Earth Science Exam 2 - CJK
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Created by:
xchrisk on September 23, 2011
Subjects:
plate tectonics, volcanoes, earthquakes, earth science
Description:
Earth Science Exam 2 covering Plat Tectonics, Volcanoes, and Earth Quakes
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95 terms
Terms | Definitions |
|---|---|
 Define stress, and explain how the term applies to geologic materials. | In geology stress is a general term referring to force applied on a rock. An object is under stress when a force is applied to it. |
| Define strain, and explain how the term applies to geologic materials. | Strain is deformation resulting from stress. In geology a rock under stress may change shape or size this change is referred to as strain. |
| Define compressive stress, and explain how the term applies to geologic materials. | Compressive stress is caused by the squeezing or compressing of an object. In geology this may be due to a massive amount of weight placed on rock causing the rock below to compress. Imagine having a piece of clay that you push down on with both of your hands. This will flatten the clay and is a type of compressive stress. |
| Define tensile stress, and explain how the term applies to geologic materials. | Tensile stress is a pulling or stretching of an object. In geology rock that is pulled in a part would be under tensile stress. Imagine having a piece of clay in your hands and you pull your left hand to the left and your right hand to the right. This pulling apart will result in tensile stress in the center of the clay. |
| Define shearing, and explain how the term applies to geologic materials. | Shearing stress is when a piece of rock is moved in different directions or at different rates. Imagine you have a piece of clay in your hands and in one hand you push forward, in the other hand you pull back. The stress between the two movements is shearing stress. This can happen in geology when two plates are moving past each other, the rock in between can be pulled in opposite directions at the same time. |
| Define elastic deformation, and explain how the term applies to geologic materials. | Elastic deformation is a temporary strain. The object recovers original size and shape once the stress is removed. Imagine a rubber band. You can make the band bigger, temporarily, but once you remove the force making the band bigger it snaps right back into place. Rocks can undergo elastic deformation, especially in subduction faults prone to earthquakes. |
| Define elastic limit, and explain how the term applies to geologic materials. | Elastic limit is the point at which elastic strain becomes permanent. At this point an object may undergo plastic deformation. Imagine stretching a rubber band until it breaks. When the band breaks you have past the elastic limit of the rubber band. In geology if the elastic limit of a rock is broken the rock will undergo a rapid period of plastic deformation. In a subduction zone this may result in an earthquake. |
| Define plastic deformation, and explain how the term applies to geologic materials. | Once the elastic limit of a material is breached the material may deform permanently with little additional stress. Rock folds are an example of plastic deformation. |
| What is rupture? What factors can determine when of if rocks will rupture? | Rupture is the breaking of rocks due to stress. Rocks may rupture under heat, pressure, or stress. Rocks that are brittle may rupture before plastic deformation occurs. |
| What are external factors that may affect the physical behavior of rocks? | Temperature (Pliable due to heat? Brittle due to cold?) Confining Pressure Intrinsic Rock Characteristics Different rocks respond differently to different stresses The length of time stress is applied is also a factor. Sudden stress, and prolonged stress may both effect the physical nature of a rock. |
| What effect does time have on brittleness or other behaviors? | A rock under sudden stress may break/rupture brittle rocks. This may result in an earthquake. A rock under prolonged stress may result in plastic deformation of rocks. An example would be how rocks deform due to centuries of being under extreme weight. |
| Define lithosphere. What are the characteristics of the lithosphere? (Location, composition, physical properties, etc...) | The Lithosphere refers to the outer solid layer of earth. (Crust and upper mantle) The lithosphere varies in thickness from place to place. It is thinnest underneath the oceans, where it extends to a depth of about 50 kilometers (30 miles). Under the continents the lithosphere is both thicker on average, and more variable in thickness, extending in places to about 250 kilometers (over 150 miles) beneath the highest mountain ranges. The lithosphere is solid, somewhat brittle, and elastic. |
