Chapter 5: Volcanic eruptions ∙ A highpressure, fastmoving mixture of pyroclastic debris including fragments and gas typically ejected skyward from a volcanic vent is called an eIf you want to learn more check out Why might thinking not be strictly restricted by language?
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ruptive cloud or column o A lahar is a volcanic mudflow o Filaments of volcanic glass are Pele’s hair o Ignimbrite is a sheet of tuff formed from a pyroclastic flow ∙ A moving, glowing cloud of hot gases and volcanic pieces is called a pyroclastic flow or nuee ardente o A glowing cloud of gases and pieces is not uncommon with explosive eruptions; shield volcanoes, including those of Hawaii, are associated with effusive, not explosive, eruptions. ∙ Lava of low viscosity o can flow farther than intermediate or highviscosity lava. o indicates an area that has little potential for explosive eruptions. o has low silica content. ∙ Plate tectonics theory explains why volcanic activity occurs where it does. For example o active volcanoes in East Africa, such as Kilimanjaro, are the result of rifting (divergence) in continental crust. o rifting above a plume produced flood basalts such as the Columbia River Plateau of Washington and Oregon and the Deccan Plateau of India. o the Ring of Fire bordering much of the Pacific Ocean is a long chain of subductionzone volcanoes. ∙ Rhyolite lava o has more silica than basalt lava does. o indicates the tendency for explosive activity. o may form a lava dome above the vent. ∙ The eruption of Mt. Tambora, Indonesia, in 1815 o resulted in extremely low temperatures in the northern hemisphere during 1816. o produced "the year without a summer." o produced such dreary weather it inspired the writing of Frankenstein. o Franklin proposed his idea based on the effects of a huge volcanic eruption in Iceland in 1783. Since 1815, the 1883 eruption of Krakatau and the 1991 eruption of Pinatubo both caused global dips in temperature. ∙ Volcanic gases o are more abundant in felsic lavas than mafic lavas. o killed over 1,700 people at Lake Nyos, Cameroon, Africa, in 1986. o are released by magma as it rises and the pressure decreases. ∙ in the 1980s, over 1700 people and thousands of heads of cattle from a village surrounding Lake Nyos, a volcanic lake in Cameroon, died unexpectedly after the lake overturned. They were not scalded, they were not poisoned, and the area did not smell bad. What volcanic gas killed the villagers and their cattle, and snuffed out their cooking fires? o carbon dioxide∙ Lahars, composed of ash, debris, and water o occur only in arctic regions because snow supplies the water for mud. o are extremely rare. o are called nuée ardentes. o Volcanic mud and debris flows, called lahars, are fairly common, fastmoving, deadly events associated with volcanic eruptions worldwide. Volcanic outgassing alone provides enough moisture to form mud, and melted snow just adds to the danger. Nuée ardentes (pyroclastic flows) are deadly avalanches of hot pyroclastic debris and gas. ∙ Lava is o molten rock that cools and hardens on Earth's surface. o Lava is molten rock that solidifies at the surface. Many types of lava exist, with different chemical compositions. Often volcanic eruptions don't produce any lava, and when it is present, it usually moves slowly enough that people can get out of its way. ∙ Mt. St. Helens erupted explosively in 1980. Geologists find evidence of many eruptions of Mt. St. Helens, dating back 37,000 years. The mountain is huge and is composed of layers of lava and pyroclastics. o Mt. St. Helens is a stratovolcano (or composite volcano). o The longevity, large size, and alternating eruptions of pyroclastics and lava are classic attributes of stratovolcanoes (composite cones) that form along convergent plate boundaries where subduction is occurring. These types of eruptions are produced by andesitic or rhyolitic magmas, not basaltic ones. And the lack of erosive features (indicated by the size) and location within an active subduction zone suggest that the volcano is not extinct. ∙ Mt. Vesuvius erupted in a very violent explosion in 79 C.E. and buried the residents of Pompeii in ash. On the basis of this information, which of the following would you LEAST expect to find at Vesuvius? o basaltic lava o Basaltic lava is associated with nonviolent, effusive eruptions; rhyolite lava and lapilli and ignimbrite (all pyroclastic products) indicate a rock chemistry that results in explosive eruptions. ∙ The presence of pillow lava is evidence of what volcanic circumstance? o a submarine volcano o Pillow lava is a lowsilicacontent, basaltic lava associated with underwater effusive eruptions ∙ These volcanic products cover 70% of Earth's surface. o midocean ridge volcanism o Hot spots, LIPs (large igneous provinces), and flood basalts are relatively isolated geologic occurrences and do not cover 70% of the surface of the planet.