Weathering, Soil & Erosion via Mass Movement & Gravity
Weathering, Soil & Erosion via Mass Movement & Gravity TB Ch. 8 & BFRB 95 - 101 Regents Earth Science Mrs. O’Gorman
Name: __________________
Weathering & Soil Vocabulary Primer Directions: Use your TB and BFRB to define each term in the second column. If neither has the definition, look it up on the Internet. When we study the concept in class, draw pics, make additional notes, record memory aids, etc. in the third column. Vocab Word: Definition: Additional Notes/Pics/Memory Aids/Etc.
Weathering
Bedrock
Outcrop/Outcropping of Rock Physical (Mechanical) Weathering
Frost Action/ Frost Wedging
Abrasion
Exfoliation (as in a type of Physical Weathering) Chemical Weathering
Hydrolysis/Chemical weathering of granite feldspars
Oxidation
Acid Rain
Surface Area
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Soil
Residual Soil
Transported Soil
Soil Horizon
Humus
Leaching
Regolith
pH
Mass Movement/Mass Wasting Creep (as it relates to erosion) Slump (as it relates to erosion) Landslide (as it relates to erosion) Lahar/Mudflow (as it relates to erosion)
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What are the Agents of Physical & Chemical Weathering?
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Weathering and Erosion
Chapter 8
• Weathering - Def. - the break down of rocks that have been exposed to the atmosphere. • Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion. • Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity. • VIF - Most erosion that takes place on Earth is caused by moving water
Weathering, Soils and Mass Movement BFRB Pages 95 - 101
What is W.E.D.?
Remember the Rock Cycle Diagram? Page 6 of the “Handy Dandy” ESRT’s…
• Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes. • Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is called Erosion. • Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.
2 Types of Weathering Physical weathering – rocks are broken down into smaller pieces without changing their chemical composition (what they’re made of). AKA - mechanical weathering
Agents of Physical Weathering
Chemical weathering – rocks break down as their minerals change in chemical composition (they become different substances).
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Types of Physical Weathering • #1 - Frost action (aka Ice Wedging) – water enters small cracks in the rock. – when water freezes, it expands and forces the crack to open more. – the ice melts back into liquid water and fills the crack again. – the process repeats over and over again until the rock breaks apart.
Close up shows jagged rocks from FROST wedging!
Mt. Brewster – looks solid, right?
Types of Physical Weathering • #2 - Abrasion – It is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in streams and rivers, windy areas, or under glaciers. – It can also happen during rock slides (gravity)
This boulder has been split apart by frost action!!!
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Rocks that have undergone different kinds of abrasion look very differently! Rock weathered by a rockfall
Types of Physical Weathering • #3 Plant Roots
The roots of trees often wedge in between cracks in rocks and force apart rocks even further as they grow!
Rock weathered by a stream
Types of Physical Weathering
Types of Physical Weathering • #5 Wetting and drying – Breaks up rocks that are made from clay. – When they are wet they expand, and they shrink as they dry. – As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!
• #4 Animals Animals (worms, groundhogs, rabbits, etc.) burrow into the ground exposing more rock surfaces to the agents of weathering.
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Types of Physical Weathering • # 6 - Exfoliation – Soil and rock is removed (glaciers melting, rocks being uplifted, overlying rocks eroded), exposing rock that was found deep underground under tremendous pressure. – This releases the pressure causing the surface of the rock to expand and eventually crack and flake off.
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Exfoliation Dome
Exfoliation Dome
“onion skin” exfoliation
Exfoliation Dome
Agents of Chemical Weathering #1 - Plant Acids Lichen & Moss These plants live and grow on rocks and eventually break them apart by the weak acids that they secrete!
Agents of Chemical Weathering
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Lichen – light green/looks like bread mold
Moss – dark green
Agents of Chemical Weathering • #2 - Oxidation – oxygen reacts with some minerals, especially those containing iron to form rust (called iron oxide). – The rusty spots weaken the rock and it breaks apart. – Water is not needed for oxidation to occur, but it does speed up the process!
