Weathering, Soil, & Erosion

1. Weathering, Soil, & Erosion Two types of weathering : A. Mechanical Weathering- involves the physical disintegration of rock. The process produces smaller rock particles that have the same composition as the parent material. I. WEATHERING -changes occur in rock material as the result of exposure to air and water. -takes place anywhere that water and/or air can penetrate. -provides the material that becomes soil or sedimentary rock B. Chemical Weathering- involves the decomposition of rock, transforms the parent material chemically, and releases mineral grains.

2. MECHANICAL (physical) occur as a result of: • Frost Action/Frost Wedging - the 9% expansion of water during freezing in rock fractures breaks off pieces of rock • It is most effective where there is: • -abundant water • -many cracks and pore spaces in the rock • -a climate with temperature fluctuations across the freezing point

3. example

4. Exfoliation - removal of overlying rock which causes the underlying rock to expand and fracture due to pressure release. Fractures develop parallel to the rock surface and tend to peel off • Thermal Expansion and Contraction - solids expand when heated and contract when cooled. Although such expansion due to changes in temperature from day to night or from summer to winter may contribute to rock disintegration, experiments indicate it has only a minor effect.

5. Abrasion - particles moved by water, ice, and air can be effective in wearing away rock.

6. Other forms • Salt Crystal Growth - similar to frost wedging, the force of growing salt crystals in fractures and pore spaces can pry loose grains and expand openings. Such a process is important in arid and coastal areas. • Action of Plants and Animals - roots of plants can widen cracks and burrowing animals can mix soil/sediment particles and allow water to penetrate more quickly and deeply, speeding other weathering processes.

8. Chemical Weathering • Solution - dissolving of minerals into solution. Most minerals have low solubility in pure water, but rain contains carbonic acid, so that carbonate minerals dissolve readily in acidic solutions.

9. Oxidation - atmospheric oxygen combines with metal ions to form oxides (or hydroxides). Oxidation of pyrite, for example, produces sulfuric acid.

10. Chemical Weathering • Hydrolysis - reaction between a mineral and water can produce a new mineral or dissolved material. Hydrolysis of feldspar, for example, produces clay.

11. What Factors Control the Rate of Chemical Weathering? The rate of weathering is controlled by: • Surface Area (Related to particle size) controls weathering because the smaller the particle size, the larger the surface area exposed to weathering for a given volume of material. *The presence of joints therefore increases a rock's surface area. • Climate controls weathering in that rocks experience the most thorough and rapid chemical weathering in warm, humid climates. *Weathering rates are lowest in desert and cold climates. • Parent Material (mineral composition of rock) controls weathering processes because minerals that form at high temperature and high pressure are less stable at the Earth's surface than low temperature, low pressure minerals. • Presence of Plants and Animals influence weathering as chemical and physical weathering rates are increased by the action of plants and animals. • Topographyaffects weathering as irregular, steep topography exposes more rock to weathering than horizontal surfaces. surface area animation

14. What is Soil? • Soil, a non-renewable resource, is the final product of weathering, and is defined as that portion of the regolith (unconsolidated rock and mineral fragments covering the land surface) which is capable of supporting plant life. -Regolith can be generally grouped as either residual (soils formed on bedrock) or transported (soil formed on material that has been moved to its current location).

15. What Factors Control Soil Formation? The factors controlling soil formation are similar to those controlling the rate of chemical weathering: • Climate is most important factor influencing soil type and depth. • Parent material exerts some control on soil type and depth, particularly for immature soils. The original rock particles control the fertility of the soil by providing the inorganic nutrients. • Organisms contribute to soil formation and fertility. • Relief and Slope (Topography) Elevation affects climate and slope affects soil formation and erosion. • Time affects soil maturity in that soil develops faster on unconsolidated material than on bedrock. outline

