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Volcanoes

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Introduction to volcanoes, shape, lava, landforms, resources.

Introduction to volcanoes, shape, lava, landforms, resources.

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  • 1. Volcanoes
  • 2.  
  • 3. Geyser (Old Faithful)
  • 4.  
  • 5. Classification of volcanoes <ul><li>This is your homework – make sure you have examples of the various types of volcanoes </li></ul>
  • 6. Lava flows
  • 7. Basalt
  • 8. Aa lava
  • 9. Mr..Cooke will be in school late today
  • 10. Rhyolite (left) and Basalt (right)
  • 11. Andesite
  • 12.  
  • 13. Volcano Irazu Costa Rica
  • 14. Volcanic hazards <ul><li>Here is your volcanic hazard check list – </li></ul>
  • 15. Pyroclastic flow
  • 16. <ul><li>What is a pyroclastic flow? </li></ul><ul><li>Pyroclastic flows are heavier-than-air gas-particle emulsions that travel across the ground at velocities ranging from 10 m/sec to 300 m/sec. They can attain temperatures of over 1000 C. They range from high density flows that move down valleys and can move beneath water, to dilute flows that extend over mountains and can move across water. The term &quot;pyroclastic surge&quot; is a synonym for &quot;dilute pyroclastic flow.&quot; As shown by lateral facies transitions in pyroclastic flow deposits , pyroclastic flows and surges commonly develop simultaneously from the same flow and evolve one from the other. </li></ul>
  • 17. Pyroclastic flow Mount Pelee
  • 18. Debris avalanches <ul><li>Throughout Mount Hood's history, rapid landslides, called debris avalanches , of various sizes have occurred. The largest ones removed the summit and sizable parts of the volcano's flanks and formed lahars that flowed to the Columbia River. Large debris avalanches occur infrequently and are usually triggered by eruptive activity. But small ones not associated with eruptive activity occur more frequently. Small avalanches can occur when rocks, altered and weakened by acidic volcanic fluids or by weathering, such as freezing and thawing, fail spontaneously. </li></ul>
  • 19. Lahar
  • 20. Lahar damage <ul><li>Lahars are often associated with eruptive activity, but they can also be generated by rapid erosion of loose rock during heavy rains or by sudden outbursts of glacial water. On Christmas Day 1980, an intense rainstorm rapidly melted snow and triggered a small landslide in fragmental debris in upper Polallie Creek. The resulting lahar moved downvalley at 25 to 35 miles per hour. At the mouth of Polallie Creek, the lahar spread out, killing a camper and temporarily damming the East Fork Hood River. Flooding after failure of this temporary dam destroyed 5 miles of highway, three bridges, and a state park—at a cost of at least $13 million. Small lahars such as this occur every few years at Mount Hood, but few have been as destructive. </li></ul>
  • 21. Lahar
  • 22. Case study of Mount Hood Mount Hood from Portland, Oregon. When Mount Hood next erupts, Portland could be affected by light ashfalls similar to those it experienced during the 1980 eruptions of Mount St. Helens. The city will not be directly affected by lava flows, pyroclastic flows, or lahars, but regional transportation and water supplies could be disrupted. (Photo by David Wieprecht, USGS)
  • 23. <ul><li>Mount Hood's last major eruption occurred in the 1790's not long before Lewis and Clark's expedition to the Pacific Northwest. In the mid-1800's, local residents reported minor explosive activity, but since that time the volcano has been quiet. Someday, however, Mount Hood will erupt again. What will those eruptions be like and how will they affect us? Scientists from the U.S. Geological Survey (USGS) are studying the volcano's past eruptive behavior to better anticipate and prepare for future eruptive activity. </li></ul>
  • 24. Subduction of the Juan de Fuca Plate under the North American Plate controls the distribution of earthquakes and volcanoes in the Pacific Northwest. Mount Hood is just one of several recently active, major volcanic centers in the Cascade Range.