| Define asthenosphere. What are the characteristics of the asthenosphere? (Location, composition, physical properties, etc...) | The layer below the lithosphere is the asthenosphere. The asthenosphere extends to an average depth of about 300 kilometers (close to 200 miles) in the mantel. Its lack of strength or rigidity results from a combination of high temperatures and moderate confining pressures that allows the rock to flow plastically under stress. Below the asthenosphere, as pressures increase faster than temperatures with depth, the mantle again becomes more rigid and elastic. |
| What types of evidence have been used to locate plate boundaries? | Plate boundaries are indicated by the distribution of earthquakes and volcanic eruptions. |
| What types of evidence indicate plate movements do occur? | The topography of the sea floor General Magnetism in rock Paleomagnetism Seafloor spreading Age of the ocean floor Polar-wander curves Sedimentary rocks and the fossils contained within Continental shelves and how they fit together Pangaea |
| What is the Curie temperature? | Curie temperature is the temperature below which each magnetic mineral remains magnetic. When a mineral exceeds its curie temperature it looses its magnetism. The curie temperature is always lower then the melting temperature of a mineral. |
| What does magnetism have to do with rocks? | Most iron-bearing minerals are at least weakly magnetic at surface temperatures. As crystallization occurs in the formation of rocks the crystals align towards magnetic north. |
| What is paleomagnetism? | Paleomagnetism is the study of magnetism in fossils. Magnetic north has not always been the same place. Based on the magnetic orientation of rocks scientists can get an idea of the time period differences between bands of rocks. |
| How does magnetism in rocks support the theory of plate tectonics? | Rocks that form together at the same time are all magnetized orientated in the same direction. Over time the magnetic poles have changed resulting in rocks forming with different magnetic orientations. Scientists have been able to identify bands of rock formations in different areas on the sea floor with similar magnetic polarization. By being able to compare these bands of similarly magnetized rocks and the distance between similar bands scientists have been able to theorize that the seafloor is spreading and the plates moving. |
| What is the relationship between seafloor spreading, paleomagnetism, and polarity reversals? | As rocks are formed at a seafloor rift they crystallize with the same magnetic orientation. When the polarization of the earth changes any new rock formed will have crystals pointing towards the new magnetic north. This results in bands of rock on the sea floor with crystals all facing the same direction. As the sea floor spreads these bands move farther apart. |
| What are polar-wander curves? What is their significance? | Magnetic rocks of different ages on a single continent may point to very different apparent magnetic pole positions. The magnetic north and south poles may not simply be reversed but may be rotated or titled from the present magnetic north and south. When the directions of magnetization and latitudes of many rocks of various ages from one continent are determined and plotted on a map, it appears that the magnetic poles have meandered far over the surface of the earth -- if the position of the continent is assumed to have been fixed on the earth throughout time. The resulting curve, showing the apparent movement of the magnetic pole relative to the continent as a function of time, is called the polar-wander curve for that continent. We know now, however, that it isn't that the poles have wandered, but the continents. |
| What is(was) Pangaea? Why is it significant? | The Pangaea was a super continent about 200 million years ago. It's existence is evidence that the contents have since moved apart from one another. |
| What is the significance of global distribution of fossils? | Fossils of the same species can be observed located on completely separate continents. These fossils could not have been moved from one continent to another unless the contents were joined together at some point. |
| What are the different types of plate boundaries? | Divergent boundaries Transform boundaries Convergent boundaries |
| What movement is associated with divergent plate boundaries? What type of things are associated with this movement? | Divergent plate boundaries are two plates moving away from each other. This results in oceanic ridges and continental rifts. As plates move apart in oceanic ridges, pressure releases allow magma to move up and form new lithosphere. In continental rifting, volcanoes or lava flows may be active early. If rifting continues, land masses separate and new ocean basins form. Examples are the Red Sea, East Africa, and locally the New Madrid fault. |
| What movement is associated with transform boundaries? What type of things are associated with this movement? | A transform boundary occurs when opposite sides of a fault, on two different plates, move in opposite directions. Earthquakes may occur on transform fault lines. An example is the San Andreas fault. |