16. What is a Soil Profile? Soil consists of a series of horizontal layers called horizons. -A soil with well-developed horizons is called mature, -A soil with poorly developed horizons is called immature. Soil horizons from top to bottom are as follows: Plants account for most of the organic remains. Remains such as leaves or pine needles are calledLitter Horizon O= This is where you see plants growing. "O" is the organic layer of "A". Horizon A = this is where the topsoil is located, it contains humus, clay, and various minerals. Horizon B = this is also called subsoil, clay and silt dominate this layer. Some small amount of humus is present, and roots. Horizon C = partly weathered rocks from the bedrock. Rocks are various sizes, such as gravel and sand. Plant roots may be present. Bedrock

17. organic zone, that contains humus zone of leaching (topsoil) zone of accumulation (subsoil) partially decomposed bedrock

18. Texture • Sandy Soils- have a gritty texture and are formed from weathered rocks such as limestone, quartz, granite, and shale. (drains—tough to hold nutrients) • Silty Soil- is considered to be among the most fertile of soils. Usually composed of minerals (predominantly quartz) and fine organic particles. • Clay Soil-wet they are very sticky, lumpy and pliable but when they dry they form rock-hard clots. Clay soils are composed of very fine particles with few air spaces, thus they are hard to work and often drain poorly. Loamy Soil • Considered to be the perfect soil, Loamy soils are a combination of roughly 40 % sand, 40% silt and 20% clay.

19. Example, a soil is 40% sand, 30% silt, and 30% clay, the texture is “clay loam”. Sand- extend line upward from % sand at 120 degrees (parallel with side labeled silt) Silt- extend line downward from % silt at 60 degrees parallel with side labeled clay Clay- extend line horizontal from the % clay (parallel with side labeled sand)

21. The different soil types are categorized by the following: Tundra, Northern Forest, Prairie, Mountain, Southern Forest, Desert, and Tropical.

23. What causes Soil Degradation? Soil degradation can be caused by any decrease in soil fertility, including erosion, chemical deterioration, and physical deterioration: • Erosion involves the movement (transportation) of weathered materials to a place of deposition. About 25% of U.S. cropland is eroding faster than it is being replaced by soil-forming processes. Improved farming practices have significantly reduced erosion rates. Agents of erosion include gravity, water, ice, and wind. Water erosion, for example, involves: • sheet erosion where erosion is fairly evenly distributed over the surface and removes thin layers of soil. • rill erosion where erosion occurs in channels scoured by running water, producing rills (shallow channels) and gullies (>30 cm).

24. What affects the rate of erosion? • It can be estimated by the amount of sediment (particles and dissolved material) carried by streams in an area. • Rates vary widely depending upon climate, topography, rock type, and human influences (agriculture). • Differences in erosion rate are usually caused by: -compositional or grain-size differences -the presence/absence of fractures/joints -by differences in sunlight intensity

25. Differential erosion occurs where different portions of a rock body erode at different rates, and typically produces unusual surfaces, shapes, and formations. • The amount of precipitation falling on each segment is the same.  • Water accumulated in segment A runs off adding to what falls into segment B by precipitation. The water in B runs into to C and C into D and so on. As a result the water in each segment increases as you move down slope.  •  Additionally, as the water runs down slope its velocity is increasing.  • Erosion causes stripping of the soil thus preventing parent material to stay in place to develop into a soil.  • Soils on slopes, especially at the mid-slope and near the bottom of the slope tend to be weakly developed.

26. Name some AGENTS of Erosion • Water, wind, ice, and waves are the “agents oferosion” that wear away at the surface of the earth.

27. Water Erosion

28. Is water in all its forms erosional? • Raindrops (especially in dry environments) create splash erosion that moves tiny particles of soil. • Water collecting on the surface of the soil collects as it moves towards tiny rivulets and streams and creates sheet erosion & rill erosion. *Fine sand can be moved by streams flowing as slowly as three-quarters of a mile per hour • In streams, the faster water moves the larger objects it can pick up and transport. (critical erosion velocity)

30. How does a stream erode material? animation • Streams erode their banks in three different ways: 1) the hydraulic action of the water itself moves the sediments 2) water corrodes sediments by removing ions and dissolving them 3) particles in the water strike bedrock and erode it http://search.live.com/images/results.aspx?q=down+cutting+of+a+stream&go=&form=QBIR#focal=f250a4f89cd92d2f4be486191647ad65&furl=http%3A%2F%2Fbrownsguides.com%2Fsrl%2Ffiles%2F2008%2F10%2Fstreamterrace1rgb400.jpg

