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Weathering, Erosion, and Transportation Shaping Earth’s Surface Chapter 7 Shaping Earth’s Surface •The Earth is constantly undergoing gradual changes •Earth is moved by weathering, erosion, and then transported to different areas on Earth W e a t h e ri n g •_______________ –the process of ______________ ______ ______________ at the Earth's surface by the action of wind, rain and ice •Participates in rock cycle, used in formation of soils, and helps in movement of rock material over Earth’s surface •The piles of rocks and rock fragments around a mass of solid rock is evidence that the solid rock is slowly crumbling away. This solid rock that is crumbling to rock fragments is in the Grand Canyon, Arizona. •______________ Erosion –The process of _____________ ____________ weathered materials _________ _________ •_____________ ____ _________ ___________ by rivers, glaciers, wind, or waves _ _ _ _ _ _ _ _ _ _ _ _ _ W e a t h e ri n g •_________ __________ _____ of rocks •no change in chemical composition •“______________” Frost Wedging (know this is a type of mechanical weathering) •repeated freezing and thawing of water in cracks in rocks –as process repeats cracks become larger Results of Frost Wedging Exfoliation (know this is a type of mechanical weathering) •Spalling off layers of rock •caused by reduced pressure on rocks --as material is removed from above the rock expands –causes outer layers to break free in sheets •Common in granite Exfoliation –rounded boulders –dome-shaped hills Block Disintegration •Sharp temperature changes •desert rocks expand and contract •enlarge joints T r e e Ro o t s •Widen cracks in rock as they grow _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ W e a th e r i n g •The ____________ ___ __________ by ____________ ____________ with water, atmospheric gases, or solutions •“______________ “ –dissolving of minerals in rocks ______ _____ •A reaction between oxygen and the minerals making up rocks –metal oxides •iron •magnesium –characteristic color _______ ______ •A reaction between carbonic acid and minerals in rocks CO2 + H2O H2CO3 •Limestone caves Caves _______ _______ •A reaction between water and the minerals in rocks –dissolves material –water combines with mineral to form a hydrate Agents of Weathering & Erosion Mass Movement Also called Mass Wasting _ _________ _ __________ •__________ __________ of rock, regolith, and soil under the influence of _______ –does not require the aid of a transporting agent such as water, ice, or wind –regolith - loose uncemented mixture of soil and rock particles that covers the Earth’s surface Angle of _________ •_________ at which _________ _________________ ___________ (gravel, sand, soil) sits at ________. –typically _______ _________ –slightly wet unconsolidated materials exhibit a very high angle of repose because of surface tension between the water and grains hold grains in place •(e.g, sandcastle) –saturated material has low repose angle due to fluidity of material Angle of Repose •If angle of repose is steepened, mass wasting will begin –e.g., road cuts and excavations Types of mass wasting •Rapid movement –rock fall –slump –rockslide or debris slide –debris flow or mudflow Types of mass wasting •Slow movement –Creep Rock Falls •Free fall of detached pieces of material of any size (know definition) –may fall directly downward or bounce and roll –common in mountainous areas Slumps •Involves mass of soil or other material sliding along a curved, rotational surface (know definition) –like a spoon –forms small crescent shaped cliffs (scarps) Slide •Similar to slump except material does not rotate •occurs when blocks of rock or masses of unconsolidated material slide down a slope –___________ ____________ of mass movements Debris Flow •Rapid movement of a mixture of rock/soil with a significant component of water or air (know definition) Creep •Imperceptibly slow flow downhill of soil (know definition) –causes curved tree trunks, tilted utility poles, fence posts, tombstones and breaks retaining walls Triggering of Mass Wasting •Shocks –earthquakes, heavy truck rumbling down road, man made explosions •slope modification •undercutting –streams eroding banks or surf action along coast •exceptional precipitation •volcanic eruptions Running Water ____________ ___________ of all erosional agents of gravity Stream •A body of running water that is confined in a channel and moves downhill under the influence of gravity Three ways streams transport materials •As dissolved material in solution (solution load) •As materials carried in suspension (suspended load) •As sand and larger materials that are rolled, bounced, and slid along bottom of stream bed (bed load) Erosion by Streams •Dissolves soluable materials directly from rocks and sediments •Quarry and pluck fragments and pieces of rock from beds of solid rock by hydraulic action •Grinding and filing action on fragments and wearing away of bed by more massive fragments that are rolled, bounced and slid along stream bed and each other (most stream erosion accomplished) ______ ______ •___________ in a stream –develops due to slumping which slows stream by increasing its load Meanders •Have dramatic effect on erosion –water moves faster around outside bank –has greater erosional ability on outside –widens floor of valley by eroding on outside of