found in a short account of the 1737 eruption of Vesuvius, written by Francesco Serao, who described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of ...
The eruption of overlapping andesitic lava flows accumulated to build the volcano. By the time it reached its peak size, the volcano was immense, measuring at its base between 11 mi (18 km) and 15 mi (24 km) wide and more than 11,000 ft (3,353 m) tall. [ 7 ]
South Belknap is a small volcano 1 mile (1.6 km) to the south of Belknap, which was breached on its southwestern side by lava flows that also extended over Belknap Crater's southern base. Early lava flows near South Belknap were covered by a later lava flow, which was produced by a vent located about 300 feet (91 m) northwestward. [17]