| What movement is associated with convergent plate boundaries? What type of things are associated with this movement? | Convergent plates move towards each other. What happens at convergent plate boundaries depends on what type of plates are converging. Continental plates are buoyant and float on the asthenosphere. Denser oceanic plates are forced into the asthenosphere. Ocean-continent collision results in the forming of a subduction zone and produces a trench when one plate is forced under the other. Subduction zones are geologically very active. Volcanoes and earthquakes are often a result. Ocean-Ocean convergence will often result in a line of volcanoes, and / or an island arc. Continent-continent collision results in the collision, crumpling, and deformation of both plates. Earthquakes are frequent during active collisions and the formation of mountains may result. The Himalayan Mountains are an example of continent to continent convergence. |
| What is a subduction zone? | A subduction zone is created when two tectonic plates converge. If one plate goes under the other plate a subduction zone is created. The plate going under is subducted. |
| What is a mantel hot spot? | A mantel hot spot is an isolated area of volcanic activity not associated with plate boundaries. Hot spots remain fixed in position while plates move over them - results in chains of volcanoes. |
| Why do plates move? What are possible causes of movement? | There are a few hypothesis as to why plates move. The most widely accepted explanation is that the movement is due to convection cells and magma currents. Essentially, magma rises at the ridges of plates, some spreads out sideways and cools, then cools and sinks. The motion of rising hot magma and sinking cooled magma results in a conveyor like force under the plates causing them to gradually move. Another possible explanation is that the weight of subducting plates pulls the rest of the trailing plate with it. In this hypothesis the idea is that the movement of the plates is what causes the magma to cycle. |
| How do scientists determine past motions and present velocities of tectonic plates? | Scientists determine past motions and present velocities by looking at polar-wander curves and seafloor spreading. |
| Define and explain fault in terms of geology. | Faults are planar breaks in rocks along which displacement of one side occurs relative to the other side. |
| Define and explain creep in terms of geology. | Creep is gradual and relatively smooth movement along a fault. It is sometimes termed aseismic slip, meaning fault displacement without significant earthquake activity. Creep can be inconvenient but rarely causes serious damage. |
| Define and explain earthquake in terms of geology. | An earthquake will occur when stress exceeds rupture strength of the rock resulting in a sudden movement to release the stress. An earthquake could also occur due to friction along a pre-existing fault. Friction may prevent rocks from slipping easily or when stressed rock is not already ruptured. |
| Define and explain elastic rebound in terms of geology. | Elastic rebound occurs when rocks snap back elastically to previous dimensions due to sudden displacement and stress release. |
| Define and explain focus in terms of geology. | Focus is the point on a fault at which the first movement or break occurs during the earthquake. This is the point on the fault, typically far below ground, where the event originates. |
| Define and explain epicenter in terms of geology. | Epicenter is the point on earth's surface directly above the focus. |
| Where do earthquakes usually occur? | Most major earthquake epicenters are concentrated in linear belts. These belts correspond to plate boundaries. Not all earthquakes occur at plate boundaries, but most do. Furthermore earthquakes generally occur in the lithosphere where rocks are rigid and brittle, rupture and slip. Below the lithosphere rock becomes more liquid and material flows. Deep focus earthquakes are concentrated in subduction zones where the lithosphere subducts. |
| What is the difference between body waves and seismic surface waves? | A body wave travels through the earth. Body waves come in two types: P-waves (compression waves) and S-waves (shear waves). A seismic surface wave travels along the surface. A seismic surface wave displaces rock and soil in such a way that the ground surface ripples or undulates. Surface waves also come in two types: Vertical ground motions, like ripples on a pond; and horizontal shearing motions. Surface waves are larger in amplitude (representing the amount of ground displaced) then body waves from the same earthquake. Therefor, most of the shaking and resultant structural damage from earthquakes is caused by the surface waves. |
