erosion soils
DESCRIPTION
soil erosionTRANSCRIPT
Weathering, Erosion, and SoilWhat type of rock is this, how can you tell?
Yosemite Valley, California
Mountains Carved by Glaciers
Grand Canyon, Arizona
Carved out by the Colorado River
Bryce Canyon, UtahAcidic Rainfall has worn away these rocks.The harder rocks remain standing… but for how long?
Weathering• Process by which rocks are broken down
due to exposure to processes occurring at the Earth’s surface
• Caused by– Water– Waves– Wind – Gravity– Glaciers
The 2 G’s and the 3 W’s
2 Types of Weathering• A. Mechanical Weathering also called
Physical weathering– Rock is broken down into smaller pieces
of the same material – (no change in composition)
• B. Chemical Weathering– The breakdown or decomposition of rock that occurs
when minerals are changed into different substances– (change in composition)
Mechanical/Physical Weathering1. Frost (Ice) Wedging
– Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes.
– Occurs where there are frequent freezes and thaws.
Explain what is happening.
• Frost/Ice Wedging Frost/Ice Wedging can cause can cause PotholesPotholes to form to form in pavementin pavement
Mechanical/Physical Weathering2. Abrasion
– The wearing away of rock material by grinding action
– Usually caused by sediment in Wind, Water, and Glaciers
Wind abrasion- sandblasting effect on stationary rocks as seen here in Arches National
Park
Hydraulic abrasion- water & sediments flowing over boulders as seen here in Ohiopyle State Park, Pennsylvania
Notice the rounded river rocks
Mechanical/Physical Weathering
3. Plants and Animals– Plant roots can split
rock– Also known as: “Root pry”
or “Root action”– Animals dig holes ,breaks
up rocks
Tree growingout of rock, ShenandoahNational ParkTree roots
also break up sidewalks
Mechanical/Physical Weathering
Exfoliation- gradual peeling of layers due to uplift and frost action, typical of granite domes like those in Yosemite N.P.
Exfoliation of Igneous rock
Chemical Weathering• Chemical Weathering
– The breakdown or decomposition of rock that occurs when minerals are changed into different substances
– (change in composition)
• Involves Water ,water vapor, Acids, and/or Oxygen
OO22
Chemical Weathering1. Hydrolysis• Carbonic Carbonic AcidAcid in in
water water dissolvesdissolves CalciteCalcite. This . This chemical chemical weathering can weathering can hollow out hollow out underground underground CavernsCaverns Limestone and Dolomite both
dissolve because they contain Calcite
Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone
Chemical Weathering2. Oxidation• Oxidation of minerals Oxidation of minerals
with with ironiron (magnetite, (magnetite, pyrite) results in the pyrite) results in the formation of formation of rustrust or or iron oxide.iron oxide.
• This is why This is why MarsMars is the red planetis the red planet
• Copper turns rocks Copper turns rocks greengreen
Rate of Weathering• How fast a rock weathers depends
on 3 factors:
–Surface area–Rock composition–Climate
Rate of Weathering• Surface area
– The greater the surface area, the faster the weathering rate
– There are more surfaces to be weathered
Rate of Weathering• Rock composition
– Some minerals are more resistant than others
– For example, quartz is more resistant (harder) than calcite
Quartz Calcite
Rate of Weathering• Climate (long term pattern of moisture and temperature)
– Weathering rates are faster in warm, wet climates
Desert vs. Rainforest
Erosion• Erosion
– The removal and transport of weathered materials by natural agents such as
– Caused by1. Glaciers 2. Running water 3. Gravity4. Wind5. Waves
Glaciers• Mass of compacted ice and snow
that moves under its own weight
Glaciers• Friction at the base of the glacier is reducedreduced
by a thin film of melt water.• Glaciers account for about 75% of the fresh fresh
water on Earthwater on Earth
• Glaciers can leave behind large boulders that are known as an erratic
Glaciers• Glaciers can move lots of sediment that
can carve striations (grooves) into rocks
These Striations show how glaciers moved
Glacial Deposits• Drift or Till - all sediment that is deposited by
glacial activity– Loess: fine powder, pulverized rock, that
blankets much of the northern mid-west– Moraine: ridge or pile of boulders, gravel, sand, and silt
left at the end of a glacier
Esker: type of outwash that accumulates in the channels and tunnels of a glacier
Glacial Landforms• Cirque
– Steep-walled bowl-shaped depression
• Horne: a pyramid shaped peak where 3 or more cirques meet
Glacial Landforms• Trough
–U-shaped valley, Glaciers carve U shaped valleys
Glacial Landforms• Hanging valley
– Straight drop-off at the end of a trough
• Arete– Narrow flat-topped
ridge that forms between two parallel troughs or cirques
Glacial Landforms• Moraine: Pile of mixed sediments that
have been carried and dropped by the glacier
Glacial Landforms• Eskers -Mounds of rock from melt tunnels
Streams and Rivers• Velocity - How fast the water moves• Gradient - The steepness, the slope that a river or
stream travels• Discharge - The amount of water that moves past a
certain point in a river in a given amount of time• If there is a steep gradient, high velocity, and
a large discharge, then Erosion will be severe!
