Earth Science Handouts: Exogenic Processes PDF

HANDOUTS in EARTH SCIENCE temperatures change, rocks expand when heated and contract when cooled. Over time, this repeated Exogenic Processes expansion and contraction weakens...

HANDOUTS in EARTH SCIENCE temperatures change, rocks expand when heated and contract when cooled. Over time, this repeated Exogenic Processes expansion and contraction weakens the rock's structure These are geologic phenomena that occur on or above and eventually causes it to crumble. the Earth’s surface and are driven by external forces. These processes are responsible for shaping the Earth’s surface and are often destructive. Exogenic processes are influenced by the atmosphere, hydrosphere, and biosphere, and can also be affected by external sources like the Sun and Moon. The rate and activity of exogenic processes is often dependent on local conditions and can be accelerated by human activity. Examples of exogenic processes include weathering, erosion, mass wasting and deposition. WEATHERING Weathering is the process by which rocks, soils, and minerals break down at or near the Earth's surface. It is caused by interactions between water, air, sunlight, and living organisms. Weathering is different from erosion, which is the process of transporting weathered materials Exfoliation happens when the sun heats up the rock which away from their source. causes it to expand. When it cools, it contracts and gets smaller. Types of Weathering: Physical weathering Chemical weathering : Process where rocks are physically broken into smaller : Occurs when minerals in the rock react with water and pieces due to any force without any alteration of its acids. For example, water can dissolve some minerals, composition like salt. Chemical weathering is more common in hot : Occurs when physical processes like wind, rain, and humid areas. temperature changes, and waves affect the rock : Usually involves complex : Depends on some applied forces to break rocks into processes that alter the pieces internal structure of minerals by removing and/or adding Ice/Frost Wedging: This occurs when water gets inside elements the joints, alternate freezing and thawing episodes pry the rock apart Water: Water weathers rock by dissolving minerals in rocks. Oxygen: Iron combines with oxygen in the presence of water in a process called oxidation; the product of oxidation is rust. Abrasion: Wearing away the rocks by constant collision of loose particles Carbon dioxide: CO2 dissolves in rainwater and creates carbonic acid. Carbonic acid easily weathers limestone and marble. Acid rain: Compounds from burning coal, oil and gas Temperature changes: Temperature changes can react chemically with water forming acids; Acid rain cause rocks to expand and contract, which can lead to causes very rapid chemical weathering. physical weathering and the breakdown of rocks. When  Time Length of exposure to agents of weather determines the degree of weathering of a rock MASS WASTING Mass wasting, also known as mass movement or slope movement, is the downslope movement of soil, rock, and debris due to gravity. It's a common process on planetary surfaces that can happen slowly or quickly, and be shallow or deep. Biological weathering Mass wasting occurs when the force of gravity on a : a slow process that occurs when plants, animals, and mountain overcomes the mountain's shear strength, microbes break down and weaken rocks. It can have a which is the resistive forces that keep the soil and rocks significant impact on the formation of landscapes and in place. the planet's geology. : it may be caused by several biological activities like Influencing Factors: growth and movement of organisms; they also bring Slope angle conditions for physical and chemical weathering - The steeper the slope, the greater the potential for gravity to pull objects down. Roots: As plants grow, their roots can widen cracks in rocks or force them apart. Role of water Burrowing: Animals like rabbits and piddocks can - Water can reduce the friction along a sliding surface. burrow into rocks, making them bigger and eventually splitting them. Presence of clays Acid secretion: Some organisms can secrete acid to - Clay particles can absorb water and prevent it from dissolve rocks such as lichens. passing through the ground. This can create a layer on a Bacterial activity: Bacteria can dissolve rocks through slope that prevents water from filtering through. biological processes. - Clay content is a factor that influences the initiation of debris flows. The amount of clay and other large debris Factors Affecting Weathering: in a debris flow can affect runout. Climate Temperature and precipitation are the primary drivers Presence of weak