Exogenic Processes of the Earth PDF

Official Business Exogenic Processes of the Earth Course Outcome 4 GEO01 – Earth Science Materials Prepared by: Ryo Jerome C. Tuzon, LPT Video Lectur...

Official Business Exogenic Processes of the Earth Course Outcome 4 GEO01 – Earth Science Materials Prepared by: Ryo Jerome C. Tuzon, LPT Video Lecture Prepared by: Perseval S. Pineda, LPT Official Business Mass Wasting Official Business Mass Wasting Mass wasting is the downhill movement of masses of bedrock, rock debris, or soil driven by the pull of gravity mass wasting is, with proper planning, perhaps the most easily avoidable of all major geologic hazards. Official Business Controlling Factors in Mass Wasting Table 9.2 Summary of Controls of Mass Wasting Triggers: (1) earthquakes; (2) weight added to upper part of a slope; (4) heavy rainfall Official Business Gravity Gravity – the driving force for mass wasting Normal Force. Shear Force. Shear Resistance. Shear resistance < shear force = landslide Steep slopes – shear forces maximized by gravity Official Business Shear Strength and Water Shear Strength – resistance to movement or deformation Saturated soil has reduced shear strength due to increased pore pressure. However, a small amount of water in soil can prevent downslope movement. Like building a sandcastle. Official Business Mass Wasting Triggers Seismic (earthquake) activity. Heavy Rainfall. Construction. Lack of vegetation – no roots to hold rock/soil in place. Landslide triggered by an earthquake in New Zealand, 2016 Official Business Classification of Mass Wasting Rate of movement < 1cm/year – >100 km/hour. Type of material Solid bedrock or debris (unconsolidated material at Earth’s surface). Type of movement flow, slide, or fall Official Business Some Types of Mass Wasting TABLE 9.1 Some Types of Mass Wasting Note: The type of material at the start of movement is shown in parentheses. Rates given are typical velocities for each type of movement. Official Business Creep Creep (or soil creep) - very slow downslope movement of soil Major contributing factors include water in soil and daily freeze – thaw cycles. Can be costly to maintain homes, etc., Source: C.F.S. Shape on creeping ground as foundations, walls, pipes and driveways crack and shift downslope over time. Official Business Flows: Earthflow and Solifluction Flow – descending mass moves downhill as a viscous fluid Earthflow – debris moves Earthflow downslope, slowly or rapidly, Source: Robert L.Schuster, U.S. Geological survey as a viscous fluid. Solifluction Permafrost – flow of water-saturated soil over impermeable material. Common in colder climates. Solifluction Official Business Flows: Debris Flow, Mudflow, Avalanche Debris Flow and Mudflow – flowing mixture of debris and water, usually down a channel. Mudflow is only soil and water. Debris Avalanches are very rapid and turbulent. Debris flow from Mudflow from Debris avalanche California, 2005 California, 2015 from Peru, 19 70 Official Business Falls Falls – material free-falls or bounces down a cliff Rockfall – a block of bedrock breaks free and falls or bounces down a cliff Commonly an apron of fallen rock fragments (talus) accumulates at cliff base. Official Business Slides Slides – descending mass remains relatively intact, and descends along well-defined surfaces Translational slide – movement along plane parallel to motion. Rotational slide (slump) – movement along a curved surface. Rockslide and Rock Avalanche – the rapid sliding of a mass of bedrock along an inclined surface of weakness Underwater Landslides Turbidity Currents. Can create a tsunami. Official Business Preventing Landslides Preventing Rockfalls and Rockslides on Highways Remove Loose material. Stitch slopes together. Preventing Mass Wasting of Soil Construct retaining wall with drains. Don’t oversteepen slopes during construction. Remove all rock that is prone to sliding. Add vegetative cover. Cover roads. Official Business Streams and Floods Official Business Hydrologic Cycle The Hydrologic Cycle – the movement and interchange of water between the sea, air, and land Evaporation – solar radiation provides energy Precipitation – rain or snow Transpiration – evaporation from plants Runoff – water flowing over land surface FIGURE 10.1 The hydrologic cycle. Water vapor evaporates from the land and ocean, condenses to form Infiltration – water soaking into clouds, and falls as precipitation (rain and snow). Water falling on land runs off over the surface as streams or the ground infiltrates into the ground to become groundwater. It returns to the atmosphere again by evaporation and transpiration (the loss of water to the air by