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Conceptual
PhysicalScience5th Edition
Chapter 22:
SHAPING EARTH’S
SURFACE
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This lecture will help you
understand:• The Hydrologic Cycle
• Groundwater
•The Work of Groundwater
• Surface Water and Drainage Systems
• The Work of Surface Water
•Glaciers and Glaciation
• The Work of Glaciers
• The Work of Air
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The Hydrologic Cycle
More than 97% of all
Earth’s water is in
the oceans.
Only 1 % of Earth’s
water is available to
us as water vapor,
groundwater, and
freshwater.
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Earth’s waters are constantly circulating.
The driving forces are:
• Heat from the Sun
• Force of gravity
The Hydrologic Cycle
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The hydrologic cycle is the set of processesthat controls the circulation of water onEarth.
Processes involved in the hydrologic cycle:• Evaporation
• Precipitation
• Infiltration
•
Runoff
The Hydrologic Cycle
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The Hydrologic Cycle
Water that goes from the ocean back tothe ocean makes a complete loop in the
hydrologic cycle.
The journey is not always direct.
•
Water can flow as streams, rivers, andgroundwater
• Water can also be frozen in ice caps andglaciers
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Earth’s natural supply of fresh water comes from:
A. Ice caps.B. Artesian springs.
C. Glaciers.
D. Rain and snow.
The Hydrologic Cycle
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Earth’s natural supply of fresh water comes from:
A. Ice caps.B. Artesian springs.
C. Glaciers.
D. Rain and snow.
Explanation:
Rain and snow deliver the water that forms ice caps, aquifers,
glaciers, and streams.
The Hydrologic Cycle
CHECK YOUR ANSWER
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Groundwater
Factors that influence storage andmovement of groundwater:
• Porosity : ratio of open space in soil, sediment,or rock to total volume of solids plus voids—the amount of open space underground.
• Greater porosity equals more potential tostore greater amounts of groundwater.
•
Particle size, shape, and sorting influenceporosity.—Soil with rounded particles of similar size has
higher porosity than soil with various sizes.
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Groundwater
Permeability• Degree to which groundwater can flow
through a porous material—higher
permeability, greater potential for fluid flow.
• Sediment packing and connectedness of
pores influences permeability.
• Hydraulic conductivity—a measure of
permeability—tells us the degree to which thematerial can transmit water.
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Groundwater The Water Table
Water beneath the ground exists asgroundwater and soil moisture.
•Groundwater occurs in the saturated zone
—
water has filled all pore spaces.
• Soil moisture is above the saturated zone inthe unsaturated zone—pores filled with water
and air.
The water table is the boundary betweenthese two zones.
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Groundwater The Water Table
The depth of the water table varies withprecipitation and climate.
• Zero in marshes and swamps, hundreds of meters in some deserts.
• At perennial lakes and streams, the water table is above the land surface.
• The water table tends to rise and fall with thesurface topography.
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Groundwater Aquifers and Springs
Aquifers are reservoirs of groundwater.
• Aquifers are a vital source of fresh water.
• Aquifers generally have high porosity and highpermeability.
• Aquifers underlie the land surface in manyareas.
•It is important to keep this vital source of freshwater clean and contaminant free.
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Groundwater Aquifers and Springs
A perched water table occurs when
discontinuous, low-permeability layers
in an unconfined aquifer intercept
percolating water above the water
table.
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Groundwater
Aquifers and SpringsGeologists can often use springs to locate
faults, because a spring can indicate
that there are cracks or breaks in therock.
G d t
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A soil with rounded particles of similar size willhave a higher porosity than a soil with rounded
particles of various sizes, because
A. it will have a higher permeability.B. water flows more easily through rounded particles.
C. smaller sediment grains will fill the open pore spaces between
larger grains.
D. poorly sorted sediment will have more open pore spaces.
Groundwater
CHECK YOUR NEIGHBOR
G d t
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A soil with rounded particles of similar size willhave a higher porosity than a soil with rounded
particles of various sizes, because
A. it will have a higher permeability.B. water flows more easily through rounded particles.
C. smaller sediment grains will fill the open pore spaces
between larger grains.
D. poorly sorted sediment will have more open pore spaces.
Groundwater
CHECK YOUR NEIGHBOR
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Groundwater Groundwater Movement
The elevation of a water table above a
particular location—usually sea level—
is called the hydraulic head.
