2-1 THE ~COO.t:UN Why Rocks Crack Physical and...
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2-1 THE ~COO.t: UN ~UlL Why Rocks Crack It would be nice to age without changes occurring in our appearance. Unfortunately, human flesh deteriorates over time, and wewitness this deteriora- tion as alterations in our appearance. Changes in appearance can be seen in non- living things as well as living things. The earth has changed in its appearance over the passage of time. Like the flesh of the human body, the rocks that compose the earth are worn down and deteriorate with age. Many factors contribute to the breakdown of the rocks of the earth. The process of breaking down the rocks that compose the earth is called weathering. Weathering can be chemical or physical. Physical and Chemical Weathering Physical weathering changes the size of a rock but does not alter the composition of the rock. Temperature changes can cause physical weathering to occur. Rocks expand in the summer and contract in the winter. If you are unclear on the terms expansion and contraction, think about how tight your rings feel in the summer and how loose they feel in the winter. In other words, the fingers swell (expand) in hot weather and shrink (contract) in cold weather. This alteration of expand- ing and contracting in rocks weakens the rock and can cause it to crack and break into pieces. Roots from shrubs and trees can also grow between the openings in rocks, causing them to break apart. This also represents physical weathering. Chemical weathering may change not only the size but the composition of a rock. In this type of weathering a new material is formed. Oxidation and car- bonization are two forms of chemical weathering. Oxidation is the process of com- bining oxygen with other materials to form new substances. Some rocks can appear to have a black, brown, or orange coloration because of oxidation. Iron oxide (rust) has developed on these rocks when the iron mineral in the rock is exposed to the atmosphere to form iron oxide. In effect, the rock has rusted. Carbonization is another agent of chemical weathering. Carbonization forms limestone caves when the carbonic acid (formed from the union of rainwater and carbon dioxide in the atmosphere) reacts with limestone rock to dissolve it slow- ly. Over thousands of years a cave is formed. As time goes by, the cave will increase in size. What determines the speed and intensity of the weathering process? These factors include (1) the type of rock, (2) the type and hardness ofthe materials in the rock, and (3) the cli- mate. Rocks that dissolve easily in water or acid weather much more quickly than insoluble rocks. Sedimentary rocks generally weather more quickly than igneous or meta- morphic rocks. Sandstone weathers more quickly than granite. This is because the sandstone is sand grains cemented .to.get-?-er ~th natural materials and is more porous than ·~anite. The more precipitation in an area, the more quickly the rock weathers. (The amount of precIpI~atI~n can affect weathering.) A lot of weathering, occurs in areas with hot, humid climates. Weathering can. create and shape structures. Mountains can be shaped through t~e weathering process. Weathering can also break down rocks into use- ful materials suc~ as soil. Over time, weathering causes the bedrock of the earth to deco:npo~e. W~th the passage of years, soil is formed. The formation of soil occurs ~ soil ~onzons or layers. The uppermost layer (Horizon A) is composed of the nutrient-rich topsoil. It is here that plants are nurtured with essential min- erals. Decayed plants ~d. animals form humus, which enriches the topsoil. The layer beneath .the topsoil IS the subsoil (Horizon B). This layer has some nutri- ents, b~t certainly not t,othe extent found in the topsoil. Horizon B has an orange coloration du~ to the high con~ent of clay particles. Water and most plant roots have great diffi~ulty ~enetratmg through the subsoil. Horizon C is the layer below the subsoil and Just above the bedrock. It is composed of broken pieces of rock. When the process of soil formation is completed, all three soil layers exist. Whe.n:ock has ~ot been s~cientl~ transformed by weathering into all three lay- er~, ~t IS called immature soil. As time passes, weathering will change immature soil into mature soil (soil with all three layers present). As w~athering ?cc:rrs, pieces of rock break off and fall to the ground. Some ofthese pieces remam.m that location, and other pieces are carried away by nat- ural agents such ~s ~d or water. The transportation of these broken pieces of ::ock to other,tocations IS called erosion. The four most common agents of erosion mclude running water, glaciers, gravity, and wind. Erosion by Water In most areas, running water is a dominant agent of erosion. Rivers and streams transport eroded material. All material transported by rivers and streams is called the stream load. The composition of the stream load is dependent on the speed and volume of water in the stream. Heavier particles of material bounce along the bottom of the stream, grinding and wearing down surfaces they strike. This action is called abrasion. Lighter particles become suspended in the water and are eventually dropped when the stream slows in velocity. The weight and composition of these particles influence the order in which the deposition of par- ticles takes place. Running water can even be so powerful that it creates new landscapes. Rainwater carries particles down mountain slopes and forms river valleys between two mountains. Erosion by Glaciers Glaciers (mounds of sliding snow on t6p of ice) can cause erosion. The icy bottom of the glacier. causes it to flow smoothly. It may move only an inch a day, but this is enough to carry along particles underneath it. Glaciers can transport small particlesand large boulders, but they cover much less area than running water. . Erosion by Gravity . Gravity is the last and most influential agent of erosion. This is so because gravity is the underlying force behind all erosion. Gravity causes water to run downhill, it causes glaciers to flow, and it produces winds by pulling heavy cold- er air beneath lighter warm air. Gravity is the factor responsible for phenomena such as landslides, rock slides.rand snow slides. . ; ,)~
Transcript of 2-1 THE ~COO.t:UN Why Rocks Crack Physical and...