plants). The distribution of water in the hydrosphere includes the oceans (96.5%), glacial ice (1.76%), groundwater (1.70%), lakes and streams (0.014%), soil moisture (0.001%), and the atmosphere (0.001%). Glacial ice and groundwater contain 98.8% of the fresh water on Earth. Official Business Running Water Stream – a body of running water, confined to a channel, that runs downhill under the influence of gravity Headwaters – upper part of stream near its source in the mountains Mouth – place where a stream enters sea, lake or larger stream Channel – a long, narrow depression eroded by a stream into rock or sediment Stream banks - sides of channel Streambed – bottom of the channel Floodplain – flat valley floor composed of sediment deposited by the stream Official Business Drainage Basins Drainage basin – the total area drained by a stream and its tributaries Tributary – a small stream flowing into a larger one. Divide – ridge or high ground that divides one drainage basin from another Continental Divide separates the streams that flow into the Pacific from those that flow into the Atlantic and Gulf of Mexico Official Business Factors Affecting Stream Erosion and Deposition Velocity Maximum velocity near center of channel. Higher stream velocities promote erosion and transport of coarser sediments. Floods involve increased velocity and erosion. Gradient (slope) Channel Shape and Roughness Discharge (volume of water passing a particular point in a stream over time) Official Business Stream Erosion Streams cut their own valleys, deepening and widening them over time and carrying away the sediment Hydraulic action – ability to pick up and move rock and sediment. Solution – dissolving of rocks. Abrasion – grinding away of stream channel by the friction and impact of the sediment load. Potholes are eroded into streambed by the abrasive action of the sediment load in the stream. Official Business Stream Transportation of Sediment Bed load – large or heavy particles that travel on the streambed Traction load – large particles that travel along the streambed by rolling, sliding or dragging. Saltation load – medium particles that travel by bouncing along. Suspended load – small/light sediment that remains above the stream bottom by turbulent flow for an indefinite period of time Dissolved load – dissolved ions produced by chemical weathering of soluble minerals upstream Official Business Stream Deposition Bars – sediments temporarily deposited along stream course Placer Deposits – concentrated heavy sediment Official Business Braided Streams Braided streams contain sediment deposited as numerous bars around which water flows in highly interconnected rivulets Resembles braids of hair or rope. Common for streams carrying a lot of sediment. C. Source: Earth Sciences and Image analysis laboratory at Johnson Space Center/N ASA Official Business Meandering Streams Rivers that develop pronounced, sinuous curves called meanders Water flows faster along the outside of bends causing erosion and created cut banks. Flows slower along the inside, depositing point bars on the insides of the meanders. Official Business Meandering Cutoffs Meander cutoffs may form when a new, shorter channel is cut through the narrow neck of a meander (as during a flood) Official Business Floodplains Floodplains are broad strips of land built up by sedimentation on either side of a stream channel Floodplain sediments are left behind as flood waters slow and recede at the end of flood events. Main channel has slightly raised banks with respect to the floodplain known as natural levees. Official Business Deltas Delta – body of sediment deposited at the mouth of a river when flow velocity decreases Surface marked by shifting distributary channels. Shape of a delta depends on whether its wave- dominated, tide - dominated, or stream – dominated. (A) Source: Jacques Descloitres, MODIS Land Science Team/NASA; (B) ©M-Sat Ltd/Science Source; (C) Source: Japan ASTER Science Team/GSFC/METI/ERSDAC/JAROS, and U.S./N AS A Official Business Alluvial Fans Alluvial fan – large, fan – or cone-shaped pile of sediment that forms where stream velocity decreases as it emerges from a narrow mountain canyon onto a flat plain Well – developed in desert regions, such as the southwestern U.S. Larger fans show grading from large sediments nearest the mountains to finer sediments farther away. FIGURE 10.28 (A) An alluvial fan at the mouth of a desert canyon. (B) This alluvial fan is from the Delaware Mountains of west Texas and formed, as sediment was washed out of the canyon by flash floods. (B) Moment Open/Getty Images Official Business Stream Valley Development: Downcutting Valleys are