| What is the difference between P waves and S waves? | P-waves are compression waves. As P waves travel through matter, the matter is alternately compressed and expanded. P waves travel through the earth, then as much as sound waves travel through air. A compression sort of wave can be illustrated with a slinky toy by stretching the coil out wide. Then pushing one end in suddenly while holding the other end still. The resulting wave of compressed coils will flow from one side of the slinky to the other away from the end that was originally moved. S-waves are shear waves, involving a side-to-side motion of molecules. Sear-type waves can also be demonstrated with a slinky by stretching the coil out and then twitching one of the ends sideways. As the wave moves along the length of the slinky the loops of coil move sideways relative to each other, not closer together and farther apart as with the compression wave. |
| What is the difference between vertical ground motion and horizontal shearing motions? | Vertical ground motions are like ripples on a pond. Horizontal shearing motions waves that move side to side horizontally. |
| What is amplitude? | The measure of something's size, especially in terms of width or breadth; largeness, magnitude. In regards to earthquakes the highest amplitude is determined by the measurement of the largest seismic wave. |
| How is the epicenter of a earthquake located? | An earthquake's epicenter is located by measuring the distance in arrival time between the first P-wave and first S-wave. The difference in time between these two waves corresponds to how far away the two waves originated from because the two waves travel at different speeds. Once it is known how far away an earthquake originated from a circle can be drawn around the recording scale representing this distance. With the data from at least 3 recording stations one can determine the epicenter of an earthquake by finding where the three circles meet. |
| What data is needed to determine the epicenter of a earthquake? | The arrival times of the first P-wave and S-wave to the seismograph. More specifically you need to know the difference in arrival times between the two waves. This information is needed from at least 3 different seismographs. |
| What is magnitude? How is it measured? What scale is used? | Magnitude is the mount of ground motion related to an earthquake. It is measured with a seismograph. The magnitude number corresponds to the amount of ground displacement produced near the epicenter. The highest amplitude is determined by the largest seismic wave. The Richter scale is a logarithmic scale used to rate earthquakes based on their magnitudes. Earthquake measurement is relative because not all rock types respond in the same way. Some rocks may be more brittle, more elastic, or respond differently to heat. |
| What is intensity? How is it measured? What scale is used? | Intensity is the effect an earthquake has on humans, and their structures, due to the earthquake's release of energy. It is measured subjectively and can vary greatly due to construction quality, distance from epicenter, and local geology. The scale used to rank intensity is the Modified Mercalli Intensity Scale. Ranks are defined by Roman Numerals. Intensity does not always correspond to magnitude. |
| What is a logarithmic scale? Explain why the scale of magnitude and energy release are logarithmic. | Logarithmic means that each step is 10 times more powerful. Each step on the Richter scale is 10 times more powerful then the previous. (I.e. 5 is ten times more powerful then 4.) |
| What are possible ways of reducing injury and damage due to earthquakes? | Power lines and pipelines can be built with extra slack or "give" for stretching. Building codes can be instituted for creating Earthquake-resistant buildings. |
| What are aftershocks? | Severe earthquakes are generally followed by many aftershocks, earthquakes that are weaker than the principle tremor. |
| Explain the types of ground failure: Landslides and liquefaction. How do these affect damage rates during an earthquake? | Landslides happen when unstable slopes give way and collapse. Liquifaction occurs in wet ground, filled land near the coasts, places with high water table. When liquifaction occurs the ground becomes like quicksand, buildings fall over or sink into the ground. Both of these events increase damage rates dramatically during an earthquake. Buildings that were built to withstand the movement associated with earthquakes can be destroyed by either of these types of ground failure. |
| What causes tsunamis? | Water displacement is the cause of tsunamis. Water may be displaced through sudden movement of the sea floor which sets up waves like ripples. Earthquakes can cause the sudden movement on the sea floor. |
| What are the effects of a tsunami? | Coastal flooding due to subsidence Uplift of the sea floor Fires due to broken fuel lines, tanks, and power lines. |