  • 25. <ul><li>Unlike its neighbor to the north, Mount St. Helens, Mount Hood does not have a history of violent explosive eruptions. Instead, lava flows (see Volcano Hazards graphic for definitions of bold terms), rarely traveling more than 6 to 8 miles from their source, have built up the flanks of the volcano one sector at a time. Sometimes, instead of flowing slowly downhill, lava piles up over its vent forming a lava dome many hundreds of feet high. On the steep upper slopes of Mount Hood, growing lava domes have repeatedly collapsed to form extremely hot, fast-moving pyroclastic flows . Few of these pyroclastic flows have traveled more than 8 miles. But because they are extremely hot, such flows can melt significant quantities of snow and ice to produce lahars that flow down river valleys, often far beyond the flanks of the volcano. Over the past 30,000 years, growth and collapse of lava domes and generation of lahars have dominated Mount Hood's eruptive activity. </li></ul>
  • 26. Note that most of the volcanic hazards have been displayed by Mount Hood at one time or other. The volcano very often changes the materials it erupts – this is due to complex changes in the chemistry of the magma supply.
  • 27. One way to protect against volcanic hazards is to zone the land around them
  • 28. Gas eruptions
  • 29. Case study of Nyos <ul><li>In 1986, more than 1700 people died when toxic gas erupted from Lake Nyos , a volcanic lake in the West African nation of Cameroon. The gas was carbon dioxide which, being more dense than air, hugged the ground and flowed down valleys. The cloud travelled as far as 15 miles (25 km) from the lake. It was moving fast enough to flatten vegetation, including a few trees. In addition to the human deaths caused by suffocation , 845 people were hospitalized and 3,000 cattle died. Lake Nyos is a few square kilometres in area, and is around 200 m deep.  It is situated in the crater formed from the collapse of the pipe feeding a now extinct volcano. </li></ul>
  • 30. <ul><li>The science behind the disaster is fairly simple. Lake Nyos is a deep pool of water sitting in the throat of a dormant volcano. The real culprit is a pool of hot magma, laying almost 50 miles below the lake. The magma releases the carbon dioxide and other gases, which travel upward through the earth. The gases gets trapped in natural spring water, which eventually rises toward the surface and feed into the crater lake. </li></ul>
  • 31. <ul><li>The carbon dioxide, instead of being released harmlessly into the atmosphere, collects in the cold water at the bottom of the lake. The amount of gas that can be dissolved in the water is dependent on water temperature and pressure. The greater the pressure, the more gas can be trapped. None of this would be particularly hazardous if the water at the bottom of the lake were to regularly rise to the surface, where the gas could be safely released. The problem is that the waters of Lake Nyos, like many tropical lakes, are steady and still, with little annual mixing of the water layers. </li></ul>
  • 32. <ul><li>Over time, the lowest levels of the lake become more and more saturated with gas. And eventually, when they reach 100% saturation, the gas can bubble spontaneously out of the lake, creating a foaming column of carbonated water. This eruption, or release, can be triggered even before saturation is reached by a landslide, earthquake, violent storm, or other disturbance of the waters. </li></ul>
  • 33. <ul><li>The eruption itself isn't dangerous, but the suddenly released gas cloud can be fatal. Carbon dioxide is heavier than air, and when released, it pours over the rim of the crater and slides down into the surrounding low-lying valley. Carbon dioxide normally makes up 0.03% of air, and concentrations of more than 10% can be fatal. The unfortunate villagers around Lake Nyos literally suffocated under the heavy poisonous cloud of gas. </li></ul>
  • 34. Lake Nyos (Cameroon)
