ENV 101 Ch06 lecture ppt_a
- 1. 6-1 Environmental Geology James Reichard Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
- 2. 6-2 Chapter 6 Volcanoes and Related Hazards © Image Plan/Corbis
- 3. 6-3 Volcanoes and Related Hazards Photo by R. Janda, Cascade Volcano Observatory/USGS Jump to long description
- 4. 6-4 Nature of Volcanic Activity Magma • Basaltic • Andesitic • Rhyolitic J.D. Griggs/USGS Jump to long description
- 5. 6-5 Magma and Plate Tectonics • Hot Spots • Divergent Boundaries • Subduction Zones Jump to long description
- 6. 6-6 Volcanic Eruptions (1) Jump to long description
- 7. 6-7 Volcanic Eruptions (2) Jump to long description
- 8. 6-8 Volcanic Eruptions (3) A. Mount St. Helens, Washington B. Kilauea, Hawaii a: USGS; b: J.D. Griggs/U.S. Geological Survey Jump to long description
- 9. 6-9 Volcanic Landforms Lava Flows • Small • Large Lava domes Continental Flood Basalts A. Basalt, Pu’u O’o, Hawaii B. Andesite, Lassen, California C. Rhyolite, Long Valley, California a: Photograph by J.D. Griggs, USGS Photo Library, Denver, CO; b: Michael Clynne USGS and USDA; c: USGS Jump to long description
- 10. 6-10 Flood Basalt Jump to long description
- 11. 6-11 Volcanoes • Cinder cones • Shield • Composite cone A.Pu’u O’o, Hawaii, 1986 B.Mount Etna, Sicily, Italy, 2001 (a-b): USGS Jump to long description
- 12. 6-12 Shield Volcanoes © J.S. Griggs/U.S. Geological Survey Jump to long description
- 13. 6-13 Composite cone volcanoes © Image Plan/Corbis Jump to long description
- 14. 6-14 Size comparison Jump to long description
- 15. 6-15 Hawaiian Hot Spot Jump to long description
- 16. 6-16 Yellowstone Hot Spot Jump to long description
- 17. 6-17 Calderas b: © Jim Reichard Jump to long description
- 18. 6-18 Volcanic Hazards (1) • Lava Flows • Explosive Blasts • Pyroclastic Flows • Volcanic Ash • Volcanic Glass • Tsunamis A. Kalapana, Hawaii, 1986 B. Volcanoes national Park, Hawaii, 1989 a: USGS; b: J.D. Griggs, USGS Jump to long description
- 19. 6-19 Volcanic Hazards (2) Jump to long description
- 20. 6-20 The eruption of Mount St. Helens (1) Original illustrations by T.R. Alpha, U.S. Geological Survey Jump to long description
- 21. 6-21 The eruption of Mount St. Helens (2) Jump to long description
- 22. 6-22 Mass Wasting on Volcanoes Volcanic landslides Volcanic mudflows • Lahars • Debris flows (inset): Underwood & Underwood/Library of Congress Jump to long description
- 23. 6-23 Large volcanic mudflows (all): Michael Rymer, USGS Jump to long description
- 24. 6-24 The Seattle-Tacoma area is under extreme risk Steve Brantley/USGS Jump to long description
- 25. 6-25 The Cascade Range in the Pacific Northwest Jump to long description
- 26. 6-26 Predicting Eruptions & Minimizing Risks Predictive Tools • Geologic history • Topographic changes • Seismic monitoring • Monitoring of volcanic glass • Geophysical and groundwater changes
- 27. 6-27 Predicting Eruptions © Jim Reichard Jump to long description
- 28. 6-28 Appendix of Image Long Descriptions
- 29. 6-29 Volcanoes and Related Hazards Long Description Three-quarters of the residents of Armero, Colombia, were killed when a massive mudflow came roaring down a canyon and emptied out onto the valley floor where the city was built. The mudflow formed when Nevado del Ruiz, located 46 miles (74 km) away, began to erupt, causing its glacial ice cap to melt. Jump back to slide containing original image
- 30. 6-30 Nature of Volcanic Activity Long Description How easily magma flows depends on its viscosity, which is controlled by its SiO2 content and temperature. Shown here is high-temperature, silica-poor basaltic magma of relatively low viscosity. Photo taken during the 1989 eruption of Kilauea volcano, Hawaii. Jump back to slide containing original image
- 31. 6-31 Magma and Plate Tectonics Long Description Location of active volcanoes and their relationship to tectonic plate boundaries. Most volcanoes derive their magma from subduction zones or from the upper mantle in what are referred to as hot spots. Hot spot volcanoes in an oceanic setting produce basaltic magma, and those on continents generate more rhyolitic magma. Depending on the tectonic setting, subduction zone volcanoes will produce basaltic, andesitic, or rhyolitic magmas. Jump back to slide containing original image
