· weathering, erosion, and deposition are a main force behind landscape types
· But they are not the only reason for a plain, plateau, and mountain region to form
o Other factors such as glaciation and tectonic activity lead to landscape building
§ In New York State, glaciation is one of the main causes of many types of landscape regions
o the water cycle or hydrologic cycle (see graphic below) is the driving force behind WED (weathering, erosion, and deposition)
o winds also help form the surface landscape
o But without gravity and the sun this whole process would not occur
Water Cycle Diagram
The water cycle process looks like this:
Evaporation ̃ condensation ̃ precipitation ̃ infiltration ̃ run-off
Without this process, weathering, erosion, and deposition would have a difficult time occurring on Earth.
-- chemical and physical processes that change the characteristics of rocks on the Earth’s surface.
o also known as the preparation for erosion
o for weathering to occur, the rock sample must change and rock needs to be exposed to water and air
o Human processes such as pollution, (like acid rain) along with the acts of other living organisms, can cause chemical weathering to occur at faster rates.
· These agents can change the physical and chemical characteristics of rocks.
· As rocks are broken down (weathered), they can be classified as different types of sediments, which are:
o boulders, cobbles, pebbles, sand, silt, clay, and colloids.
· Think of a physical change (e.g., ripping a piece of paper) -- will change size, but all other characteristics will remain the same
· Types of physical weathering:
o Frost action/ice wedging -- breakup of rock caused by the freezing and thawing (contracting and expansion) of water. A very similar process occurs on roads, which causes potholes.
Frost Wedging Diagram
o Abrasion --physical wearing down of rocks as they rub or bounce against each other--most common in windy areas, under glaciers, or in stream channels.
o Exfoliation --peeling away of large sheets of loosened materials at the surface of a rock. Common in shale, slate, and mica.
· Such as the change a piece of paper would go through after being burned.
· Main agents of chemical weathering are oxygen, rainwater, carbon dioxide, and acids produced by decaying plants and animals that leads to the formation of soil.
· There are a few types of chemical weathering such as:
o Oxidation -- when oxygen interacts chemically with minerals. Ex.: when a nail rusts oxygen combines with the iron in the nail to form iron oxide.
o Hydration -- when water interacts chemically with minerals. Ex., when hornblende and feldspar unite with water they eventually form into clay.
o Carbonation -- when carbon dioxide interacts chemically with minerals.
§ carbon dioxide -- dissolved in water, forms weak carbonic acid.
§ Carbonic acid -- comes in contact with the surface of the earth dissolves large masses of limestone, creating caves and caverns.
§ Other common terms associated with carbonation are sink holes, karst topography, stalactites and stalagmites.
· Weathering rates --depend on 3 different factors:
o Particle size/surface area exposed to the surface
o Mineral composition
· One of the major products of weathering is soil
· Soil -- combination of particles of rocks, minerals, and organic matter
· Soil contains the necessary nutrients to support plant and animal life
· As a result of the weathering processes and biologic activity, soil horizons (layers) form
· Soil horizons vary in depth depending on an areas climate and weathering rates
The below diagram is a mature soil profile common to New York State:
Soil Profile Diagram
Once a rock material has been weathered, it is ready to be transported, or eroded. 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.
· usually takes many years for erosion to be noticed, such is the case with the Grand Canyon.
· But it is common to see erosion take place in a quick fashion.
· Ex. --Recent erosion along the California coastline. Many homes and land has eroded into the Pacific Ocean due to intense wave action and weak soil/bedrock compositions (erosion).
Factors Affecting Transportation of Sediments
· Running water is the primary agent of erosion on Earth
· Most running water is found in streams and rivers
· Many factors affect the movement of sediments in a stream:
o Gradient (slope), discharge, and channel shape influence a stream’s velocity and the erosion and deposition of sediments.
· Sediments carried by a stream are almost always rounded due to the grinding action of the water on the rocks, a process called abrasion
· Streams are usually formed in V-shaped valleys; and 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).
· The average velocity (speed) of a stream depends on its slope and discharge, which in turn can explain the carrying power of a stream.
o As velocity of the stream water increases, size of the particles carried in the stream also increases, a direct relationship.
· Streams carry materials in 4 distinct ways:
o Floatation, solution (dissolved particles), suspension (within the water profile), and bed load (bouncing and dragging along the stream bed.
· Meanders -- another very important part of stream erosion.
o In a meandering stream velocity is lowest (High Potential Energy) along the inner banks
o Along a straight channel segment, water moves the fastest in mid-channel, near the surface.
o But as water moves around a bend, the zone of high velocity (High Kinetic Energy) swings to the outside of the channel.
o another landform -- an oxbow lake -- can develop-- forming an independent loop that will become a lake (see below).
Oxbow Lake Formation Diagram
Adapted from original illustration by Steven Fick, Canadian Geographic, July/Aug '93
Valleys Eroded by Streams and Glaciers
· Valleys that have been eroded:
o by streams are v-shaped
o by glaciers are u-shaped
Effect of Humans
· highway and construction,
· destruction of forests (clear-cutting),
· set forest fires,
· poor landfill projects, etc…
· Today, human activities contribute more than ever to the erosion on the Earth’s surface
Adapted from: Regents Exam Prep Center http://regentsprep.org/Regents/earthsci/earthsci.cfm