Chemical weathering of basalt - an iron rich (mafic) igneous rock! You see, it all comes together!!!
Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)
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Agents of Chemical Weathering
“Gnarled Rock” – a formation of limestone chemically weathered by acid rain
• #3 - Acids in rain water and groundwater – Carbon dioxide, nitrogen dioxide, and sulfur dioxide dissolve in water and create carbonic acid, nitric acid, and sulfuric acid. – This acidic water can cause rocks to dissolve, especially those containing calcite like limestone and marble! – Acids may be found in ground water (carbonic acid forms caves) or in rain water (sulfuric and nitric acid rain).
Pitted limestone from rainfall
• Carbonic acid forms when groundwater combines with decaying organic material. – When the acidic groundwater comes in contact with limestone, the limestone dissolves and caves and caverns are formed. – Howe Caverns in NY and Carlsbad Caverns in NM are examples of these beautiful geologic formations
Stalactites
Stalagmites Carlsbad Caverns – New Mexico
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Agents of Chemical Weathering • #4 - Hydrolysis – water (hydro) reacts with minerals such as feldspar and hornblende to form clay which weakens the rock and breaks it apart..
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Link to visualization
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What factors affect the rate at which rocks weather? Page 17 of 62
Factors that affect rates of weathering: • Rock’s resistance to weathering (HARDNESS) • Amount of surface area • Climate:
Rates of Weathering
– Chemical weathering occurs faster in warm, wet climates – Mechanical weathering occurs faster in cold or dry climates
Rock’s resistance to Weathering More resistant rocks will look different than less resistant rocks in a photo or diagram. Which rocks are the most resistant rocks in these pictures/ diagrams?
The central area of rock was less resistant to weathering…thus the “arch” was formed! This is differential weathering.
Devil’s Tower, Wyoming - An igneous intrusion (volcanic neck – the underneath of the volcano) surrounded by less resistant sedimentary rock layers. Erosion has exposed this monolith! This is an example of differential weathering!!! You may recognize it if you’ve ever seen “Close Encounters of the Third Kind”
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Surface Area • Greater surface area increases the rate of weathering • Surface area is the amount of rock surfaces (area) exposed to the atmosphere • Weathering creates more surface area • For 2 samples of rock that have the same mass and volume, the sample that has more surface area will weather faster.
Dry Climate = Mechanical Weathering
Climate
(via wind blown sediment)
• Different climates will affect the rates of physical and chemical weathering in different ways. • This is due to the factors that affect chemical reaction rates and how effective physical weathering agents are.
Wet Climate = Chemical Weathering!
Dry Climate = Mechanical Weathering!
Devil’s Marbles, Australia – Mechanical weathering from wind and sand!
(water speeds up chemical reactions)
Water runoff seeps into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away granite minerals such as feldspar and mica!
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Temperate Climate (alternating freeze and thaw) = Mechanical Weathering (via frost action)
Warm & Moist Climate = Chemical Weathering (heat & moisture speed up chemical reactions)
Parthenon – Athens, Greece
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How is soil created?
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What is soil made of?
Soil Formation
Soil has 4 components: • Weathered rock • Organic material (humus) • Air • Water
Cross section of soil layers
There are 2 types of soil….
Each layer is called a HORIZON
PARENT MATERIAL is the rock that the soil forms from When the parent material is the underlying bedrock of the area, the soil is called RESIDUAL SOIL (residual = what is left behind when the bedrock weathers – it still “resides” or lives with the parent material)
Horizon O/A = Topsoil (mostly humus, some weathered rock) Horizon B = Mostly weathered rock, some organic material (mineral rich zone)
If the soil was formed in one place and carried (transported) elsewhere (by wind, water, glaciers, etc…) then the soil is called TRANSPORTED SOIL
Horizon C = Broken Bedrock
VIF - MUCH OF THE SOIL IN NYS IS TRANSPORTED SOIL LEFT BEHIND BY GLACIERS!
BEDROCK
Leaching is the process in which precipitation entering the soil infiltrates downward, dissolves nutrients, and carries them and colloids to lower layers of soil where they are deposited. Excessive Leaching can remove the humus making the soil unfit for growing vegetation.
