Gradational processes Tectonic processes build up of roughen up the earth Gradational forces level off highs and fill in lows. Weathering = breakdown of material in place Gradation = leveling of land degradation (erosion) = removal of highs transportation = movement of material aggradation (deposition) = filling in lows Ultimate gradation --> level smooth plain at "base level" base level ≈ sea level, cannot erode farther downward Before material can be moved by any gradational agent, Principal agents of gradation it must be freed from its parent material or bedrock. gravity water wind ice Landforms are usually result of more than one of these Mountains do not move “en masse” to the sea Breakdown of rock material in place = WEATHERING Weathering does not, by itself, move material. Three types of weathering Physical Chemical Biological Processes not mutually exclusive one or the other may dominate due to climate or rock type Mass wasting: Gravity as an agent of gradation Erosion Transportation 1 Physical: makes smaller pieces from bigger pieces Bedding planes, joints, fractures, make rock more does not change chemical composition of rock susceptible to weathering disintegration Massive (non-jointed) rocks are slower to weather Important because 1. smaller pieces easier to move 2. increases surface area for chemical attack Examples of Physical Weathering Examples of Physical Weathering 1. Freezing water...expansion in cracks 2. Salt weathering...salt crystal expansion most effective where daily freeze-thaw events capillary water evaporates leaving salt behind high elevations in mid-high latitudes sandstone especially susceptible not important in tropics or polar regions action similar to frost wedging arid and semi arid regions Examples of Physical Weathering Examples of Physical Weathering 3. Differential expansion 4. Unloading...removing pressure of overlying rock minerals expand and contract differently with exfoliation...peeling of thick concentric layers heat and cold common in granite granite especially susceptible (unloading causes rock bursts in mines) fire promotes this diurnal temperature changes may also be factor Causes peeling of thin concentric shells Half-dome in Yosemite Æ 2 Exfoliation Evidence of physical weathering Domes Angular debris and jagged forms Talus slopes (piles of broken rock) Above tree line in the Sierra Nevada. Three types of weathering Physical Physical √ weathering Chemical dominates Biological Processes not mutually exclusive one or the other may dominate due to climate or rock type Chemical weathering is fastest in warm wet climates Chemical : decays rock by chemical reactions decomposition Wet Operates in three ways by creating 1. new materials less resistant to erosion 2. new materials with greater volume Æ expansion 3. soluble materials which are easily dissolved Hot and transported in water Most chemical weathering requires water Dry heat speeds up reaction Cold Soil profile showing depth of chemical weathering ‘front” 3 Examples of Chemical Examples of Chemical Weathering Weathering 2. Hydration...water attached without chemical change Æ expansion, solution 1. Oxidation chemical union with oxygen usually creates softer and finer material increase in volume (expansion) Examples of Chemical Weathering Examples of Chemical Weathering 5. Solution...dissolves minerals 3. Hydrolysis...water unites chemically Æ new compounds Æ expansion, Æ soluble compounds water soluble...NaCl, CaSO4 (gypsum) 4. Carbonation...formation of soluble carbonates acid soluble carbonic acid, acid rain can dissolve limestone and marble (CaCO3) Evidence of chemical weathering Edges and corners along joints and bedding planes are Spheroidal weathering...in place weathered more rapidly than flat surfaces Æ rounded edges 4 Elephant Rocks State Park, Missouri, Grapevine Hills, Big Bend, TX Chemically weathered niche, New Mexico Chemical weathering Æ niche where water seeps out Biological weathering Three types of weathering living organisms break down rock physically and/or chemically Physical √ Chemical √ Physical examples Biological plant roots burrowing animals Processes not mutually exclusive one or the other may dominate due to climate or rock type 5 Biological weathering living organisms break down rock Chemical weathering dominates in warm & wet climates physically and/or chemically Æ rounded shapes Physical examples Physical weathering dominates in drier cooler climates plant roots Æ angular, jagged shapes burrowing animals Chemical examples lichen acid litter Differential weathering Examples of differential weathering in different climates one material breaks In warm wet