Ecol 185n - Weathering and Mass Movement PDF

23/10/2023 Ecol 185n - Landscape Ecology | Module 2 Ecol 185n - Landscape Ecology | Module 2 Weathering and Mass Geologic Processes:...

23/10/2023 Ecol 185n - Landscape Ecology | Module 2 Ecol 185n - Landscape Ecology | Module 2 Weathering and Mass Geologic Processes: Movement The Dynamic Earth Ecol 185n - Landscape Ecology | Lesson 2.4 L2.1: The Earth’s Structure LEARNING OUTCOMES L2.2: The Geologic Timescale and the Geologic Cycle At the end of this lesson, you are expected that you will be able to:  Classify the types of weathering and mass movement L2.3: Tectonics, Earthquakes, and Volcanism  Discuss the factors controlling weathering and mass movement L2.4: Weathering and Mass Movement  Analyze the impacts of mass movement on landscape pattern Weathering Types of Weathering Weathering – refers to the disintegration and decomposition of rocks; Mechanical/Physical Weathering- processes that break a rock or mineral the physical and chemical breakdown of rock exposed to air, moisture and living into smaller pieces without altering its composition organisms ▪ the breakdown of rock into solid fragments by physical processes ▪ chemical composition of rock NOT altered Regolith – a loose layer of fragments that covers much of Earth’s surface Chemical Weathering - processes that change the chemical composition of Soil – the uppermost layer of regolith, rocks and minerals which can support rooted plants ▪ the decomposition of rocks and minerals by chemical and biochemical reactions ▪ chemical composition of rock is altered Processes and Agents of Frost Wedging Mechanical/Physical Weathering cracking of rock mass by the expansion of water as it freezes in crevices and cracks These are some actions that break down Earth materials: ▪ frost wedging ▪ thermal expansion and contraction ▪ mechanical exfoliation ▪ abrasion by wind, water or gravity ▪ plant growth 1  23/10/2023 Thermal Expansion and Contraction repeated heating and cooling of materials cause rigid substances to crack and separate I mage source: w w w.geologypics.com I mage source: w w w. uregina.ca Source: w w w.study blue.com Source: w w w.geol.umd.edu Exfoliation the process in which rocks weather by peeling off in sheets rather than eroding grain by grain Source: ht t ps://w ww.flickr.com/phot os/w enchmagnet /2350134660 Source: geophy sics.ou.edu ▪ As underlying rock layers are exposed, there is less pressure on them and they expand ▪ This causes the rigid layers to crack and sections to slide off and the Source: ht t p://geography classroom2014.w eebly.com expanding layers often form a dome. Abrasion by Wind, Water or Gravity Abrasion – the gradual wearing down of bedrock by the constant battering of loose particles transported by wind, water/ice or gravity the sediments can be moved by wind or water and the large rock sections by gravity Source: ht t p://geology.about.com/od/geoproces s es /ig/mechw eat hering/exfoliat ion.ht m 2  23/10/2023 potholes Source: w orldlywise.pbw orks.com Source: rev isionw orld.com Source: ht t p://hsc.sca.nsw.gov.au Source: t hebrit ishgeographer.w eebly.com Source: w w w.goodw p.com Source: desert landforms.w eebly.com Source: ht t p://3.bp.blogspot.com Source: maps.unomaha.edu Plant Growth as plants such as trees send out root systems, the fine roots find their way into cracks in the rocks Source: ht t ps://s-media-cache-ak0.pinimg.com Ta Prohm Temple, Angkor, Cambodia Source: w w w.earthporm.com As the roots increase in size, they force the rock sections apart, increasing the separation and weathering. Source: ht t p://w ww.as.uky.edu Source: ht t p://redrockcany onopenspace.org Processes and Agents of Chemical Weathering DISSOLUTION, OXIDATION AND HYDROLYSIS Dissolution Dissolution Water, often containing acid from dissolved carbon dioxide the separation of materials (carbonic acid), will dissolve into ions in a solution by a minerals from a rock body solvent, such as water or acid leaving cavities in the rock these cavities may generate ex. rainwater acts as weak sinkholes or cave features solution of carbonic acid (acid such as stalactites and The marble grave marker has The grave marker on the rain); anthropogenic actions been attacked by acidic rain right, while old, has not been stalagmites Source: ht t ps://upload.w ikimedia.org/w ikipedia/commons/a/a1/Labeled_speleot hems.jpg influence acidity of rainwater because of the calcite dissolved because of its Limestone cave features result of dissolution. composition. granite composition. 3  23/10/2023 Oxidation Minerals may combine with oxygen to form new minerals. For example, the iron-containing mineral pyrite forms a rusty-colored Underground River, Puerto Princesa, Palawan Source: ht t p://w ww.new snish.com mineral called limonite. Jenolan Caves in Australia Source: ht t ps://upload.wikimedia.org/wikipedia/commons/4/4d/Jenolan_Caves_Imperial_Cave_3.jpg pyrite limonite Bukilat Cave, Camotes Island, Cebu Tham Lod Caves in Thailand Source: ht t p://w ww.telegraph.co.uk / Phot o by : John Spies Hydrolysis Factors Affecting Weathering ▪ Minerals may chemically combine with water to form new minerals ▪ These are generally not as hard as the original material Tectonic Setting - young, rising mountains weather relatively rapidly - mechanical weathering most common feldspar kaolinite (clay) Factors Affecting Weathering Factors Affecting Weathering Rock Composition Rock Structure - minerals weather at different - distribution of joints influence rate of weathering rates - relatively close joints weather Examples: faster calcite weathers quickly through dissolution Joints - fractures of rock, along quartz is very resistant to chemical which no appreciable movement and mechanical weathering has occurred 4  23/10/2023 Factors Affecting Weathering Factors Affecting Weathering Topography Vegetation - contribute to mechanical and chemical - weathering occurs faster weathering on steeper slopes - promotes weathering due to increased - rockslides are common water retention in steeper slopes - vegetation removal increases soil loss Biological Activity - presence of bacteria can increase breakdown of rock Factors Affecting Weathering Products of Weathering Climate