  • 35. Protecting against further gas eruptions <ul><li>In an effort to side-step another catastrophe, an international team of scientists, supported by the U.S. Office of Foreign Disaster Assistance, have developed a plan to try to remove the gas from the lakes. The plan is to place large pipes in Lakes Nyos and Monoun. These pipes, each about five inches in diameter, will be placed on a floating platform and sent down to the lowest layers of water, creating a vent to the surface. Water will be pumped from the bottom of the lake, and the gas-water fountain that results releases the carbon dioxide harmlessly into the atmosphere. </li></ul>
  • 36. Mt. Pinatubo
  • 37. Aerosols <ul><li>The images above show the effect that the 1991 eruption of Mt. Pinatubo had on the atmosphere. The picture in the upper left shows the atmosphere before the eruption, with low levels of aerosols present. (The thicker the optical depth is, the more aerosols are in the air.) The image in the upper right shows the atmosphere after the eruption, with large amounts of the volcanic aerosols having spread around the world. Because the dominant winds are east-west, the aerosols by this time have not had a chance to travel to higher latitudes. The lower two images, taken in the months following the eruption, show the aerosols moving to higher latitudes and eventually being spread evenly throughout the entire atmosphere. These images were taken by a satellite instrument called the Stratospheric Aerosol and Gas Experiment (SAGE) II. </li></ul>
  • 38. Effect of dust emissions from Pinatubo
  • 39. HOMEWORK TEST <ul><li>If you have completed the homework task the next few slides will make some sense. They are great revision. </li></ul><ul><li>Look at the funny looking kid at the back who forgot to do his homework. </li></ul>
  • 40.  
  • 41. Volcano types <ul><li>Effusive Eruptions </li></ul><ul><li>Effusive eruptions are those that create vast lava flows of low viscosity, fluid lava.   Magma associated with effusive-type eruptions is relatively low in silica and thus &quot;easily&quot; flows up the vent and spreads across the surface. Moving across the land, these lava flows can take on two different forms. Pahoehoe (a Hawaiian term) lava has a glistening, ropy like appearance as it moves and cools.  AA lava is more pasty than pahoehoe and forms a sharp, clinkery, rough surface. As the core of the flow moves across the surface, the rough &quot;clinkers&quot; are carried along the top of the flow. At the leading edge of the flow, the clinkers tumble forward into a heap. </li></ul>
  • 42. Shield volcano (Mauna Loa)
  • 43. <ul><li>Shield volcanoes are a product of effusive eruptions . As the fluid lava flows out onto the surface, it spreads out and cools into a broad, low-angled slope. The final shape looks much like a warrior's shield with the convex side pointing towards the sky. The Hawaiian Islands are an example of shield volcanoes. Though much lava pours from the summit caldera, flank eruptions from lateral vents spreads molten lava along the sides of the volcano. As the lava flow cools, tubes may form in the flow .   These are conduits through which lava flows beneath a skin of solidified lava. Occasionally lava will accumulate as a lava pond too. </li></ul>
  • 44. Shield volcano - features
  • 45. <ul><li>Explosive Eruptions </li></ul><ul><li>A second category of volcanoes are those characterized by explosive eruptions. Explosive eruptions are common to volcanoes with very viscous lava and high amounts of gas under pressure.  The viscosity, or stickiness, of the lava relates to the silica content. Magma high in silica is more viscous than lavas low in silica. Explosive eruptions are common to volcanoes along the &quot; Ring of Fire &quot;, a string of volcanoes extending from the northwest coast of the United States, up through the Aleutian Islands, and into Japan . As the magma rises through the central vent, it gets stuck and gases build to high pressures until an eruption of great force occurs.  </li></ul>
  • 46. <ul><li>Mt. St. Helens, a composite volcano </li></ul><ul><li>Vast amount of ash and pyroclastic material can be ejected from these kinds of volcanoes. Accompanying many of these eruptions are vast outpourings of noxious gases and fine particulate matter called &quot; Nuees Ardentees &quot; or &quot;glowing clouds or avalanches&quot;. These clouds can rush down the flanks of a volcano at speeds reaching 60 mph. These are pyroclastic flows. Escape from such clouds is virtually impossible </li></ul>
