chapter 9: surface water -...
TRANSCRIPT
210
SurfaceWaterSurfaceWater
99What Yoursquoll Learnbull What landscape features
on Earth are formed andchanged by surfacewater
bull How surface watermoves materials andimpacts humans
Why Itrsquos ImportantLandscape featuresformed by surface waterare among the mostnumerous and visible features on EarthRunning water has thegreatest impact onhumans because wedepend on streams fordrinking-water suppliesand irrigation Humansalso experience the nega-tive effects of floods
To find out more about surface water visit theEarth Science Web Site at earthgeucom
91 Sur face Water Movement 211
When water seeps into the groundit moves at various rates through thedifferent materials that make upEarthrsquos surface These Earth materialsare comprised of different particlesizes In this activity you will inves-tigate the movement of water as itseeps through two different kinds ofEarth materials
1 Place a small window screen oneach of two clear plastic shoeboxes
2 Place an 8 cm 16 cm clump ofgrass or sod on one screen
3 Place an 8 cm 16 cm clump of
barren soil on the other screen
4 Lightly sprinkle 500 mL of wateron each clump
CAUTION Always wear anapron in the lab
Observe In your sciencejournal describe what happensto the water after five minutesMeasure how much water passesthrough each clump and collects in the plastic shoe box Explainany differences in the amount of water collected in each plastic shoe box
Modeling WaterMovement
Discovery LabDiscovery Lab
OBJECTIVES
bull Explain how surfacewater can move weath-ered materials
bull Explain how a streamcarries its load
bull Describe how a flood-plain develops
VOCABULARY
runoff bed loadwatershed dischargedivide floodsolution floodplainsuspension
Earthrsquos water supply is recycled in a continuous process called thewater cycle Water molecules move continuously through the watercycle following many pathways they evaporate from a body of wateror the surface of Earth condense into cloud droplets fall as precipi-tation back to Earthrsquos surface and soak into the ground As part ofa continuous cycle the water eventually evaporates back into theatmosphere again forms clouds again falls as precipitation and soon Understanding the mechanics of the water cycle helps to explainthe reasons for variations in the amount of water that is availablethroughout the world
Often a water moleculersquos pathway involves time spent within a liv-ing organism or as part of a snowfield glacier lake or oceanAlthough water molecules may follow a number of different path-ways the overall process is one of repeated evaporation and conden-sation powered by the Sunrsquos energy What happens once water reachesEarthrsquos surface Does all the water sink into the ground or evaporate
Surface Water Movement9191
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Figure 9-1 The water cycle also referred to as the hydrologic cycle is a never-endingnatural circulation of water through Earthrsquos systems The Sun provides the energy forthe water cycle Radiation from the Sun causes water to change to a gas called watervapor The process of water vapor changing to a fluid is called condensation
RUNOFFAs shown in Figure 9-1 precipitation falls to Earthrsquos surface in theform of rain snow sleet or hail In most instances solid forms ofprecipitation such as snow sleet and hail may eventually melt Orthey can also be incorporated into the mass of a glacier Once waterreaches Earthrsquos surface it can evaporate into the atmosphere soakinto the ground or flow down slopes on Earthrsquos surface Water flow-ing downslope along Earthrsquos surface is called runoff Runoff mayreach a stream river or lake may evaporate or it may accumulate aspuddles in low-lying small depressions and eventually seep into theground During and after heavy rains you can observe theseprocesses occurring in your own yard or local park Water that seepsinto Earthrsquos surface becomes groundwater
A number of conditions determine whether water on Earthrsquos sur-face will seep into the ground or become runoff For water to enterthe ground there must be large enough pores or spaces in thegroundrsquos surface materials to accommodate the waterrsquos volume as inthe loose soil illustrated in Figure 9-2A If the pores already containwater the newly fallen precipitation will either remain standing ontop of the ground or if the area has a slope run downhill Waterstanding on the surface of Earth eventually evaporates or flows away
212 CHAPTER 9 Sur face Water
Land
Evaporation
Evaporation
Transpiration
Condensation
Precipitation
Precipitation
Oceans
Runoff
InfiltratesGroundwater
Vegetation Soils that contain grasses or other vegetation allowmore water to enter the ground than do soils with no vegetationPrecipitation falling on vegetation slowly flows down leaves andbranches and it eventually drops gently to the ground In contrastprecipitation falls with far more force onto barren land In suchareas soil particles clump together and form dense aggregates withfew pores or spaces between them The force of falling rain may thenpush the soil clumps together thereby closing pores and allowing lesswater to enter as illustrated in Figure 9-2B This is why gardeners donot pack the soil around their plants Compacting the soil reducesthe spaces between the particles that are available for water to seepin thus reducing the amount of water that is available to the plantsrsquoroots
Rate of Precipitation Light gentle precipitation infiltrates thedry ground However the rate of precipitation may temporarilyexceed the rate of infiltration For example during heavy precipita-tion water falls too quickly to soak into the ground and becomesrunoff Thus a gentle long-lasting rainfall is more beneficial toplants and causes less erosion by runoff than a torrential downpourIf you have a garden remember that more water will enter theground if you water your plants slowly and gently
Soil Composition The physical and chemical composition ofsoil also affects its water-holding capacity Soil consists of decayedorganic matter called humus and minerals Humus creates pores inthe soil thereby increasing a soilrsquos ability to retain water The min-erals in soil have different particle sizes which are classified as sandsilt or clay As you learned in Chapter 7 the percentages of particlesof each size vary from soil to soil Soil with a high percentage ofcoarse particles such as sand has relatively large pores between itsparticles that allow water to enter and pass through the soil quicklyIn contrast soil with a high percentage of fine particles such as clayclumps together and has few or no spaces between the particles
91 Sur face Water Movement 213
Figure 9-2 Soil that hasopen surface pores orspaces between particlesallows water to infiltrate(A) Soil that has few orno pores or spaces canrestrict waterrsquos ability toseep in (B)
A B
Steep slopendashrapid runoff
Little slopendashlittle runoff
Slope
Figure 9-4 Numerous trib-utaries flow into severalstream systems that draininto the Salton Sea inCalifornia
214 CHAPTER 9 Sur face Water
Such small pores restrict both the amount of water that can enterthe ground and the ease of movement of water through the soil
Slope As you have learned the slope of a land area plays a large rolein determining the ability of water to enter the ground as shown inFigure 9-3 Water from precipitation falling on slopes flows to areasof lower elevation The steeper the slope the faster the water flowsThere is also greater potential for erosion on steep slopes In areaswith steep slopes little water seeps into the ground before it runs off