- 32. 6-32 Volcanic Eruptions (1) Long Description The viscosity of magma increases with increasing SiO2 content and decreasing temperature. Basaltic magmas are the least viscous because they form in the upper mantle where the temperature is high and the SiO2 content of the rocks is relatively low. Andesitic and rhyolitic magmas form at much shallower and cooler depths and under processes that cause these magmas to become enriched in SiO2. Jump back to slide containing original image
- 33. 6-33 Volcanic Eruptions (2) Long Description Molten rock eventually accumulates in what is called a magma chamber. The weight of the overlying column of rock creates overburden (confining) pressure, which is offset by the magma’s fluid pressure. As magma continues to rise and encounters less overburden, the fluid pressure is able to open fractures, creating possible pathways to the surface. At the surface the pressurized magma is allowed to expand freely. Jump back to slide containing original image
- 34. 6-34 Volcanic Eruptions (3) Long Description Volcanic eruptions occur when pressurized magma breaches the surface. Explosive eruptions (A) are associated with more viscous and gas-charged magmas in which the dissolved gases rapidly decompress, ejecting rock and ash into the atmosphere. Nonexplosive eruptions (B) are associated with hot fluid magma containing less dissolved gas; in which case the eruption generates lava fountains and lava flows. Jump back to slide containing original image
- 35. 6-35 Volcanic Landforms Long Description The shape and thickness of a lava flow depend upon the magma’s viscosity and the slope of the land surface. Low-viscosity basaltic lava flows (A) tend to travel greater distances and spread out into thin sheets in areas where the terrain is more relatively flat. Andesitic lava is more viscous and creates thicker flows (B) that travel relatively short distances. Highly viscous rhyolitic lava (C) hardly flows at all, but rather builds into a mound-shaped feature called a lava dome. Jump back to slide containing original image
- 36. 6-36 Flood Basalt Long Description Extensive lava flows, called flood basalts, form when large volumes of highly fluid basaltic magma are extruded, usually along fracture zones. The map shows the extent of the Columbia River flood basalts in the Pacific Northwest region of the United States. These extensive flows reach a thickness of over 2,000 feet (600 m). The Cascade Range is a volcanic arc that contains subduction zone volcanoes. Jump back to slide containing original image
- 37. 6-37 Volcanoes Long Description A volcanic vent can coincide with a fault or fracture, resulting in a linear extrusion known as a fissure eruption (A). In other cases the vent is a single opening whereby the ejected material creates the familiar coneshaped feature known as a volcano (B). Jump back to slide containing original image
- 38. 6-38 Shield Volcanoes Long Description Shield volcanoes (A) are composed primarily of basaltic lava flows that accumulate over geologic time. Photo shows Mauna Loa (B) in the Hawaiian Islands, which sits over a hot spot, providing a steady supply of magma that has allowed it to grow to 14,400 feet (4,400 m) above sea level. Jump back to slide containing original image
- 39. 6-39 Composite cone volcanoes Long Description Composite cone volcanoes (A) are composed of alternating layers of pyroclastic material and lava flows. Viscous andesitic lavas tend to form short and thick flows that enable the volcano to maintain steep slopes and reach great heights. Composite cones are typically quite symmetrical, like Mount Fuji (B) in Japan. Jump back to slide containing original image
- 40. 6-40 Size comparison Long Description Size comparison of one of the larger composite cones in the Cascade Range, Mount Rainier, with the shield volcanoes on the island of Hawaii (see Case Study 6.1). Jump back to slide containing original image
- 41. 6-41 Hawaiian Hot Spot Long Description The Hawaiian Islands are part of a long chain of islands and submerged volcanic remnants known as the Hawaiian Ridge–Emperor Seamount chain. The active shield volcanoes on the big island of Hawaii are currently situated over a stationary mantle plume, which has been generating basaltic magma for approximately 70 million years while the Pacific plate slowly moves to the northwest. Jump back to slide containing original image
- 42. 6-42 Yellowstone Hot Spot Long Description Map (A) showing the location of ancient calderas associated with the Yellowstone hot spot. Yellowstone National Park is the site of the most recent caldera, which formed after a colossal eruption 640,000 years ago. Cross section (B) showing how rising basaltic magma from the hot spot can cause melting of granitic crust, resulting in a rhyolitic magma chamber. The accumulation of new magma and release of hot fluids are believed to be responsible for recent earthquake activity and changing land elevations within the caldera. Jump back to slide containing original image