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Groundwater Groundwater Movement
Darcy’s law:
Groundwater flow rate =hydraulic conductivity cross-sectional area hydraulic gradient
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The Work of Groundwater
Flowing groundwater can alter andchange features at the surface:
• Land subsidence• Caves and caverns
• Sinkholes
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The Work of Groundwater Land Subsidence
•
Extreme groundwater withdrawalby pumping from wells can resultin lowering of the land—landsubsidence.
•
Land subsidence is especiallyprevalent in areas underlain by
aquifers made of sandy sediments
and interbedded clays. The clays
leak water to the sand, then whenwater is pumped out, the clays
shrink and compact, causing
subsidence.
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The Work of Groundwater Caverns and Caves
• The dissolving action of groundwater “eats
away” at rock—limestone in particular.
•
Rainwater chemically reacts with CO2 in the air and soil, producing carbonic acid. The acidified
water seeps into rock (especially limestone),
partially dissolving it.
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The Work of Groundwater Caverns and Caves
Groundwater has carved out magnificent
caves and caverns (a cavern is a large
cave).
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The Work of Groundwater Sinkholes
• Sinkholes are funnel-shaped cavities inthe ground that are open to the sky.
•Sinkholes are formed in a manner similar to caves.
• Sinkholes can also be formed fromconditions of drought and the over-
withdrawal of groundwater.
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The Work of Groundwater Karst Regions
Karst regions are characterized by soft
rolling hills or sharp, rugged surfaces.
Karst regions are areas where sinkholes,
caves, and caverns define the land
surface.
The Work of Groundwater
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What kind of formation is this?
A. Floodplain
B. Karst
C. Glacier
D. Artesian spring
The Work of Groundwater
CHECK YOUR NEIGHBOR
The Work of Groundwater
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What kind of formation is this?
A. Floodplain
B. Karst
C. Glacier
D. Artesian spring
The Work of Groundwater
CHECK YOUR NEIGHBOR
S f W t
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Surface Water
and Drainage Systems
Surface water includes streams, rivers,lakes, and reservoirs.
Infiltration of water is controlled by:• Intensity and duration of precipitation
• Prior wetness condition of the soil
•
Soil type• Slope of the land
• Nature of the vegetative cover
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Surface Water
and Drainage Systems
Running water shapes Earth’s surface
in two opposing ways:
• It carves out the landscape.
• It deposits sediments.
S f W t
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Surface Water
and Drainage Systems
Stream Flow Geometry
Factors that determine stream velocity:
• Gradient, or slope
• Discharge—volume of water moving past a
given point in a certain amount of time
• Channel geometry characteristics
— shape and size
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Surface Water
and Drainage SystemsStream Flow Geometry
Average stream speed =
discharge / cross-sectional area
Stream speed is usually not constant along the
length of a stream. As the stream moves
downslope, the gradient decreases and thechannel widens. Discharge usually increases
as tributaries add water.
S f W t
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Surface Water
and Drainage Systems
Stream Flow GeometryStream speed varies within a channel. It is
slower along the stream bed (friction) and
faster near the surface.• In a straight channel, maximum flow speed
is mid-channel.
•In a curving channel,maximum flow speed
is on the outside of
each bend.
S f W t
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Surface Water
and Drainage Systems
Drainage Basins and NetworksThe land area that contributes water to a stream is called
the drainage basin.
Drainage basins are separated by drainage divides.
The largest drainage divides are continental divides.
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The Work of Surface Water
Flowing surface water sculpts and shapes
Earth’s surface:
• Erosion—erosive sculpting action carves thelandscape
• Deposition—shapes the land as sediment is
deposited
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The Work of Surface Water
Streamflow—two types of flow• Laminar flow—slow and gentle
• Turbulent flow—fast and rapid
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The Work of Surface Water
Streams transport great amounts of sedimentfrom one location to another.
Laminar flows can lift and carry only the very
smallest and lightest particles.
A turbulent flow can move and carry a range of particle sizes—it moves particles downstream
mainly by lifting them into the flow or byrolling and sliding them along the channelbottom. The smaller, finer particles remainsuspended to make the water murky.