STREAM SYSTEMSPrecipitation that does not enter the ground usually runs off the sur-face quickly Some surface water flows in thin sheets and eventuallycollects in small channels As the amount of runoff increases thechannels widen deepen and become longer Although it is commonfor these small channels to dry up shortly after precipitation stops thechannels again fill with water each time it rains and become largerand longer If a sufficient supply of water develops the water beginsto flow more permanently in a channel and can become a stream
All streams flow downslope in a watery path to lower elevationsHowever the path of a stream can vary considerably depending onthe slope of the land and the type of material through which thestream flows Some streams flow into lakes while others flow directlyinto the ocean Still others called tributaries flow into other streamsas shown in Figure 9-4 Each tributary increases the size of thestream it is joining and adds water to it A large stream is called ariver and all its tributaries make up a stream or river system Smallstreams are called brooks and creeks If there are any brooks orstreams near your home can you locate where they feed into otherstreams or lakes
Figure 9-3 The angle of a slope is one variable thatinfluences the movement ofsurface water on a slope
To learn more about rivers go to theNational GeographicExpedition on page 870
WATERSHEDS AND DIVIDESAll of the land area whose water drains into a stream system is calledthe systemrsquos watershed or drainage basin Watersheds can be rela-tively small or extremely large in area A divide is a high land areathat separates one watershed from another Each tributary in astream system has its own watershed and divides but they are all partof the larger stream system to which the tributary belongs Thewatershed of the Mississippi River shown in Figure 9-5 is the largestin North America
STREAM LOADAll the materials that the water in a stream carries is known as thestreamrsquos load The living components of water include microscopiclife-forms as well as larger plants and animals The nonliving com-ponents of surface water include sediments dissolved solids and dis-solved atmospheric gases such as oxygen There are three ways inwhich a stream carries its load
Solution Material is carried in solution after it becomes dissolvedin a streamrsquos water How much of a streamrsquos load is carried in solu-tion depends on the material through which the streamrsquos water haspassed When water runs through or over rocks containing soluble
Figure 9-5 The watershedof the Mississippi Riverincludes a large stream system How many majorrivers are part of theMississippi watershed
91 Sur face Water Movement 215
500 kmMississippiDelta0
Red River
White R
Cumberland
R
Tennes
see
R
Illin
ois R
Wab
as
hR
Arkansas River
Ohio Rive
r
Missouri
River
Mississippi R
Watershed of the Mississippi River
minerals it dissolves small amounts of the minerals and carries themaway in solution Water may readily dissolve calcium carbonate fromlimestone and marble for example Streams also commonly carrysoluble magnesium compounds Groundwater adds most of the dis-solved load to stream water while runoff adds only a very smallamount
The amount of dissolved material that water carries is oftenexpressed in parts per million or ppm as shown in Table 9-1 Forexample a measurement of 10 ppm means that there are 10 parts ofdissolved material for every 1 million parts of water The total con-centration of materials in solution in streams averages 115ndash120 ppmalthough some streams carry as little dissolved materials as 10 ppmValues greater than 10 000 ppm have been observed for streamsdraining desert basins Measuring the amount of material in solutionhelps scientists monitor water quality
Suspension All particles small enough to be held up by the tur-bulence of a streamrsquos moving water are carried in suspensionParticles such as silt clay and sand that are carried in suspensionare part of a streamrsquos suspended load The amount of material in sus-pension varies with the volume and velocity of the stream waterRapidly moving water can carry larger particles in suspension thanslowly moving water can As the velocity of water decreases the heav-ier particles settle to the bottom as you can see by doing theProblem-Solving Lab on the next page
216 CHAPTER 9 Sur face Water
Table 9-1 Concentrations of Some Materials Dissolved in River Water and Seawater
Materials Concentration (ppm)
Amazon Mississippi World AverageRiver River Average (est) Seawater
Silica (SiO2) 70 67 130 64
Calcium (Ca2+) 43 420 150 4000
Sodium (Na+) 18 250 63 10 5000
Potassium (K+) mdash 29 23 3800
Magnesium (Mg2+) 11 120 41 13500
Chloride (CIndash) 19 300 78 19 0000
Fluoride (Fndash) 02 02 mdash 13
Sulfate (SO42ndash) 30 560 110 27000
Bicarbonate (HCO3ndash) 190 1320 580 1420
Nitrate (NO3ndash) 01 24 10 05
Source J D Hem Study and Interpretation of the Chemical Characteristics of Natural Water US Geological Survey Water-Supply Paper 1473 1970 pp 11 12 and 50
Bed Load Sediments that are too large or heavy to be held up byturbulent water are transported by streams in another manner Astreamrsquos bed load consists of sand pebbles and cobbles that thestreamrsquos water can roll or push along the bed of the stream The fasterthe water moves the larger the particles it can carry both in suspen-sion and as part of its bed load As the particles move they rubscrape and grind against one another or against the solid rock of thestreambed in a process called abrasion the wearing away of solidEarth material This action contributes to the physical weathering ofthe streamrsquos bottom and sides and it provides an additional sourceof material to be eroded by the stream either in solution or as partof the suspended load
As gravity pulls stream water to lower elevations the streamrsquos loadmoves along with the water The moving water continuously tossesand tumbles the weathered material whose pieces become smoothand rounded over time as shown in Figure 9-6 Most pebbles alongthe bottoms and sides of streams are round and polished as a resultof this process
Bed load sediments not only wear away one another but they alsoabrade the surface of the streambed Potholes may form on the bot-toms of streams where pebbles have continued to swirl around in
91 Sur face Water Movement 217
Using Graphs
1000
100
10
01
001
Par
ticl
e d
iam
eter
(cm
)
0001
0000100004 cm
0006 cm
Silt
Sand
Pebbles
CobblesBoulders
Clay
02 cm
64 cm256 cm
000001100 200 300 400
Stream velocity (cms)
500 600 700 8000
Stream Velocity and Particle Size
Figure 9-6 The roundedshapes and smooth pebbleswere caused by the streamerosion of the Snake Riverin Grand Teton NationalPark Wyoming
Predict how sediments move in a stream The velocity of water affectsthe transport of different-sized particles
Analysis1 Study the graph at right2 At what velocity would flowing
water pick up a pebble3 Over what range of velocities would
flowing water carry a pebble
Thinking Critically4 Infer which of the following objects
would not fall into the same sizerange as a pebble a large chicken egga baseball a golf ball a table-tennisball a volleyball and a pea Howwould you test your conclusions
