12. earth's surface land & water

8/22/2019 12. Earth's Surface Land & Water

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Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Natural Science 1

EARTH’S SURFACE—

LAND AND WATER




This lecture will help you

understand:• A survey of Earth’s landforms

• Folds and faults and how they areclassified

• The different types of mountains

• The topography of the ocean floor

• Earth’s water and where it is found • The different erosive agents that sculpt

Earth’s surface




Earth’s Many Landforms

Earth consists of seven continents:

Africa, Antarctica, Asia, Australia,

Europe, North America, and South

America

Continental elevations vary between

• Mt. Everest (8848 m)• Dead Sea shores ( –400 m)





Earth has three oceans:The Pacific Ocean

• Largest, deepest, and oldest

The Atlantic Ocean• Coldest and saltiest

The Indian Ocean

•

SmallestBUT, the oceans are all connected

• In reality, there is just one big ocean.





Continental land features• High mountains, plateaus, lowland plains

Ocean features

•

Deep trenches to mid-ocean ridge systemTectonic force and landforms

• Folds, faults, mountains

Erosive force and landforms• Valleys, canyons, deltas, and floodplains




Crustal Deformation

Deformation is a general term that refersto all changes from the original formand/or size of a rock body.

Most crustal deformation occurs alongplate margins.

How rocks deform:

• Rocks subjected to stresses begin todeform.


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Crustal Deformation

Compressional stress—convergent plateboundary

• Pushing together of rock masses

Tensional stress—divergent plateboundary

• Pulling apart of rock masses

Shear stress—transform fault-plateboundary

• Rock masses sliding past one another



Crustal Deformation

Elastic deformation• Size and shape deform, but rock returns to

original form when stress is removed

Fracture

• Elastic limit of rock exceeded; rock breaks

• Colder, surface rock

Plastic deformation• Elastic limit of rock exceeded; shape

changed permanently—folds

• Warmer, subsurface rock



Folds

During crustal deformation, rocks areoften bent into a series of wave-like

undulations called folds.

Characteristics of folds:• Most folds result from compressional

stresses that shorten and thicken the crust.



Folds

•

Anticlines—upfolded or arch-shaped rocklayers.• Oldest rock layers at the fold core, rock layers get

younger away from core.

• Synclines—downfolds or trough-shaped rock

layers.• Youngest rocks at the fold core, rock layers get

older away from the core.



Faults

―Strength‖ of rock exceeded • Faults are fractures with displacement.

• Sudden fault movement causes most

earthquakes.• Faults classified by relative

displacement

—Dip-slip (vertical), strike-slip (horizontal),or oblique



Dip-Slip Faults

Dip-slip fault movement is up or down• Footwall—rock below the fault surface

where a miner could stand.

• Hanging wall—rock above the fault surface

where a miner could hang a lamp.

Normal fault: hanging wall moves down

relative to footwall—tension

Reverse fault: hanging wall moves up

relative to footwall—compression



Dip-Slip Faults



Strike-Slip Faults

Displacement is horizontal, right-lateral, or left-lateral depending on direction of

movement.

Facing the fault:• Block on opposite side of fault moves to

the right (right-lateral)

• Block on opposite side of fault moves to

the left (left-lateral)



Strike-Slip Faults

Transform fault-plate boundary:• Large strike-slip fault that cuts through

the lithosphere, accommodates motion

between two tectonic plates• San Andreas Fault zone—major

transform fault separating Pacific Plate

and North American Plate



Strike-Slip Faults



Oblique-Slip Faults

Faults with combined motion:• Move horizontally as in a strike-slip

fault

•Move vertically as in a dip-slip fault

• Oblique faulting occurs when

tensional and shear forces or

compressional and shear forces exist.

C t l D f ti



Rocks begin to deform when they

A. become subjected to folding and faulting.

B. are subjected to compressional, tensional, or shear forces.

C. break.

D. undergo partial melting.

Crustal Deformation

CHECK YOUR NEIGHBOR

C t l D f ti



Rocks begin to deform when they

A. become subjected to folding and faulting.

B. are subjected to compressional, tensional, or shear forces.

C. break.

D. undergo partial melting.

Crustal Deformation

CHECK YOUR ANSWER

C t l D f ti



Rocks deform and fold in response to

A. tensional forces that elongate the crust.

B. tensional forces that shorten the crust.

C. compressional forces that elongate the crust.

D. compressional forces that shorten the crust.

Crustal Deformation

CHECK YOUR NEIGHBOR

Crustal Deformation



Rocks deform and fold in response to

A. tensional forces that elongate the crust.

B. tensional forces that shorten the crust.

C. compressional forces that elongate the crust.

D. compressional forces that shorten the crust.

Crustal Deformation

CHECK YOUR ANSWER

Crustal Deformation



A normal fault is created as rock in the hanging wall

A. drops down relative to rocks in the footwall. Tension pulls the rock

apart.