2-1 THE ~COO.t:UN ~UlLWhy Rocks Crack
It would be nice to age without changes occurring in our appearance.Unfortunately, human flesh deteriorates over time, and wewitness this deteriora-tion as alterations in our appearance. Changes in appearance can be seen in non-living things as well as living things. The earth has changed in its appearance overthe passage of time. Like the flesh of the human body, the rocks that compose theearth are worn down and deteriorate with age. Many factors contribute to thebreakdown of the rocks of the earth. The process of breaking down the rocks thatcompose the earth is called weathering. Weathering can be chemical or physical.
Physical and Chemical Weathering
Physical weathering changes the size of a rock but does not alter the compositionof the rock. Temperature changes can cause physical weathering to occur. Rocksexpand in the summer and contract in the winter. If you are unclear on the termsexpansion and contraction, think about how tight your rings feel in the summerand how loose they feel in the winter. In other words, the fingers swell (expand)in hot weather and shrink (contract) in cold weather. This alteration of expand-ing and contracting in rocks weakens the rock and can cause it to crack and breakinto pieces. Roots from shrubs and trees can also grow between the openings inrocks, causing them to break apart. This also represents physical weathering.
Chemical weathering may change not only the size but the composition of arock. In this type of weathering a new material is formed. Oxidation and car-bonization are two forms of chemical weathering. Oxidation is the process of com-bining oxygen with other materials to form new substances. Some rocks canappear to have a black, brown, or orange coloration because of oxidation. Ironoxide (rust) has developed on these rocks when the iron mineral in the rock isexposed to the atmosphere to form iron oxide. In effect, the rock has rusted.Carbonization is another agent of chemical weathering. Carbonization formslimestone caves when the carbonic acid (formed from the union of rainwater andcarbon dioxide in the atmosphere) reacts with limestone rock to dissolve it slow-ly. Over thousands of years a cave is formed. As time goes by, the cave willincrease in size.
What determines the speed andintensity of the weathering process?These factors include (1) the type ofrock, (2) the type and hardness ofthematerials in the rock, and (3) the cli-mate. Rocks that dissolve easily inwater or acid weather much morequickly than insoluble rocks.Sedimentary rocks generally weathermore quickly than igneous or meta-morphic rocks. Sandstone weathersmore quickly than granite. This isbecause the sandstone is sand grains
cemented .to.get-?-er~th natural materials and is more porous than ·~anite. Themore precipitation in an area, the more quickly the rock weathers. (The amountof precIpI~atI~n can affect weathering.) A lot of weathering, occurs in areas withhot, humid climates.
Weathering can. create and shape structures. Mountains can be shapedthrough t~e weathering process. Weathering can also break down rocks into use-ful materials suc~ as soil. Over time, weathering causes the bedrock of the earthto deco:npo~e. W~th the passage of years, soil is formed. The formation of soiloccurs ~ soil ~onzons or layers. The uppermost layer (Horizon A) is composed ofthe nutrient-rich topsoil. It is here that plants are nurtured with essential min-erals. Decayed plants ~d. animals form humus, which enriches the topsoil. Thelayer beneath .the topsoil IS the subsoil (Horizon B). This layer has some nutri-ents, b~t certainly not t,othe extent found in the topsoil. Horizon B has an orangecoloration du~ to the high con~ent of clay particles. Water and most plant rootshave great diffi~ulty ~enetratmg through the subsoil. Horizon C is the layerbelow the subsoil and Just above the bedrock. It is composed of broken pieces ofrock. When the process of soil formation is completed, all three soil layers exist.Whe.n:ock has ~ot been s~cientl~ transformed by weathering into all three lay-er~, ~t IS called immature soil. As time passes, weathering will change immaturesoil into mature soil (soil with all three layers present).
As w~athering ?cc:rrs, pieces of rock break off and fall to the ground. Someofthese pieces remam.m that location, and other pieces are carried away by nat-ural agents such ~s ~d or water. The transportation of these broken pieces of::ock to other,tocations IS called erosion. The four most common agents of erosionmclude running water, glaciers, gravity, and wind.