one area and have slowly worn holes intosolid rock For example potholes morethan 3 m deep have formed near LittleFalls New York in the Mohawk RiverValley Potholes can be found even instreambeds composed of very hardexposed bedrock The huge depressionsin the streambed of the Wisconsin Rivershown in Figure 9-7 were scoured out ofgranite Large streambed potholes dra-matically illustrate the powerful abrasiveaction caused by a streamrsquos bed load
STREAM VELOCITY AND CARRYING CAPACITYThe ability of a stream to transport material referred to as its carry-ing capacity depends on both the velocity and the amount of watermoving in the stream Study Figure 9-8 as you read The channelrsquosslope depth and width all affect the speed and direction in whichwater moves within it A streamrsquos water moves more quickly wherethere is less friction consequently smooth-sided channels with greatslope and depth allow water to move most rapidly The total volumeof moving water also affects a streamrsquos carrying capacity Dischargeis the measure of the volume of stream water that flows over a par-ticular location within a given period of time Discharge is com-monly expressed in cubic meters per second (m3s) The followingformula is used to calculate the discharge of a stream
discharge width depth velocity(m3s) (m) (m) (ms)
The largest river in North America the Mississippi has a hugeaverage discharge of 173 600 m3s However the Amazon River thelargest in the world has an incredible discharge ten times thatamount The discharge from the Amazon River over a 24-hourperiod would supply New York Cityrsquos water needs for nine years
218 CHAPTER 9 Sur face Water
Figure 9-7 The potholes in thisWisconsin River streambed werescoured out by the abrasive action ofthe streamrsquos bed load The river islocated at Grandfather Falls Wisconsin
As a streamrsquos discharge increases the streamrsquos carrying capacityincreases as well The increased discharge results in a stream withgreater carrying capacity as modeled in the GeoLab at the end of thechapter Both water velocity and volume increase during times ofheavy precipitation rapid melting of snow and flooding In addi-tion to increasing a streamrsquos carrying capacity these conditionsheighten a streamrsquos ability to erode the land over which it passes Asa result of an increase in erosional power a streambed can widenand deepen thereby increasing the stream slope and further addingto the streamrsquos carrying capacity As shown in Figure 9-9 the extra-ordinary power of water during such times can be especiallyhazardous for people who do not anticipate the dangersassociated with flooding
FLOODPLAINSThe amount of water being transported in a particularstream at any given time varies with weather conditionsSometimes more water pours into a stream than the banksof the stream channel can hold A flood occurs when waterspills over the sides of a streamrsquos banks onto the adjacentland The broad flat area that extends out from a streamrsquosbank and is covered by excess water during times of floodingis known as the streamrsquos floodplain Floodwater carriesalong with it a great amount of sediment eroded from Earthrsquossurface and the sides of the stream channel As floodwaterrecedes and its volume and speed decrease the water dropsits sediment load onto the streamrsquos floodplain
91 Sur face Water Movement 219
A
B
C
Figure 9-8 Describe thechanges in the downstreamdirection of the streamrsquoschannel as the water flowsfrom section A to section C
Figure 9-9 Several days ofheavy rains in Buenos AiresArgentina caused floodwaters to strand traffic inthe city
Figure 9-10 illustrates a floodplain after a river overflows its channel Floodplains develop highly fertile soils as more sediment isdeposited with each subsequent flood These fertile soils have histor-ically enticed farmers to use the land for crop production even at therisk of losing homes and crops to subsequent flooding
FLOODSFloods are a natural occurrence When a stream reaches its floodstage a flood can occur as shown in Figure 9-11 Flood stage is thelevel at which a stream overflows its banks and the crest of the streamis the maximum height Because it takes time for runoff to collect instreams the water continues to rise and may reach its crest days afterprecipitation ends The resulting flooding may occur over localizedsmall areas or across large regions The flooding of a small area isknown as an upstream flood Sudden rainstorms that drop largeamounts of rain within a short period of time cause upstream floods
Figure 9-11 DavenportIowa was just one of manyareas that was flooded bythe Mississippi River in 1993
220 CHAPTER 9 Sur face Water
Floodplaindeposits
Rock
River channel
Floodplain
Figure 9-10 Floodplaindeposits contain fertile soils
Topic FloodsTo find out more aboutfloods and flood preven-tion visit the Earth ScienceWeb Site at earthgeucom
Activity Write a briefreport to compare andcontrast the flooding ofthe Yellow River in Chinathe Nile River in Egypt and the Mississippi River in the United States
as do dam failures Although they are localized upstream floods cando a great deal of damage within a very short period of time
Heavy accumulations of excess water from large regional drainagesystems result in downstream floods Such floods occur during orafter long-lasting intense storms or spring thaws of large snowpacksThe tremendous volumes of water involved in a downstream floodcan result in extensive damage For example the devastating floodsin 1993 along the Mississippi River which frequently causes down-stream flooding left landscape scars that are still visible today
FLOOD MONITORING AND WARNING SYSTEMSIn an attempt to provide warnings for people at risk govern-
ment agencies monitor potential flood conditions The NationalWeather Service monitors changing weather conditions Earth-orbiting weather satellites photograph Earth and collect and trans-mit information about weather conditions storms and streams Inaddition the US Geological Survey (USGS) has established gaug-ing stations as shown in Figure 9-12 on approximately 4400streams in the United States The gauging stations provide a contin-uous record of the water level in each stream Technological advanceshave made it possible for anyone with Internet access to obtain real-time data on streams through government-sponsored Web sites
In areas that are prone to severe flooding warning systems arethe first step in implementing emergency management plans Floodwarnings and emergency plans often allow people to safely evacuatean area in advance of a flood
91 Sur face Water Movement 221
1 Describe ways in which moving water cancarve a landscape
2 Explain the three ways in which a streamcarries its load
3 What is the relationship between the carrying capacity of a stream and its discharge and velocity
4 Explain why little water from runoff seepsinto the ground in areas of steep slopes
5 Discuss how a floodplain forms and whypeople live on floodplains
6 Thinking Critically Under what conditionsmight a streamrsquos volume increase andunder what conditions might it decreaseHow would the size of the sediment par-ticles in the streamrsquos load differ in thetwo situations
SKILL REVIEW
7 Making Tables Design a data table thatcompares how silt clay sand and largepebbles settle to the bottom of a streamas the velocity of water decreases Formore help refer to the Skill Handbook
Figure 9-12 This USGSstream gauging station islocated in the northwestsection of Washington State
