3 WeatheringWeathering: Process by which rocks on or near Earth’s surface break down and changeTypes of Weathering:Mechanical: process by which rocks and minerals break down into smaller pieces (does not change rocks composition, only size and shape.Chemical: process by which rocks and minerals undergo changes in their composition as a result of chemical reactions
4 Factors of Mechanical Weathering Temperature: Drop in temperature causes water to begin to freeze, water then expands, taking up more space than in liquid form- Frost Wedging: repeated thawing and freezing of water in the cracks of rocks causing them to break apart (example: Potholes)
5 Factors of Mechanical Weathering 2. Pressure: Layers of rocks put pressure on rocks below; when rock layers are removed (exfoliation), pressure is reduced, causing expansion of the rock and long, curved cracks to formExfoliation: outer rock layers are stripped away
6 Factors of Chemical Weathering Water: can dissolve many kinds of minerals and rocks; Can react with other substances (hydrolysis) which occurs during the decomposition of one mineral to another.2. Oxygen: can chemically react with other substances (oxidation); ex: oxygen in the atmosphere can combine with iron in rocks and minerals
7 Factors of Chemical Weathering 3. Carbon Dioxide: atmospheric gas when combined with water in the atmosphere produces weak carbonic acid; can react with certain minerals to dissolve rocks 4. Acid Precipitation: caused by the oxidation of sulfur dioxide and nitrogen oxides in the atmosphere by human activity; has a pH below 5.6; creates problems for many organisms living in aquatic environments
8 What affects the rate of weathering? Climate: interaction between temperature and precipitation -Chemical weathering: common in warm temps, abundant rainfall, lush vegetation -Mechanical weathering: cool, dry climates where water undergoes repeated freezing and thawing Rock Type and Composition: sedimentary rocks are more easily weathered than harder igneous and metamorphic Surface area: more surface area=more weathering Topography: slope of the landscape determines the weathering
10 ErosionErosion: removal of weathered rock and soil from its original location Deposition: After the material is transported they are dropped into another location
11 Gravity’s Role in Erosion Force of gravity tends to pull all materials downslope. Without gravity, glaciers would not move downslope and streams would not flow Also an agent in mass movements: landslides, mudflows, and avalanches.
12 Erosion by Running Water **Swiftly flowing water has greater erosional power than wind and can also carry more material along with it and over a greater distance. Rill Erosion: erosion by running water in small channels, on the side of a slope; form on a slope Gully Erosion: when channel becomes deep and wide; can be more than 3 m deep and causes major problems in farming and grazing areas **Weathering and Erosion occur also in oceans and islands: currents, waves, and tides carves out cliffs, arches, and more and a lot of the weathering and erosion occurs along the shorelines.
13 Glacial Erosion-Glaciers scrape and gouge out large sections of Earth’s landscape; they are so dense and have ability to carry huge rocks and other debris long distances -Leave behind valleys with waterfalls, lakes, and variously shaped deposits of sediment
14 Moving Masses of iceForm near Earth’s poles and mountainous areas at high elevations 10% of Earth’s surface Valley Glaciers: glaciers form in valleys in high, mountainous areas; Continental Glacier: glaciers that cover broad, continent-sized areas; thickest at its center and much larger than valley glaciers
15 Glacial erosionMost powerful erosional agent due to size, weight, and density. Create U-shaped valleys (valley glaciers) and also scoop out deep depressions known as cirquesSwitzerland’s Matterhorn: formed where there were glaciers on three or more sides of this moutaintop and this peak formed. (known as a horn)
16 Wind ErosionMajor erosional agent in areas with limited precipitation and high temperaturesCan easily pick up and move the fine, dry particlesEffects can be dramatic and devastatingCan damage natural features and human made structuresVery common in Death ValleyShore areas also experience wind erosionRunning water and glacial activity still more powerfulWind barriers can reduce the effects of wind erosion for farmers (trees and other plants)
17 Wind erosion and transport Wind cant carry particles as large as those transported by water Ability of wind to erode materials is less than that of other agents (i.e. water and ice) Suspension: method of transport by which strong winds cause particles to stay airborne for long distances Saltation: causes bouncing motion (sand transport)
18 Wind erosion and transport Occur where there is little precipitation and vegetative cover (like deserts) Can be major problem in the agricultural areas abrasion (process of erosion): particles rub against the surface of rocks or other materials Wind abrasion very effective agent of erosion Ventifacts: rocks shaped by wind-blown sediments
19 LoessDef: thick, wind blown silt deposits (another material wind also carries in great quantities and long distances) Loess deposits located Illinois, Iowa, Missouri, South Dakota, Nebraska, Kansas, and Idaho. With adequate precipitation, loess soils are some of the most fertile on Earth due to their abundance in minerals and nutrients
20 Erosion by Plants, Animals, and Humans -Plants and animals move Earth’s surface materials from one place to another -Animals burrow, humans excavate areas and move soil, planting a garden, developing new athletic fields, building a highway all result in the moving of earth’s materials from one place to another -Effects of erosion by plants, animals, or humans is minimal compared to water, wind, or glaciers.