Geog 132, Exam 1 Study Guide
Geog 132, Exam 1 Study Guide GEOG 132
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GEOGRAPHY 132 EXAM 1 STUDY GUIDE Geologic Time and the Earth’s Structure Relative time is the time with relation to something else, while absolute time is the actual amount of time Superposition states that younger materials will lie atop older materials, and stratigraphy is the examination of the strata (layers) in rock do assess again Uniformitarianism states that the processes changing earth’s features today are operating at the same rate as they have been for the entirety of earth’s time Earth is 4.6 billion years old and formed from molten material which was sorted by gravity, heavier materials going inside and less heavy materials going out (internal differentiation) The units of the geologic time scale, from largest to smallest are eon, era, period, and epoch. Currently we are in the Holocene epoch of the Quaternary period Continental crust is mostly granitic and relatively low density, while oceanic crust is basaltic and higher in density. Continental crust is also ~30 km thick, compared to oceanic crust, which is around ~10 km thick The earth is composed of a solid iron inner core, molten liquid iron outer core, rigid lower mantle, and three part upper mantle. The 3 parts of the upper mantle are the rigid upper mantle, plastic asthenosphere, and rigid uppermost mantle. Earth’s magnetic field is created by its solid iron core Isostasy is the combo of balance and buoyancy that explains the vertical movements of earth’s crust, and isostatic rebound is the uplift of bodies of land after large glacial ice sheets were removed from atop them Interpreting Topographic Maps Topography is the features of landscape that give earth its texture. Relief is the amount of difference in elevations in a given area Topo maps use contour lines, which connect all points at a given elevation, to portray a landform’s elevation above a vertical datum, usu. mean sea level Lines of latitude are parallel and run east-west on the globe, with 0 at the equator. Lines of longitude run north-south, are not parallel (they grow closer together at the poles), and have 0 at the Prime Meridian, which runs through Greenwich, England Index contours are darkened and have their elevation labeled and are every 5 contour line, the contour interval is the difference between each contour line on a map, and the representative fraction represents how much one of any given unit on the map covers on the actual area displayed Streams flow downhill, leaving a V pointing in the opposite direction of the way the stream flows, hilltops are marked by closed circles with no more contour lines inside, and depressions are indicated by hachures, which are small hashes on the contour lines Water is blue and vegetation is green Rocks and the Rock Cycle Endogenic processes are internal and driven by earth’s internal heat, while exogenic processes are external and driven by solar energy The rock cycle is one of 3 major systems in the geologic cycle, the other 2 being the hydrologic cycle and the tectonic cycle 8 elements compose 99% of earth’s crust: oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium Minerals are inorganic, natural compounds with specific chemical compositions and crystalline structure Common mineral families are silicates (silicon and oxygen) like quartz, oxides, sulfides, and sulfates (oxygen/sulfur/both) like hematite or anhydrite, and carbonates (carbon and oxygen) like calcite A rock can be a mass of 1 mineral, a cluster of several minerals, or a mass of solid organic material. The 3 types of rocks are igneous, sedimentary, and metamorphic Igneous rocks form from solidified lava (if above ground) or magma (if below ground). Igneous rocks that cool below earth’s surface cool more slowly and have time to develop large crystals, where rocks that cool above the surface cool quickly and don’t have time to develop crystals, making them glassy and fine-grained Intrusive igneous features are called plutons and include features such as batholiths (large rocks), sills (layers between strata), and dikes (cut across strata). Extrusive features are volcanic eruptions and lava flows Felsic rocks have low density, light color, and a low melting point, and are high in silicon, aluminum, potassium, and sodium (name comes from feldspar + silica). Mafic rocks have a high melting point, dark color, and high density (name comes from magnesium + ferric) Sedimentary rocks form when weathered rock is moved and deposited in layers, then buried, compacted, and lithified, composed of fragments of existing rock or organic materials. Classification is based on particle size Sedimentation is when particles are deposited in horizontal layers, which form strata and allow scientists to examine the stratigraphy, and determine the relative age due to the principle of superposition In clastic sedimentation, broken pieces of other rock are cemented together, but in chemical sedimentation, rocks are formed when dissolved minerals precipitate from a chemical solution Metamorphic rocks form when igneous or sedimentary rocks are subjected to extreme heat or pressure below earth’s surface, like at a tectonic collision or fault line. This makes the rocks harder and more resistant than the other 2 kinds Metamorphism can happen when the bottom layer of sediment in a depression changes or when the layer closest to magma gets cooked Shale becomes slate, slate becomes phyllite, phyllite becomes schist, and schist becomes gneiss. Limestone becomes marble, and sandstone becomes quartzite. Plate Tectonics I Wegener first proposed continental drift in 1912 and nobody believed him, then in 1944 Holmes came up with more evidence and still nobody was really on board, then Harry Hess realized the seafloor was not flat and discovered mid-ocean ridges and seafloor spreading. This combined with continental drift to say that convection