EnvironmentalConnection
earthgeucomself_check_quiz
As a stream develops it changes in shape width and size as well asthe landscapes over which it flows Stream flow is part of a dynamicsystem that is greatly influenced by the varying environmental con-ditions of the streamrsquos surroundings
MOVING WATER CARVES A PATHThe first and foremost condition necessary for stream formation isan adequate supply of water Precipitation provides the water for thebeginnings of stream formation In areas where precipitation fallsinfrequently stream development and flow are also infrequent Forexample in some desert areas where years pass between rainfalls thestreams that form are short-lived However most parts of the tem-perate and tropical regions on Earth experience precipitation on aregular basis
The region where water first accumulates to supply a stream iscalled the headwaters It is common for a streamrsquos headwaters to behigh in the mountains Falling precipitation accumulates in smallgullies at these higher elevations and forms briskly moving streamsAs surface water first begins its flow its path may not be well definedIn time however the moving water carves a narrow pathway into thesediment or rock called a stream channel The channel widens anddeepens as more and more water accumulates and cuts into Earthrsquossurface As shown in Figure 9-13 the moving water is held within theconfines of the stream channel by the stream banks the groundbordering the stream on each side If you have ever fished in astream you might have sat on a stream bank to do so
9292 Stream Development
Figure 9-13 The riverbanks confine the water ofthe San Pedro River in the San Pedro Riparian NationalConservation Area inArizona
OBJECTIVES
bull Describe some of thephysical features ofstream development
bull Explain the process ofrejuvenation in streamdevelopment
VOCABULARY
stream channelstream bankmeanderdeltarejuvenation
222 CHAPTER 9 Sur face Water
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92 Stream Development 223
Figure 9-14 The headwarderosion of stream B cutsinto stream A and drawsaway its waters into onestream
Stream A Stream B Stream B
A B
The process by which small streams erode away the rock or soil atthe head of a stream is known as headward erosion Headward ero-sion involves lengthening the stream Streams at this point in theirdevelopment are relatively small and narrow These streams moveswiftly over the rough terrain and they often form waterfalls andrapids as they flow over steep inclines
Sometimes a stream erodes its way through the high area sepa-rating two drainage basins joins another stream and then drawsaway its water This process is called stream capture or stream piracyAs shown in Figure 9-14 the lower portion of the captured streamloses its water source while the invading stream gains an additionalsource of water
FORMATION OF STREAM VALLEYSAs a stream actively erodes its path through the sediment or rocka V-shaped channel develops V-shaped channels have steep sidesand sometimes form canyons or gorges The Grand Canyon is per-haps the best-known example of a V-shaped valley carved by a stream the Colorado River Ausable Chasm in New York Stateis another impressive but verynarrow deep gorge carved by astream Figure 9-15 shows theclassic V-shaped valley created bythe Yellowstone River
A stream continues to erodeuntil it reaches its base level theelevation at which it enters anotherstream or body of water The lowestbase level possible for any stream issea level the point at which thestream enters the ocean As astream continues to erode its chan-nel toward its base level erosionwill continue along the sides of the
Figure 9-15 A V-shapedvalley was formed on theLower Falls of the Yellow-stone River in Wyoming
V-shaped channel As shown in Figure 9-16 intime a V-shaped valley will be eroded into a broader valley that has gentle slopes
MEANDERING STREAMSAs stream channels develop into broader valleysthe volume of water and sediment that they are ableto carry increases In addition a streamrsquos slope orgradient decreases as it nears its base level and as aresult the channel gets wider The decrease in gradi-ent causes water to build up within the streamchannel Sometimes the water begins to erode thesides of the channel in such a way that the overallpath of the stream starts to bend or wind As shownin Figure 9-17 a bend or curve in a stream channelcaused by moving water is called a meander
Water in the straight parts of a stream flows at different velocitiesdepending on the location of the water in the channel In a straightlength of a stream water in the center of the channel is flowing at themaximum velocity Water along the bottom and sides of the channelflows more slowly because it experiences friction as it moves againstthe land In contrast the water moving along the outside of a mean-der curve experiences the greatest rate of flow within the meanderThe water that flows along this outside part of the curve continues toerode away the sides of the streambed thus making the meanderlarger Along the inside of the meander the water moves more slowlyand deposition is dominant These differences in the rate of waterflow within meanders cause the meanders to become more accentu-ated over time Figure 9-18 illustrates the processes of erosion and
Figure 9-16 The DelawareWater Gap in Pennsylvaniahas been eroded into a wider broader valley
224 CHAPTER 9 Sur face Water
Figure 9-17 Several mean-ders are formed in theTundra River in YukonCanada
deposition along a meander and Figure 9-19 shows the points ofmaximum water velocity within a meander and within a straightpart of a stream Stream meanders continue to develop and becomelarger and wider over time After some degree of winding howeverit is common for a stream to cut off a meander and once again flowalong a straighter path The stream then deposits material along theadjoining meander and eventually blocks off its water supply asshown in Figure 9-20 The blocked-off meander becomes an oxbowlake which eventually dries up
As a stream approaches a larger body of water or its ultimate endpoint the ocean the streambedrsquos gradient flattens out and its chan-nel becomes very wide The area of the stream that leads into theocean or another large body of water is called the mouth Themouth of the Mississippi River is extremely wide
Maximumvelocity
Maximumvelocity
Depositionof point bar
Erosionof cutbank
92 Stream Development 225
Figure 9-19 The maximumvelocity of water in a stream will change itsdirection as the streammeanders
Figure 9-20 The Devilrsquos Elbow is an oxbow lake along the CongareeRiver in Congaree Swamp National Monument in South Carolina
Figure 9-18 The high velocity ofwater in a meandering stream erodesone side of the streamrsquos bankDeposition occurs when the velocity of the water in a meandering streamslows down
DEPOSITION OF SEDIMENTStreams that lose velocity also lose theirability to carry sediment A streamrsquos veloc-ity lessens and its sediment load dropswhen its gradient abruptly decreases Indry regions where mountain streams com-monly flow down narrow valleys ontobroad flat valley floors a streamrsquos gradientmay suddenly decrease causing the streamto drop its sediment as a fan-shapeddeposit called an alluvial fan Alluvial fans
are sloping depositional features formed at the bases of slopes andcomposed mostly of sand and gravel They are found worldwide butare most common in dry mountainous regions such as Death ValleyCalifornia shown in Figure 9-21