Erosion by WaterIn most areas, running water is a dominant agent of erosion. Rivers and streamstransport eroded material. All material transported by rivers and streams iscalled the stream load. The composition of the stream load is dependent on thespeed and volume of water in the stream. Heavier particles of material bouncealong the bottom of the stream, grinding and wearing down surfaces they strike.This action is called abrasion. Lighter particles become suspended in the waterand are eventually dropped when the stream slows in velocity. The weight andcomposition of these particles influence the order in which the deposition of par-ticles takes place. Running water can even be so powerful that it creates newlandscapes. Rainwater carries particles down mountain slopes and forms rivervalleys between two mountains.
Erosion by GlaciersGlaciers (mounds of sliding snow on t6p of ice) can cause erosion. The icy bottomof the glacier. causes it to flow smoothly. It may move only an inch a day, but thisis enough to carry along particles underneath it. Glaciers can transport smallparticlesand large boulders, but they cover much less area than running water.
. Erosion by Gravity .Gravity is the last and most influential agent of erosion. This is so because
gravity is the underlying force behind all erosion. Gravity causes water to rundownhill, it causes glaciers to flow, and it produces winds by pulling heavy cold-er air beneath lighter warm air. Gravity is the factor responsible for phenomenasuch as landslides, rock slides.rand snow slides. .
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c1imau:-sedimentschemicaldissolves
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airmineralscfackscarbonic aCid
oxidationdesertice wedgingtemperatures
Weathering is the breaking of rocks into -'- . There are two main
types of weathering. we~thering involl!i!f breaking rocks without
changing their chemical ~omposition. For example, rocksmay collide Wi.~·other rocks and break•\o~:
apan. In , water trapped in rockcncltt~es and expands,
forcing the rocks apart. ~- __ can also cause mechanical weathering. &
their roots grow and pin pressure on rocks, widen and rock
fragments may ral~ off. weathering invo.IVes water. air, and oth-er'.(.~.:
substances reacting with the minerals in the rocks. Water 'f·-· the'i:~.minerals in rocks or combines with compounds in the ~ __ -- . 'When
metal is exposed to water and oxygen, 'pcCurs and nut Cornu.
___________ in plant roots and mosses can also dissOlve the;.'~~
__________ ~. in rocks. Water and carbon dioxide combine to form\.;.~-i:
______________ , whkh dissolves minerals such as calcl~ in limestone.. t~\~··
How rapidly weathering occurs in an area depends on the,.. • In-c.:»
-- regions, chemical weathering is most. rapid. ChemiCal weathering
happens more slowly in areasand ~ regio~ due to a la~k of
__ -..,. andlor low ,'<? . Whenever'. ·7:V{., .
-- and thawing alternate, mechanical w~thering becomes an• ;(.r:,: .:
il'I'rpor~t!.O'f!lI()f..!!'~ath~~. .. .. __..... ". ---,:;~-,:..-_:_---.-----
NAME __ ~ ,.. DATE_...--- ClASS,--- _
ChapIW$
Weathering Tut Pages 122-127
Weatheri·ng includes mechanical weathering and chemical weathering. MCl:hanical weatheringis any.pfoccs;sthat breab ~p rock withou~ chapging its chem~CaI composition. Chemical weatheringis any process in whkh water, air, or other substances react with the minerals in the rock a~dchange ~e.chemtc:a'1 composition of the rock,
D«itk if the ful/w!lng descriptiOns Mr exam/Jte:· of JlltcMnical wtalhning or chemical fUtO.tlatrint- Write tluiWO'rd ·"",hatiital" or -thtInical" in t1l4 hUznlr(Jt i1l4 left. .
1. Mosses growing on the surface of rocks. producing pits in the rocks
___________ . t. The wedgin gOf tree roots along natural joints in gr~jte outcrops
3. Limestone ',~IYed by carbonic acid
04. The Oxidation of minerals that (on lain iron
.5: Animal burrows d,ug in rock that Jet in water aI;ld .air.. 'j..' ....
6. Repeated f~ezing and. thawing of water that cra~b·rock '.
_________ .. '1. the. action ofwattr,sa1t; and atr on car fenders and panels
8. Adds from plant roots which break up rocks
_________ ..~. F~~tiO~:?flxitho!es ~~ s~el5 during seve.ie Winters
________ . 10. Lifted seCtit)DS of sidewalk along tree-lined streets
____ ~ 11. A large rocl~ falIinS from a cliff' and then breaking
_________ 12. Feld.par mixed with water, producing clay minerals
__ ~ IS. Rocks that have.been carried l)y str~3xns and. ha .•••e become smaller .and more rQunded .
________ .. 14. Decaying p~antldjlSOlving ,?me of the ini~erals in rocks
_________ 15. Tree roots ,"racking the' concrete foundation of a house
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