HORIZON A
HORIZON B
HORIZON C
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NAME
DATE
CLASS
Chapter 20
Text Pages 562–567
STUDY GUIDE
Acid Rain
Use the words in the boxes to fill in the blanks.
acidic basic cars
factories nitrogen gases Midwest
soil wind sulfur
The amount of acid rain in an area depends on the number of
and
in the area. This is because they are the sources of and
that become acid rain.
Does acid rain fall where the pollution starts? It depends on the
,
which sometimes carries the pollution away. When acid rain does fall, the damage it does depends partly on the kind of in the area. Some soils are already
,
and plants that grow in them can’t survive when more acid is added. Other soils are , and the damage is less when acid rain falls on these. As a rule, soils in the
are basic and soils in the northeastern states are acidic.
sulfur car exhaust cost nitric acid
coal-burning public transportation scrubber
jobs car pooling coal
Acid rain is created when moisture in the air combines with nitrogen oxide to form . Do you know what the main source of nitrogen oxide is? It comes from
. Two ways people can help to reduce nitric acid are by and using
.
Another source of acid rain comes from
power plants that release
into the air. Power plants can help this situation in two ways. They can wash the
, and they can run the smoke through a .
Why don’t people insist that power plants make their exhaust cleaner? Because the of electricity would increase and because many people could lose their .
80
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Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
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Name ____________________________________ Date __________ Class ___________________
SECTION 7-3
SECTION SUMMARY
Soil Conservation Guide for Reading
Why is soil one of Earth’s most valuable resources? ◆ What caused the Dust Bowl? ◆ What are some ways that soil can be conserved? ◆
Unit 2 Resources
Science Explorer Grade 7
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rairie soil is among the most fertile soils in the world. It is rich with humus because of the tall grass. The thick mass of tough roots at the soil’s surface is called sod. It keeps the soil in place and holds onto moisture. Soil is one of Earth’s most valuable resources because everything that lives on land depends directly or indirectly on soil. Plants depend directly on soil to live and grow. Animals depend on plants for food. Fertile soil is valuable because there is a limited supply. Less than one eighth of the land on Earth has soils that are well suited for farming. A renewable resource is one that is naturally replaced in a relatively short time. Soil is a renewable resource that can be found wherever weathering occurs. But it can take hundreds of years for just a few centimeters of soil to form. Soil can be damaged or lost. For example, soil can become exhausted, or lose its fertility. This occurred in large parts of the South in the late 1800s in areas where only cotton had been grown. In the early 1900s, a scientist named George Washington Carver developed new crops and farming methods that helped restore soil fertility in the South. Soil can be lost to erosion by water or wind. Water or wind erosion can occur wherever soil is not protected by plant cover. Plants break the force of rain, and plant roots hold soil in place. Wind erosion, combined with farming methods not suited to dry conditions, was the cause of soil loss on the Great Plains in the 1930s. The Great Plains cover an area east from the prairies to the base of the Rocky Mountains, including parts of North and South Dakota, Nebraska, Kansas, Oklahoma, and Texas. By 1930, almost all of the Great Plains had been turned into farms or ranches. Plowing removed the grass from the Great Plains and exposed the soil. In times of drought, the topsoil quickly dried out, turned to dust, and blew away. Wind blew the soil east in great, black clouds. The problem was most serious in the southern Plains states. There, the drought and topsoil loss lasted until 1938. This area was called the Dust Bowl. Many people in Dust Bowl states moved away. Soil conservation is the management of soil to prevent its destruction. Two ways that soil can be conserved include contour plowing and conservation plowing. Contour plowing is the practice of plowing fields along the curves of a slope. This slows the runoff of excess rainfall and prevents rain from washing soil away. Conservation plowing disturbs the soil and its plant cover as little as possible. Dead weeds and stalks of the previous year’s crop are left in the ground to help return soil nutrients, retain moisture, and hold soil in place.
