GEOG 1114 1st Edition Lecture 23Outline of Last Lecture- Landforms- Internal vs. external- Geological time- Crustal rearrangement- Plate Tectonics- Types of boundaries-Outline of Current Lecture -Vulcanism- Volcanic peaks-Volcanic DistributionCurrent Lecture Special SituationMantle 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 rockVolcanoes – Eruption of Magma – Extrusive VolcanismLava: 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 magmaVolcanic PeaksCinder Cones: small cone-shaped peak that develops almost entirely from ejected pyroclastic material.-Often-basaltic magma -Slopes from pyroclastic materials -S.W. United StatesShield 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 volcanoesLave 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 volcanoesCaldera: 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 OceanIntrusive 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 intrusionTypes of Igneous IntrusionsBatholith: 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. DiastrophismThe breaking apart of rock materialFolding: Takes place when rock structure is subjected to great compressional stresses over long periods of time.Anticline– up folds that form ridgesSynclines – down folds that form valleys.Faulting: breaking and displacement of a rock structureOccurs along zones of weakness in the
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