weathering, erosion, deposition, landscapes
TRANSCRIPT
Unit #10: Weathering, Erosion, Deposition and Landscapes
Why do rocks weather? rocks below the
surface are protected from the exposure to wind, water and biological processes
once uplifted and exposed rocks begin to weather
Weathering
the breakdown of rock due to physical or chemical changes
Physical Weathering
changes the size and/or shape of a rock, without changing the rock’s chemical composition
Example: breaking a rock into smaller pieces
harder minerals are more resistant to physical weathering
Types of Physical Weathering:
Frost action alternating temperatures above and below 0C, allow water to melt and freeze, causing expansion of the cracks
Biological Factors roots of plants can grow within cracks in the rocks and increase the crack size, leading to crumbling of the rock
Abrasion collisions between particles caused by wind, moving ice and gravity, these particles act like sandpaper of the rocks
Chemical Weathering
changes in the chemical composition of rock, thereby forming new substances.
Example: rusting of iron rich mineral
chemical weather requires heat and water some minerals are more resistant to chemical weathering, such as quartz slightly acid water can cause significant weathering of limestone forming caves emissions of atmospheric pollutants such as oxides of sulfur and nitrogen can cause rain to be acid and increase chemical erosioncarbonic, nitric, and sulfuric acid are able to change hard limestone into a soft residue
Chemical Weathering
How do soils form?
Soil --> mixture of weathered rock and organic remains that usually cover bedrock
Develop through:
physical weathering
chemical weathering
organic activity
Nature of soils dependent upon:
rocks from which it weathered
local climate
amount of organic activity (plants and animals)
Soils Horizons
--> distinct layers of soil created by different amounts of organic and inorganic material
Thickness of Soil horizons
young/immature soils do not show distinct horizons mature soils show distinct A, B, and C horizons arid climates have thin soils humid climates have thick soils steep sloping areas have thin soils gentle sloping areas have thick soils
Escarpments in an arid climate
--> Soils must be conserved from wind and water erosion
--> it takes between 100 and 400 years for one centimeter of topsoil to form
--> Conservation methods include:
Contour farming
Terracing
Increase vegetation cover
Wind blocks
Types of Soils
Residual soils --> form directly above the parent bedrock, thinner
Transported soil --> form from sediments that has been moved into that area
How are weathered Material Transported?
Sediments --> rocks that have been broken into fragment, regardless of their size
Erosion
--> the transporting of sediments away from their place of origin and the depositing of them elsewhere
Force behind erosion: gravity
Example: rock falling from a cliff
Water moving down slope
Erosion by Water
Watering is the primary agent of erosion on the Earth’s surface
each year streams and rivers carry millions of tons of sediments downstream and into the oceans
Transportation of sediments by water:
1) Solution --> smallest particles dissolved in the water, can’t be filtered
2) Suspension --> large particles, not dissolved, can be filtered
3) bouncing and rolling --> largest particles will travel along the bottom of the stream channel
Faster moving water carry larger particles and small particles
Slower moving water carry small particles, only
The Velocity of Streams. controlled by the slope of the landscape and the volume of water
Stream gradient increases, water velocity increases
Increase volume of water will also increase velocity
Discharge
--> volume of water that is traveling in a stream
Increases with velocity and volume
Speed of water
Equilibrium exists between the force of gravity and the friction created by the channel
In a straight stream, water will flow the fastest in the middle of the channel, less friction
Meandering Stream
--> curving stream path
Erosion on the outside of the turn, velocity is fastest
Deposition on the inside of the turn, velocity is slowest
•
--> Gentle valleys, like Milford, will have meandering stream, more horizontal erosion
--> Steep valleys, like ravine behind the school, has straighter streams, more vertical erosion
Erosion By Wind
--> pick up loose rock materials such as sand, silt and clay and carry them away
--> occurs in arid climates with little vegetation
--> erosion of clay and silt (smallest) particles leaving behind only larger particles called: desert pavement
--> can also erode by abrasion--> similar to sandpaper rubbing
against a rock creating angular, but smooth sediments called: ventifacts
Erosion by Ice
--> when the snow during the winter does not melt during the summer and begins to accumulate year after year--> Ice can get up to a mile thick--> Ice will start to move down slope under its own weight
--> Glaciers will trap all sizes of sediments within the ice, creating a massive piece of sandpaper that will scour the valley it travels through
Evidence of Glaciation--> Glaciers will deepen and widen preexisting valley to
give them a characteristic U-shape.--> Stream cut through valleys with vertical
erosion to create a V-shapeUnsorted deposits --> deposition of sediments of
all sizes in one areaStriations --> scratches in the bedrock caused by
the rough undersurface of the parallel grooves that align with the glaciers movement--> In NYS these striation run from NW to SE, indicating that the last glacial advancement came from Canada
Four Periods of continental glaciation in the past two million years in NYS
due to glaciation, NYS is covered with thick transported soils
The last glacial advancement was the Wisconsin glacier approximately 11,500 years ago
o Created U-shaped valleyso Rounded mountain topso Polished bedrock with striationso Unsorted sedimentso Long Island and Cape Codo Finger lakeso Thick transported soilsLarge miscellaneous boulders called: Glacial erratic
What is depositions?
Deposition --> when an agent of erosion deposits, or lays down, particles and fragments of earth materials
also called sedimentation most deposition
occurs in water
Factors that affect deposition
Rate of deposition is dependent upon factors such as:
Size
Shape
Density
Speed of the transporting material
Particle Size:
--> Inverse relationship
large a particles settle first, while small particles settle last
particles in solution or suspension may stay suspended indefinitely
Particle Shape:
--> flat, angular and irregularly shaped particles settle more slowly than smooth, rounded particle
Particle Density
--> denser particles settle faster
--> less dense particles settle more slowly
Settling Rate and Settling Time
--> Inverse relationship
--> faster rate indicates less settling time
--> slower rate indicates more settling time
Settling Time of Particles
Mass (g) (Size)
Tim
e
Settling Rate of Particles
Mass (g)(Size)
Rat
e (m
eter
s/se
c.)