Name ____________________________________ Date __________ Class ___________________
SECTION 7-3
REVIEW AND REINFORCE
Soil Conservation ◆
Understanding Main Ideas
Complete the flowchart below by filling in the blanks.
_______________ exposed the soil of the Great Plains. ➞ A(n) _______________ , or lack of rain, turned the topsoil to dust. ➞ Wind blew the soil away, creating an area called the _______________ . 1.
2.
3.
Answer the following questions on a separate sheet of paper. 4. 5. 6.
◆
Why is soil valuable? What causes soil damage and loss? When and where did the Dust Bowl occur?
Building Vocabulary
Fill in the blank to complete each statement. 7.
8.
© Prentice-Hall, Inc.
9.
10.
The practice of plowing fields along the curves of a slope is called _______________ . _______________ is the management of soil to prevent its destruction. A method of planting crops that disturbs the soil and its plant cover as little as possible is called _______________ . The thick mass of tough roots at the surface of the soil in a grassland is called _______________ .
Science Explorer Grade 7
Unit 2 Resources
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What are mass movements?
What is the driving force behind mass movements?
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CREEP
(Slow Mass Movement)
MASS MOVEMENTS (aka Mass Wasting)
• Very slow downward movement of soil
MOVEMENTS OF SOIL, ROCK, AND LOOSE MATERIALS CAUSED BY THE FORCE OF GRAVITY They can be slow, fast or very rapid.
– Only noticeable by the results of trees, fence posts, telephone poles, etc… that are tilted downhill
CREEP
(Slow Mass Movement)
• In winter, the water soaked soil expands, then thaws in spring and summer, producing a rise and fall of the surface soil layer and thus, creep.
Slump
(Slow to Fast Mass Movement) – SLUMP – small areas of land moving downhill in a curved shape - especially along roadways that cut into the side of hills or on hills of loose not adhered together well.
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LANDSLIDE
(Rapid Mass Movement) • Sudden movement of soil, rocks or snow downhill (usually on a very steep slope) – AVALANCHE – landslide made of Ice & Snow as well as Soil
LANDSLIDE
(Rapid Mass Movement)
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MUDFLOW or LAHAR (Rapid Mass Movement)
• Very fast & dangerous movement of water saturated soil (MUD)
All around the world, people live in places where the threat of natural disaster is high. On the North Island of New Zealand, the Mount Ruapehu volcano is just such a threat. A towering, active stratovolcano (the classic cone-shaped volcano), snow-capped Ruapehu Volcano is pictured in this enhanced-color image. The image is made from topography data collected by the Shuttle Radar Topography Mission aboard the Space Shuttle Endeavour, launched on February 11, 2000, and imagery collected by the Landsat satellite on October 23, 2002. Ruapehu is one of New Zealand’s most active volcanoes, with ten eruptions since 1861. The eruptions aren’t the only threat from the volcano, however. Among the most serious threats is a volcanic mudflow called a lahar. In between eruptions, a lake forms in the volcano’s caldera from melting snow. If a previous eruption has deposited a dam of ash, rocks and mud in the lake’s natural overflow point, then the lake becomes dangerously full, held back only by the temporary dam. In this scene, the lake is nestled among the ridges at the top of the volcano. Eventually, the dam gives way and a massive flow of mud and debris comes down the mountain toward farmland and towns below. Scientists estimate that Ruapehu has experienced 60 lahars in the last 150 years. A devastating lahar in 1953 killed more than 150 people, who died when a passenger train plunged into a ravine when a railroad bridge was taken out by the lahar. The flank (side) of the volcano below the lake is deeply carved by the path of previous lahars; the gouge can be seen just left of image center. Currently scientists in the region are predicting that the lake will overflow in a lahar sometime in the next year. There is great controversy about how to deal with the threat. News reports from the region indicate that the government is planning to invest in a high-tech warning system that will alert those who might be affected well in advance of any catastrophic release. Others feel that the government should combat the threat through engineering at the top of the mountain, for example, by undertaking a controlled release of the lake.
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Here is the Crater Lake – very acidic water and temp usually around 60° C.