∙ columnar jointing. o columnar jointing forms during the final stages of lava cooling, as flows shrink and fracture into polygonal columns. ∙ This stratovolcano recently erupted in the United States. Although it warned of its impending eruption, it still killed people, partly because it first blew sideways and produced a monstrous landslide. The volcano is o Mt. St. Helens. o The descriptive information all fits Mt. St. Helens, but none of the others. ∙ Which volcanic hazards associated with the Mt. St. Helens eruption in 1980 affected areas greater than 14 miles from the volcanic center? o lateral blast and mud/debris flows o While pyroclastic flows affected areas to the north of the volcano for a significant distance, only the lateral blast and mud and debris flows, which followed pre existing river valleys, traveled greater than 14 miles from the vent. Lava associated with the eruptive dome is highly localized to the vent center. ∙ Vesicles are frozen bubbles within lava that form as gases depressurize and are released during eruption. o ∙ describe a structural feature of a volcano? o A vent is the volcano's opening to Earth's surface; a fissure is a vertical elongated crack that serves as a conduit; and the magma chamber is the underground zone where magma accumulates. ∙ Which of the following explosive eruptions was enhanced by seawater flooding the magma chamber? o Krakatau, Indonesia, 1883o An explosive eruption involving the reaction of water with magma is called a phreatomagmatic eruption. Only Krakatau, Indonesia, 1883, fits this description. ∙ Which of the following is NOT a form of lava? o Lapilli o Lapilli are marblesized pyroclastic pieces, explosively ejected; the others are all forms of molten rock that flow from a volcanic opening, that is, lavas. ∙ Which of the following is NOT considered a warning sign of imminent eruption? o a period of quiescence in the volcano's activity o Because a volcano has not erupted recently does not mean that it is "due" to erupt. ∙ Which of the following is responsible for the broad, dark areas of the Moon called Maria, as shown in the image? o flood basalts o The flood basalts on the Moon that formed the Maria formed when huge meteors collided with the Moon, creating large craters that decreased the Moon's mantle pressure and triggered partial melting o ∙ Which of the following volcanic areas is NOT part of the Ring of Fire? o Iceland o Iceland is part of an oceanic hotspot volcanic area straddling the MidAtlantic Ridge; the others all ring the Pacific Ocean. Chapter 7: Metamorphism ∙ According to this metamorphic facies graph, which of the following statements is TRUE? o Blueschist facies rocks form at high pressures and low temperatures.o Blueschist facies rocks do form under high pressure but low temperature conditions. However, hornfels facies rocks form under a wide range of temperatures, greenschist facies form at depths less than ~35 km, and the highest pressure facies on this diagram is the eclogite facies. ∙ Choose the listing that shows the rocks in increasing degrees of metamorphism (i.e., from lower to higher grade). o metaconglomerate, gneiss, migmatite o Metaconglomerate is barely metamorphosed higher heat changes the rock into a gneiss (Fig. 7.6a); and migmatite has been so strongly heated, some rock has melted and become new igneous rock. ∙ Hydrothermal fluids o may consist of hot water, gases, or supercritical fluids. o can accelerate metamorphic reactions. o can be derived from groundwater or magma, or can be the product of metamorphic reactions. o They do change the chemical composition, but the process is known as metasomatism. Exhumation means that deeply buried rocks can eventually be exposed at Earth's surface. ∙ Metamorphic aureoles typically contain nonfoliated rock like hornfels because o they form adjacent to an intruding pluton, which provides heat for metamorphism o Aureoles typically form around igneous intrusions by contact/thermal metamorphism. The addition of heat, but little pressure, produces nonfoliated metamorphic rocks. ∙ Quartzite o is basically a solid mass of interlocking quartz grains. o Quartzite