• Rivers have energy to move lots of sediment, and even large boulders.
River stages affect:
Velocity,Gradient,
& discharge
which cause
Erosion
Seven Bends of the Shenandoah
Is the Shenandoah and old river or a young river?
River meandersBends in the river, shows how mature a river is.
Erosion-Mass Movement• The downward transportation of weathered
materials by gravity
Massive Landslide
Erosion-Mass Movement• Creep• Slump• Mudflow/Earthflow• Landslide/Rockslide
Erosion-Mass Movement: A large mass of sediment drops down!
Erosion-Mass Movement• Creep
– Very slow movement of earth material.– Caused by repeated freezing and thawing.
Sediments are loosened by expanding frost and contracting thaw.
Leaning fence posts and telephone poles are a sign of Creep.
Fence posts leaning due to creep
Erosion-Mass Movement• Slump
– Slow downward movement of a large mass of soil
Occurs when underlying sediments are weakened by heavy rainsCharacterized by a curved scar in the land surface.
Slump can cause road hazards
Erosion-Mass Movement• Mudflow/Earthflow
– Thick pastes of sediments that travel downhill at great speedsUsually occur in dry areas that get a large quantity of rain all at once
Leaves a cone shaped deposit
Mudflow in the Blue RidgeMooreman’s Gap near Charlottesville
Erosion-Mass Movement• Landslide/Rockslide
– Fast movement of large blocks of rock
Occurs in very steep vertical cliffs
Accelerated by ice wedging
At the bottom of an old rock slide in N.C. 2011
Wave Erosion• The crashing of waves on a shoreline
combined with storms continually shape the beach. This is a shoreline with erosion.
Wind and Waves• Wind moves
sand dunes at the beach and in the deserts.
Wind and Waves• Wind can carve out landscapes
as it carries sediment
Wind and Waves• Many storms combine water
and wind to cause significant erosion on landforms.
• Strong winds are capable of moving large amounts of sediment
Deposition: The process of dropping or depositing soil
and sediments.
Soil (dirt)• Soil includes loose weathered rock,
and organic material in which plant roots can grow
Soil Composition
Use this pie chart to answer the questions in your notes.
Soil Composition
What do the arrows mean?
Where soil forms• Residual soil
– The parent rock is the bedrock beneath the soil (the soil has not moved)
• Transported soil– Soil forms from parent material left by
winds, rivers, glaciers, or soil that was moved from its original location. This soil has been transported by erosion and deposition
Factors that affect Soil Composition• Parent material: What bedrock is it from?• Time: How long has it had to decompose?• Plants and animals: How have roots and
animals helped break up the rocks? Were there acid producing mosses that help break down the rocks (chemical weathering)?
• Topography: What is the shape of the landscape?
• Climate: Is it warm & wet? Were there glaciers present? Was there acid rain?
Soil Profile• Cross
section of soil layers revealing all soil horizons
Soil Horizon• A soil layer with physical and chemical
properties that are differentdifferent from adjacent layers
• O Horizon= organic material (humus)• A Horizon = topsoil• B Horizon = subsoil• C Horizon = partially weathered
parent material
Idealized Soil Profile
Humus:Dark organic matter in soil that is rich in nutrients.
Leaching: The removal of nutrients or toxins in soil as water passes through the layers.
Soil Texture• The size
of soil particles
Particle size ranges for sand, silt and clay
Type of Mineral Particle Size Range
Sand 2.0 - 0.06 millimeters
Silt 0.06 - 0.002 millimeters
Clay less than 0.002 millimeters
Large/ Coarse
Medium
Small/ Fine
EROSION
erosioerosionn
WeatheringWeathering
DepositioDepositionn
SedimentSedimentatiationon
to “settle”to “settle”