B. drops down relative to rocks in the footwall. Tension pushes the

rock together.

C. moves up relative to rocks in the footwall. Compression pulls the

rock apart.D. moves up relative to rocks in the footwall. Compression pushes

the rock together.

Crustal Deformation

CHECK YOUR NEIGHBOR

Crustal Deformation



A normal fault is created as rock in the hanging wall

A. drops down relative to rocks in the footwall. Tension pulls

the rock apart.


rock together.



the rock together.

Crustal Deformation

CHECK YOUR ANSWER

Crustal Deformation



A reverse fault is created as rock in the hanging wall


apart.


rock together.



the rock together.

Crustal Deformation

CHECK YOUR NEIGHBOR

Crustal Deformation




A reverse fault is created as rock in the hanging wall


apart.


rock together.


rock apart.D. moves up relative to rocks in the footwall. Compression

pushes the rock together.

Crustal Deformation

CHECK YOUR ANSWER




Mountains

Mountains are thick sections of crust

elevated with respect to the surrounding

crust.

Mountains are classified according to their structural features:

• Folded Mountains

• Upwarped Mountains

• Fault-Block Mountains

• Volcanic Mountains




Folded Mountains

Mountains mostly occur at convergentplate boundaries—crustal thickeningcauses uplift.

•

Compression folds, thickens, andshortens the crust—isostatic uplift

Continental collision creates highestmountains

• Himalayas—India and Eurasia

• Appalachians—North America and Africa




Upwarped Mountains

Broad upwarping of deeper rock deformsoverlying sedimentary rock, producingroughly circular structures—domes.

• Older rocks are in the center, and younger rocks are on the flanks.

• The Black Hills of South Dakota are a large,domed structure generated by upwarping.




Fault-Block Mountains

• Fault-block mountains occur within large

areas of broad uplift.

• Overall force is usually compression.

• But crust is also stretched in such settings,like a balloon is stretched when inflated.

• Another example: When a tree branch is

bent, compression occurs on the inside of the bend and tension occurs on the outside

of the bend.




Fault-Block Mountains

Normal faults in stretched crust let huge blocks dropdownward. Block left standing is the mountain. Broaduplift continues.

• The Sierra Nevada Mountains

• The Grand Teton Mountains

• The Basin and Range Province

—The Great Basin, geographically

—Covers most of Nevada and parts of Arizona, California,and Utah




Volcanic Mountains

Volcanic mountains formed by eruptionsof lava, ash, and rock fragments.

Opening at the summit of a volcano:

•

Crater: steep-walled depression at thesummit, less than 1 km in diameter

• Caldera: summit depression greater than 1 km diameter, produced by

collapse following a massive eruptionVent—an opening connected to the

magma chamber via a pipe




Volcanic Mountains

Shield volcano:• Broad, large, slightly dome-shaped volcano

• Composed primarily of basaltic lava

• Mild eruptions of large volumes of lava• Mauna Loa on Hawaii

Cinder cone:

• Ejected lava (mainly cinder-sized) fragments

• Steep slope angle, small in size

• Sunset Crater in Arizona




Volcanic Mountains

Composite cone:• Large, classic-shaped volcano (thousands

of feet high and several miles wide atbase)

• Composed of interbedded lava flows andalternating layers of ash, cinder, and mud

• Many are located adjacent to the PacificOcean (Mount Fuji, Mount St. Helens)

• Very violent, explosive volcanic activity (Mt.Vesuvius)




Volcanic Mountains

Most volcanoes form near plate boundarieswhere converging plates meet.

About 75% of the world’s volcanoes are found

in the ―Ring of Fire‖ that encircles the Pacific

Ocean.




Volcanic Mountains

Hot spots—stationary, deep, very hot. Hotmantle rock moves upward by convection.

