Earth Science
Chapter 5: Section 1
Surface Processes and
Landscapes
Water and the Ground
• The continuous movement of water
between the atmosphere and the ground
is called the water cycle.
– Evaporation – changing liquid to gas
– Transpiration – process plants release water
into the atmosphere
– Evapotranspiration – all the water released
into the atmosphere by both evaporation and
transpiration.
Water and the Ground
• Once on Earth’s surface water can:
– Flow along the surface as runoff
– Sink into the ground (infiltration) and become
part of the ground water supply
– Remain on the surface as snow or ice
– Evapotranspire back into the atmosphere
again
Water and the Ground
• Most precipitation that reaches the Earth’s
surface infiltrates into the ground.
• This can only happen if the ground is
permeable (allows water to pass through it).
– The more saturated the ground, the less
infiltration
– The steeper the slope, the less infiltration
Water and the Ground
• Permeability is the ability of the regolith
(loose soil on top of bedrock) to allow
water to pass through it.
– In order for the ground to be permeable, pore
spaces within the regolith must be
interconnected.
– Material that does not allow water to pass
through it is said to be impermeable.
Water and the Ground
• As it rains, water infiltrates the regolith until
it reaches an impermeable bedrock layer.
• The water cannot infiltrate further, so it fills
in the pores above the impermeable layer of
bedrock, forming the zone of saturation.
• The upper surface of the zone of saturation
is called the water table.
• The zone above the water table is called
the zone of aeration.
Water and the Ground
• The porosity of a material is the amount of
open pore space between particles.
– Expressed as a percentage of open space
– Dependent upon shape, packing, and sorting.
• Rounded particles have greater porosity
than angular particles
• Loosely packed particles have a greater
porosity than tightly packed particles
• Sorted particles have a greater porosity
than unsorted particles.
• Particle size does not affect porosity
Water and the Ground
• Water retained by particles
– Particle size of a material does not affect
porosity, but it does affect the amount of water
retained.
• Smaller particles will retain more water than
larger particles, because smaller particles
have a greater total surface area.
Water and the Ground
• Capillarity is the ability of water to rise
through pore spaces.
– Water can move upward through soil, much as
water rises from the roots to the limbs of a tree.
– In loose materials, the smaller the pore size,
the greater the capillarity.
Water and the Ground
• Runoff occurs when rain falls faster than it
can seep into the ground
– The factors that will increase runoff are:
• Saturated pore spaces in the ground
• Steep slopes
• Little vegetation
• Impermeable surfaces
– Most runoff is carried into streams and ends
up in the ocean.
Weathering
• Weathering vs. erosion
– Weathering is the chemical and physical
breakdown of rocks
• Weathering is a preparation for erosion
– Erosion is the movement of weathered
materials from one place to another
• The two general types of weathering are
chemical and physical.
Weathering
• Physical weathering occurs when rock is
cracked, split or broken into sediments.
– Types of physical weathering:
• Frost action – breakup of rocks caused by
alternate freezing and thawing of water.
• Abrasion – wearing down of rocks as they rub or
bounce against each other.
• Exfoliation – the peeling away of large sheets of
loosened material.
• Plant and animal action – roots grow in cracks of
rocks or animals burrow through soil and rock
Weathering
• Chemical weathering occurs when rock is
broken down by chemical action resulting in
the change in composition of the rock.
– Oxidation - O2 chemically unites with minerals
– Hydration - H2O chemically unites with minerals
– Carbonation – dissolved CO2 in water forms
carbonic acid & dissolves limestone
– Organic Decay – acids from dead plants dissolve
in water, then the water solution dissolves rocks
Weathering
• Climate and Weathering
– Physical weathering is more pronounced in
moist, cold climates where alternate freezing
and thawing occur.
– Chemical weathering is more intense in warm,
moist climates.
– Usually, the more moisture available, the
more weathering occurs.