brings magma to crust and spreads the seafloor laterally, which is not the whole truth, and the findings were backed up by the band created due to earth’s magnetic reversals. Plate tectonics is supported by the bands created by magnetic reversals, the finding of fossils across different continents with different current climates, the way the edges of continents fit together, and the finding of certain types of rock very far from their home continents Seafloor spreading happens at mid-ocean ridges where magma wells up from the mantle and pushes the already existing crust out and creates new crust in between, which is in turn cracked itself by successive upwelling magma and pushed aside, spreading the seafloor Magnetic reversals are events where the polarity of the earth will suddenly switch for reasons unknown to scientists and this supported plate tectonics because during different polarities, the iron in the sea floor would line up different directions, so bands formed of the iron facing different directions as a result of the magnetic reversals, which showed scientists that the oceanic crust formed during different orientations of the earth’s polarity and was thus not all the same age Magma wells up at mid-ocean ridges and pushes the crust apart to spread the seafloor as new crust is formed The 3 types of plate boundaries are diverging (where plates move away from each other), converging (where plates collide with each other), and transform (where plates slide past each other) Subduction zones are found at converging plate boundaries and subduction occurs when one plate (typically oceanic) is forced under the other plate and melted by the magma in the mantle Pangaea was a huge supercontinent made of all current continents ~300 million years ago, and it broke apart ~175 million years ago due to continuous movement of plate tectonics pulling it apart and eventually moving our continents to where they are today Mountains and volcanoes are often found near subduction zones along converging boundaries, earthquakes often occur at transform plate boundaries, and seafloor spreading and continental rifts occur at diverging plate boundaries Hot spots are sites where magma wells up that are fixed in regards to tectonic movement, so magma bubbles up and forms an island, then as the plate moves over time, more magma bubbles up and forms another, adjacent island until an island chain is formed. An example of this process is Hawaii Plate Tectonics II Relief and topography played a vital role in human history because people will choose to go places that it is easier to get to (for example, they will avoid going over mountains) There are 3 crustal orders of relief defined by scale. 1 order is the broadest, covering whole continents. 2 ndorder is intermediate, rd covering a mountain range or a plain or lowland. 3 order is the most detailed, covering an individual physical feature Hypsographic curve displays all the relief on earth from the highest mountain to the lowest sea trench, and shows that most of earth’s relief is below the ocean Earth’s topographic regions are classified by the amount of local relief Crust formed from ancient tectonic activity was formed from cratons, which are large nuclei of crystalline rock (existing crust), and a continental shield is an area where the craton is exposed Crust also forms from recent activity, which is the upwelling of magma in the form of melt (a molten mix of oceanic crust, seawater, sediments, and surrounding crust) which is high in silica and aluminum and can form plutons or volcanoes and add to crust Terranes are pieces of other crust that get stuck onto shields, and they are accreted when pieces of land formed in the sea are moved toward cratons and eventually crash into and become part of the total crust. This was the process that formed the western United States Tectonic processes put rock under stress in 3 forms: tension (pulling apart), compression (pushing together), and shearing (twisting and tearing). They respond with strain Brittle rocks are inflexible and will break when subjected to stress, but ductile rocks are slightly flexible and will bend and fold When tensional stress is applied to brittle rocks, they will break and one part will fall down, forming a normal fault. When compressional stress is applied to brittle rocks, they will break and one part will be shoved over the other, forming a thrust or reverse fault. When rocks are subjected to shearing stress, they will break and slide past each other in other directions, forming a strike-slip fault When ductile rocks are compressed, they will fold. Anticlines are areas of higher elevation formed when upwelling beneath the crust causes tensional stress and stretched the crust apart. Synclines are areas where the crust was compressed and formed a lower valley. The rock of anticlines is weakened due to stretching and therefore wears away more easily than surrounding rock, leaving anticlinal valleys. The rock of synclines is strengthened because of being compressed, so it resists weathering more than the surrounding rock and leaved behind synclinal ridges as a result Domes are sites where magma welled up and created a sort of bubble, then was weathered away, leaving a pit with strata sloping down away from the center of the dome. Basins are the opposite of domes, formed when a large sheet of ice created a depression on the land then melted away, leaving a sunken area with strata sloping up away from the center. An example of a dome is Nashville and an example of a basin is Michigan Mountain Building Orogenesis literally means the birth of mountains, and refers to any event which creates a mountain Causes of orogeny are the thickening of crust due to crustal deformation (folding and faulting), accretion of exotic terranes, volcanism, pluton intrusion, and erosion of material Extreme erosion of uplifted areas can cause karst formations and “false mountains” where less resistant