ESCI 1000 Lecture Notes - Lecture 4: Dacite, Volcanic Gas, Lapilli
15 Oct 2016
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Document Summary
Volcanism is directly related to plate tectonics. Most active volcanoes located near plate boundaries. Two-thirds of all acti(cid:448)e (cid:448)olca(cid:374)oes are located alo(cid:374)g the (cid:862)ri(cid:374)g of fire(cid:863) (cid:449)hich surrou(cid:374)ds the. Magma: described by silica content and amount of dissolved gasses, basalt (most common volcanic rock, 45-52% silica, andesite (52-63% silica, dacite (63-68% silica, rhyolite (>68% silica) Eruption style depends on lava"s viscosity and amount of dissolved gas content. Viscosity: liquid"s resistance to flow (determined by silica content and lava temperature). Quiet flow (low viscous basalt flow) to violent explosion (high viscous lava eruption). Shield volcanoes, composite volcanoes, volcanic domes, cinder cones. Hot spring: groundwater contacts hot water, becomes heated, and discharges at surface geyser: hot groundwater circulation produces steam and hot water. Most common and abundant type: basaltic lava flow. Pahoehoe lava: less viscous, higher temp, with a smooth ropy surface texture. Aa lava: more viscous, lower temp, with a blocky surface texture.