Weathering
•
Weathering rates depend on 3 variables
1. Particle size and surface area
– Larger, solid particles of rock weather more
slowly than do smaller, loose pieces
2. Mineral composition
– Harder rocks weather slower than soft rocks
3. Climate
– Humid climates have more weathering than
dry climates
Soils
• Soil is the part of the weathered regolith in
which rooted plants will grow.
– Major product of weathering
– Composed primarily of particles of rocks,
minerals, and organic matter.
– Contains solids, liquids, and gasses
Soils
• As soils mature, they grow richer, developing
a series of layers called a soil profile.
Erosion
• Erosion is the transportation of loose sediments
or rocks produced by weathering.
– Residual sediment is rock that has remained
in the place it has been weathered.
– Transported sediment is rock that has been
moved from its place of origin to another
location.
• Transported sediment is far more common.
Erosion
• The major agents (forces) of erosion are:
– Gravity
– Running water
– Glaciers
– Wind
– Waves
Erosion
• Gravity
– Primary driving force behind all erosional
systems
• When acting with another erosional agent
gravity provides the kinetic energy
necessary to transport sediments
– Gravity acting alone, like pulling rock down a
steep cliff or slope, usually results in angular
rocks
Erosion
• Running Water
– Primary agent of erosion on Earth
– Sediments carried by water are usually smooth
and rounded due to abrasion.
– Valleys carved by streams are V-shaped.
– Most running water is found in streams or rivers.
• A direct relationship exists between the volume
of water in the stream (stream discharge)
and/or gradient and stream velocity.
Erosion
– The stream velocity is generally greatest just
below the surface near the center of the channel.
greatest velocity
Erosion
– Water near the outside of a curve has a
greater velocity than water near the inside of
a curve.
• Erosion takes place at the outside of the
curve and deposition occurs at the inside.
Erosion
– The size of particles a stream can carry
increases as the stream velocity increases
– Streams can carry sediments in 3 ways
• Dissolved particles in a solution
• Fine sediments in suspension
• Larger rocks bounced, pushed, or rolled
along the stream bed (saltation).
Erosion
• Glaciers
– Most of NYS has evidence of glacial erosion
– Valleys carved by glaciers are U-shaped.
– Rocks are unsorted, angular and may have
parallel scratches or one polished side.
– Like with running water, the greater the volume
of ice and/or the steeper the slope, the greater
the velocity and the more the glacier erodes.
– Can transport the largest particles
Erosion
• Wind
– Sediments are usually angular and, although
smooth, not as smooth as by running water.
– Rocks are often pitted and frosted.
– Like with running water and glaciers, the
greater velocity the larger the particles the
wind can carry.
Deposition
• Deposition is the release of sediments
from an erosional system.
– Caused by the decrease of carrying power of
an erosional agent.
• Factors Affecting Deposition
– Particle size
• The settling rate of particles is determined
mainly by its particle size
Deposition
• With all other factors equal, larger particles
settle faster than smaller particles because
they weigh more.
• In running water, very small particles
remain suspended for long periods of time.
• When a mixture of sediment sizes settle in
still water sorting in horizontal layers takes
place.
Deposition
– Particle shape
• If all other factors are equal, smooth,
spherical objects usually settle faster than
angular, flatter particles.
– Particle Density
• If particles are about the same size and
shape, higher-density particles will settle
faster than lower-density particles.
Deposition
– Velocity of Transporting Medium
• As the velocity decreases, there is a loss of
carrying power and larger, heavier, denser
particles settle out first.
– Horizontal Sorting
Deposition
– Glacial deposition
• Two main types are till and outwash.
–Till is unsorted rock material deposited
directly from glaciers.
–Outwash is rock deposited by the
meltwater of a glacier and can show
horizontal sorting.
Erosional-Depositional System
• An erosional-depositional system combines
the erosional processes, the transporting
agents and processes of deposition.
• Examples:
Erosional-Depositional System