Hot spot volcanism:

• Partial melting occurs near the surface• Localized volcanism in the overriding plate

• In oceanic crust, basaltic magma produced—Hawaiian Islands

• In continental crust, granitic magmaproduced—Yellowstone National Park

Mountains




Mountains are generally formed

A. along convergent plate boundaries.

B. by tectonic forces.

C. where continents collide.

D. where uplift results from crustal thickening.

E. all of the above.

Mountains

CHECK YOUR NEIGHBOR

Mountains




Mountains are generally formed

A. along convergent plate boundaries.

B. by tectonic forces.

C. where continents collide.

D. where uplift results from crustal thickening.

E. all of the above.

Mountains

CHECK YOUR ANSWER

Mountains




Weathering and erosion wears mountains down, but manymountains continue to maintain their lofty stature because

A. of isostatic convergence.

B. the rate of uplift counters the rate of erosion.

C. magma pushes them upward at a faster rate than erosion wears

them down.

D. tensional forces in subduction zones continue to operate and

push rock upward.

Mountains

CHECK YOUR NEIGHBOR

Mountains




Weathering and erosion wears mountains down, but manymountains continue to maintain their lofty stature because

A. of isostatic convergence.

B. the rate of uplift counters the rate of erosion.

C. magma pushes them upward at a faster rate than erosion wears

them down.

D. tensional forces in subduction zones continue to operate and

push rock upward.

ou ta s

CHECK YOUR ANSWER

Mountains




Most of the world’s volcanoes are formed around the ―Ringof Fire‖ because

A. of seafloor spreading in the Pacific Plate.

B. the Pacific Plate is surrounded by subduction zones and

associated convergent boundaries.

C. the Pacific Ocean floor is very thin, and magma plumes are very

close to the surface.

D. it burns, burns, burns.

CHECK YOUR NEIGHBOR

Mountains




Most of the world’s volcanoes are formed around the ―Ringof Fire‖ because

A. of seafloor spreading in the Pacific Plate.

B. the Pacific Plate is surrounded by subduction zones and

associated convergent boundaries.

C. the Pacific Ocean floor is very thin, and magma plumes are very

close to the surface.

D. it burns, burns, burns.

CHECK YOUR ANSWER




Earth is 71% covered by water: ~97% issaltwater in the oceans; ~3% is fresh water.

• ~2% is frozen in ice caps and glaciers.

• ~1% is liquid fresh water in groundwater, and

water in rivers, streams, and lakes.

• A small amount is water vapor.

Earth’s waters are constantly circulating. The

driving forces are:• Heat from the Sun

• Force of gravity

Earth’s Waters

E th’ W t




The hydrologic cycle is the set of processes that

controls the circulation of water on Earth.Processes involved in the hydrologic cycle:

• Evaporation

• Precipitation

• Infiltration

• Runoff

Earth’s Waters




Earth’s Waters

Water that goes from the ocean back tothe ocean completes a hydrologic cycle.

The journey is not always direct, andwater can flow as:

• Streams, rivers, and groundwater

• Water can also be frozen in ice caps and

glaciers




The Ocean Floor

Ocean floor encompasses continentalmargins and deep ocean basins.

Continental margins are between

shorelines and deep ocean basins.• Continental shelf —shallow; underwater

extension of the continent.

• Continental slope—marks boundary

between continental and oceanic crust.

• Continental rise—wedge of accumulated

sediment at base of continental slope.




The ocean bottom is not flat, it is etchedwith deep canyons, trenches, crevasses.

Underwater mountains rise upward from

the seafloor.The deep-ocean basin:

• Basalt from seafloor spreading plus thick

accumulations of sediment

• Abyssal plains, ocean trenches, and

seamounts

The Ocean Floor




The deep-ocean basin:• Abyssal plains—flattest part of the ocean floor due

to accumulated sediment

• Ocean trenches—long, deep, steep troughs at

subduction zones• Seamounts—elevated seafloor from volcanism

Mid-ocean ridges:

• Sites of seafloor spreading (volcanic and tectonic

activity)

• A global mid-ocean ridge system winds all around

the Earth

The Ocean Floor




The Ocean Floor

The deepest parts of the ocean are at theocean trenches near some of thecontinents.

The shallowest waters are in the middle of the oceans around underwater mountains (mid-ocean ridge system).

The Ocean




Ocean trenches are the deepest parts of the ocean floor because

A. that is where oceanic crust meets continental crust.

B. that is where subduction occurs.

C. no sediment accumulates in trenches.

D. all accumulated sediment settles in the abyssal plain.

CHECK YOUR NEIGHBOR

The Ocean




Ocean trenches are the deepest parts of the ocean floor because

A. that is where oceanic crust meets continental crust.

B. that is where subduction occurs.

C. no sediment accumulates in trenches.

D. all accumulated sediment settles in the abyssal plain.

CHECK YOUR ANSWER

O W




Ocean Waves

Characteristics of waves—waves get their energy from the wind.