material was weathered away and left a small section of uplift behind that looks like a mountain With extension, the ground is pulled apart, causing sections to drop down and others consequently to be uplifted. This creates a basin & range landscape, which can also be known as horst & graben (where horst is lifted up and graben is dropped down) When an oceanic plate collides with a continental plate, the oceanic plate is subducted because it is more dense, then it melts in the asthenosphere and the lava uplifts to form an inland line of volcanoes and an offshore trench When 2 oceanic places collide, 1 is subducted under the other, and a volcanic island arc and trenches are formed When 2 continental plates collide, crust gets crushed and deformed and piles up, which results in folding, overthrusting, faulting, and uplift. The Himalayas were created this way Tilted fault block mountains are formed through isostatic rebound when one section of land raises up and exposes the batholith, then overlying sediment is worn away, leaving a mountain with one steep face and one gently sloping side. The Grand Tetons are an example of this The Appalachian mountains were formed through uplift and through accretion of terranes when the African and North American plates collided during the formation of Pangaea Seafloor fossils and limestone exist at the top of Mount Everest because originally, part of the Indian plate was under the Tethys ocean, and when it crashed into the Asian plate, it was forced up into the crash and became part of the Himalayas and Everest Some places violate the law of superposition due to thrust faulting; the acropolis, for example, has older limestone on top of younger Athenian “schist” because after its deposition, the overlying Athenian schist was worn away and a thrust fault pushed it up and over onto the top of the younger rock, creating the legendary hill Volcanism Volcanic activity occurs in 3 settings: along plate subduction boundaries, along seafloor spreading centers, and at hot spots The Pacific ring of fire is created by subduction zones and trenches that circle much of the ocean and thus cause lots of volcanic activity and earthquakes Volcanoes are formed at vents from the asthenosphere that rise through the crust. They have craters at their summits, which are depressions. Lava and magma are both molten rock made of melt, but lava is above ground and magma is below ground. A fissure is a large crack through which lava may flow, and pyroclasts are hot, fiery rock materials The 2 types of flowing lava are aa, which is rough and jagged, and pahoehoe, which is fluid, smooth, and ropey Mafic lava flows well and releases gas easily so it is not very explosive, instead producing effusive eruptions. Felsic lava flows poorly and does not release gas, which causes explosive eruptions Effusive eruptions produce a lot of lava from a single vent (fissure) that flows gently, while explosive eruptions result from the buildup of pressure from gases or blocked conduits and harshly eject lava and pyroclastic material Shield volcanoes are very large and are formed by successive eruptions piling on top of each other until a large, gently sloping volcano with a crater is formed, and they produce effusive eruptions. An example of a shield volcano is Mauna Loa in Hawaii. Composite volcanoes are formed from the buildup of successive ash layers and have very steep sides with a conical, often symmetrical shape, and they produce explosive eruptions with pyroclastic materials such as ash, slag (mineral particles), and cinders, and cause lots of damage. An example of a composite volcano is Mount St. Helens Plateau basalts occur where material is ejected from hot spots along fissures, like in continental rift valleys. Plateau basalts also produce effusive explosions Cinder cones are small, moderately-explosive cone-shaped hills that are really just small composite volcanoes, and they produce explosive eruptions Calderas are collapsed craters formed when the summit of a large volcano collapses, which can have explosive or effusive eruptions They often form lakes, and one example is the Yellowstone Caldera, which is frequently called a supervolcano and produces geysers because it is over a hotspot It is difficult to predict when volcanic eruptions will occur, but some methods scientists use are placing a tilt meter to monitor the angle (which will change as magma wells up) and monitoring the gases that are emitted by the volcano Faults and Earthquakes Earthquakes are violent, often destructive movements of the earth caused by seismic waves, which are created from movements in the crust Seismic waves can be generated in areas like subduction zones and from magma movement. High intensity waves are generated along transform faults, while low intensity waves are generated along rift zones. Harmonic tremors are another type of seismic wave generated at sites of volcanic eruptions before the volcano erupts The focus of an earthquake is the area of the rupture below the earth’s surface, and the epicenter is the location on earth’s surface directly above the focus. Seismologists are scientists who study earthquakes and seismic waves, and a seismograph is a machine that records seismic waves. A seismic gap is an area along a fault known to be under stress but not releasing strain, which is therefore expected to rupture and cause an earthquake When stress builds up, it must eventually be expressed, and when it is, energy moves out in waves from the focus. In brittle crust, sharp movement or displacement is caused Elastic-rebound theory states that friction between plates is concentrated at sites called asperities and pressure builds up until one of the asperities fails, causing movement along the fault which causes an earthquake Foreshocks are small earthquakes that precede the main quake and are useful in predicting when a quake will occur. Aftershocks are small quakes that happen after