Topic 9 Weathering and Erosion Weathering:The chemical and physical breakdown of rock Types of Weathering Chemical Weathering:Breakdown of rock forms new substances A) Oxidation:Minerals combine with O 2 to form different minerals Reaction Rim:Outer layer of oxidation Chemical Weathering Continued B) Dissolving:Water removes minerals from rocks C) Acids:Carbonic acid from rain enters the ground and reacts with rocks Physical Weathering: breaking rocks into smaller pieces without changing what they are. A) Temperature Change:Rocks may break when exposed to rapid temp. change. B) Root pry:Roots break rock as it grows C) Frost Action:The expansion of water due to freezing in the cracks of rocks D) Abrasion:Rocks grinding past each other and wear down -Water abrasion rounds and smoothes -Wind abrasion causes pitting Factors Affecting the Rate and Type of Weathering 1) Exposure:The closer to the surface the higher the rate What is the relationship between depth and rate of weathering? 2) Particle Size:Greater surface area = more weathering Surface area is the amount of exposed surface Relationship (Surface area vs. weathering)Direct Inverse 3) Mineral Composition:Hard minerals are more resistant to weathering Resistant minerals Quartz Olivine Feldspar Weak Minerals Calcite Mica 4) Climate:Warm and moist = Chemical Weathering Cold and moist = Physical Soil Formation Soil:Weathered rock and organic material Residual Soil:Formed in place (same minerals as bedrock) Transported Soil:Formed somewhere else (different minerals than bedrock) Why doesnt NYS have mature soil? Erosion:Transport of weathered material Parts of an Erosional System 1) Agent:Thing that does the moving 2) Sediment:Weathered material 3) Force:Force that causes motion 2 Primary Forces of Erosion The sun causes unequal heating of the Earth and winds Gravity causes rivers to flow and particles to fall Gravity Erosion Indirectly:Causes water and ice to flow Directly:Sediments fall downhill What are the two Forces involved?Gravity and Friction When does gravitational erosion take place?G > F Angle of Repose:Angle which particles naturally settle (35) Types of Gravitational Erosion From Fastest to Slowest 1) Rock Fall:Rocks fall off cliffs 2) Mudflow:Soil becomes saturated and flows 3) Debris flow:Composed of dirt and other materials 4) Soil Creep:Gradual downhill movement of soil Running Water Erosion and Streams Stream:Running water confined to a channel Tributary:Small stream that feeds larger Methods of Stream Erosion 1) Solution:Dissolved material 2) Suspension:Particles are carried by the stream Muddy water is evidence 3) Saltation:Rolling and bouncing along bottom Watershed:Area drained by one stream or river Stream load:Total amount of sediment in a stream What shape are valleys formed by rivers? 4 Factors that Affect Stream Velocity 1) Gradient: Relationship: Change in elevation / distance Direct 2) Discharge:Amount of water flowing past a certain spot in a given amount of time Relationship:Direct How do tributaries affect this?They increase discharge 3) Channel Shape:Semicircle channel have most velocity What is the determining factor or force?friction 4) Position in the Stream:Just below the surface and at the outside of bends is fast Relationship Between Velocity and Particles Carried How fast does a stream have to travel to carry particles that are cobble sized? How fast does a stream have to travel to carry particles that are.2cm in diameter? Evolution of a Stream AgeGradientErosionDischargeLoadFeatures Young Mature High Waterfalls, rapids Low Meanders, oxbows, flood plains Meanders:Series of bends and turns Flood plain:Wider valley that becomes flooded Delta: Fan of sediments at the end of a river Oxbow Lake:Lake formed from a meander cut-off Features of a Mature River How Flood Plains Work Formation of an Oxbow Lake Listening Questions From Mark Twains Life on the Mississippi 1)The width of the United States is about 3,000 miles; Mississippi River is 4,300 miles long. How can the river be longer than the U.S. is wide? 2) Why does the Mississippi have such a large discharge (volume)? 3) What is the depth of the Mississippi at its deepest and where does this occur? 4) Why has the Mississippi been called the Great Sewer? 5) Explain how a river can shorten itself by over 30 miles? 6) How can river shortening be disastrous to towns along the Mississippi? 7) Contrast what the Mississippi does to the land at its source and its mouth? Watershed Drainage Patterns are Determined by The Geology and Landscape Features of a Region Wind Erosion Where does wind erosion take place?Most commonly in warm dry climates How does it happen? Particles are moved by wind 2 Main Types of Wind Erosion 1) Deflation:Particles are moved to desert base level Desert Pavement:Large particles left behind dont move 2) Sandblasting:Sand and wind blast rocks Features:Pitting and frosting Formations from sandblasting:Arches, mushroom rocks Why is only the bottom eroded?Wind can only raise particles 2m Glacial Erosion Why are glaciers important to NYS?They once covered NYS Two Types of Glaciers 1) Continental: Huge ice sheets 2) Alpine:Mountain glaciers What direction do glaciers move?Downhill How do they recede?Melting > Accumulation Where do glaciers have the greatest velocity? Where there is less friction Evidence of Glaciers 1) Glacial plucking:Glaciers pull rocks from earth 2) Glacial grooves (striations):Scratches made from glaciers (show direction) 3) Erratics:Random rocks left from glaciers 4) U-shaped valleys:Broad U valleys How have glaciers affected NYS? 1) Soil:Immature soil (scraped to PA) 2) Lakes:Finger lakes carved by glaciers How long ago were the glaciers here?10,000 yrs. Wave and Current Erosion What happens to beach sediments? Abrasion rounds and smoothes What rock material is left on the beaches?Quartz Features of Wave and Current Erosion Beachfronts:Steep slopes and cliffs Long-shore Drift:Waves come in at an angle and move sediment down shore Bays: Sandbars: Spits: Small body of water connected to a larger Ridge of sand formed just off the shore Type of bar that forms from re-entrance