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The Dominion Post (daily newspaper, New Zealand) Tuesday 2 January 2007 Dam on the brink of bursting by Emily Watt Mt Ruapehu's crater lake is at a record high level, and the dam wall is beginning to erode. Scientists say if the lake keeps rising as predicted, the dam could blow by March. They say it is a case of "not if, but when" for the lahar, which is expected to burst the dam and flow down the Whangaehu River on the eastern side of the mountain to Tangiwai and out to the coast. Unlike the 1953 lahar that led to the Tangiwai rail disaster that killed 151 people, this one is unlikely to threaten residential areas but roads, bridges and rail lines could be affected. When a multimillion-dollar early warning system sounds, police will have 20 minutes to cordon off key roads, including State Highway 1. The system also triggers automatic road and rail barriers. A 300-metre concrete barrier has been built to prevent the flow entering the Waikato Stream and Tongariro River; the road bridge on State Highway 49 has been raised and strengthened; and riverbanks have been cleared of pine trees to lessen the risk of their being wedged against the bridge. Last Friday, Conservation Department staff measured the lake at a record high of 2.8 metres below the top of the dam, and there is evidence of the dam seeping at up to 10 litres a second. Department earth scientist Harry Keys said that marked the beginning of the dam's eroding. The lower the lake levels when this happens, the less water that escapes. "The sooner it happens the better," Dr Keys said. "This needs to be resolved. It's an issue hanging over the local community." The lahar warning level remains at two, with a 1 to 2 per cent chance of an immediate lahar. There is also a wave hazard as chunks of the ice cliff fall into the lake, causing water to slosh on to the top of the dam. A large wave could spill over the dam and flow down the mountain. The lahar threat becomes more significant when the lake rises another 0.8 metres, which could be in two weeks, but more likely by February.
Lahar sweeps down New Zealand mountain Sunday 18 March 2007 4:59 GMT (1st Lead) Wellington, New Zealand -- A massive lahar, or volcanic mudflow, swept down New Zealand's 2,797-metre high Mount Ruapehu on Sunday after its steaming crater lake burst its banks releasing thousands of tonnes of rock-filled water. It had long been expected and police and civil defence officials said alarms and safety system installed after a similar lahar 54 years ago which killed 151 people on a train when a rail bridge was swept away, had worked perfectly. They said the lahar, confined by a new stopbank, had kept to its expected course down the mountain into the Whangaehu River valley and past the village of Tangiwai, near the rail bridge, without incident. Police, alerted by a series of automatic alarms monitoring the crater lake's temperature and level, closed all roads in the area, including the highway between the capital Wellington and the country's biggest city Auckland, and stopped trains on the main trunk line. Hundreds of motorists and train passengers were stranded but officials said the lahar had not reached the road, nobody was hurt and no settlements had been affected. The lahar kept to its predicted path eventually moving out to the sea. Civil Defence Minister Rick Barker said bad weather over the weekend had fortuitously kept hikers and climbers off the mountain, an active volcano that is the North Island's highest peak. Scientists had been closely monitoring the 17-hectare crater lake, which sits about 250 metres below the summit of Mount Ruapehu, since January when seeping water threatened to sweep away the rim. Weathermen said extremely heavy rain had fallen on the mountain for more than three hours which probably accounted for the rising lake level. The Department of Conservation had earlier predicted that a lahar would travel at about 21 kilometres an hour down the mountain and a spokesman described Sunday's event as 'moderate.' The National Crisis Centre in Wellington was activated and officials said the lahar emergency response plan had worked as expected.
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Even though rapid mass movement is more noticeable than slow mass movement, overall, more material is transported via creep than all others combined – because it is occurring in many more places and all the time!!!!