Clay - tiny mineral particles of any kind that have physical properties like those of - chemical weathering is more the clay minerals prevalent in warm, wet tropical climates Sand - a sediment made of relatively - mechanical weathering less important coarse mineral grains here Soil - mixture of minerals with different - mechanical weathering is more grain sizes, along with some materials of prevalent in cold, relatively dry regions biologic origin (ex. humus) - chemical weathering occurs slowly here Erosion Agents of Erosion : Water the removal of weathering products from the source and most often the wearing away of bedrock and transport of loosened particles by water occurs by natural agents such as water, wind or ice flowing water will lift and carry small sediments such as silt and sand where water moves more swiftly, there will be more erosion where the water slows down, sediments will be deposited example: sediment moved along a stream 5  23/10/2023 Agents of Erosion : Wind Agents of Erosion : Ice particles of sand are Glacier - a semi-permanent frozen transported close to the body of ice, consisting of surface recrystallized snow, that moves finer particles of silt and clay under the pull of gravity can be transported to great distances glaciers remove, break and transport Wind-blown fine sediments such as this dust cloud rock pieces; scour valleys and can be transported across oceans deposit piles of debris as moraines Mass Movement a.k.a. mass wasting; the downslope movement of regolith and/or bedrock masses due to the pull of gravity Slope failure - the falling, slumping or sliding of relatively coherent masses of rock Results in downhill transport of broken rocks: rock slide rock fall slumping Mass Movement Mass Movement and Slope One of the surficial processes (other than erosion, transportation, deposition, etc.) All mass movements occur on slopes it can also be submarine landslides beneath the ocean under the influence of gravity content can range from dry to wet, slow to fast, or small to large, and from free-falling to gradual or intermittent Angle of repose – the angle that interchangeably called mass wasting – general process involved in mass movements represents the balance of the driving and erosion of the landscape force and resisting force  Driving force – gravity  Resisting force – shearing strength of slope material (cohesiveness & internal friction) rock slide rock fall slumping 6  23/10/2023 Factors Controlling Mass Movement Rate of Movement Factors Most Stable Situation Most Unstable Situation Rapid (fast) - km/hour Type of or even meters/second Rate of Movement 1. Slope angle gentle or horizontal steep or vertical Movement 2. Local relief (elevation) low high Slow 5km/hr km/hr 3. Thickness of debris thin thick Wide range from < Debris & over bedrock Flow Creep Earthflow Mudflow 1cm/year to >100 rock avalanche 4. Climatic km/hour Slide Debris slide Ice temperature above freezing freezing and thawing Rock slide Water in soil or debris film of water around particles saturation Fall Rock fall long drought with episodes of Precipitation frequent but light heavy precipitation Debris fall 5. Vegetation densely vegetated sparsely vegetated Classification of Mass Movement Classification : Fall Fall – free-falling pieces; material free-fall or bouncing down a cliff; this happens in areas with very steep slopes Rockfall – volume of rock that falls – individual pieces fall independently through the air and and characteristically form a cone- hits a surface commonly an apron of shaped pile of irregular broken fallen rock fragments (talus) accumulates at rocks in a talus slope at the base cliff base of a steep incline, where several Talus slope. Rockfall and talus deposits at the base of the steep slope along Duve talus cones coalesce Fjord, Nordaustlandet Island, Norway Classification of Mass Movement Classification : Slide Slide – material moves a coherent Landslide – sudden rapid movement mass; descending mass remains of a cohesive mass of regolith or bedrock Rockslide - the rapid sliding of a mass of bedrock along an inclined surface relatively intact, and descends along that is not saturated with moisture; large well-defined surfaces amount of material failing simultaneously Translational slide (glide) – movement along plane parallel to motion Rotational slide (slump) – movement along a curved surface Debris Slide - a coherent mass of debris moving along a well-defined surface 7  23/10/2023 Classification of Mass Movement Classification : Flow Flow - movement in which Earthflow - downslope viscous Solifluction - the gradual movement of wet soil or other material down a slope, unconsolidated materials like soil, flow of fine-grained materials that have especially where frozen subsoil acts as a barrier to the percolation of water been saturated with water and moves sediment or rock fragments (debris) under the pull of gravity; commonly becomes over-saturated with water occurs on steep hills, with thick debris and move as a liquid cover, after heavy rains grains do not often touch each other during the movement because of too much water types: earthflow, mudflow, debris flow Classification : Flow Classification : Flow Mud Flow – wet and can Debris Flow – wet, fast and scary involving all sizes of clasts with more be very fast, consists mostly than half of the particles being larger than sand (gravel to boulders) of sand and mud size particles - most likely to occur on steep unvegetated slopes with thick debris cover - heavy rains on the slopes of volcanoes with fresh ash Lahar – an Indonesian word referring to layers are triggered mudflows of volcanic origin Classification : Flow Classification : Flow Creep - slowest form (cm or mm per year); movement of unconsolidated material downslope; occurs everywhere, even on gentle slopes affects only the top few meters; top moves faster than bottom (due to friction); caused by freeze-thaw, or wetting-drying events or rain Debris Avalanche - mass of falling and tumbling rocks, debris, drop splashes, gravity, animals and soil; very rapid and turbulent resulting from ice and water that burrowing, wind fluidize the debris 8  23/10/2023 Human-Induced Mass Movement (Scarification) Questions? 9