Sorting of Sediments
--> velocity of transporting material plays a major role in determining when deposition of particles will occur
--> initiated by a reduction in velocity
Stream is moving at a velocity of 500 cm/secit is carrying all sized particles.
Slow down, drop sediment load
Pebbles
Sand
Silt
Clay
Horizontal sorting sorting with largest, densest and roundest first and then farther out the smallest, least dense and flattest particles farther out (horizontal arrangement)
Vertical sorting (graded bedding)
particles are deposited in layers with the largest, densest and roundest particles on the bottom and then the smallest, least dense and flattest particles on top
Example: dropping a mix of particles into water (can be repetitive)
Deposition by streams:
Sandbars shallow area in a stream due to low water velocityo frequently dredged to keep the stream deep
Delta deposits created when a stream enters a larger body of watero land around the mouth of the Mississippi is a delta, New Orleans, Mississippi delta is thousands of square miles
Deposition by Wind
generally sorted by size and located in arid climates
wind leaves behind larger sediments creating
Sand dunes
hills of wind blown deposits
Deposition by Gravity
gravity pulls sediments toward the Earth’s center, they are not sorted when deposited by gravity, angular
Deposition by Glaciers
deposition occurs when the glacier melts leaving behind eroded sediments
unconsolidated and unsorted
Glacial erratic large rocks that have been transported by glacial ice
Adult person
Two types of Glacial sediments:
1) unsorted sediments deposited directly by the glacier
2) sorted sediments deposited by the moving melt water of the glacier
New York and The Ice Ages
NYS’ climate has changed over the last 2 million years causing 4 different ice ages
Accumulation of snow and ice creates a glacier that will then begin to move to lower elevations due to its own weight
When the climate warms again, glaciers melt, releasing tremendous amounts of water causing even more erosion
Types of Glaciers:
1) Alpine glaciers (valley glaciers) occur in mountain regions
2) Continental glaciers (ice sheets) large glaciers that start in colder regions and move down slope this type of glacier produced most of NYS
glacial features
Evidence of Glaciation in NYS
U-shaped valleys
glacial polish, rounded hills: bedrock that has been smoothed by the scouring action of the ice and collected sediments
striations grooves and scratches in the bedrock, indicate the direction of flow
drumlins small rounded mounds created when a glacier goes over hills of unconsolidated sediments
Evidence of Glaciation in NYS
moraines unconsolidated, unsorted sediments that were pushed forward by the glacier as it advanced
o form Long Island and Cape Cod
o created the valley head moraine, which allowed for the formation of the Finger Lakes
outwash plan area of sorted sediments created by glacial melt water
Evidence of Glaciation in NYS
The Oceans and Costal Processes
Earth is 71% covered by seawater
Average depth 3 miles
Most sediments from land will be eroded to the oceans
Edges of the oceans are places of rapid change caused by the action of waves and longshore currents.
Waves
water does not move forward with the waves, but circulate transferring energy
movement of waves and longshore currents create many typical features along the shoreline
humans love to live near the ocean, but the rapid rate of erosion cause destruction of property
humans build structures to reduce the damage created by waveso breakwaters – shelter harbors, boats jetties – build to keep sand from eroding away from the beach
What is a Landscape?
Landscape a region on Earth’s surface in which physical features, such as hills, valleys and streams are related by a common origin
Topography general shape of the landscape
landscape features are determined by:
o climate
o bedrock
o geologic structures
o human activities
Landscape regions:Mountains greatest relief, often
igneous and metamorphic or nonhorizontal sedimentary rocks Example: Rockies, Adirondacks, Alps, Himalayas
Landscape regions:Plateau relatively flat or rolling uplands, underlain by flat sedimentary bedrock
Example: Milford area, Grand Canyon
Landscape regions:
Plains little topographic relief, flat low elevation
Example: Florida & Midwest
The Influence of Climate humid areas have more rounded landscapes
arid areas have more sharp angles and steeper slopes to the landscape
Moisture is important to the rate of chemical weathering
causing more rounded landscapes
thicker soils
promotes plant growth
Arid environments produce:
greater amounts of physical weathering
thin soils
deserts have the most rapid stream erosion after a rainfall
Landscapes of the United States
abrupt changes in landscape is a result of change in the bedrock
How do geologic Factors influence the landscape?
within the same climate landscape regions can develop very differently hard minerals create rocks that are very resistant to weathering and erosiono creating cliffs or escarpments near regions of less resistant rockstreams also follow areas of weaker, softer rock
Landscapes affect drainage patterns
Landscapes of New York StateSt. Lawrence/ Champlain Lowlands plains areas, predominantly layers of sedimentary rocks
Appalachian Uplands (Allegheny Plateau)
largest landscape region in NYSo underlain by flat layers of sedimentary rockso landscape have been uplifted 1000 of meters, which were later eroded by streams (dissected plateau)Finger lakes have been eroded out of this landscape
Erie-Ontario Lowlands
areas south of these lakes
o created by sediments left by glacial meltwater
great soils for agricultural purposes
Adirondack Highlands
o only true mountain landscape in NYSo uplifted ancient metamorphic and igneous rocks creating a domeo very hard and resistant to weatheringNYS highest mountain: Mount Marcy (5240 feet)
Landscape vs. Age
Streams will continue to erode an area to produce a wide flat valley and many meanders in the stream