Answer four Earth Science Essays with a minimum of 200 words in APA Format

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Foundations of Earth

Science, 6e

Lutgens, Tarbuck, & Tasa

Landscapes Fashioned

by Water Foundations, 6e - Chapter 3

Stan Hatfield

Southwestern Illinois College

Earth’s external processes

• Weathering, mass wasting, and

erosion are all called external

processes because they occur at or

near Earth’s surface

• Internal processes, such as

mountain building and volcanic

activity, derive their energy from

Earth’s interior

Mass wasting: The

work of gravity

• Mass wasting is the downslope movement of rock and soil due to gravity

• Controls and triggers of mass wasting

• Water — reduces the internal resistance of materials and adds weight to a slope

• Oversteepening of slopes

Mass wasting: The

work of gravity

• Controls and triggers of mass

wasting

• Removal of vegetation

• Root systems bind soil and regolith

together

• Earthquakes

• Earthquakes and aftershocks can dislodge

large volumes of rock and unconsolidated

material

Water cycle

• The hydrologic cycle is a summary of the circulation of Earth’s water supply

• Processes in the water cycle

• Precipitation

• Evaporation

• Infiltration

• Runoff

• Transpiration

The hydrologic cycle

Running water

• Streamflow

• The ability of a stream to erode and

transport materials is determined by

velocity

• Factors that determine velocity

• Gradient, or slope

• Channel characteristics including shape,

size, and roughness

Running water

• Streamflow

• Factors that determine velocity • Discharge—The volume of water moving

past a given point in a certain amount of time

• Changes along a stream

• Cross-sectional view of a stream is called the profile

• Viewed from the head (headwaters or source) to the mouth of a stream

Running water

• Changes from upstream to downstream

• Profile • Profile is a smooth curve

• Gradient decreases downstream

• Factors that increase downstream • Velocity

• Discharge

• Channel size

Longitudinal profile

of California’s Kings River

Base level

• Base level and stream erosion

• Base level is the lowest point to which a

stream can erode

• Two general types of base level

• Ultimate (sea level)

• Local or temporary

Base level

• Base level and stream erosion

• Changing conditions causes

readjustment of stream activities

• Raising base level causes deposition

• Lowering base level causes erosion

Adjustment of base level

to changing conditions

The work of streams

• Stream erosion

• Lifting loosely consolidated particles by

• Abrasion

• Dissolution

• Stronger currents lift particles more

effectively

The work of streams

• Transport of sediment by streams

• Transported material is called the stream’s load

• Types of load • Dissolved load

• Suspended load

• Bed load

• Capacity—the maximum load a stream can transport

The work of streams

• Competence

• Indicates the maximum particle size a

stream can transport

• Determined by the stream’s velocity

The work of streams

• Deposition of sediment by a stream

• Caused by a decrease in velocity

• Competence is reduced

• Sediment begins to drop out

• Stream sediments

• Generally well sorted

• Stream sediments are known as alluvium

The work of streams

• Deposition of sediment by a stream

• Delta—Body of sediment where a

stream enters a lake or the ocean

• Results from a sudden decrease in velocity

• Natural levees—Form parallel to the

stream channel by successive floods

over many years

Structure of a simple delta

Natural levees

The work of streams

• Deposition of sediment by a stream

• Floodplain deposits

• Back swamps

• Yazoo tributaries

Stream valleys

• The most common landforms on Earth’s surface

• Two general types of stream valleys

• Narrow valleys • V-shaped

• Downcutting toward base level

• Features often include rapids and waterfalls

V-shaped valley of the

Yellowstone River

Stream valleys

• Two general types of stream valleys

• Wide valleys

• Stream is near base level

• Downward erosion is less dominant

• Stream energy is directed from side to side

forming a floodplain

Stream valleys

• Features of wide valleys often include

• Floodplains

• Depositional floodplains

• Meanders

• Cut banks and point bars

• Cutoffs and oxbow lakes

Oxbow lakes and meanders in a

wide stream valley

Drainage basins and patterns

• Drainage networks

• Land area that contributes water to the

stream is the drainage basin

• Imaginary line separating one basin

from another is called a divide

Drainage basin of the

Mississippi River

Drainage basins and patterns

• Drainage pattern

• Pattern of the interconnected network of

streams in an area

• Common drainage patterns

• Dendritic

• Radial

• Rectangular

• Trellis

Drainage patterns

Floods and flood control

• Floods and flood control

• Floods are the most common and most

destructive geologic hazard

• Causes of flooding

• Result from naturally occurring and human-

induced factors

• Causes include heavy rains, rapid snow

melt, dam failure, topography, and surface

conditions

Water beneath the surface

• Largest freshwater reservoir for

humans

• Geological roles

• As an erosional agent, dissolving by

groundwater produces

• Sinkholes

• Caverns

• An equalizer of stream flow

Distribution of fresh water in

the hydrosphere

Water beneath the surface

• Distribution and movement of

groundwater

• Distribution of groundwater

• Belt of soil moisture

• Zone of aeration

• Unsaturated zone

• Pore spaces in the material are filled

mainly with air

Water beneath the surface

• Distribution and movement of

groundwater

• Distribution of groundwater

• Zone of saturation

• All pore spaces in the material are filled

with water

• Water within the pores is groundwater

• Water table — The upper limit of the zone of

saturation

Features associated with

subsurface water

Water beneath the surface

• Movement of groundwater

• Porosity

• Percentage of pore spaces

• Determines how much groundwater can be

stored

Water beneath the surface

• Movement of groundwater

• Permeability

• Ability to transmit water through connected

pores

• Aquitard — An impermeable layer of

material

• Aquifer — A permeable layer of material

Water beneath the surface

• Springs

• Hot springs

• Water is 6 – 9 °C warmer than the mean air

temperature of the locality

• Heated by cooling of igneous rock

• Geysers

• Intermittent hot springs

• Water turns to steam and erupts

Wintertime eruption of Old

Faithful

Water beneath the surface

• Wells

• Pumping can cause a drawdown (lowering)

of the water table

• Pumping can form a cone of depression in

the water table

Water beneath the surface

• Artesian wells

• Water in the well rises higher than the

initial groundwater level

• Artesian wells act as “natural pipelines”

moving water from remote areas of

recharge great distances to the points of

discharge

Formation of a cone

of depression

An artesian well resulting

from an inclined aquifer

Water beneath the surface

• Environmental problems associated

with groundwater

• Treating it as a nonrenewable resource

• Land subsidence caused by its withdrawal

• Contamination

Water beneath the surface

• Geologic work of groundwater

• Groundwater is often mildly acidic

• Contains weak carbonic acid

• Dissolves calcite in limestone

• Caverns

• Formed by dissolving rock beneath Earth’s

surface

• Formed in the zone of saturation

Water beneath the surface

• Caverns

• Features found with caverns

• Form in the zone of aeration

• Composed of dripstone

• Common features include stalactites

(hanging from the ceiling) and stalagmites

(growing upward from the floor)

Stalactites and stalagmites in

Carlsbad Caverns National Park

Water beneath the surface

• Karst topography

• Formed by dissolving rock at, or near,

Earth’s surface

• Common features

• Sinkholes – surface depressions

• Sinkholes form by dissolving bedrock and

caver collapse

• Caves and caverns

• Area lacks good surface drainage

Features of karst topography

End of Chapter 3