Transcript Surface Processes Weathering

Surface Processes and
Landscapes
Weathering
Weathering and Erosion
Weathering is the chemical and physical
breakdown of rocks into smaller
fragments.
Erosion is the movement of weathered
material from one place to another.
Weathering Types
The two general types of weathering are
physical and chemical.
Physical weathering occurs when rock is
cracked, split, or broken into sediments
with no change in the rock composition.
Chemical weathering occurs when rock is
broken down by chemical action
resulting in a change in the composition
of the rock.
Types of Physical Weathering
• Frost action – caused by alternate freezing
and thawing of water.
• Abrasion – caused as rocks rub or bounce
against each other.
• Exfoliation is the peeling away of large
sheets of loosened surface material.
• Roots from large trees and shrubs as well
as roots from lichens and mosses will split
rocks as they grow.
Types of Chemical Weathering
Oxidation occurs when oxygen combines chemically
with minerals. Ex. is rust.
Hydration occurs when water combines chemically
with minerals. Ex. is when feldspar or hornblende
combine with water and form clay.
Carbonation occurs when carbon dioxide combines
with minerals. Example is carbonic acid which
dissolves limestone creating caves, sink holes,
stalactites and stalagmites.
Organic Decay occurs when acids from decaying
organic matter dissolve rock minerals.
Soils
Soil is one of the major products of
weathering.
Soil is the part of the weathered
regolith in which rooted plants will
grow.
Soil is composed of rock minerals and
organic matter and consists of all 3
states of matter.
Soil Formation
Soil types depend upon their place of
origin.
Soil formed by the weathering of the
bedrock found beneath it is called
residual soil.
Soil formed from rock that was moved to
its present location is called
transported soil.
Soil Profile
As soils mature they grow richer and develop
a series of layers called a profile.
Topsoil is the uppermost layer containing the
most organic matter and the most
weathered rocks.
Subsoil is below the topsoil and is rich in claysized particles but contains little organic
matter.
Below the subsoil is partly weathered bedrock
on top of unweathered bedrock.
Soil Solution
• A soil solution is the end product of
weathering; a solution of ground water
containing ions of potassium, nitrate,
phosphate, calcium and iron that the water
picked up as it seeps through soil.
Soil Conservation
• Due to the large demands upon earth’s
farmable land, use of soil must be
carefully planned and managed.
• Depletion occurs when too many nutrients
are removed form the soil for crops to
grow.
• Crop rotation, contour plowing, strip
cropping, terracing, and wind breaks are
all farming practices designed to preserve
soil.
Erosion
• Erosion is the transportation of loose
sediments or rocks produced by
weathering.
• The major mechanisms of erosion are:
– Gravity
– Running water
– Glaciers
– Wind and
– Waves
Types of Sediment
• Transported sediment is rock material that
has been moved to another location.
– Transported materials will become abraded as
they grind and bump against other rock
material. These materials begin to appear
rounded as they are abraded.
• Residual sediment is rock material that has
weathered and remained in its place or
origin.
Running Water and Erosion
Any running water makes a stream.
Gradient, discharge, and channel shape
influence a stream’s velocity and the erosion
and deposition of sediments.
Stream features include: v-shaped valleys,
deltas, flood plains and meanders.
A watershed area is the area drained by a
stream and it’s tributaries.
Stream Velocity
• Carrying power is the ability of a
stream to move particles of different
sizes and this depends upon velocity.
• Velocity (speed) of a stream depends
upon stream discharge and gradient.
– Discharge is the volume of water.
– Gradient is the steepness of the slope.
Stream Velocity and Gradient
Velocity and Channel Shape
Velocity and Sediment Size
Greater stream
velocity will carry
larger sediments.
Stream load is the
material that a
stream carries.
Stream Load
• Load is the material
that a stream carries.
• 3 ways to carry load:
– Solution = disssolved
– Suspension = floating
– Saltation = bouncing
Wind and Ice Erosion
• Wind: greater
velocity carries
larger particles.
• Ice: greater
volume carries
larger particles.
Glacial Erosion
Effects of Erosional Agents:
Valley Shapes
River erosion creates
“V-Shaped” valleys.
Glacial erosion creates
“U-Shaped” valleys.
Deposition
• Deposition is the final step in an erosionaldepositional system.
– Factors affecting deposition are:
• Particle size, shape, density
• Velocity
• gradient
– Rock particles are eventually deposited
somewhere:
• by sedimentation = dropping of particles
• by precipitation = dissolved minerals “fall” out of
solution.
Horizontal Sorting
• As a stream or river
enters a larger body
of water, the velocity
decreases as distance
from the mouth
increases.
– As a result the biggest
particles fall out first
and the smallest travel
the farthest.
Crossbedding
Glacial Deposition
• Glacial deposits are unsorted (all mixed with no
layering or bedding) and deposits are mostly 2
types:
– Till is unsorted rock deposited directly by the glacier;
– Outwash is rock material deposited by the meltwater of a glacier.
• Outwash can show horizontal sorting.
– Erratics are large boulders deposited by glaciers.
Erosional – Depositional System
• An erosional-depositional system combines the erosion
process, transportation agents, and deposition.
• A river is a combination of continual erosion and
deposition.
River Terms
•
•
•
•
•
•
Source = beginning w/most
potential energy.
Mouth = end, where it flows
downstream to.
Meander = curve or bend.
Flood plain = land between the
stream and steep walls of the
valley.
Delta = deposit of sediment at
the mouth of a river.
Alluvial fan = deposit of
sediment formed where river
slows as it flows out of
mountains.
Flood Plain (above)
and stream history,
oxbow, (left)