  • 47. Mount St. Helens
  • 48. <ul><li>Two types of volcanoes characteristically produce explosive eruptions, cinder cones and composite volcanoes. Cinder cones are primarily composed of layers of pyroclastic material built from rock fragments once lodged in the central vent of the volcano . Mt. Paricutin is one of the most famous cinder cones erupting from a Mexican farmer's field in 1943. </li></ul>
  • 49. Composite or strato volcano
  • 50. Cinder cone (Mt. Paricutin, Mexico)
  • 51. <ul><li>Composite , or stratovolcanoes also produce explosive eruptions. Composite volcanoes form from alternating eruptions dominated by pyroclastics or lava. As a result, composite volcanoes display layers of these alternating flows. Composite volcanoes are among the tallest volcanoes on earth, with Mt. Fuji, Mt. St. Helens, and Mt. Kilimanjaro being examples. Composite volcanoes are often associated with convergent plate boundaries where subduction is occurring.  </li></ul>
  • 52. Case studies <ul><li>Pinatubo, Philippines, 1991 </li></ul><ul><li>On June 15, 1991 Mt. Pinatubo, a stratovolcano on the &quot;Ring of Fire&quot; exploded hurling two cubic miles of tephra into the air and sent a cloud of sulfur dioxide 25 miles into the stratosphere. Pyroclastic flows swept down the sides of the mountain filling valleys and extending 11 miles from the site of the eruption. </li></ul><ul><li>Results </li></ul><ul><li>Pinatubo's toll was devastating: nearly 900 dead, 42,000 homes destroyed, 100,000 acres of cropland covered in ash and billions of dollars in economic losses. Ash and dust injected into the stratosphere spread across the globe depressing global temperatures by .5oC. </li></ul>
  • 53. Pinatubo
  • 54. Mount St. Helens <ul><li>Mt. St. Helens is a stratovolcano found in southern Washington that on May 18, 1980 erupted with a violent fury wreaking devastation over thousands of square kilometers. For weeks the volcano had been venting steam and ash for weeks. A huge bulge on the side of mountain warned scientists that a major explosion was about to occur. When Mt. St. Helens erupted, four hundred meters (1,300 feet) of  the north summit blew away. A cloud of ash, hot steam and poisonous gas raced down the side of the mountain at speeds approaching 320 km per hour (20 mph) destroying forests, lakes, and camping sites as far away as 32 kilometers (20 mi.). </li></ul>
  • 55. <ul><li>Huge mud flows choked streams and valleys. Hundreds of homes were buried or damaged and a thick covering of ash coated nearby cities. Sixty people and an untold numbers of animals were killed as a result of the eruption. </li></ul>
  • 56. St. Helens (before and after)
  • 57. <ul><li>Paricutin, Mexico, 1943 </li></ul><ul><li>In the winter of 1943, the countryside near Paricutin, Mexico was rocked by a series of earthquakes. The tremors lasted for nearly two weeks when a fissure open in a farmer's field and the birth of cinder cone was underway. Within 12 hours of the initial eruption, the fissure was ejecting pyroclastic material as well as huge clouds of gas and ash. Within 24 hours a 40 meter high cone hurling volcanic bombs several kilometers away had been built. Lava began to spill from the base of the cone building the volcano laterally. After nine years of activity, two villages had been buried and 50 km2 of farmland had been devastated and abandon. </li></ul>
  • 58. Paricutin (Mexico)
  • 59. <ul><li>Krakatoa, Indonesia, 1883. </li></ul><ul><li>The small, inhabited island of Krakatoa was the site of the greatest explosion ever witnessed by humans. The island situated in an ancient caldera between Java and Sumatra exploded on August 27, 1883. Beneath the earth, pressure from steam was building by the intense heating of groundwater in the old volcano. The explosion hurdled 20 cubic kilometers of debris into the air leaving a 300 meter deep hole inside the caldera. The explosion was so great that it could be heard 2000 km away in Australia and airborne debris caused total darkness 150 km away. The force of the explosion created a air pressure wave  felt halfway around the world. A massive, a 40 m high ocean wave radiated across the ocean killing an estimated 30,000 people living in coastal locations. </li></ul>