the most common landform on Earth Formed by stream erosion. Different valley morphologies depend on the erosional processes that created them. Downcutting – process of deepening a valley by erosion of the streambed V – shaped valleys typically form from downcutting combined with mass wasting and sheet erosion. Streams cannot erode below their base level. Official Business Stream Valley Development: Grading, Later Erosion, Headward Erosion Graded streams – have concave- up longitudinal profile, lack rapids and waterfalls, represent a balance between available sediment load and transport capacity Lateral erosion – widens stream valleys by undercutting of stream banks and valley walls as stream swings from side to side across the valley floor Headward erosion – the slow uphill growth of a valley above its original source by gullying, mass wasting, and sheet erosion  Stream Valley Development: Official Business Terraces Stream Terraces – step – like landforms found above a stream and its floodplain Occurs when river rapidly cuts downward into its own floodplain. Represents relatively sudden change from deposition to erosion. Can be caused by rapid uplift, drops in base level, or climate changes. Official Business Stream Valley Development: Incised Meanders Incised meanders Retain sinuous pattern as they cut vertically downward. May be produced by profound base level changes, as when rapid tectonic uplift occurs. Official Business Flooding When water levels rise and overtop the banks of a river, flooding occurs Natural process on all rivers. Described by recurrence intervals. Can cause great damage in heavily populated areas. High velocity and large volume of water causes flood erosion. Slowing of waters as flood ends causes flood deposits to be deposited in the floodplain. Official Business Flooding and Urbanization Urbanization creates many impermeable surfaces which increases runoff flooding Water is delivered to streams faster which increases peak discharge and hastens occurrence of flood. Official Business Flash Flooding Flash floods are local, sudden floods of large volume and short duration Typically triggered by heavy thunderstorms. Source: W.R. Hansen U.S. Geological Survey Official Business Reducing Flood Risk Dams – designed to trap flood waters in reservoirs upstream and release it gradually over time Artificial levees – designed to increase capacity of river channel and works well until stream overtops levees, leading to extremely rapid flooding and erosion Wise land-use planning – including prevention of building within 100-year floodplains, is most effective Official Business Impact of Dams Societal Benefits Environmental Concerns Electricity production. Trapping of sediment and nutrients behind Flooding control. the dam. Reservoir for drinking water. Habitat destruction. Destabilizing the river valley when the reservoir fills. Can lead to landslides. Official Business Groundwater Official Business The Importance of Ground Water Ground Water – lies beneath the ground surface, filling pores in sediments and sedimentary rocks and fractures in other rock types Represents 1.7% of the hydrosphere (100x the fresh water in all lakes and rivers combined) Resupplied by slow infiltration of precipitation. Generally cleaner than surface water. Accessed by wells. Tremendously important resource. Growing population has a large impact on groundwater resources. Being removed at ever increasing rates. Pollution impacts are increasing. Official Business The Water Table Saturated zone – subsurface zone in which all rock openings are filled with water Water table – top of the saturated zone Water level at surface of most lakes and rivers corresponds to local water table. Unsaturated zone – unsaturated region above the water table Perched water table – above and separated from main water table by an unsaturated zone Commonly produced by thin lenses of impermeable rock (for example, shale or clays) within permeable ones. Official Business Official Business Porosity and Permeability Porosity - the percentage of rock or sediment that consists of voids or openings Measurement of a rock’s ability to hold water. Loose sand has approximately 30-50% porosity. Compacted sandstone may have only 10-20% porosity. Permeability - the capacity of a rock to transmit fluid through pores and fractures Interconnectedness of pore spaces. Most sandstones and conglomerates are porous and permeable. Granites, schists, unfractured limestones are impermeable. Official Business Aquifers and Aquitards Aquifer - body of saturated rock or sediment through which water can move easily Unconfined – has a water table and is only partly filled. Confined – completely filled with water under pressure. Aquitard - rock/sediment that retards ground water flow due to low porosity and/or permeability Shale, clay, unfractured crystalline rocks. Official Business The Movement of Groundwater Movement of ground water through pores and fractures is relatively slow (cm to meters/day) compared to flow of water in surface streams Flow velocities in cavernous limestones can be much higher (km/day). Flow velocity depends upon: Slope of the water table. Permeability of the rock or sediment. Official Business Wells Well - a deep hole dug or drilled into the ground to obtain water from an aquifer For wells in unconfined aquifers, water level before pumping is the water table. Water enters well from pore spaces within the surrounding aquifer. Water table can be lowered by pumping, a process known as drawdown. Water may rise to a level above the top of a confined aquifer, producing an artesian well. Official Business Springs & Streams Spring - a place where water flows naturally from rock or sediment onto the ground surface Gaining streams - receive water from the saturated zone Gaining stream surface is local water table. Losing streams - lose water to the saturated zone Stream beds lie above the water table. Maximum infiltration occurs through streambed, producing permanent “mound” in the water table beneath dry channel. Official Business Contamination of Groundwater Infiltrating water may bring contaminants down to the water table, including: Pesticides/herbicides. Fertilizers. Landfill pollutants. Heavy metals. Bacteria, viruses and parasites from sewage. Industrial chemicals (P C Bs, T C E). Acid mine drainage. Radioactive waste. Oil and gasoline. Contaminated ground water can be extremely difficult and expensive to clean up Exa Official Business mpl es of Con tam inat ion Official Business Pollution Caused by Pumping Wells Official Business Balancing Withdrawal & Recharge If ground water is withdrawn more rapidly than it is recharged, the water table will drop Dropping water table can lead to ground subsidence. Subsidence can crack foundations, roads and pipelines. Areas of extremely high ground water pumping (such as for crop irrigation in dry regions) have subsided 7-9 meters. Source: Richard O.Ireland U.S Geological Survey Official Business Geologic Effects of Groundwater Groundwater can easily dissolve soluble bedrock, such as limestone This creates cave systems, sinkholes, karst topography, and other effects. Official Business Caves Caves - naturally-formed underground chambers Acidic ground water dissolves limestone along joints and bedding planes Stalagmites – dripstone that forms on cave floors Stalactites – dripstone formations that hang from cave ceilings Official Business Cave Formation Official Business Karst Topography Karst topography – area with rolling hills, disappearing streams, and sinkholes FIGURE 11.24 Karst towers in China’s Li River Valley. As indicated by the haze, this is a warm, humid climate. The towers are erosional remnants of pillars that separated caverns. The roofs of caverns collapsed and heavy, monsoon rainfall washed away the debris, leaving the present valleys between the pillars. Charles C. Plummer Official Business Sinkholes and Karst Topography Sinkholes – caves near the surface that have collapsed Source: Rick Duerling, Courtesy of Florida Geological Survey Official Business Other Effects of Groundwater Preservation of Fossils Petrified Wood. Concretions. Geodes Petrified Wood Concretions Geodes Official Business Hot Water Underground Hot springs - springs in which the water is warmer than human body temperature Ground water heated by nearby magma bodies or circulation to unusually deep (and warm) levels within the crust. Hot water is less dense than cool water and thus rises back to the surface on its own. Geysers - hot springs that periodically erupt hot water and steam Minerals often precipitate around geysers as hot water cools rapidly in the air. Official Business Geothermal Energy Geothermal energy – produced using natural steam or superheated water No CO2 or acid rain are produced (clean energy source) Some toxic gases given off (for example, sulfur compounds) Can be used directly to heat buildings Superheated water can be very corrosive to pipes and equipment Official Business Glaciers & Glaciation Official Business What is a Glacier? Glacier – a large, long-lasting mass of ice, formed on land, that moves downhill under its own weight Glaciated Terranes Alpine – found in mountainous regions. Continental – large parts of continents covered by glacial ice. approximately 70% of the world’s supply of fresh water is locked up in glacial ice