Published on March 10, 2014
What Causes the Landscape to be Different? Weathering Erosion Deposition
What is Weathering? • Weathering is the chemical and physical/mechanical processes that change the characteristics of rocks on the Earth’s surface. • Occurs when rocks are exposed to the hydrosphere (water) and atmosphere (air) • These weathering agents can change the physical and chemical characteristics of rocks.
Physical/Mechanical Weathering • Click for video on physical weathering • when rocks are broken into smaller pieces without changing the chemical composition of the rock • Different Types of Physical Weathering: – Frost action/ice wedging – Abrasion – Exfoliation – Wind
Click Picture for Lab
Frost action/ice wedging • breakup of rock caused by the freezing and thawing (contracting and expansion) of water. • Water seeps into cracks of a rock and as the climate cools the water freezes and expands breaking the rock apart.
Abrasion • The physical wearing down of rocks as they rub or bounce against each other. • This process is most common in windy areas, under glaciers, or in stream channels.
Exfoliation • the peeling away of large sheets of loosened materials at the surface of a rock. • Common in shale, slate, and mica. Enchanted State Rock Park, Texas
Chemical Weathering • Click for video on chemical weathering • occurs when a rock is broken down by chemical action resulting in a change in the composition of a rock. • Main agents of chemical weathering are: • -oxygen -rainwater • -carbon dioxide -acids produced by decaying plants and animals that leads to the formation of soil.
Types of Chemical Weathering • Oxidation – when oxygen interacts chemically with minerals. (ex. when a nail rusts) • Hydration/Hydrolysis – when water interacts chemically with minerals. (ex: when hornblende and feldspar join with water they eventually form into clay) • Carbonation – when carbon dioxide interacts chemically with minerals. Forms carbonic acid--> ex:dissolves limestone creating caverns and caves. Karst Topography
Carbonation: Acid Rain
Karst Topography • Occurs in limestone bedrock • limestone easily weathers chemically (carbonation) by weak acids in groundwater • landforms created: –caverns –sinkholes –disappearing rivers
Stalactites and Stalagmites
Weathering Rates Depend on 3 Factors • Particle size/surface area exposed to the surface • Mineral composition • Climate
What is a Major Product of Weathering? • Soil: – is a combination of particles of rocks, minerals, and organic matter produced through weathering processes. – contains the necessary nutrients to support various forms of plant and animal life. • As a result of weathering processes and biologic activity, soil horizons (layers) form.
Soil Horizons • vary in depth depending on an areas climate and weathering rates • Soil Horizons: – O Horizon – A Horizon – B Horizon – C Horizon – D Horizon
• Horizon O refers to the organic material on the upper most part of the profile (this layer is usually very thin). • Horizon A commonly known as topsoil. this layer includes organic material (humus), such as fallen leaves, twigs, decaying plant and animal remains. • The material helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. • Provides plants with nutrients
• Horizon B is known as the subsoil. • much less humus. • usually will contain a fair amount of clay and iron oxides, but also may contain some elements from horizon A because of the process of leaching. • Leaching resembles what happens in a coffee pot as the water drips through the coffee grounds. Leaching may also bring some minerals from horizon B down to horizon C.
• Horizon C consists mostly of weatherized big rocks known as Parent material (the rock that the soil formed from). • Horizon D which is not shown in this illustration, usually contains solid bedrock.
Erosion • Erosion refers to the transportation of rock, soil, and mineral particles from one location to another. • Erosion is different from weathering since erosion has the moving element. • The main driving force behind all agents of erosion is gravity. • Without gravity the other major natural agents of erosion such as: wind, running water, glaciers, waves, and rain would not occur.
Factors Affecting Transportation of Sediment • Running water is the primary agent of erosion on Earth. • Most running water is found in streams and rivers. • Sediments carried by a stream are almost always rounded due to the grinding action of the water on the rocks, a process called abrasion • There are many factors that affect the movement of sediments in a stream.
Factors Affecting Transportation of Sediment • Gradient (slope), discharge, and channel shape influence a stream’s velocity and the erosion and deposition of sediments • V-shaped valleys are eroded by streams and U-shaped valleys are eroded by glaciers • deltas, flood plains, and meanders are results of what a stream can form. • The watershed of a stream is the area drained by a stream and its tributaries (smaller feeder streams).
Delta and Floodplains Delta Floodplains
Floodplain Development Floodplain of creek near Millersville, NC Photograph by Jimmie D. Agnew Normal Stage
Floodplain Development Rain Stage Creek with floodplain near Millersville, NC Photograph by Jimmie D. Agnew
Floodplain Development Creek at flood stage, occupting part of its floodplain near Millersville, NC Photograph by Jimmie D. Agnew Flood Stage
M E A N D E R I N G S T R E A M
Meandering Stream with development of Oxbow Lakes and an Oxbow lake
Water Erosion by Wave Action
Erosion by Gravity: Landslide
Deposition • is the final step in the erosional-depositional system. • Rock particles picked up and transported will ultimately be deposited (left behind) somewhere else. • Final deposition of particles (sediments) usually occurs at the mouth of a stream. This is due to the faster flowing stream emptying into a slower larger body of water. • The sediments that were once carried down the stream are arranged from largest to smallest.
Factors Affecting Deposition • particle size, • shape, • density, and • the velocity of the transporting stream.
Particle Size • smaller particles settle more slowly than the larger particles, due to the pull of gravity. • The smaller particles tend to stay in suspension for longer periods of time. • This form of deposition is called graded bedding • Click on picture
Particle Shape • A round sediment compared to a flat (skipping stone) sediment of equal size will settle faster in a body of water. • This is due to the resistance the flat particle will undergo as it settles through the water. The round particle will meet little resistance and settle at a must faster rate.
Density and Velocity • Density: – If particles are the same size but have different densities the higher density particle will settle faster. • Velocity: – velocity (speed) of the transporting stream determines when sediments will be deposited. – If the stream slows down, carrying power will decrease and the particle sizes carried and deposited will also decrease. – If a stream is flowing faster, then the carrying power of the stream will increase and the sizes of particles deposited will increase as well.
Deposition & Erosion of a Stream
Glacial Deposition • As glaciers move over the land they act as a "bulldozer" changing the view of the landscape • As glaciers pass over the land they leave distinct features
Let’s Review • Click for Review of Weathering and Erosion
References • http://regentsprep.org/Regents/earthsci/units/weathering/in dex.cfm • www.elon.edu/ geo/new_river.htm • http://libraries.risd.org/skylib/SCIENCE PAGE/Erosion_and_weathering.htm
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