• The crest is the peak of the wave.

• The trough is the low area between waves.

• Wave height is the distance between a troughand a crest.

• Wavelength is the horizontal distance betweencrests.

• Wave period is the time interval between thepassage of two successive crests.




Ocean Waves

Height, length, and period of a wavedepend on:

• Wind speed

• Length of time wind has blown

• Fetch—the distance that the wind hastraveled across open water

Ocean Waves




Ocean WavesWave of oscillation:

• Wave energy moves forward, not water

• Occurs in the open sea in deep water

Wave of translation:• Shallow water; depth about one-half wavelength—wave

begins to ―feel bottom‖

• Wave grows higher as it slows and wavelength shortens

• Steep wave front collapses, wave breaks• Turbulent water goes up the shore and forms surf

Ocean Waves




When a wave approaches the shore, the water depth

decreases. This affects the wave by flattening its circular

motion,

A. decreasing its speed, and increasing distance between waves

and wave height.

B. increasing its speed and distance between waves, and

decreasing wave period.

C. decreasing its speed and distance between waves, causing wave

height to increase.

D. increasing its speed and distance between waves, causing waveheight to increase.

CHECK YOUR NEIGHBOR

Ocean Waves




When a wave approaches the shore, the water depth

decreases. This affects the wave by flattening its circular

motion,

A. decreasing its speed, and increasing distance between waves

and wave height.

B. increasing its speed and distance between waves, and

decreasing wave period.

C. decreasing its speed and distance between waves, causing

wave height to increase.

D. increasing its speed and distance between waves, causing waveheight to increase.

CHECK YOUR ANSWER

O W t




Ocean Water

Ocean water is a complex solution of mineral salts,dissolved gases, and decomposed biologicalmaterial.

Salinity: the proportion of salts to pure water.• ~35 grams salts per 1000 grams of water

Salinity and temperature control density• Salty, cold water is denser than less salty, warmer

water

O W t




Ocean Water

Salinity is variable:Salinity decreases as fresh water enters

the ocean:• Runoff from streams and rivers

• Precipitation

• Melting of glacial ice

Salinity increases as fresh water leaves

the ocean:• Evaporation

• Formation of sea ice

Ocean Water CHECK YOUR NEIGHBOR




The density of seawater is controlled by

A. salinity.

B. temperature and salinity.

C. pressure and salinity.

D. sea ice and runoff.

CHECK YOUR NEIGHBOR

Ocean Water CHECK YOUR ANSWER




The density of seawater is controlled by

A. salinity.

B. temperature and salinity.

C. pressure and salinity.

D. sea ice and runoff.

CHECK YOUR ANSWER

Ocean Water CHECK YOUR NEIGHBOR




The salinity and, hence, density of seawater increase by

A. evaporation and precipitation.

B. evaporation and formation of ice.

C. evaporation, runoff, and melting of sea ice.

D. runoff, precipitation, and melting of glacial ice.

CHECK YOUR NEIGHBOR

Ocean Water CHECK YOUR ANSWER




The salinity and, hence, density of seawater increase by

A. evaporation and precipitation.

B. evaporation and formation of ice.

C. evaporation, runoff, and melting of sea ice.

D. runoff, precipitation, and melting of glacial ice.

CHECK YOUR ANSWER

E th’ F h W t




Earth’s Fresh Water

Only ~3% of Earth’s water is ―fresh.‖

Of the 3%,

~85% is frozen in ice sheets and glaciers

~14% is groundwater

~0.8% is in lakes and reservoirs, soilmoisture, and rivers

~0.04% is water vapor

S f W t




Surface Water

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

S f W t




Surface Water

The land area that contributes water to a streamis called the drainage basin.

Drainage basins are separated by drainagedivides.

The largest drainage divides are continentaldivides.

G d t




Groundwater

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 zonein the unsaturated zone—pores filledwith water and air.

The water table is the boundary betweenthese two zones.

G d t




Groundwater

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.

G d t




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 to

store greater amounts of groundwater.

• Particle size, shape, and sorting influenceporosity.

—Soil with rounded particles of similar size hashigher porosity than soil with various sizes.

G d t




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—example of

clay and sandstone:

—Both have high porosity, but clay’s small, flattened

sediment grains makes for tighter packing and

smaller pores. Water cannot flow easily through

small pores— so clay has low permeability.