31. What 3 places of the channel does water erode? • Streams can erode in three different places: 1) lateral erosion- erodes the sediment on the sides of the stream channel 2) down cutting- erodes the stream bed deeper 3) headward erosion- erodes the channel upslope. Meander Cut-Offs and Oxbow Lakes

33. STREAM STAGES

34. http://search.live.com/images/results.aspx?q=downcutting&FORM=BIRE#focal=e322f7769dc937521b83ed615d84a563&furl=http%3A%2F%2Fgeography.sierracollege.edu%2Fbooth%2FCalifornia%2F3_hydrosphere%2Fgeomorphic_evolution.gifhttp://search.live.com/images/results.aspx?q=downcutting&FORM=BIRE#focal=e322f7769dc937521b83ed615d84a563&furl=http%3A%2F%2Fgeography.sierracollege.edu%2Fbooth%2FCalifornia%2F3_hydrosphere%2Fgeomorphic_evolution.gif

35. Youth • V-Shaped Valley • Rapids • Waterfalls • No Flood Plain • Drainage Divides Broad and Flat, Undissected by Erosion • Valley Being Deepened • General Agreement on this stage, lots of examples

36. Maturity (Early) • V-Shaped Valley • Beginnings of Flood Plain • Sand and Gravel Bars • Sharp Divides • Relief Reaches Maximum • Valleys stop deepening

37. Maturity (Late) • Valley has flat bottom • Narrow Flood Plain • Divides begin to round off • Relief diminishes • Sediment builds up, flood plain widens • River begins to meander • Lots of Disagreement from here on; some geologists believe slopes stay steep but simply retreat.

38. Old Age • Very Wide Flood Plain • Land worn down to flat surface • Resistant rocks form residual hills • Pronounced River Meanders • Cut-off Meanders (Ox-bow lakes)

39. Ice Erosion • Glaciers can perform two erosive functions: 1)Plucking - water enters cracks under the glacier, freezes, and breaks off pieces of rock that are then transported by the glacier 2) Abrasion- cuts into the rock under the glacier, scoops rock up like a bulldozer, and smoothes and polishes the rock surface • Ice more powerful, but water more abundant

40. Wave Erosion Coastal Straightening • coastal erosion -waves in oceans and other large bodies of water • large storm waves can produce 2000 pounds of pressure per square foot • chemical content of the water waveMotion ***Erosion of sand is much easier for the waves and sometimes, there's an annual cycle where sand is removed from a beach during one season, only to be returned by waves in another. Seasonal Cycle of a Beach Spits and Baymouth Bars Longshore Drift of Sand

41. Wind Erosion • Erosion by wind is known as Aeolian (or eolian) erosion • (named after Aeolus, the Greek god of winds) • Occurs almost always in deserts. • Aeolian erosion of sand in the desert is partially responsible for the formation of sand dunes. Formation of a Sand Dune

42. DEPOSITION --the geological process by which material is added to a landform or land mass. • stream will overtop its banks and flow onto the floodplain where the velocity will then suddenly decrease. This results in deposition of such features as levees and floodplains. • If the gradient of the stream suddenly changes by emptying into a flat-floored basin, an ocean basin, or a lake, the velocity of the stream will suddenly decrease resulting in deposition of sediment that can no longer be transported. This can result in deposition of such features as alluvial fans and deltas.

43. Examples of Deposition • flood plain- Is flat or nearly flat land adjacent to a stream or river that experiences occasional or periodic flooding FLOOD PLAIN & TERRACE

44. Examples of Deposition Sediment (mud, sand, gravel, etc.) deposited by a stream or river. • A fan-shaped deposit of sediment that forms where a stream drops downward from a higher elevation and encounters the valley floor. The stream slows down, depositing fine silt, sand, or other sediments it is carrying. ALLUVIAL FAN

45. Examples of Deposition • Deltas - When a stream enters a standing body of water such as a lake or ocean, again there is a sudden decrease in velocity and the stream deposits its sediment in a deposit called a delta.

46. DEPOSITION

48. groundwater