Streams also lose velocity and the ability to carry sediment whenthey join larger bodies of quiet water The triangular deposit thatforms where a stream enters a large body of water is called a deltanamed for the triangle-shaped Greek letter delta () Delta depositsusually consist of silt and clay particles As a delta develops sedi-ments build up and slow the stream water sometimes even blockingits movement Smaller distributary streams then form to carry thestream water through the developing delta The Mississippi RiverDelta shown in Figure 9-22 began forming millions of years agoToday the city of New Orleans Louisiana is located on that delta anarea that was under seawater only 5000 years ago
Figure 9-22 This photoshows a portion of theMississippi River Delta Thedelta consists of silt sandand clay deposits
Figure 9-21 An alluvial fanwas formed at MormonPoint beneath BlackMountain in Death ValleyNational Park in California
Using Numbers Ifa streamrsquos averagevelocity is 5 ms itswidth is 30 m andits average depth is10 m what is theamount of thestreamrsquos discharge
226 CHAPTER 9 Sur face Water
92 Stream Development 227
1 Describe the formation of an oxbow lake
2 Compare the rate of water flow on theinside of a meander curve with that onthe outside of the curve
3 Describe four changes that a streamundergoes as it works its way toward theocean
4 What are the differences between analluvial fan and a delta
5 Thinking Critically How does the type ofbedrock over which a stream flows affect
the time it takes for the stream to reachits base level
SKILL REVIEW
6 Making Graphs Make a line graph thatplots the direction of change in a hypo-thetical streamrsquos rate of flow at thestreamrsquos headwaters at midstream andat its mouth For more help refer to theSkill Handbook
Figure 9-23 A steep-sidedcanyon occurs along a mean-der on the Escalante River in Glen Canyon NationalRecreation Area in Utah
REJUVENATIONDuring the process of stream formation downcutting or the wear-ing away of the streambed is a major erosional process until thestream reaches its base level when downcutting stops However ifthe land over which the stream is flowing uplifts or if the base levellowers the stream undergoes rejuvenation Rejuvenation means ldquotomake young againrdquo During rejuvenation the stream activelyresumes the process of downcutting toward its base level Thiscauses an increase in the streamrsquos rate of flow and the streamrsquos chan-nel once again becomes V-shaped If rejuvenation occurs in an areawhere there are meanders deep sided canyons are formed Thiseffect is evident in Utahrsquos Escalante River shown in Figure 9-23
earthgeucomself_check_quiz
9393 Lakes and Freshwater Wetlands
You have probably swum in fished in or gazed at the beauty of a lakeBut did you ever think about how lakes form A lake is a depressionin the surface materials of a landscape that collects and holds waterAs shown in the MiniLab on the following page surface materialsdetermine where a lake can form Lakes sometimes accumulate waterfrom streams and runoff that flow into them Lakes also receive waterfrom local precipitation springs and other sources Most lakes haveoutlets from which water flows to rivers and to the ocean Peoplesometimes build small lakes called ponds to serve as sources of waterfor livestock to maintain fish supplies to attract wildlife or for theirnatural beauty Reservoirs are lakes made for the primary purpose ofstoring water for a communityrsquos use
ORIGINS OF LAKESNatural lakes form in different ways in surface depressions and in lowareas As you have learned oxbow lakes form when streams cut offmeanders and leave isolated channels of water Lakes can also formwhen stream flow becomes blocked by sediment from landslidesOther lakes such as Utahrsquos Great Salt Lake shown in Figure 9-24 areremnants of prehistoric lakes that have receded to lower-lying areas
Still other lakes have glacial origins as you learned in Chapter 8The basins of these lakes formed as glaciers gouged out the land dur-ing the ice ages Most of the lakes in Europe and North America are inrecently glaciated areas Glacial moraines originally dammed some ofthese depressions and restricted the outward flow of water The lakesthat formed as a result are known as moraine-dammed lakes shown inFigure 9-25 In another process cirques carved high in the mountainsby valley glaciers filled with water to form cirque lakes Other lakes
OBJECTIVES
bull Explain the formation of freshwater lakes andwetlands
bull Describe the process ofeutrophication
bull Recognize the effects ofhuman activity on lakedevelopment
VOCABULARY
lakeeutrophication wetland
Figure 9-24 The Great SaltLake in northern Utah has a much greater salinity thanthe oceans
228 CHAPTER 9 Sur face Water
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eng - iTunes_CDDB_TrackNumber3
formed as blocks of ice left on the outwashplain ahead of melting glaciers eventuallymelted and left depressions called kettlesWhen these depressions filled with waterthey formed kettle lakes
Many lakes are found in areas wherelimestone is the dominant bedrock Asgroundwater percolating through limestonebedrock slowly dissolves calcium carbonateit leaves holes in the limestone and formscaverns In some places the ceilings of thesecaverns become so thin and weak that theycollapse which leaves depressions that mayfill with water in time
LAKES UNDERGO CHANGEWater from precipitation runoff andunderground sources can maintain a lakersquoswater supply Some lakes contain water onlyduring times of heavy rain or excessiverunoff from spring thaws A depression thatreceives more water than it loses to evapora-tion or use by humans will exist as a lake fora long period of time However lakes aretemporary water-holding areas over hun-dreds of thousands of years lakes usually fillin with sediment and become part of a newlandscape
Eutrophication Through the process ofphotosynthesis plants add oxygen and wasteproducts to lake water Animals that live in alake use the waterrsquos oxygen and add wasteproducts to the water as they conduct theirlife processes The decay process that occursafter plants and animals die also uses up dis-solved oxygen supplies The amount of dis-solved oxygen helps determine the quality oflake water and its ability to support life
93 Lakes and Freshwater Wetlands 229
Surface materials determinewhere a lake can form
Model how different Earth materials mayallow lakes to form Lakes form whendepressions or low areas fill with water
Procedure CAUTION Always wear safety goggles and an apron in the lab
1 Use three clear plastic shoe boxes Half fill each one with Earth materials claysand and gravel
2 Slightly compress the material in eachshoe box Then make a shallow depressionin each surface
3 Slowly pour 500 mL of water into each ofthe depressions
Analyze and Conclude1 Describe what happened to the 500 mL of
water that was added to each shoe box2 How is this activity similar to what actually
happens on Earthrsquos surface when a lakeforms
3 What can you infer about the Earth mate-rials in which lakes most commonly form
Figure 9-25 The moraine-dammed lakesin Banff National Park in Alberta Canadawere formed from glacial activity
Figure 9-27 This bog inNorway has acid-rich soilthat supports a variety oforganisms