| What are the warning signs of a tsunami? | In the open sea a tsunami will appear as a sudden broad swell on the water surface. On land the waves become large, breaking waves. Possibly over 15 meters in height due to large quakes. Coastal areas may be hit by several breakers in succession. Between breakers water may be pulled seaward which empties the bay or harbor. |
| Why is fire considred a hazard of earthquakes? | Earthquakes can break fuel lines, tanks, and power lines leading to fires. For example in the 1906 San Francisco earthquake 70% of the damage was due to fire. |
| What are some methods being researched as a possible way to predict earthquake activity? | Seismic gaps are sections of fault-line with little or no seismic activity. Seismic gaps represent locked sections where friction prevents slipping. Scientists look at seismic gaps as areas where potential earthquakes could happen. However, there really is no accurate way of predicting earthquakes. |
| What are some earthquake precursors? | Changes in rock property Ground surface may uplift and tilt Seismic-wave velocities in rocks near the fault may change Resistance of rocks to flowing electrical current may change Change sin water levels in wells Changes in radon content Abnormal animal behavior. There are no reliable predictors, quakes may occur with no warning, warnings may occur with no quake activity. |
| Explain the earthquake cycle. | The earthquake cycle refers to the interval between quakes. There is a period of stress buildup followed by a sudden fault rupture. Followed by aftershocks due to adjustments followed by more stress buildup. Then another long period of stress build up. |
| Are there any reliable methods of predicting an earthquake? | no |
| What is a possible method of earthquake control? Is it safe and reliable? | Liquid injection. It is neither safe nor reliable. |
| Where does magma origniate? | Magma tends to originate 50 to 250km deep into the crust and upper mantle. |
| What types of magma are there? | Mafic Felsic |
| What rocks are associated with each type of magma? | Basalt - rich in ferromagnesians, forms new sea floor at rifts. Rhyolite - Volcanic equivalent of granite, silica rich. Andesite - Intermediate between Mafic basalt and Felsic rhyolite. |
| What is Mafic composed of? | Mafic is rich in iron, magnesium, and ferromagnesium silicates |
| What is Felsic composed of? | Felsic is rich in silica and feldspar |
| What is the ring of fire? | The ring of fire is a ring of subduction zones rimming the pacific ocean. The ring of subduction zones around the pacific ocean has resulted in an abundance of volcanoes. |
| What are some examples of continental rift volcanoes? | Killimanjaro |
| What are some examples of hot spot volcanoes? | Hawaii, Galapagos Islands, Iceland, Yellowstone |
| What does seafloor spreading have to do with volcano activity? | Most volcanic rock is actually created at the seafloor spreading ridges, where magma fills cracks in the lithosphere and crystallizes close to the surface. Spreading ridges spread at a rate of only a few centimeters per year, but there are some 50,000km (about 30,000 miles) of these ridges presently active in the world. All in all, that adds up to an immense volume of volcanic rock. However, most of this activity is out of sight under the oceans, where it is largely unnoticed, and it involves quietly erupting Mafic magma, so it presents no dangers to people. |
| What is a fissure eruption? | A fissure eruption is the eruption of magma out of a crack in the lithosphere, rather then from a single pipe or vent. The outpouring of magma at spreading ridges is an example of a fissure eruption. |
| What is a shield volcano? what are it's characteristics (shape, physical appearance, type of magma, intensity of eruption, etc...)? | A shield volcano has a low, shield like shape, very flat and low relative to the diameter. A shield volcano contains mafic basaltic lavas which are relatively fluid. Lava from shield volcanoes flows freely and for great distances. An Example is Kilauea in Hawaii. |
| What is a volcanic dome? what are it's characteristics (shape, physical appearance, type of magma, intensity of eruption, etc...)? | A volcanic dome is a rounded accumulation around a volcanic vent of congealed lava too viscous to flow away quickly; hence usually rhyolite lava A volcanic dome is a compact, steep sided, structure formed from slow moving lava that has cooled. Domes are typically formed by rhyolitic and andesitic lavas which are more viscous, and don't flow as easily. The volcanic dome is the top, or cap, of the volcano. An example is Mount St. Helens. |
| What are cinder cones? | From the book: While basaltic magmas generally erupt as fluid lava flows, they sometimes produce small volumes of chunky volcanic cinders that fall close to the vent from which they are thrown. The cinders may pile up into a very symmetric cone-shaped heap known as a cinder cone. From Wiki: A cinder cone is a steep conical hill of volcanic fragments that accumulate around and downwind from a volcanic vent. The rock fragments, often called cinders, are glassy and contain numerous gas bubbles "frozen" into place as magma exploded into the air and then cooled quickly. Cinder cones range in size from tens to hundreds of metres tall. Cinder cones are made of pyroclastic material. From Class: Cinder cones tend to be taller then shield volcanoes, but not as big as composite volcanoes. |