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Name ____________________________________ Date __________ Class ___________________
SECTION 8-1
SECTION SUMMARY
Changing Earth’s Surface Guide for Reading
What processes wear down and build up Earth’s surface? ◆ What force pulls rock and soil down slopes? ◆ What are different types of mass movement? ◆
Unit 2 Resources
Science Explorer Grade 7
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E
rosion is the process by which natural forces move weathered rock and soil from one place to another. Gravity, running water, glaciers, waves, and wind all cause erosion. The material moved by erosion is sediment. When the agents of erosion lay down sediment, deposition occurs. Deposition changes the shape of the land. Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface. Erosion and deposition are at work everywhere on Earth. Sometimes, they work slowly. At other times, they work more quickly. Erosion and deposition are never-ending. Gravity pulls everything toward the center of Earth. Gravity is the force that moves rock and other materials downhill. Gravity causes mass movement, any one of several processes that move sediment downhill. Mass movement can be rapid or slow. The different types of mass movement include landslides, mudslides, slump, and creep. The most destructive type of mass movement is a landslide, which occurs when rock and soil slide quickly down a steep slope. Some landslides may contain huge masses of rock, while others may contain only a small amount of rock and soil. A mudflow is the rapid movement of a mixture of water, rock, and soil. The amount of water in a mudflow can be as high as 60 percent. Mudflows often occur after heavy rains in a normally dry area. In clay soils with a high water content, mudflows may occur even on very gentle slopes. An earthquake can trigger both mudflows and landslides. In the type of mass movement known as slump, a mass of rock and soil suddenly slips down a slope in one large mass. It looks as if someone pulled the bottom out from under part of the slope. Slump often occurs when water soaks the base of a mass of soil that is rich in clay. Creep is the very slow downhill movement of rock and soil. It occurs most often on gentle slopes. Creep is so slow that you can barely notice it, but you can see its effects in objects such as telephone poles, gravestones, and fenceposts. Creep may tilt these objects at unusual angles. Creep often results from the freezing and thawing of water in cracked layers of rock beneath the soil.
Name ____________________________________ Date __________ Class ___________________
SECTION 8-1
REVIEW AND REINFORCE
Changing Earth’s Surface ◆
Understanding Main Ideas
Identify each of the examples below by writing landslide, mudslide, slump, or creep on the line beside it.
_________________ _________________ _________________ _________________ _________________ _________________ _________________ _________________
1.
2.
3.
4.
5.
6.
7.
8.
Watery clay soil slides down a mountain. A telephone poll leans downhill. Rock at the top of a cliff suddenly falls. As you step on the mountain path, bits of rock and soil fall downhill. After a heavy rainfall, soil on a desert hill slides to the bottom. After many years, a gravestone on a hillside falls over. Rock and soil suddenly slip downhill in one large mass. During an earthquake, rock and soil move down a slope.
Answer the following questions on a separate sheet of paper. 9.
© Prentice-Hall, Inc.
10.
11.
◆
What causes mass movement? Describe how three processes act together to wear down and build up Earth’s surface. What is the difference between a mudflow and a landslide?
Building Vocabulary
Fill in the blank to complete each statement. 12.
13.
14.
15.
The agents of erosion lay down sediment in new locations in a process called _______________ . The material moved by erosion is called _______________ . The process by which natural forces move weathered rock and soil from one place to another is called _______________ . _______________ includes several processes caused by gravity that move sediment downhill.