the main event, and are typically what kill the most people and mess things up Energy is transferred through p-waves and s-waves. P-waves are compressional waves that move laterally out from the focus and push material in the direction they move. S-waves are shear waves that move in right angles to the other waves and push material sideways The Mercalli scale rates earthquake strength based on the amount of damage the quake causes (qualitative) while the Richter scale measures the amplitude of seismic waves through use of a logarithm (quantitative). The moment-magnitude scale is a more recent quantitative scale that provides greater accuracy for large earthquakes and considers material and fault slippage Earthquakes in the US most commonly happen in areas along transform faults with high risk like California. Earthquakes in Tennessee occur most commonly in West Tennessee because that’s where the New Madrid fault is located Weathering Geomorphology is the science that organizes & describes the origin, evolution, form, and spatial distribution of landforms. Weathering is the actions of natural processes that break down rocks, and denudation is all gravity-powered forces that degrade a landscape. Deflation is sediments that get blown away, and regolith is broken-down bedrock that is the parent of soils The 2 categories of weathering are physical and chemical, and the agents of erosion are gravity, wind, water, glaciers, and oceans The dynamic equilibrium model states that all landscapes at a balanced state in-between forces until a destabilizing event occurs and the land must adjust itself to reach a new equilibrium Slopes are curved, inclined surfaces that search for an angle of equilibrium, which balances the force of gravity with the strength of the slope’s material and its inertia Physical weathering is the breakdown of larger rocks into smaller rocks, with no alteration on the chemical composition of the rock. Freeze-thaw action causes breakdown of rocks by expansion of water that gets into cracks between rocks and freezes, cracking the rock, like joint-block separation. Crystallization is nearly the same process but instead happens when salt crystals get in between cracks and solidify as minerals, cracking the rock. Pressure-release jointing occurs when a rock is under tremendous pressure and cracks once the pressure is removed, and exfoliation is when sheets are taken off the cracked rock Chemical weathering decomposes rock or changes its chemical composition. Spheroidal weathering is when chemicals decompose the corners of a rock first because of their greater surface area and slowly round out the rock. Hydration is when water becomes part of the chemical composition, like in gypsum, and then cycles of hydration and dehydration break down the material. Hydrolysis is when chemical bonds are created with the water, making the material weaker and more susceptible to weathering, and oxidation is when metals in rock form oxides with oxygen (like rust) and weaken the structure of the rock. Carbonation is when minerals dissolve in solution, like the slight acidity of rainwater decaying materials Weathering is influenced by the type of rock, joints, climate conditions, direction the slope faces, and whether or not there is vegetation Differential weathering is when the process of weathering works at different rates on different rock types in the same area Mass Movement Mass movement is any unit movement of material caused by gravity. It can be on land or underwater, and happens typically on slopes that have been weakened by weathering. When surface rock is weakened by weathering, gravity tends to pull it down, increasing the likeihood of mass movement The forces involved in mass movement are gravity, which pulls materials down, and shear strength, which resists the force of gravity as it tries to pull materials down and depends on the type of rock The angle of repose is the maximum angle at which a slope of dry particles can be at rest without falling down, and it depends on the material in the slope Mass movement can be caused by the increase of mass on a steep slope, an increase of the angle of a slope, or a decrease in the cohesion of the material in the slope (like when it rains a lot and the soil gets saturated or when there is an earthquake) The types of mass movement are falls, avalanches, slides, flows, and creep Falls are fast and dry, when volumes of material fall separately through the open air and pile up in cone-shaped talus slopes below. Avalanches are fast and semi-wet, where rocks and tumble and fall along with mud. Avalanches are often caused by periods of heavy rainfall but can also be caused by earthquakes Slides occur when large amounts of material move in one large body simultaneously. Translational slides are when the body of material moves along a planar surface, and rotational slides are when the material rotates in its setting and creates a slump Flows are very wet and fast and consist of material flowing at great speeds downhill. Earthflows have a high water content, and mudflows have an even higher water content Solifluction is the slow flow of long-frozen soil that has unfrozen, and is like a flow but much slower and with less water content. A lahar is a volcanic sort of flow when volcanic activity melts ice on a volcano and sends it rushing down with rocks, pyroclastic material, and other debris. Lahars are very fast and very wet Creep is a persistent and slow form of mass movement caused by the expansion and contraction of freeze-thaw cycles, which slowly move materials downhill and bend rock layers. Effects of creep can only be noticed after it has been happening because it is a process too slow to observe directly Humans often move large volumes of materials, oversteepening slopes and destabilizing the environment, and this causes mass movements of the earth seeking its new equilibrium
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