Official Business Types of Glaciers Develop as snow is compacted and recrystallized, first into firn and then glacial ice Can only form where more snow accumulates during the winter than melts away during the spring and summer Alpine glaciation occurs in mountainous regions as valley glaciers. Continental glaciation covers large land masses in Earth’s polar regions in the form of ice sheets. Glaciation occurs in areas cold enough to allow accumulated snow to persist from year to year. Official Business Distribution of Glaciers Most extensive in polar climates but can occur anywhere where more snow falls than melts during the year. Approximately 10% of Earth’s surface is covered by glaciers. Approximately 85% of all glacial ice is in Antarctica. If all the ice on Antarctica were to melt sea level would rice approximately 65 meter (213 feet) flooding the worlds coastal cities. Official Business Formation and Growth of Glaciers Snowfall. Compaction of the snow removes air. Snowflakes recrystallize into granules. Firn – transitional between granular snow and glacial ice. Glacial Ice – formed once the firn is further compacted and more air removed and has a crystallize texture similar to the metamorphic rock quartzite. Gravity causes the glacier to move downslope. Ablation – loss of the glacier due to melting, evaporation, or calving of icebergs Official Business Glacial Erosion Glaciers erode underlying rock by plucking of rock fragments and abrasion as they are dragged along Basal abrasion polishes and striates the underlying rock surface and produces abundant fine rock powder known as rock flour. Official Business Landscapes Associated with Continental Glaciation Rounded topography is more common Weight and thickness of continental ice sheets produce more pronounced effects Rounded knobs. Grooved or striated rock (several meters deep and kilometers long). Thick enough to bury mountains rounding off ridges and summits Official Business More Indirect Effects Lowering and Rising of Sea level Fiords – coastal inlets formed by drowning of glacially carved valleys by rising sea level. Crustal Rebound Great Lakes region continues to rebound as crust adjust to removal of the last ice sheet. Official Business Deserts & Wind Action Official Business Deserts Desert – any arid region that receives less than 25 cm of precipitation per year. Running water is the predominant force shaping most desert landscapes. Rare and often violent flash flood events produce most desert erosion. Official Business Where and How Deserts Form Deserts can be found anywhere that the atmosphere (air) is usually dry. Most deserts are associated with areas where air is descending. Most common near 30° north or south latitude. Source: U.S. Department of Agriculture Official Business Rain Shadow Deserts Rain shadow deserts form downwind of where moist air rises over high mountain ranges. Official Business Some Characteristics of Deserts Intermittent stream flow Streambeds are dry most of the year Lack through-flowing streams. Exceptions include the Colorado and Nile Rivers. Internal drainage – streams flow to land locked basins. Flash Floods – common in arid regions due to short-lived high volume rain storms. Desert washes or arroyos are commonly steep-sided, with flat floors covered by loose sediments - a result of rare but highly erosive flash flood events. Official Business Wind Large daily temperature and pressure differences lead to strong wind. Dust storms may occur if fine-grained sediments are readily available. Dust can be transported 1000s of km by atmospheric winds. Dust Bowl – continuing dust storms in the prairie states during the droughts of the 1930s. Saharan Desert sediments have carried across the Atlantic Oceana. Volcanic Ash. Source: National Oceanic and Atmospheric Administration Official Business Wind Erosion and Transportation Wind can keep dust in suspension, but larger sand grains move by saltation. Sand grains moving in high- speed winds can effectively sand-blast rocks into ventifacts. Deflation of fine sediments: Blowouts. Desert pavement. Official Business Wind Deposition: Sand Dunes Sand dunes – mounds of loose sand piled up by the wind. Most likely to develop in areas with large sand supply and winds that generally blow in the same direction. Small patches of dunes are common in southwestern U.S., but huge sand seas exist in the Sahara and Arabian deserts. Dunes may also form just inland of beaches along the coasts of seas and large lakes. Official Business Shaping Dunes Shapes depend upon: Wind velocity and direction(s). Amount of available sand. Distribution of vegetation cover. Official Business Reference: Official Business