The process by which lakes become rich in nutrients from thesurrounding watershed thereby resulting in a change in the kinds oforganisms in the lake is called eutrophication Figure 9-26 showsa pond undergoing eutrophication Although eutrophication is anatural process it can be sped up with the addition of nutrientssuch as fertilizers that contain nitrogen and phosphorus When thishappens the animal and plant communities in the lake can changerapidly Algae growing in the water may suddenly multiply veryquickly The excessive algae growth in a lake or pond appears asgreen scum Other organisms that eat the algae can multiply innumbers as well The resulting overpopulation and decay of a largenumber of plants and animals depletes the waterrsquos oxygen supplyFish and other sensitive organisms may die as a result of the lack ofoxygen in the water
Other major sources of nutrients that concentrate in lakes areanimal wastes and phosphate detergents Lakes can also suffer fromthe release of toxins from nearby industries and untreated sewage asshown in the Science amp the Environment feature at the end ofthe chapter
Freshwater Wetlands A wetland is a land area that is coveredwith water for a large part of the year Wetlands include environ-ments commonly known as bogs marshes and swamps They havecertain soil types and support specific plant species
A bog shown in Figure 9-27 is an interesting wetland thatdeserves a closer look Bogs are not stream-fed but instead receivetheir water from precipitation The waterlogged soil tends to be richin Sphagnum also called peat moss The breakdown of peat mossproduces acids thereby contributing to the soilrsquos acidity The water-logged acidic soil supports unusual plant species including insect-eating pitcher plants sundew and Venusrsquo flytrap
Figure 9-26 The aquaticspecies of this pond willchange over the yearsbecause of the effects of eutrophication
230 CHAPTER 9 Sur face Water
93 Lakes and Freshwater Wetlands 231
1 Describe the process of eutrophication
2 What human activities affect the processof eutrophication
3 What conditions are necessary for the for-mation of a natural lake
4 Thinking Critically Describe a situation inwhich protection of wetlands may conflictwith human plans for land use
SKILL REVIEW
5 Making Tables Design a data table thatcompares the various types of lakes theirorigins and their characteristics For morehelp refer to the Skill Handbook
Freshwater marshes frequently form along themouths of streams and in areas with extensive deltasThe constant supply of water allows for the lushgrowth of marsh grasses The shallow roots of thegrasses anchor deposits of silt and mud on the deltathereby slowing the water and expanding the marsharea Grasses reeds sedges and rushes along withabundant wildlife are common in marsh areas
Swamps are low-lying areas often located nearstreams Swamps may develop from marshes that havefilled in sufficiently to support the growth of shrubsand trees As these larger plants grow and begin toshade the marsh plants the marsh plants die Swampsthat existed 250 million years ago developed into present-day coal reserves that are common inPennsylvania and many other locations in the UnitedStates and around the world
Wetlands play a valuable role in improving water quality Theyserve as a filtering system that traps pollutants sediments and path-ogenic bacteria contained in water sources Wetlands also providevital habitats for migratory waterbirds and homes for an abundanceof other wildlife as shown in Figure 9-28 Unfortunately peoplersquosdesire for land often conflicts with the need to preserve wetlands Inthe past it was common for wetland areas to be filled in to createmore land on which to build Government data reveal that from thelate 1700s to the mid-1980s the continental United States lost 50percent of its wetlands By 1985 it was estimated that 50 percent ofthe wetlands in Europe were drained Now however the preservationof wetland areas has become a global concern
Figure 9-28 The wetlandsin Bosque del ApacheNational Wildlife Refuge inNew Mexico are home tomigrating snow geese
earthgeucomself_check_quiz
Modeling StreamVelocity and Slope
Water in streams flows from areas of higher elevation toareas of lower elevation The rate of stream flow varies
from one stream to another and also in different areas of thesame stream
ProblemDetermine how slope may affectstream-flow velocity
Materials1-m length of vinyl gutter pipering stand and clampwater source with long hoseprotractor with plumb bobsink or container to catch waterstopwatchgrease pencilmeterstickpaperhole punch
ObjectivesIn this GeoLab you willbull Measure the time it takes for water to
flow down a channel at differentslopes and depths
bull Organize your data in a tablebull Plot the data on a graph to show how
stream velocity is directly propor-tional to the stream channelrsquos slopeand depth
bull Describe the relationship betweenslope and rate of stream flow
Safety PrecautionsAlways wear safety goggles in the lab
Preparation
232 CHAPTER 9 Sur face Water
GeoLab 233
1 Why is it important to keep thewater flow constant in this activity
2 Which variables had to be con-trolled to avoid errors in your data
3 Using your graph predict the veloc-ity of water flow for a 35deg slope
1 What is the relationship between therate of water flow and the angle ofthe slope
2 Describe one reason why a streamrsquosslope might change
3 Where would you expect to findstreams with the highest water-flow velocity
Analyze
Conclude amp Apply
1 Use the hole punch to make 10 to15 paper circles to be used as float-ing markers
2 Use the illustration below as a guideto set up the protractor with theplumb bob
3 Use the grease pencil to mark twolines across the inside of the gutterpipe at a distance of 40 cm apart
4 Use the ring stand and clamp tohold the gutter pipe at an angle of10deg Place the end of the pipe in asink or basin to collect the dis-charged flow of water
5 Attach a long hose to a water faucetin the sink
6 Keep the hose in the sink until youare ready to use it Then turn on thewater and adjust the flow until thewater is moving quickly enough toprovide a steady flow
7 Bend the hose temporarily to blockthe water flow until the hose is posi-tioned at least 5 cm above the topline marked on the pipe
8 Keep the water moving at the samerate of flow for all slope anglesbeing investigated
9 Drop a floating marker approxi-mately 4 cm above the top line on the pipe and into the flowing waterMeasure the time it takes for thefloating marker to move from thetop line to the bottom line Recordthe time in your science journal
10 Repeat step 9 two more times11 Repeat steps 9 and 10 but change the
slope to 20deg then 30deg and then 40deg12 Make a line graph of the average
stream-flow velocity
Procedure
String
Protractor
Weight
90deg
234 CHAPTER 9 Sur face Water
A Natural ParadiseKnown as the ldquoJewel of Siberiardquo Lake Baikal
is the oldest and largest freshwater lake onEarth Estimated to be 25 million years old LakeBaikal contains 20 of Earthrsquos unfrozen fresh-water that is one-fifth of the worldrsquos fresh sur-face water The lake contains approximately 80 of the former Soviet Unionrsquos freshwater supply and covers approximately 31 500 km2It reaches a maximum depth of approximately1637 m making it the deepest lake in the world
Fed by 330 tributaries and surrounded byforests and mountain ranges it is home to awide variety of plant and animal species Thearea is home to everything from microscopicorganisms to large mammals including elkmoose deer and the brown bear