Groundwater CHECK YOUR NEIGHBOR




A soil with rounded particles of similar size will have 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.

CHECK YOUR NEIGHBOR

Groundwater CHECK YOUR ANSWER




A soil with rounded particles of similar size will have 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.

CHECK YOUR ANSWER

Groundwater




Groundwater Aquifers are reservoirs of groundwater.

Aquifers generally have high porosity and highpermeability.

Aquifers underlie the land surface in many areas; theyare a vital source of fresh water.

It is important to keep this vital source of fresh water

clean and contaminant free.

Surface Processes




Surface Processes

• Earth’s surface is worn away by theprocesses of erosion.

• Agents of erosion include:

•

Gravity• Water

• Wind

•

Ice

The Work of Gravity




The Work of Gravity

Mass movement—the downslope movement of Earth material (rock, soil, debris, land), due to

gravity.

Rapid movement:

• Debris avalanche, rock fall, rock slide, landslide,

debris flow

• Evidence: concave scars, debris, buried structures

Slow movement:

• Soil creep, rock slump

• Evidence: broken retaining walls, bent tree trunks

The Work of Surface Water





Running water shapes Earth’s surface in twoopposing ways: fast water transports sediment,

slow water deposits sediment.

Streamflow—two types of flow; stream speed

• Laminar flow—slow and gentle

• Turbulent flow—fast and rapid

Factors that determine velocity:

•

Gradient, or slope• Channel characteristics (shape and size)

• Discharge—volume of water moving past a given

point in a certain amount of time






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

Downward limit to stream erosion:• The lowest point to which a stream can erode is

called base level.

Th W k f S f W t





Two general types of base level:• Ultimate (sea level)

• Local or temporary (lake, etc.)

• Raising base level causes deposition

• Lowering base level causes erosion

Transportation of sediment by streams:• Capacity: maximum load a stream can transport—

controlled by stream discharge• Competence: maximum particle size a stream can

transport— controlled by stream velocity

The Work of S rface Water





Decreased velocity causes sedimentdeposition—competence and capacity

reduced, sediment drops out of flow.

Stream sediments (alluvium) are generally well

sorted.• Natural levees—form parallel to stream channel

by successive floods

• Alluvial fans develop where a high-gradient

stream abruptly leaves a narrow valley

• Deltas form when stream enters an ocean, bay,

or lake—creates new land

The Work of Surface Water CHECK YOUR NEIGHBOR




As a river flows down to lower elevations, stream velocity

A. increases, capacity and competence decrease.

B. decreases, causing capacity and competence to decrease.

C. decreases, and capacity and competence increase.

D. increases as it forms a delta.

CHECK YOUR NEIGHBOR

The Work of Surface Water CHECK YOUR ANSWER




As a river flows down to lower elevations, stream velocity

A. increases, capacity and competence decrease.

B. decreases, causing capacity and competence to decrease.

C. decreases, and capacity and competence increase.

D. increases as it forms a delta.

CHECK YOUR ANSWER

The Work of Groundwater





Flowing groundwater can alter andchange features at the surface:

• Land subsidence

• Caves and caverns• Sinkholes






Land Subsidence:• Extreme groundwater withdrawal

by pumping from wells can result

in lowering of the land—land

subsidence.• Land subsidence is especially

prevalent in aquifers made of

sandy sediments and interbedded

clays. The clays leak water to the

sand, then when water is pumped

out, the clays shrink and compact,

causing subsidence.






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 dissolvingit.

• Such action has carved out magnificentcaves and caverns (a cavern is a largecave).






Sinkholes are funnel-shaped cavities inthe ground that are open to the sky;they are formed similar to caves. Theycan also be formed from conditions of

drought and the over withdrawal of groundwater.

The Work of Wind




The Work of Wind

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

The Work of Glaciers





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.






A glacier is an accumulation of snow and ice

thick enough to move under its own weight.

• Two types of glaciers:

— Alpine

—Continental

• Alpine glaciers develop in mountainous areas,

generally confined to individual valleys.

—Cascades, Rockies, Andes, Alps, Himalayas—Erosional landforms: cirque, arête, horn, hanging

valley, U-shaped valley






Continental Glaciers:• Spread over large areas

— Antarctica, Greenland, Alaska

• Erosional landforms

—Roches moutonees, striations

• Depositional landforms

—Moraine, kame, esker, drumlin

Surface ProcessesCHECK YOUR NEIGHBOR




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.

Surface ProcessesCHECK YOUR ANSWER



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.

12. earth's surface land & water

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