is a nonfoliated (no banding) metamorphic rock that may be white, gray, purple, or green; it breaks across, not around, its component grains. ∙ Recrystallization o changes the texture (shape and size) of the grains. o The recrystallization process doesn't change the identity or chemical composition of the mineral, it just produces larger crystals of the mineral so it changes the texture of the grains. Plastic deformation occurs when rocks behave like soft plastic; neocrystallization forms new minerals that differ from the protolith; and pressure solution occurs when grains push against each other and cause dissolution. ∙ Tension (a type of stress) o is created by a pull perpendicular to a surface. o Tension is a stress created by pulling perpendicular to a surface, such as grabbing two ends of a piece of taffy and pulling your hands apart. A balloon collapses in a pool because of pressure; shear occurs when rocks move sideways; and pressure (again) occurs when compression is exerted equally from all sides. ∙ What is the protolith of marble? o Limestone ∙ What type of foliation does slate, a common material used for roof shingles, exhibit?o Cleavage o Slate is used in roofing because its slaty cleavage causes it to break in regular, thin sheets ∙ Which is NOT a common process by which metamorphic rocks are formed? o Schistosity o Schistosity is not a process; it is the type of foliation in schists that results from the preferred orientation of large mica flakes. ∙ Which of the following does NOT describe a change induced on protolith rocks due to mountain building as a result of convergentmargin tectonics and continental collision? o Hot magma rising beneath the converging continents heats seawater, which then rises through the crust to react with the surface rocks. o During hydrothermal metamorphism at midocean ridges, hot magma rises beneath the ridge axis, where it heats seawater to create hydrothermal fluids—but this does not happen during mountain building. ∙ Which of the following is NOT a common metamorphic facies? o Mafic o The term mafic refers to minerals and/or rocks that are high in iron and magnesium; it does not refer to a metamorphic facies. See Box 7.1 for further explanation of each facies and formation conditions. ∙ Which of the following locations could not possibly be part of a shield? o Hawaii o Shields are the oldest areas of Earth's surface; Hawaii is a recently formed hot spot island ∙ pressure solution o This image shows the process of pressure solution. Grains that were once spherical dissolve on the sides experiencing pressure where they push against neighboring grains. The dissolved ions migrate away and new minerals precipitate in the regions of low pressure. ∙ Which of the following rocks is classified as nonfoliated? o Hornfels o Hornfels is a nonfoliated metamorphic rock because it was formed in the absence of differential stress. ∙ Which of the following statements about metamorphic rocks and their characteristic environments is TRUE? o Slate, phyllite, schist, and gneiss are found in areas of continental collision. o Gneiss, a foliated metamorphic rock, requires shearing stress to form; plutons do not cause shearing and they create nonfoliated rock. Mylonites form due to shearing stress along faults deep in the crust, not the heat of convergent boundaries. Blueschists form where there is extreme pressure and low heat, which does not describe midocean ridge conditions.∙ A metamorphic rock o may be composed of different minerals than its protolith. o may develop a texture of interlocking grains. o may have preferred mineral orientation caused by differential stress. o The upper limit of the metamorphic range is 1200°C. Most metamorphism occurs between 200° and 850°C ∙ Dynamic metamorphism o may happen as uplift and erosion bring rock closer to Earth's surface. o occurs as a consequence of shearing. o happens under conditions of decreasing temperature and pressure. ∙ Mylonite o forms by recrystallization in a fault zone. o is produced by shear stress on softened rock. o has pronounced foliation parallel to the direction of faulting. o : A migmatite (not mylonite) is a product of gneiss melting to produce a felsic magma and a stillsolid mafic rock ∙ Shields o are composed of some of the oldest rock on Earth (Precambrian). o are composed of rocks that were metamorphosed during ancient mountain building events. o make up large areas of Canada, southern Africa, and South America. ∙ Shock metamorphism o involves high temperatures and compressional stress. o can