One animal found only in this area is theNerpa or Baikal seal The Nerpa is the onlyknown species of freshwater seal It is believedthat the seal may have migrated to the area insearch of food while the lake was being formedthousands of years ago
Threatened Pollution has begun to slowly take its toll on
animal and plant species in the region Studieshave reported that the fish population is dyingout and thousands of the Baikal seals have diedHigh toxin levels from a nearby pulp and paperfactory may be the cause According to other
The Jewel of SiberiaPollution is threatening the ecosystems of Lake Baikal the oldestlargest and deepest freshwater lake on Earth What is causing theproblems Are there any solutions for saving the lake
Form small groups to research and discusspossible solutions to the problems threat-ening the ecosystems of Lake Baikal Howcan the lake and its inhabitants be pre-served without having to totally removeindustry from the area Visit the EarthScience Web Site at earthgeucom to learnmore about the struggle to save LakeBaikal and its many inhabitants
Activity
studies DDT and other pesticides have enteredthe waters via aerial spraying and have beenfound in the lakersquos sediment
Attempts to restrict the release of toxins intothe freshwater lake have failed due to concernover the loss of industry and jobs For exampleif a lakeside pulp and paper factory were forcedto close many people would be left unemployed
Many organizations have banded together inRussia to attempt to preserve the Lake Baikalarea There is even cooperation between groupsin the United States and Russia who have beenworking together to come up with solutions to theproblems facing the industry and the environ-ment Their activities range from efforts to savethe Baikal seal to promoting tourism as a moreattractive form of economic stability in the area
Summary
Vocabularybed load (p 217)discharge (p 218)divide (p 215)flood (p 219)floodplain (p 219)runoff (p 212)solution (p 215)suspension (p 216)watershed (p 215)
Vocabularydelta (p 226)meander (p 224)rejuvenation (p 227)stream bank (p 222)stream channel
(p 222)
Vocabularyeutrophication
(p 230)lake (p 228)wetland (p 230)
Main Ideasbull Water on Earth may follow a variety of pathways as it is recycled
through the processes of evaporation and condensationbull Infiltration of water into the ground depends on the number of
open pores or spaces in Earth materials and on the presence ofunsaturated pores in the ground
bull All the land area that drains into a stream system is the systemrsquoswatershed or drainage basin Elevated land areas called dividesseparate one watershed from another
bull A streamrsquos load is all the material the stream carries includingmaterial in solution in suspension and as bed load
bull A floodplain is a broad flat area that extends out from a streamrsquosbank during times of flooding
bull Flooding occurs in small localized areas as upstream floods or inlarge downstream floods Damage from flooding can be devastating
Main Ideasbull Water from precipitation gathers in gullies at a streamrsquos source
area or headwaters The streamrsquos water flows in channels con-fined by the streamrsquos banks
bull Alluvial fans and deltas form when stream velocity decreasesand sediment is deposited Alluvial fans are fan shaped andthey form where water flows down steep slopes onto flat plainsDeltas are triangular and they form when streams enter largerelatively quiet bodies of water
Main Ideasbull Lakes form in a variety of ways when depressions on land fill
with water Lakes may be natural or human-madebull Eutrophication is a natural nutrient enrichment process that may
be sped up when nutrients from fertilizers detergents orsewage are added
bull Wetlands are low-lying areas that are periodically saturated withwater and support specific plant species Wetlands include bogsmarshes and swamps
SECTION 91
Surface WaterMovement
SECTION 92
StreamDevelopment
SECTION 93
Lakes andFreshwaterWetlands
Study Guide 235earthgeucomvocabulary_puzzlemaker
236 CHAPTER 9 Sur face Water
1 Which factor least affects the rate of runoffa slope c volume of runoffb vegetation d nearness to water
2 What areas are most likely to contain fertile soilsa watersheds c floodplainsb dried-up streambeds d mountainous areas
3 Which substance is most likely to be carried by a stream in solutiona quartz c calciteb sand d silt
4 What material plays a major role in the eutro-phication of lakesa iron c ozoneb phosphate d salt
5 During the process of eutrophication what happens to the oxygen present in a lakea It increases c It stays the sameb It decreases d It evaporates
6 What kind of streams form V-shaped valleysa streams that are first formingb streams that carry much sedimentc streams that move slowlyd streams that have meanders
7 Where does water move most rapidly in thestraight length of a streama along the bottom c near the surfaceb along the sides d in the center
8 If a stream is carrying sand silt clay and smallpebbles which one is deposited last as thestream begins to slow downa clay c sandb silt d small pebbles
Understanding Main Ideas 9 Where do alluvial fans forma on the outside of meandersb where streams enter the oceanc near lakesd along the bases of mountains
10 In what ways are a delta and an alluvial fan simi-lar and in what ways are they different
11 Why is it important to preserve wetlands
12 What means do governments use to try to prevent the loss of life and property in flood-prone areas
Use the following aerial view of a stream to answerquestions 13ndash15
Applying Main Ideas
BEAT THE CLOCKmdashAND THEN GO BACKAs you take a practice test pace yourself to fin-ish each section just a few minutes early so youcan go back and check over your work You willsometimes find a mistake or two
Test-Taking Tip
AB
C
D
E
earthgeucomchapter_test
Assessment 237
1 Which condition would create the mostrunoffa land covered with vegetationb plants in densely packed soilc light precipitationd soil with a high percentage of sand
2 In which part of a meander does the watertravel the fastesta the water that moves along the inside
curve of the meanderb the water that moves along the
bottom of the meanderc the water that moves along the
outside curve of a meanderd all water flows at the same rate
3 Which of the following is NOT a value ofwetlandsa feeding lakes and deltas with nutrient-
and oxygen-rich water b filtering water by trapping pollutants
sediments and pathogenic bacteriac providing habitats for migratory birds
and other wildlifed preserving fossils due to the anaerobic
and acidic conditions
4 As the velocity of a stream decreases whichtransported particle size would settle to thestreamrsquos bottom firsta clay c pebbleb silt d sand
5 Which condition helps determine the qualityof lake watera the amount of nitrogenb the amount of dissolved calcium carbonatec the amount of potassiumd the amount of dissolved oxygen
13 At which location in the aerial view does thestreamrsquos water have the greatest velocity
14 At which location is deposition most activelyoccurring
15 At which location is erosion most actively occurring
16 What is the discharge of a stream that has a velocity of 300 ms and is 25-m wide and 3-m deep
17 Why is a lake with a clay bottom able to holdmore water than a lake with a sand bottom