meander –deposits material on inside of another bend downstream •erodes laterally-slowly works way across land Oxbow Lakes •Where two bends in a stream meet forming a cut-off meander •____________ •____________ •____________ •____________ How Oxbow Lakes form Oxbow lake in Malaysia Stream Deposits •_________ _____ Sandbar •A ridge of sediment, usually sand or gravel, deposited in the middle or along the banks of a stream Pointbar •The deposits a stream makes on the inside curve of a meander Fl o o d p l a i n •Wide, level floor of a valley built by a stream (know definition) –where stream floods when it spills out of its channel Delta •A sedimentary deposit that forms where a stream flows into standing water - mouth (know definition) –so-named because it may develop a crudely triangular shape resembling the Greek letter delta Alluvial Fans •_____-_________ __________ of stream sediment that forms at the bottom of dry river basins –not deposited in water –common at base of arid/semiarid mountain ranges where intermittent streams flow •intermittent - only flows when it rains or snows Glacial Erosion What is a glacier? •A _________ of ______ _____ _______ that moves under its own weight due to gravity Glaciers Today •___________ approximately _______ of Earth’s land area –_________ on ____________ and ____________ (97%) •Store 75% of world’s freshwater –melting would raise sea level 230 feet How do glaciers form? •Accumulation - material added to the mass of the glacier •Ablation - removal of material from glacier –accumulation must exceed ablation •Temperature and precipitation are the main ingredients for a glacier to form and keep growing. –Temperature must be cold enough –Precipitation must be snow How do glaciers form? •Accumulated snow is gradually transformed to ice •weight of overlying snow packs it down, drives out air, and recrystallizes it into dense interlocking ice crystals Types of Glaciers •____________ Glaciers –ice sheets •____________ Glaciers –valley glaciers •_________ glaciers Alpine Glaciers – form at ______ ___________ in ____________ regions –tend to flow downhill through valleys –also called valley glaciers Continental Ice Sheets • large masses of ice which flow outward from an area of maximum thickness and maximum ice surface elevation •flattened dome ______ ______ •__________ _____________ twice the size of Australia •14,000 feet thick •98% covered by ice Techniques of Glacial Erosion •Bulldozing •Abrasion •Plucking Bulldozing •Pushing along of rocks, soil, and sediments by leading edge of advancing glacier (know definition) –till - deposits of bulldozed material after ice melts –moraines - recognizable landform made of till Plucking •Glacier breaks off rocks that have frozen to their bed and carries remnants along (know definition) –accelerated by frost-wedging Abrasion •Rock fragments frozen into moving glacial ice scratch, polish, and grind against surrounding rocks at base at the base and along valley walls (know definition) Wind Wind versus Water •Similar processes –Erode, transport, deposit •Bed load •Suspension •Wind is considerably less efficient in modifying surface –No chemical weathering Wind is common in arid desert regions bec a us e: •Air near the surface is heated and rises, cooler air comes in to replace hot rising air and this movement of air results in winds •Arid regions have little or no soil moisture to hold rock and mineral fragments •_________ –_________ ___________ •break off particles •polish –Rocks planed or flattened Wind Erosion –Ventifacts •rocks sculpted by wind Wind Erosion •____________ –“to blow away” –_______________ _________ ____ of _________ __________ from the surface •The Dust Bowl Desert Pavement •Sheetlike surface of rock fragments that remains after wind has removed fine particles –Most wind deflation zones are desert pavement Desert Varnish •Dark, shiny stain often found on surfaces of some desert rocks that have been exposed at surface for long periods of time –manganese, iron oxides, hydroxides, clay minerals _____ _____ •__________ formed by the ___________ of __________ ____ __________ –also called “deflation basins” Yardangs •Sculpted landforms that have been streamlined by desert winds –up to tens of meters high Wind transportation •Particles are transported through –suspension –saltation –creep Suspension (know this is a type of wind erosion) •Upward currents of air support weight of suspended particles –scattered as dust or haze Saltation (know this is a type of wind erosion) •Downwind movement of particles in a series of jumps or skips –may hit other grains that jump up to continue saltation Creep (know this is a type of wind erosion) •Larger sand grains that are too heavy to continue saltation slowly “creep” forward as they are pushed by salting grains –accounts for 25% of grain movement in deserts •_________ W i n d De p o s i t s –a _______ _______ or ridge of _______ or other sediments –obstacle reduces wind velocity –wind dumps its load Sand Dune •Sand dunes form when there is –(1) a ready supply of sand –(2) a steady wind –(3) some kind of obstacle •slip face - on the lee side of the dune Barchan Dunes Transverse dunes Linear Dunes Parabolic Dunes Star Dune •__________ W i n d De p o s i t s –very _____ _______, or silt __________ __________ ___ __________ _______ –Central States •east sides of Mississippi River Basin –Eastern Washington