| What are composite volcanoes? what are it's characteristics (shape, physical appearance, type of magma, intensity of eruption, etc...)? | Composite volcanoes are built up of layers of lava and pyroclastics. Composite volcanoes erupt different materials at different times and they build up in layers. A mixture of lava and pyroclastics allow them to get larger then either domes or cinder cones. These tend to be violent and explosive. These volcanoes tend to have fairly stiff andesitic lavas that may flow. Lava may trap enough gas for an explosive eruption and form pyroclastics. Examples of composite volcanoes are Mount St. Helens, Cascade Rage, Northwest U.S.A. |
| What is a pyroclastic? What volcanoes produce them? | Pyroclastics are pieces of violently erupted volcanic material. During an eruption Magma may solidify before hitting the earth resulting in the formation of a pyroclastic. Volcanoes with thick, viscous lavas which trap more gases, are typically associated with producing pyroclastics. Some basaltic volcanoes also produce ash and fragments. The composition of pyroclastics varies greatly. Some are very fine, flour-like dust, to coarse, gritty ash to cinders up to golf ball size to huge blocks. |
| What is a volcanic bomb? | Volcanic bombs are blobs of liquid lava thrown from a volcano. |
| What is a volcanic block? | A volcanic block is a fragment of rock that measures more than 64 mm (2.5 in) in diameter and is erupted in a solid condition. (From Wikipedia) |
| What are lahars? What danger do the pose? What volcanoes produce them? What type of material are they made of? | A Lahar is an avalanche of volcanic water and mud down the slopes of a volcano. The snow from mountains melts due to heat, combines with mud and flows down the mountain side. Water may also come from rain. Lahars tend to follow stream channels, choke streams with mud causing floods. Lahars were a major cause of damage with Mount St. Helens - Toutle River Pinatubo Lahars were formed when tropical rains combined with ash. Had this volcano erupted during dry season Lahars may not have formed. Long term impacts of Lahars include leaving streams clogged with mud reducing their capacity. An increase in future flood risks. It can be very costly to repair streams clogged with mud. |
| What are pyroclastic flows? What danger do the pose? What volcanoes produce them? What type of material are they made of? | A pyroclastic flow, sometimes called nuess ardentes, is a very hot (in excess of 1000C), very fast, mixture of hot gases and fine ash that is denser then air. Lava composition has been linked to the likelihood of pyroclastic flow. Typically pyroclastic flows are preceded by steam, lava, and seismic activity. Examples are : Mount Vesuvius's destruction of Pompeii and Mount St. Helens eruption in 1980. Mont Pelee in the Caribbean in 1902 killed 25,000 to 40,000 people in 3 minutes. |
| What are toxic gases? What danger do the pose? What volcanoes produce them? What type of material are they made of? | Toxic gases from volcanoes include carbon dioxide, sulfur, carbon monoxide, and hydrochloric acid. Gases may be sudden with little to no warning. An Example is Cameroon, Africa - 1986. Like Nyos on a rift zone released a carbon dioxide cloud and killed 1700 people due to suffocation. Gases were likely released from shallow magma that had seeped into the lake and then rose to the surface during season lake overturn. |
| What are steam explosions? What danger do the pose? What volcanoes produce them? What type of material are they made of? | Steam explosions occur when seawater seeps into heated rock producing steam that builds up until it triggers an explosion. Phreatic explosion is an explosion due to steam from water intrusion. An example is Krakatoa in Indonesia - 1883. The explosion was comparable to 100 million tons of dynamite resulting in a tsunami more then 40 meters in height, more then 36000 deaths, throwing dust/ash into the air that colored sunsets red for years to come. The explosion was heard as far away as Australia (3000km away) |
| What are some secondary effects of volcano activity? | Volcanic activity may cause changes in the climate and atmospheric conditions. |
| How does volcanic activity potentially affect climate and atmospheric conditions? | The effects may be brief or long-lasting. Volcanic dust may take years to settle out of atmosphere. The dust can partially block sunlight reaching the earth resulting in measurable cooling of the earth. Large quantities of sulfur-rich gasses may enter the atmosphere producing acid rain, aggravating ozone depletion, reducing the amount of solar radiation reaching the earth by 2%-4%, and lowering global temperatures. |