  • 60. Why do people live near volcanoes? <ul><li>Water resources </li></ul><ul><li>Auckland’s volcanoes and their eruptive products have developed some very valuable water resources. Not only have some explosion craters formed lakes e.g. Lake Pupuke , but basaltic lava flows have formed aquifers to become significant sources of water supply. </li></ul><ul><li>The opposite image shows the extent of the aquifer between Mt Wellington and One Tree Hill . This aquifer provides water for the Onehunga area. </li></ul><ul><li>  </li></ul><ul><li>  </li></ul><ul><li>  </li></ul><ul><li>  Basalt lava flows are very porous and allow water to seep into the rocks. These aquifers are currently being tapped for water supply. For example at Onehunga, water &quot;is extracted from four wells sunk into the One Tree Hill lava flows. An estimated 27 300 cubic metres of water per day flows through that aquifer, reaching from as far as five kilometres away.&quot; (Jamieson, 1992). Most of Auckland’s volcanic cones support water supply reservoirs. </li></ul><ul><li>  </li></ul>
  • 61. Here is one of the volcanoes which has been developed as a water resource in New Zealand
  • 62. Mineral deposits Sulphur mine not far from Mt. Hood
  • 63. Valuable mineral deposits <ul><li>The Sulphur Works and Little Hot Springs Valley are colorful areas filled with residue from hot water and acids that have attacked the lava flows of ancient Mt. Tehama for thousands of years. The color of these residual deposits is caused by the hydrothermal action on the minerals found in the rocks with a blue residue attributed to manganese, red to iron, and yellow to sulphur. Kaolin and Opals are common products here. The Sulphur Works area once offered hot mineral baths to visitors and was considered as an avenue for profit at one time. Today, the Sulphur Works is protected by the National Park Service and is enjoyed as one of the most interesting geothermal areas in the park. </li></ul>
  • 64. ENERGY SOURCES <ul><li>Geothermal Energy </li></ul><ul><li>Geothermal energy refers to thermal or electrical power produced from the thermal energy contained in the Earth. The use of geothermal energy is based on the temperature difference between a mass of buried rock and water and a mass of water (or air) at the Earth's surface. The temperature difference thermodynamically allows the production of thermal energy which is converted directly or indirectly to mechanical or electrical energy. Iceland is one of the best examples of a country that has exploited geothermal energy from volcanoes. </li></ul>
  • 65. Geothermal energy
  • 66. Geothermal project in the US
  • 67. Soils – agricultural potential
  • 68. Agriculture <ul><li>Basic volcanic rocks such as basalt weather to produce fertile soils. Acid volcanic rocks such as rhyolite produce less fertile soils. Remember that 90% of the world’s volcanoes are basic – many of them are oceanic islands - many are densely populated. </li></ul>
  • 69. Tourism (let’s go!)
  • 70. Tourism (great fishing spot!)
  • 71. Tourism
  • 72. Lava fountains (Mauna Loa)
  • 73. Kilauea (Hawaii)
  • 74. Lava flow, Kilauea
  • 75.  
  • 76. Oceanic volcanic islands are not the same <ul><li>By analyzing radioactive isotopes in rocks from various volcanic islands, geochemists have determined that all islands are not alike. Most islands are made of mixtures of many rock types. But some islands are primarily composed of one of four chemically distinct rock types: EM1 (Enriched Mantle 1), EM2 (Enriched Mantle 2), HIMU (HIgh “MU,”from the Greek symbol µ); and DMM (Depleted Mid-ocean ridge basalt Mantle). These chemical distinctions provide clues to understand the underlying mantle plumes that create the islands. (World Ocean Floor Map. </li></ul>
  • 77.  
  • 78. Devil’s Tower Wyoming
  • 79. Mount Rushmore (granite outcrop)
  • 80. Granite

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