materials and structures of weathering; Areas that are cold and dry tend to - Weak materials and structures become slippage have slow rates of chemical weathering and surfaces if weight is added or support is removed weathering is mostly physical. (bedding planes, weak layers, joints and fractures, Chemical weathering is most active in areas with high foliation planes). temperature and rainfall. Types of Mass Wasting Rock type Creep: is a slow, gradual and continuous movement of The minerals that constitute rocks have different soil down a slope due to gravity. It's the most widespread susceptibilities to weathering. Sedimentary rocks and least noticeable type of mass wasting as the soil weather more easily than igneous rocks. travels short distances. Rock structure Signs of soil creep: Rate of weathering is affected by the presence of a. Soil rippling b. Bent tree trunks joints, folds, faults, bedding planes through which agents of weathering enter a rock mass Highly jointed/fractured rocks disintegrate faster than a solid mass of rock of the same dimension Topography Physical weathering occurs more quickly on a steep slope than on a gentle one c. Tilting of fences, posts On a gentle slope, water may stay longer in contact and pole with the rocks, hence chemical weathering is enhanced. Slump: can involve both soil and rock, travels short of their high distances and varies from slow to very rapid; It occurs velocity and when a coherent mass of rock or soil slides down a slope ability to travel along a curved surface. Slumps are often caused by an long excess of water on a steep slope. distances. They can cause trauma, damage infrastructure, and disrupt transportation. Triggers of Mass Wasting: Shocks and vibrations - such as earthquakes and minor shocks such as those produced by heavy trucks on the road, man- made explosions Rockfall: Involves rocks that move very to extremely Slope modification rapid and can travel great distances; Rockfalls can occur - creating artificially steep slope so it is no longer at when: the angle of repose (steepest angle at which a -There is a source of rock granular material can be piled on a horizontal surface above a steep slope without slumping) -There are bedrock outcrops or boulders on Undercutting steep mountainsides - the erosion of material at the base of a steep bank or cliff (can be due to wave action, rivers and glaciers, Rockfalls can cause significant damage, including: and human activities) - Damaging property beneath the fall-line of large rocks - Boulders bouncing or rolling great distances and Changes in hydrologic characteristics damaging structures or killing people - heavy rains lead to water-saturated regolith - Blocking highways and railroads increasing its weight, reducing grain to grain contact and angle of repose Debris Slide and Flow: Changes in slope strength When debris from - weathering weakens the rock and leads to slope rockfalls and slumps mix failure; vegetation holds soil in place and slows the with water, they can influx of water; tree roots strengthen slope by holding transform into debris the ground together slides that can travel great distances. Debris Volcanic eruptions flows are two to three - produce shocks; may produce large volumes of times denser than water from melting of glaciers during eruption, flooding streams, which resulting to mudflows and debris flows allows them to strip away land and pick up large objects. EROSION and DEPOSITION A. Erosion Mudslide: Erosion is the action of surface processes (such as Mudslides generally involve saturated soils moving at water flow or wind) that removes soil, rock, or dissolved very to extremely rapid velocities and travel great material from one location on the Earth's crust and then distances. They are highly fluid and can move at speeds transports it to another location. It involves the of up to 5 meters per second. Mudslides are often caused incorporation and transportation of material by a mobile by heavy rains in areas with lots of unconsolidated agent such as water, wind or ice. sediment. They can also be caused by volcanic eruptions, such as when snow or ice on a volcano's Erosion is distinct from weathering which involves no slopes melts. Mudslides can be very dangerous because movement. Erosion often occurs after rock has been disintegrated or altered through weathering. Weathered suddenly, as in a landslide. It also indirectly influences rock material is removed from its original site and other agents of erosion. Gravity moves loosened transported away by a natural agent. material from higher ground to lower ground, where it can be picked up by other erosion processes. B. Deposition Deposition is the process of dropping off eroded material in a new