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Chapter 14. Section 1 Weathering Processes. Objectives. Identify three agents of mechanical weathering. Compare mechanical and chemical weathering processes. Drill: What is a Sedimentary Rock?. Weathering Chapter 14, 16 . Erosion Chapter 14. Deposition chapters 6, 15. Compaction chpt 6.
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Chapter 14 Section 1 Weathering Processes Objectives • Identify three agents of mechanical weathering. • Compare mechanical and chemical weathering processes. • Drill: What is a Sedimentary Rock?
Weathering Chapter 14, 16 Erosion Chapter 14 Deposition chapters 6, 15 Compaction chpt 6 Lithification / Cementation chpt 6
Chapter 14 Section 1 Weathering Processes Weathering Processes Weathering: the natural process environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose rock material • Each type of weathering has different effects on rock.
There are two main types of weathering processes—mechanical weathering and chemical weathering.
Chapter 14 Section 1 Weathering Processes Mechanical Weathering mechanical weathering : the process by which rocks break down into smaller pieces by physical means
Mechanical weathering is strictly a physical process and does not change the composition of the rock. • Common agents of mechanical weathering are ice, plants and animals, gravity, running water, and wind.
Chapter 14 Section 1 Weathering Processes Mechanical Weathering, continued Ice Wedging • Occurs in cold climates • Ice wedging occurs when water seeps into the cracks in rock and freezes. • When the water freezes, its volume increases by about 10% and creates pressure on the surrounding rock. • This process eventually splits the rock apart.
Chapter 14 Section 1 Weathering Processes Mechanical Weathering, continued Abrasion: the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles • Caused by gravity, running water, and wind.
Chapter 14 Section 1 Weathering Processes Mechanical Weathering, continued Organic Activity • Plants and animals are important agents of mechanical weathering. • As plants grow, the roots grow and expand to create pressure that wedge rock apart. • Earthworms and other animals that move soil expose new rock surfaces to both mechanical and chemical weathering.
Chapter 14 Section 1 Weathering Processes Chemical Weathering chemical weathering: the process by which rocks break down as a result of chemical reactions • Chemical reactions commonly occur between rock, water, carbon dioxide, oxygen, and acids/bases. • Chemical weathering changes • composition • physical appearance of the rock.
Chapter 14 Section 1 Weathering Processes Chemical Weathering, continued Oxidation: the process by which an element combines with oxygen • Oxidation commonly occurs in rock that has iron-bearing minerals, such as hematite and magnetite.
Chapter 14 Section 1 Weathering Processes Chemical Weathering, continued Oxidation, continued • The red color of much of the soil in the southeastern United States is due to mainly the presence of iron oxide produced by oxidation.
Chapter 14 Section 1 Weathering Processes Chemical Weathering, continued Hydrolysis hydrolysis a chemical reaction between water and another substance to form two or more new substances • Minerals that are affected by hydrolysis often dissolve in water. • Water can then carry the dissolved minerals to lower layers of rock in a process called leaching.
Chapter 14 Section 1 Weathering Processes Chemical Weathering, continued The image below shows how water plays a crucial role in chemical weathering.
Chapter 14 Section 1 Weathering Processes Chemical Weathering, continued Carbonation carbonation the conversion of a compound into a carbonate • When carbon dioxide, CO2, from the air dissolves in water, H2O, a weak acid called carbonic acid, H2CO3, forms. H2O + CO2 H2CO3
Chapter 14 Section 2 Rates of Weathering Objectives • Explain how rock composition affects the rate of weathering. • Discuss how surface area affects the rate at which rock weathers. • Describe the effects of climate and topography on the rate of weathering.
Chapter 14 Section 2 Rates of Weathering Rates of Weathering • The processes of mechanical and chemical weathering generally work very slowly. • The rate at which rock weathers depends on a number of factors, including rock composition, climate, and topography.
Chapter 14 Section 2 Rates of Weathering Differential Weathering differential weathering: the process by which softer, less weather resistant rocks wear away at a faster rate than harder, more weather resistant rocks do
When igneous rocks that are rich in the mineral quartz are exposed on Earth’s surface, they remain basically unchanged, even after all of the surrounding sedimentary rock has weathered away.