18 One morning there was a torrential thunder-storm In the afternoon the skies cleared and agardener decided to plant a tree After digging inthe ground only a short distance down the gar-dener found that the ground was very dry Howcould the ground be dry despite the heavy rainsearlier in the day
19 If floodplains are such hazardous areas to live inwhy have so many people settled in these poten-tial flood zones
20 Use the following terms to construct a conceptmap to organize the major ideas in Section 91For more help refer to the Skill Handbook
Thinking Critically
Standardized Test Practice
solution silt parts permillion
suspension bed load clay
cobbles dissolvedminerals pebbles
earthgeucomstandardized_test
- Earth Science Geology the Environment and the Universe
-
- Contents in Brief
- Table of Contents
-
- Unit 1 Earth Science
-
- Chapter 1 The Nature of Science
-
- Discovery Lab Scientific Communication
- Section 11 Earth Science
-
- Earth Science Online
-
- Section 12 Methods of Scientists
-
- MiniLab How do soil and water absorb and release heat
- Earth Science Online
- Using Math Measuring
-
- Section 13 Communicating in Science
-
- Problem-Solving Lab Making and Using Graphs
-
- GeoLab Measuring in SI
- Science and Technology Willo Sue and Technology Too
- Chapter 1 Study Guide
- Chapter 1 Assessment
-
- Chapter 2 Mapping Our World
-
- Discovery Lab Make and Use a Map
- Section 21 Latitude and Longitude
-
- Using Math Using Numbers
- MiniLab How can you locate places on Earth
-
- Section 22 Types of Maps
-
- Problem-Solving Lab Analyze changes in elevation
-
- Section 23 Remote Sensing
- Mapping GeoLab Using a Topographic Map
- Science and Math Thriving in the Arctic
- Chapter 2 Study Guide
- Chapter 2 Assessment
-
- Unit 1 GeoDigest
- Unit 1 Assessment
-
- Unit 2 Composition of Earth
-
- Chapter 3 Matter and Atomic Structure
-
- Discovery Lab Fortified Cereals
- Section 31 What are elements
-
- Earth Science Online
- MiniLab Identifying Elements
- Using Math Using Numbers
-
- Section 32 How Atoms Combine
-
- Problem-Solving Lab Forming compounds
-
- Section 33 States of Matter
- GeoLab Salt Precipitation
- Science and Technology Extreme Magnification
- Chapter 3 Study Guide
- Chapter 3 Assessment
-
- Chapter 4 Minerals
-
- Discovery Lab Observing Mineral Shapes
- Section 41 What is a mineral
-
- MiniLab How can crystal systems be modeled
- Using Math Using Numbers
-
- Section 42 Identifying Minerals
-
- Earth Science Online
- Problem-Solving Lab Complete a mineral identification table
-
- Design Your Own GeoLab Making a Field Guide to Minerals
- Science and Math The Price of Diamonds
- Chapter 4 Study Guide
- Chapter 4 Assessment
-
- Chapter 5 Igneous Rocks
-
- Discovery Lab Identifying Minerals
- Section 51 What are igneous rocks
-
- Earth Science Online
-
- Section 52 Classifying Igneous Rocks
-
- MiniLab How do igneous rocks differ
- Problem-Solving Lab Estimate mineral composition
- Using Math Using Numbers
-
- GeoLab Modeling Crystal Formation
- Science and Technology Cutting-Edge Surgery
- Chapter 5 Study Guide
- Chapter 5 Assessment
-
- Chapter 6 Sedimentary and Metamorphic Rocks
-
- Discovery Lab Model Sediment Layering
- Section 61 Formation of Sedimentary Rocks
-
- MiniLab What happened here
-
- Section 62 Types of Sedimentary Rocks
-
- Using Math Using Percentages
- Earth Science Online
-
- Section 63 Metamorphic Rocks
-
- Problem-Solving Lab Determine which metamorphic minerals will form
-
- GeoLab Interpreting Changes in Rocks
- Science in the News Good NewsmdashCrayons Safe
- Chapter 6 Study Guide
- Chapter 6 Assessment
-
- Unit 2 GeoDigest
- Unit 2 Assessment
-
- Unit 3 Surface Processes on Earth
-
- Chapter 7 Weathering Erosion and Soil
-
- Discovery Lab Model Interfaces
- Section 71 Weathering
-
- Using Math Using Numbers
- Earth Science Online
-
- Section 72 Erosion and Deposition
-
- MiniLab How do rocks weather
-
- Section 73 Formation of Soil
-
- Problem-Solving Lab Classify soils by texture
-
- GeoLab Effects of Weathering
- Science and the Environment Shifting Sands
- Chapter 7 Study Guide
- Chapter 7 Assessment
-
- Chapter 8 Mass Movements Wind and Glaciers
-
- Discovery Lab Model Sand-Slope Activity
- Section 81 Mass Movements at Earths Surface
- Section 82 Wind
-
- MiniLab Where does wind erosion occur
- Earth Science Online
-
- Section 83 Glaciers
-
- Problem-Solving Lab Observe how ice cores record history
-
- Mapping GeoLab Mapping a Landslide
- Science and Math Rates of Glacial Movement
- Chapter 8 Study Guide
- Chapter 8 Assessment
-
- Chapter 9 Surface Water
-
- Discovery Lab Modeling Water Movement
- Section 91 Surface Water Movement
-
- Problem-Solving Lab Predict how sediments move in a stream
- Earth Science Online
-
- Section 92 Stream Development
-
- Using Math Using Numbers
-
- Section 93 Lakes and Freshwater Wetlands
-
- MiniLab Surface materials determine where a lake can form
-
- GeoLab Modeling Stream Velocity and Slope
- Science and the Environment The Jewel of Siberia
- Chapter 9 Study Guide
- Chapter 9 Assessment
-
- Chapter 10 Groundwater
-
- Discovery Lab Model Underground Water Storage
- Section 101 Movement and Storage of Groundwater
- Section 102 Groundwater Erosion and Deposition
-
- Using Math Using Numbers
-
- Section 103 Groundwater Systems
-
- Problem-Solving Lab Make inferences about the water levels of an artesian aquifer
- MiniLab How does an artesian well work
- Earth Science Online
-
- Mapping GeoLab Mapping Pollution
- Science and the Environment The High Plains Aquifer
- Chapter 10 Study Guide
- Chapter 10 Assessment
-
- Unit 3 GeoDigest
- Unit 3 Assessment
-
- Unit 4 The Atmosphere and the Oceans
-
- Chapter 11 Atmosphere
-
- Discovery Lab Dew Formation
- Section 111 Atmospheric Basics
- Section 112 State of the Atmosphere
-
- Using Math Using Numbers
- Problem-Solving Lab Determine relative humidity
-
- Section 113 Moisture in the Atmosphere
-
- Earth Science Online
- MiniLab What affects the formation of clouds and precipitation
-
- GeoLab Interpreting Pressure-Temperature Relationships
- Science in the News The Montreal Protocol and the Ozone Layer
- Chapter 11 Study Guide
- Chapter 11 Assessment
-
- Chapter 12 Meteorology
-
- Discovery Lab Model a Cold Air Mass
- Section 121 The Causes of Weather
-
- MiniLab How does the angle of the Suns rays differ
-
- Section 122 Weather Systems
-
- Earth Science Online
- Using Math Using Numbers
-
- Section 123 Gathering Weather Data
- Section 124 Weather Analysis
-
- Problem-Solving Lab Create and analyze isobars on a weather map
-
- Mapping GeoLab Interpreting a Weather Map
- Science and Technology Tracking Atmospheric Change
- Chapter 12 Study Guide
- Chapter 12 Assessment
-
- Chapter 13 The Nature of Storms
-
- Discovery Lab Model Thunder
- Section 131 Thunderstorms
- Section 132 Severe Weather
-
- Earth Science Online
-
- Section 133 Tropical Storms
-
- Using Math Using Numbers
-
- Section 134 Recurring Weather
-
- MiniLab How can mild rains cause floods
- Problem-Solving Lab Charting a heat wave
-
- Internet GeoLab Tracking a Hurricane
- Science and Technology Taming Lightning
- Chapter 13 Study Guide
- Chapter 13 Assessment
-
- Chapter 14 Climate
-
- Discovery Lab Model Cloud Cover
- Section 141 What is climate
-
- Problem-Solving Lab Infer climatic conditions from normals
- Earth Science Online
-
- Section 142 Climate Classification
-
- Using Math Estimating
-
- Section 143 Climatic Changes
- Section 144 The Human Factor
-
- MiniLab How does the atmosphere affect the transfer of energy
-