location. Deposition occurs when sediments settle out of the water or wind that is carrying it. Sediment can be transported as pebbles, sand and mud, or as salts dissolved in water. Salts may later be deposited by organic activity (e.g. as sea shells) or by evaporation. Erosion and deposition are related opposites that Agents of erosion: constantly happen in nature and change the way the 1. Running water Earth's surface looks over time. For example, canyons Water is a powerful and abundant agent of erosion are eroded environments where sediment is being because it can take many forms, including raindrops, removed, while beaches are depositioned environments streams, and rivers. where sediment is being deposited and built up. *Raindrops in dry environments can create a splash erosion, which moves small soil particles. Deposition is a geological process that occurs when sediments, soil and rocks are added to a landform or 2. Ocean or sea waves landmass. It can result to: Ocean currents, waves and tides can erode coastlines. Breaking waves erode the coast by suspending sediment Landform creation particles or dislodging rocks. Deposition can create landforms such as (a) sand dunes are formed by wind carrying sand grains 3. Glaciers and depositing them when the wind slows or stops. Sand Glaciers are powerful agents of erosion that use two dunes are found in deserts and coastal areas. main processes to shape landscapes: abrasion and plucking. (b) alluvial fans are formed when sediment carried by a mountain stream is deposited in an area with a lower Abrasion: The bottom of a glacier is rough with debris like slope angle. sediment and rock, which scrapes against the bedrock below, polishing and gouging it. This process creates (c) loess is formed by the deposition of silt, sand, and scratches, or striations, in the bedrock. clay-sized particles by water and glaciers. It is an unstratified, geologically recent deposit of silty or loamy Plucking: Glaciers can pick up and carry away chunks of material that is usually buff or yellowish brown in colour bedrock by freezing them to the bottom of the glacier and and is chiefly deposited by the wind. Loess is a then flowing them away. This process can occur when sedimentary deposit composed largely of silt-size grains cracks in the bedrock beneath the glacier grow together that are loosely cemented by calcium carbonate. and break off. 4. Wind (aeolian erosion) Strong winds can dislodge and carry away soil and rock particles. Wind can pick up dry particles like sand, dust, and soil, but it can't carry as large particles as flowing water. Aeolian erosion is most common in dry regions and areas with little rainfall. a. b. 5. Groundwater Groundwater carries away the dissolved material, which can create new landforms. Over time, groundwater can enlarge cracks in rocks, eventually forming caves and sinkholes. c. 6. Gravity Gravity pulls soil, mud, and rocks down hillsides and cliffs. This process can occur slowly over time or  Sedimentary rock formation The deposition rate of sediments during erosion is Sedimentary rocks are formed when sediment is influenced by various factors that dictate how quickly deposited and then compacted and cemented together sediments settle from moving water, wind, or ice onto a to form rock stable surface. Deposition occurs when the transporting medium (e.g., river water, wind, or glaciers) loses energy, and sediments can no longer be carried. Key factors affecting sediment deposition rate: 1. Particle Size and Weight Larger and heavier particles settle faster than smaller, lighter ones. This is because gravity acts more strongly on larger particles, causing them to fall out of suspension more quickly. Clay and silt particles, being lighter, can travel farther, while gravel and sand particles settle sooner. Shoreline feature creation Deposition is the process by which the sea deposits 2. Transport Medium Velocity material, such as sand, pebbles, and rocks, along or near When the speed of the transporting medium (e.g., water a coastline. This process creates a variety of shoreline or wind) decreases, sediments lose their kinetic energy features such as beaches, spits, tombolo, sand bars and and begin to settle. A river with a high velocity can carry sand dunes. large sediments over long distances, while a slower river allows for more rapid deposition. 3. Vegetation and Obstacles Plants, roots, and other obstacles can trap sediments, slowing the transport medium and enhancing deposition. Vegetated areas often have higher sedimentation rates than bare or paved surfaces. References: Teaching Guide for Senior High School. Earth Science. CHED. 2016 Petersen, J. F. et. al. Earth and Life Sciences. Manila: Rex Book Store, Inc. 2016.