climates down faster than granite...subject to chemical weathering Æ another saprolite (rotten rock) therefore, one is slower In cool dry climates, granite is resistant to erode than the other Æmountains Grand Canyon... limestone and sandstone ledges In warm wet climates limestone dissolves and shale slopes to yield topographic lows Appalachian Ridge and Valley...limestone valleys and sandstone ridges In cool or arid climates, limestone is resistant often forms topographic highs 6 At mineral level...silica (quartz) highly resistant to weathering Gulf Shores sand comes mainly from Appalachians via the Released from rock by decomposition of surrounding Apalachicola River, deposited in offshore sand sheet. material, carried by streams to oceans Æ beaches Three types of weathering GRAVITY AS AN AGENT OF GRADATION Physical √ Gravity causes mass movement (mass wasting) Chemical √ Biological √ Mass as in "matter" NOT as in large volume What kind of evidence (what would you see?) is Mass movement = movement of material downslope associated with physical weathering? Where in the under the influence of gravity world (what kind of climate) is likely to have this? What kind of evidence (what would you see?) is associated with chemical weathering? Where in the world (What kind of climate) is likely to have this? Kind of Rock Regolith Water & material (dry) & water sediment Factors influencing mass movement Kind of Falling,rolling, Flowage Fluid 1. Water motion sliding within mass flow acts as a lubricant Low Water High adds weight Content may cause “fluid” flow Slow Talus Soil creep 2. Shaking as in earthquakes, explosions, trains | creep | 3. Undercutting by streams or human activity | | 4. Freeze/thaw or wet/dry cycles Speed | | | | Fast 7 Slow Slow 1. Creep... 1. Creep... Related to freeze/thaw or wet/dry cycles Creep: gradual displacement downhill, greatest at surface, Kind of Rock Regolith Water & most material moves by creep material (dry) & water sediment Evidence of creep Kind of Falling,rolling, Flowage Fluid motion sliding within mass flow Low Water High Content Slow Talus Soil creep | creep | Solifluction | | Speed | | | | Fast 2. Solifluction... water saturated soil, high latitudes or Kind of Rock Regolith Water & elevations, permafrost beneath surface material (dry) & water sediment Kind of Falling,rolling, Flowage Fluid motion sliding within mass flow Low Water High Content Slow Talus Soil creep | creep | Solifluction | | Earthflows Speed Land-slides slumps | | | | Fast 8 1994, landslide, McClure Pass, CO Landslide...mass of material moves as a unit moves regolith (all material above bedrock) sudden, moderately high speed Earthflow...usually water soaked mass clay rich soil on a slope linear = earthflow rotational = slump All of above related to over-steepened slopes stream (or construction) undercutting earthquakes loss of vegetation water that adds weight / lubricates http://www.ngdc.noaa.gov/seg/hazard/slideset/landslides Landslide: slippage on Earth flow: material mixes straight plane Earth slump: slippage on a curved plane La Conchita, CA, 1995 9 Landslide http://www.youtube.com/watch?v=qEbYpts0Onw&fe ature=related Kind of Rock Regolith Water & Slump has a rotational element, slide does not material (dry) & water sediment Kind of Falling,rolling, Flowage Fluid motion sliding within mass flow Low Water High Content Slow Talus Soil creep | creep | Solifluction | | Earthflows Speed Land-slides slumps | | | | Rock- fall Avalanche Fast Rockfall: dry material Rockfall on Pecos River, TX “falls” downhill, common in spring thaw 10 Avalanche on Mt. Denali, Alaska Kind of Rock Regolith Water & material (dry) & water sediment Kind of Falling,rolling, Flowage Fluid motion sliding within mass flow Low Water High Content Slow Talus Soil creep | creep | Solifluction | | Earthflows Speed Land-slides slumps | | | | Rock- Debris fall Avalanche flow Stream Fast flow Debris flow...water, mud, and rock debris more fluid than earthflow moves faster and follows valleys (channelized flow) associated with heavy rain steep poorly vegetated slopes arid and semi-arid regions common in California Csa (Mediterranean) climates dry summers fire destroys vegetation wet winters 1980, San Bernadino, debris flood control basin overflowed 11 Moral of the story: Debris flow BE CAREFUL WHERE YOU BUY YOUR HOUSE http://www.youtube.com/watch?v=X4JPxw578UE&fe ature=related Speed and water content are the main classification variables for mass movement Low Water High Content Slow Talus Soil creep | creep | Solifluction | | Earthflows Speed Land-slides slumps | | | | Rock- Debris fall Avalanche flow Stream Fast flow 12.