- 43. 6-43 Calderas Long Description Calderas form (A) when magma is ejected from a shallow magma chamber, leaving its roof unsupported and eventually causing it to collapse. Photo (B) shows the water-filled caldera of Crater Lake in the Cascade Range in Oregon. Jump back to slide containing original image
- 44. 6-44 Volcanic Hazards (1) Long Description Lava flows cause considerable damage when they bury valuable real estate and infrastructure, such as the highway and personal property shown in (A). Flows are also destructive when they encounter combustible materials and cause them to catch fire, as in the case of Volcanoes National Park Visitor Center in Hawaii (B). Jump back to slide containing original image
- 45. 6-45 Volcanic Hazards (2) Long Description Pyroclastic flows are dry, hot avalanches where large rock fragments tumble along the ground surface and are overlain by a flowing cloud of finer fragments and droplets of lava. Mixed with these materials are superheated gases, creating a flow that will obliterate and incinerate everything in its path. The illustrations show some of the ways pyroclastic flows form during either explosive or nonexplosive events. Jump back to slide containing original image
- 46. 6-46 The eruption of Mount St. Helens (1) Long Description The eruption of Mount St. Helens was triggered by a small earthquake, which caused a landslide (A) over a bulge that had formed on the side of the volcano. Once the landslide removed the weight of this overlying rock (B), dissolved gases within the highly pressured magma were allowed to rapidly expand. Because of the location of the bulge, the initial blast was directed horizontally (C), devastating the landscape. Jump back to slide containing original image
- 47. 6-47 The eruption of Mount St. Helens (2) Long Description Graph comparing the volume of ash ejected in selected volcanic eruptions that have occurred in the recent geologic past. Jump back to slide containing original image
- 48. 6-48 Mass Wasting on Volcanoes Long Description St. Pierre was once a thriving seaport on the island of Martinique in the Caribbean. Then in 1902 a pyroclastic flow raced down nearby Mount Pelée and incinerated the city and its entire population of 30,000. Jump back to slide containing original image
- 49. 6-49 Large volcanic mudflows Long Description Large volcanic mudflows can form when a landslide develops beneath a glacial ice cap on a composite cone. Such landslides can be triggered when magma creates an unstable bulge in the mountainside, or when slopes are weakened by gases and hot fluids that turn solid rock into clay minerals. Jump back to slide containing original image
- 50. 6-50 The Seattle-Tacoma area is under extreme risk Long Description Mount Rainier in Washington state is an active composite cone whose snow- and ice-capped summit contains more water than all the other Cascade volcanoes combined. This volcano has a history of generating extremely large mudflows, as illustrated by the map showing ancient mudflow deposits in river valleys leading up to the volcano’s summit. Many rapidly growing communities in the Seattle-Tacoma metropolitan area are at extreme risk as they are located within river valleys draining Mount Rainer. Jump back to slide containing original image
- 51. 6-51 The Cascade Range in the Pacific NorthwestLong Description The Cascade Range in the Pacific Northwest contains active stratovolcanoes associated with a subduction zone. Most of these volcanoes have erupted in the recent geologic past; some like Mount St. Helens erupt more frequently. Jump back to slide containing original image
- 52. 6-52 Predicting Eruptions Long Description a) The monitoring of magmatic earthquakes and volcanic gases is key in predicting volcanic eruptions. Portable seismographs record the rhythmic vibrations of magmatic earthquakes and allow scientists to track the magma body as it pushes up through the crust. Measuring the chemistry of gas samples collected at the surface helps determine whether the magma is new, and hence potentially more explosive. b) A seismograph recording showing numerous magmatic earthquakes taking place on Mount St. Helens. Jump back to slide containing original image