| How are volcanoes classified? | Volcanoes are classified by activity and index. |
| Explain how volcanic activity is classified. | A volcano is considered active if it has erupted within recent history. If it has not erupted, but looks fresh and not too eroded or worn down it is regarded as dormant: Inactive for the present, but potential to again become active. If a volcano has not recently erupted, and very much eroded is considered extinct: Or unlikely to erupt again. |
| Explain the Volcanic Explosivity Index (VEI). | The Volcanic Explosivity Index (VEI) has been developed as a way to characterize the relative sizes of explosive eruptions. It takes into account the volume of pyroclastics produced, how high into the atmosphere they rose, and the length of the eruption. The VEI scale, like earthquake magnitude scales, is exponential, meaning that each unit increase in the VEI scale represents about a tenfold increase in size/severity of eruption. |
| What patterns are associated with volcanic activity? | Patterns vary widely among volcanoes. Typically a volcano will erupt once every 220 years. 20% of all volcanoes erupt less than once every 1000 years. 2% erupt less than once in 10,000 years. Long periods of inactivity do not guarantee extinction. |
| Can volcanic activity be predicted? | The first step in predicting activity is monitoring. Intense monitoring usually only takes place after a volcano shows signs of near-term activity. Currently there are 300-500 active volcanoes in the world and not nearly enough people and gear to monitor them all. Dormant volcanoes could become active anytime making the task of monitoring the volcanoes even harder. Lastly, even long-dormant extinct volcanoes can erupt at any time. For example Vesuvius was thought to be extinct until it destroyed Pompeii and Herculaneum in A.D. 79. |
| What are volcanic activity precursors? | Seismic activity - Earthquakes result from the rising Magma heating rocks. Quakes may become shallower and more numerous as magma moves upwards. Larger earthquake may trigger eruption. Bulging, tilting or uplift of the volcano surface - Indicates rising magma and or gas pressure. Indicates approaching eruption, but not time frame. Monitoring gas emissions around volcano - Changes in gas mixes released by volcano. So2 content in escaping gas may be a precursor. Warm surface area temps where magma is close to surface. Animal Behavior - Possibly |
| What volcanic hazards are in the US? | Hawaii, Cascade Range, the Aleutians, Long Valley, and Yellowstone. |
| What types of volcanoes are in Hawaii? | The Volcanoes forming the Hawaiian islands are shield volcanoes. The Hawaiian island volcanoes have been formed due to a hot spot. |
| What types of volcanoes are in the Cascade range? | The Cascade Arc includes nearly 20 major volcanoes, among a total of over 4,000 separate volcanic vents including numerous stratovolcanoes, shield volcanoes, lava domes, and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas. The Cascade range has formed due to subduction along the Cascadia subduction zone. The Cascadia subduction zone is a very long sloping fault that separates the Juan de Fuca and North America plates. The Cascades are part of the Pacific Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Ocean. All of the known historic eruptions in the contiguous United States have been from Cascade volcanoes. The two most recent were Lassen Peak in 1914 to 1921 and a major eruption of Mount St. Helens in 1980. Minor eruptions of Mount St. Helens have also occurred since, most recently in 2006 |
| What types of volcanoes are in the Aleutians? | Most Alaskan volcanoes are in the Aleutian arc which extends approximately 2,500 kilometers along the southern edge of the Bering Sea and Alaskan mainland. This classic volcanic arc contains some 80 Quaternary stratovolcanoes and calderas. Aleutian arc volcanism is the result of subduction of the Pacific Plate beneath the North American Plate. The 3,400-kilometer-long Aleutian trench that extends from the northern end of the Kamchatka trench to the Gulf of Alaska marks the boundary between the two plates |
| What is Long Valley? | Long Valley is a Caldera depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the largest calderas on earth, measuring about 20 miles (32 km) long (east-west) and 11 miles (18 km) wide (north-south). Long Valley is known as one of only six Super Volcanoes in the world. It is not known what formed the Long Valley Volcano. |
| What is Yellowstone? | Yellowstone is one of only 6 super volcanoes in the world. It is formed due to a geologic hot spot. Yellowstone is classified as a Caldera. |
| What is a caldera? | A Caldera is an enlarged volcanic summit crater. It is formed by either an explosion enlarging an existing crater (Crater Lake) or collapse of volcano after the magma chamber emptied. |
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