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The Work of Surface Water Erosion and Transport of Sediment
Chemical Weathering: Stream water carries
dissolved substances that chemically weather and
erode rock.
Hydraulic Action: Erosion
and movement of great
quantities of sediment
and rock. Abrasion: Abrasion occurs
when sediments and particles
scour a channel.
Th W k f S f W t
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The Work of Surface Water Erosion and Transport of Sediment
Stream erosion:
• Loosely consolidated particles are lifted by
abrasion and dissolution.
Stronger currents lift particles more effectively:
• Stronger currents have “higher ” energy
• Lift and transport more and bigger particles• Turbulent versus laminar flow
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The Work of Surface Water Stream Valley and Floodplains
Stream channels in high
mountain areas cut into
underlying rock.Fast-moving rapids and
beautiful waterfalls are
characteristic of V-shaped mountain
stream valleys.
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The Work of Surface Water
Stream Valleys and FloodplainsStream speed plays a role in erosion and
deposition.
In a meandering stream channel, maximum stream speed
is on the outside bend of the channel—the cut bank—a
place of erosion.
On the inside bend, stream
speed slows to create a
point bar —a place of
deposition.
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The Work of Surface Water
Stream Valleys and FloodplainsMeandering streams create a wide belt of
almost flat land: a floodplain.
When a flood occurs, sediment is deposited inthe floodplain. Large, coarse sedimentcreates natural levees.
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The Work of Surface Water
Deltas: The End of the Line for a River A delta is where a flowing stream meets a
standing body of water. The flow slows down
and the stream dumps sediment.The result is a fan-shaped deposit of new land.
The Work of Surface Water
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This picture shows an example of what
geologic feature?
A. Floodplain
B. Delta
C. Turbulent flowD. Rapids
CHECK YOUR NEIGHBOR
The Work of Surface Water
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This picture shows an example of what
geologic feature?
A. Floodplain
B. Delta
C. Turbulent flow
D. Rapids
CHECK YOUR ANSWER
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Glaciers and Glaciation
Glaciers are powerful agents of erosion. Aglacier is like a plow as it scrapes andplucks up rock and sediment.
Glaciers are also powerful agents of deposition. A glacier is like a sled as itcarries its heavy load to distant places.
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Glaciers and GlaciationGlacier Formation and Movement
A glacier is an accumulation of snow and ice
thick enough to move under its own weight.
• Two types of glaciers:
— Alpine
—Continental
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Glaciers and Glaciation
Glacier Formation and Movement• When a glacier ’s ice mass becomes about 50
meters thick, the pressure of the overlyingmaterial causes the base of the ice to move
plastically —
the entire mass shifts.• Also, meltwater at the base of the glacier
creates basal sliding.
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Glaciers and Glaciation
Glacier Formation and MovementThe mass of a glacier changes over time. As
snow falls, accumulation makes the glacier
grow. As ice melts, sublimates, or breaks off,
ablation occurs.
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The Work of GlaciersGlacial Erosion and Erosional Landforms
Alpine glaciers develop in mountainous areas,generally confined to individual valleys.—Cascades, Rockies, Andes, Himalayas
—Erosional landforms: cirque, arête, horn, hangingvalley,U-shaped valley
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The Work of GlaciersGlacial Sedimentation
and Depositional LandformsWhen glacial ice melts, it drops a poorly sorted,
heterogeneous load of boulders, pebbles,
sand, and clay.
A wide range of particle sizes is the hallmark
that differentiates glacial sediment from the
much-better-sorted
material depositedby streams and
winds.
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The Work of Air
Wind blows everywhere, but its impact onsculpting the land is minor.
Impact is greatest where:
• Strong winds blow frequently
• Vegetation is sparse or absent
—Plant roots keep particles together
—Plants deflect wind and shelter particles
• Surface particles are small—Small particles are more easily lifted and
transported
Surface Processes
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There are many erosive agents that sculpt Earth’s surface.Overall, the erosive agent that does the most work is
A. wind.
B. groundwater.
C. running water.
D. glaciers.
CHECK YOUR NEIGHBOR
Surface Processes
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There are many erosive agents that sculpt Earth’s surface.Overall, the erosive agent that does the most work is
A. wind.
B. groundwater.
C. running water.
D. glaciers.
CHECK YOUR NEIGHBOR