Earth ScienceEarth Science

Chapter 5: Section 1

Surface Processes and Landscapes

Water and the GroundWater 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 GroundWater 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 GroundWater 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 GroundWater 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 GroundWater 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 GroundWater 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 GroundWater 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 GroundWater 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 GroundWater 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.

WeatheringWeathering

• 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.

WeatheringWeathering

• 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

WeatheringWeathering

• 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

WeatheringWeathering

• 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.

WeatheringWeathering

• Weathering rates depend on 3 variables1. 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

SoilsSoils

• 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

SoilsSoils

• As soils mature, they grow richer, developing a series of layers called a soil profile.

ErosionErosion

• 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.

ErosionErosion

• The major agents (forces) of erosion are:– Gravity– Running water– Glaciers– Wind– Waves

ErosionErosion

• 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

ErosionErosion

• 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.

ErosionErosion

– The stream velocity is generally greatest just below the surface near the center of the channel.

greatest velocity

ErosionErosion

– 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.

ErosionErosion

– 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).

ErosionErosion

• 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

ErosionErosion

• 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.

DepositionDeposition

• 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

DepositionDeposition

• 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.

DepositionDeposition

– 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.

DepositionDeposition

– 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

DepositionDeposition

– 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 SystemErosional-Depositional System

• An erosional-depositional system combines the erosional processes, the transporting agents and processes of deposition.

• Examples:

Erosional-Depositional SystemErosional-Depositional System