GEOG 1114 1st Edition Lecture 23 Outline of Last Lecture Landforms Internal vs external Geological time Crustal rearrangement Plate Tectonics Types of boundaries Outline of Current Lecture Vulcanism Volcanic peaks Volcanic Distribution Current Lecture Special Situation Mantle Plumes or Hot Spots narrow plume of magma rising through plate to the surface Hot Spot underlies the Hawaiian Islands Not yet easily explained by Plate Tectonics However as plates move away from the Hot Spot the volcanoes become extinct This helps vary the speed and direction of plate movement Vulcanism All phenomena connected with the origin and movement of molten rock Volcanoes Eruption of Magma Extrusive Volcanism Lava Magma extruded on the earth s surface These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Pyroclastic Material lava and other material such as rock fragments ash dust which erupts with the volcano Styles of Eruption Nature of eruption determined by magma chemistry and by confining pressure It depends of the chemistry of magma Volcanic Peaks Cinder Cones small cone shaped peak that develops almost entirely from ejected pyroclastic material Often basaltic magma Slopes from pyroclastic materials S W United States Shield Volcanoes quiet fluid eruptions typical of volcanoes emitting basaltic lava Produce Mountains with gentle sloping side Hawaii Layer upon layer of solidified lava Composite Volcanoes explosive eruptions emitting more pyroclastic material and acidic lava Produce tall symmetrical mountains with steeper sides often called composite or Stratovolcanoes Emit higher silica lavas Form symmetric steep sided volcanoes Lave Domes develop from very viscous lava that bulges up from a vent too thick to flow Masses of very viscous lava that do not flow far Lava bulges from the vent dome grows by expansion from below and lava within Some lava domes form inside of composite volcanoes Caldera uncommon results when a volcano collapses or explodes creating a large basin shaped circular depression Often fills with water creating a lake Crate lake Oregon Volcanic Distribution Most associated with plate boundaries Most associated with the Pacific Ring of Fire produced by the subduction zones around the margins of the Pacific Ocean Intrusive Vulcanism When magma cools beneath the surface it produces a mass of intrusive igneous rock If this rock is pushed up through the crust its called an igneous intrusion Types of Igneous Intrusions Batholith The core of the mountain intrusive uplift Important in Mountain Building Laccolith Slow moving lava force between horizontal layer of existing rocks Can cause hills such as the Black Hills of South Dakota Dikes vertical thin sheet of magma thrust upward into preexisting rock often occur as radial walls extending out from the volcano Shiprock NM Sills long thin igneous intrusion formed when magma is forced between strata that are already in place Often between horizontal sedimentary layers Diastrophism The breaking apart of rock material Folding Takes place when rock structure is subjected to great compressional stresses over long periods of time Anticline up folds that form ridges Synclines down folds that form valleys Faulting breaking and displacement of a rock structure Occurs along zones of weakness in the crust
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