Transcript Slide 1
Mt. Etna, Sicily 1 Parts of a Volcano 2 Volcano Cross-section 3 Calderas • Created when a magma chamber is emptied, and the rock above collapses back into the empty chamber, causing a large depression in the ground, which often fill up with water. Crater Lake Caldera 4 Calderas Photograph by M. Williams, National Park Service, 1977 Aniakchak Caldera 5 How Volcanoes Form 6 Plate Tectonics • Volcanoes can be located in one of three locations: 1) A convergent plate boundary 2) A divergent plate boundary 3) A hotspot 7 Convergent Boundaries • Plates converge, and one slides underneath the other; oceanic crust is destroyed 8 Divergent Boundaries • About 2.4 mi3 of crust is created this way Photography courtesy of Woods Hole Oceanographic Institution and members of the Adventure dive • All divergent boundaries are in the middle of the ocean at mid-ocean spreading centers 9 Hot Spots • Hawaii is the most famous chain of islands created by hotspot activity • The plate slides over the hotspot, creating volcanoes in a chain 10 How Volcanoes Form • Weaknesses exist at these boundaries • Magma lighter than surrounding rock • Finds a weakness and pushes upwards to the surface, causing a volcano Sketch by B. Myers 11 Volcano Products 12 Lava Photograph by J.D. Griggs on 13 November 1985 Lava flowing on Kilauea Volcano, Hawaii 13 Pahoehoe • Is Basaltic lava with a ropy, smooth or bumpy surface texture 14 Gases • Mainly water, carbon dioxide, and sulfur dioxide • Toxic gases include hydrogen sulfide (rotten egg gas), sulfuric acid, and Hydrochloric acid Gases from Pu`u `O`o vent on Kilauea Volcano, Hawaii Photograph by K.A. McGee on 19 September 1995 15 Tephra: Ash • Must be smaller than 2 mm in diameter • Commonly less than 0.025 mm in Diameter • Does not dissolve in water Photograph by D.E. Wieprecht 16 Tephra: Lapilli Lapilli from the summit of Kilauea Volcano in 1959 17 Blocks and Bombs Photograph by J.P. Lockwood on July 10, 1982 18 Photograph by C. Heliker on January 26, 1988 Pyroclastic Flows • Are dangerous movements of ash, rock fragments, pumice and gas • Move very rapidly: up to 65 mph!! • Usually more than 5000 F! Pyroclastic flows are far and away the most deadly volcanic occurrences. If you see one, get as far away as fast as possible!!! Photograph by C. Newhall on 15 September 1984 19 Lahars •Volcanic mudflows, composed of volcanic material, water, mud, and anything else available Guatemala Photograph by J.N. Marso on 14 August 1989 20 Types of Volcanoes 21 Cinder Cone Volcanoes • They are the most common type, yet are the smallest type as well • Have the steepest sides of the three types, and the largest summit craters • Responsible for 648 / 1,511 of known eruptions over the past 10,000 years [42.9%] 22 Cinder Cone Volcanoes Sunset Crater. Photograph courtesy of the National Park Service. Aerial view looking west to Sunset Crater. Photography by Wendell Duffield, U.S. Geological Survey 23 Cinder Cone Volcanoes Photograph by J.P. Lockwood on 1 December 1975 Pu`u ka Pele 24 Shield Volcanoes • They are very wide, broad volcanoes • The magma that is released flows very easily, which creates their wide profile • Responsible for 164 / 1511of known eruptions over the past 10,000 years [10.8%] 25 Shield Volcanoes View of the NNW flank of Mauna Loa Volcano from the south side of Mauna Kea Volcano, Hawaii; both are shield volcanoes. 26 Shield Volcanoes Three-dimensional Space Shuttle Image of the Alcedo Shield Volcano, Galapagos. Courtesy of JPL/NASA. 27 Stratovolcanoes • Also known as composite volcanoes • Are the “most picturesque”, but also the most deadly because of the material they eject • Have gentle lower slopes, and steep upper Slopes • Not the most common, but are most famous because of deadliness • Responsible for 699 / 1,511 of known eruptions over the past 10,000 years [46.3%] 28 Stratovolcanoes Photograph by R. McGimsey on 15 July 1990 Mount Mageik, Alaska 29 Other Important Stratovolcanoes Mt. St, Helens, Washington. A view to the north of the "two tone" mountain - an appearance produced by prevailing easterly winds during the initial activity of Mount St. Helens. Photo by C. Dan Miller 30 Other Important Stratovolcanoes Mt. Fuji, Japan 31 Mt. St. Helens, 1980 Steam was seen rising out Helens in this April 10, 1980 picture Courtesy of Don Swanson, USGS 32 Mt. St. Helens, 1980 Shown is the “bulge” in the Side on April 27,1980 The “bulge” had expanded more than 100 meters out!!! Notice how large the “bulge” grew from only April 10 to April 27! 33 Mt. St. Helens, 1980 Rose to a height of more than 20 kilometers!! Lasted more than 9 Hours Ash was carried as far away as the great plains Courtesy of USGS. 34 References • Most images from USGS : http://volcanoes.usgs.gov/Products/Pglossary/pglossary.html • Most information and data from: http://www.geology.sdsu.edu/how_volcanoes_work/ 35