Chapter 14 Section 2 Rates of Weathering Amount of Exposure Surface Area • Both chemical and mechanical weathering may split rock into a number of smaller rocks. • The part of a rock that is exposed to air, water, and other agents of weathering is called the rock’s surface area. • As a rock breaks into smaller pieces, the surface area that is exposed increases.
Chapter 14 Section 2 Rates of Weathering Amount of Exposure, continued The image below shows the ratio of total surface area to volume.
Chapter 14 Section 2 Rates of Weathering Amount of Exposure, continued Fractures and Joints • Fractures and joints increase the surface area of a rock and allow weathering to take place more rapidly. • They also form natural channels through which water flows.
Chapter 14 Section 2 Rates of Weathering Climate • In general, climates that have alternating periods of hot and cold weather allow the fastest rates of weathering. • In warm, humid climates, chemical weathering is also fairly rapid. The constant moisture is highly destructive to exposed surfaces.
The slowest rates of weathering occur in hot, dry climates. The lack of water limits many weathering processes, such as carbonation and ice wedging. • Weathering is also slow in very cold climates
Chapter 14 Section 2 Rates of Weathering Topography • Because temperatures are generally cold at high elevations, ice wedging is more common at high elevations than at low elevations. • On steep slopes, such as mountainsides, weathered rock fragments are pulled downhill by gravity and washed out by heavy rains. • As a result of the removal of these surface rocks, new surfaces of the mountain are continually exposed to weathering.
Chapter 14 Section 2 Rates of Weathering Plant and Animal Activities • Rock that is disturbed or broken by plants or animals also weathers more rapidly than undisturbed rock does. • The roots of plants and trees often break apart rock.
Section 2 Groundwater and Chemical Weathering Chapter 16 Objectives • Identify two features of karst topography. • Describe how water chemically weathers rock. • Explain how caverns and sinkholes form.
Section 2 Groundwater and Chemical Weathering Chapter 16 Karst Topography karst topography a type of irregular topography that is characterized by caverns, sinkholes, and underground drainage and that forms on limestone or other soluble rock
Common features of karst topography include many closely spaced sinkholes and caverns. • Generally, karst topography forms in regions where the climate is humid and where limestone formations exist at or near the surface.
Generally, karst topography forms in regions where the climate is humid and where limestone formations exist at or near the surface.
Section 2 Groundwater and Chemical Weathering Chapter 16 Groundwater and Chemical Weathering • As groundwater passes through permeable rock, minerals in the rock dissolve. The warmer the rock is and the longer it is in contact with water, the greater the amount of dissolved minerals in the water. Quick facts: (do not have to write down) • Water that contains relatively high concentrations of dissolved minerals, especially minerals rich in calcium, magnesium, and iron, is called hard water. • Water that contains relatively low concentrations of dissolved minerals is called soft water.
Section 2 Groundwater and Chemical Weathering Chapter 16 Results of Weathering by Groundwater Caverns cavern a natural cavity that forms in rocks as a result of the dissolution of minerals; also a large cave that commonly contains many smaller, connecting chambers • Rocks that are rich in the mineral calcite, such as limestone, are especially vulnerable to chemical weathering.
Section 2 Groundwater and Chemical Weathering Chapter 16 Results of Weathering by Groundwater, continued Caverns • Although limestone is not porous, vertical and horizontal cracks commonly occur through limestone layers. • As groundwater flows through these cracks, carbonic acid slowly dissolves the limestone and enlarges the cracks. • Eventually, a cavern may form.
Section 2 Groundwater and Chemical Weathering Chapter 16 Results of Weathering by Groundwater, continued Sinkholes sinkhole a circular depression that forms when rock dissolves, when overlying sediment fills an existing cavity, or when the roof of an underground cavern or mine collapses
Section 2 Groundwater and Chemical Weathering Chapter 16 Results of Weathering by Groundwater, continued Sinkholes, continued • Collapse sinkholes may form when sediment below the surface is removed and an empty space forms within the sediment layer. • Collapse sinkholes may develop abruptly and cause extensive damage. Sink hole in Guatemala was man made from leaky water and sewer pipes!!
Objective: -SWBAT identify agents of erosion and the features that they produce. Erosion: Moving SedimentDeposition: Dumping sediment
Agents of Erosion include Gravity!!! ( First and foremost) Water Wind Glaciers
Forms of erosion: • Wave Action • Running Water • Mass Waisting • Landslides • Slump • Creep • Rock Fall • Glaciers