be caused by meteorite impact. o causes quartz to recrystallize into coesite. ∙ The extremely high heat of metamorphism o can cause some felsic minerals to begin to melt. o can produce banding by metamorphic differentiation. o is necessary to form migmatite. Chapter 9: Deformation and mountain building ∙ A horizontal line on Earth's surface has a plunge of o 0 o If something is horizontal, it has 0° plunge; vertical plunge is 90°. ∙ Brittle deformation o occurs when many atomic bonds are broken quickly and rock pieces separate. o During brittle deformation, many atomic bonds break and stay broken, leading to the formation of permanent cracks and separated rock pieces. ∙ Epeirogenic movements affect broader areas and produce more gently sloping structures than do orogenic processes. ∙ Erosion wears down mountains, and mountains collapse under their own weight. ∙ The youngest rocks of a basin are found at its center. ∙ A shieldo is part of a craton. o contains Precambrian metamorphic and igneous rocks outcropping at ground surface. o can be associated with a cratonic platform. ∙ Brittle deformation o creates earthquakes. o occurs above the brittleductile transition zone. o occurs when you drop a plate on the ground and it shatters. ∙ Mountains don't get infinitely high or exist forever because o their own weight causes them eventually to collapse. o erosion is a constant force acting to wear mountains down. o they experience orogenic collapse. ∙ It's an upward fold, therefore an anticline, and the surface Upattern of a plunging anticline points north—in the direction of plunge. ∙ dentify the structure that makes this pattern of rock layers on the ground surface— parallel stripes, showing bilateral symmetry across a midline (hinge), with rock getting older as you move outward from the hinge. o Rocks in an anticline would get younger as you moved outward; plunging folds would exhibit a Ushaped pattern; monoclines would not show bilateral symmetry. ∙ If you see small, angular fragments of shattered rock along a linear boundary between two masses of rock, you must be looking at o fault breccia. ∙ erosion of a joint set ∙ Stress o developed during orogeny can be different at various locations. o Strain (not stress) is the change in shape (deformation) produced by stress (force per unit); force does not account for the area over which a force acts, and is therefore different from stress; and stress is not the same everywhere during orogeny. ∙ The crust in the Basin and Range Province of Nevada, Utah, and Arizona is stretching; therefore, fault movement in this region must be o Stretching ∙ dipslip fault, normal ∙ When the buoyancy force pushing up on lithosphere equals the gravitational force pulling down on it, the situation is said to show o isostatic equilibrium. ∙ Which of the following conditions will tend to make rocks change by ductile deformation rather than by brittle deformation? o slowly applied stress ∙ way to recognize faults in the field? o a displaced marker bed o slip lineations on a fault plane o an offset stream channel ∙ In a dipslip fault, movement along the fault plane is vertical ∙ In a strikeslip fault, movement along the fault plane is horizontal. ∙ In an oblique fault, there's both vertical and horizontal movement along the fault plane. ∙ Major mountain ranges are the result of multiple orogenies over long geologic time. ∙ Domes and basins in the Midwestern United States are the result of epeirogeny. ∙ Faultblock mountains result when blocks of crust drop downward along normal faults. ∙ Mountains o may exhibit metamorphic and igneous rocks, due to their formation process. o are a result of uplift and deformation. o are created during orogenies that may last for millions of years. ∙ The East African Rift Valley o is a result of normal faulting. o is bordered by linear mountain ranges called faultblock mountains. o has volcanoes along it because asthenosphere is rising under the rift and supplying heat. ∙ associated with the process of mountain building? o Orogenymeans mountain building o tectonic foliationis layering created by realignment of rock grains o brittle and ductile deformationare changes in shape with or without breaking. ∙ You're looking at a fault trace in the field. You observe a polished surface, with linear grooves on it, and fine powder along it. In more technical terms, what are you seeing? o Slickensidesare polished fault surfaces o slip lineationsare linear grooves on fault surfaces o fault gougeis a fine powder of shattered rock along a fault plane.