Science Explorer Grade 7
Unit 2 Resources
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Test what you know about weathering, soil and mass movements
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Name ____________________________________ Date __________ Class ___________________
SECTION 7-1
SECTION SUMMARY
Rocks and Weathering Guide for Reading
What causes mechanical weathering? ◆ What causes chemical weathering? ◆ What determines how fast weathering occurs? ◆
Unit 2 Resources
Science Explorer Grade 7
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W
eathering is the process that breaks down rock and other substances at Earth’s surface. The forces of weathering break rocks into smaller and smaller pieces. The forces of erosion carry the pieces away. Erosion is the movement of rock particles by wind, water, ice, or gravity. Weathering and erosion work together continuously to wear down and carry away the rocks at Earth’s surface. The type of weathering in which rock is physically broken into smaller pieces is called mechanical weathering. These smaller pieces have the same composition as the rock they came from. Mechanical weathering breaks rock into pieces by freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion. Rock particles carried by wind, water, and ice can wear away rocks in the process called abrasion. Water expands when it freezes, and acts as a wedge. This process is called ice wedging. As a rock surface erodes, pressure on the rock below is reduced, and this pressure release can cause rocks to crack. Plant roots can pry apart cracked rocks. Chemical weathering is the process that breaks down rock through chemical changes. The agents of chemical weathering include water, oxygen, carbon dioxide, living organisms, and acid rain. Chemical weathering produces rock particles that have a different mineral makeup from the original rock. Chemical and mechanical weathering often work together. As mechanical weathering breaks rock into pieces, more surface area becomes exposed to chemical weathering. Water is the most important agent of chemical weathering. Water weathers rock by dissolving it. The oxygen in air is an important cause of chemical weathering. Iron combines with oxygen in the presence of water in a process called oxidation. Rock that contains iron oxidizes, or rusts. Another gas found in air, carbon dioxide, combines with rainwater to form carbonic acid. Carbonic acid easily weathers marble and limestone. Plant roots produce weak acids that slowly dissolve any rock around the roots. Lichens also produce a weak acid that weathers rock. Acid rain causes very rapid chemical weathering. The most important factors that determine the rate at which weathering occurs are type of rock and climate. Some types of rock weather more rapidly than others. For example, some rock weathers easily because it is permeable, which means that it is full of air spaces that allow water to seep through it. Both chemical and mechanical weathering occur faster in wet climates. Chemical weathering occurs more quickly where the climate is both hot and wet.
Name ____________________________________ Date __________ Class ___________________
SECTION 7-1
REVIEW AND REINFORCE
Rocks and Weathering ◆
Understanding Main Ideas
Fill in the blanks in the table below. Type
Agent
Mechanical Chemical
1. 2.
Freezing and thawing Carbon dioxide
3. 4.
Chemical Mechanical
5. 6.
Plant growth Living organisms Oxygen
7. 8. 9.
10.
Mechanical
Description
Rock particles wear away rock Forms from coal, oil, and gas burning Breaks rock by ice wedging Forms carbonic acid in water Weathers marble and limestone Burrowing in the ground breaks rock Roots pry apart cracks in rock Produce weak acid that weathers rock Causes rust on some rock Causes rock to flake off in layers
Answer the following questions on a separate sheet of paper. 11.
© Prentice-Hall, Inc.
12.
◆
How does erosion differ from weathering? What factors determine the rate of weathering?
Building Vocabulary
Fill in the blank to complete each statement. 13.
14.
15.
16. 17.
_______________ is the movement of rock particles by wind, water, ice, or gravity. _______________ means that a material has spaces that allow water to seep through it. The process that breaks down rock and other materials at Earth’s surface is called _______________ . The grinding away of rock by other rock particles is called _______________ . The process by which ice widens and deepens cracks in rocks is called _______________ .
Science Explorer Grade 7
Unit 2 Resources
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3048 - 1 - Page 1 Weathering & Erosion by Mass Wasting Pre-Test Name: ____________________________________________ 1)
2)
As a particle of sediment in a stream breaks into several smaller pieces, the rate of weathering of the sediment will A) increase due to a decrease in surface area B) decrease due to an increase in surface area C) increase due to an increase in surface area D) decrease due to a decrease in surface area
3)
Which graph best represents the chemical weathering rate of a limestone boulder as the boulder is broken into pebble-sized particles?
A)
Which substance has the greatest effect on the rate of weathering of rock? A) hydrogen C) water B) argon D) nitrogen
B)
C)
D)
4)
Chemical weathering of rocks occurs most rapidly in a climate that is A) hot and arid B) cold and arid C) cold and humid D) hot and humid
5)
A landscape having which climate would be influenced by the fewest types of weathering and erosional agents? A) arid B) glacial C) humid tropical D) subarctic
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3048 - 1 - Page 2 6)
Solid bedrock is changed to soil primarily by the process of A) erosion C) infiltration B) transpiration D) weathering
7)
The diagram below represents a geologic cross section of a portion of the Earth's crust. The rock layers have not been overturned.
Which type of rock appears to be most resistant to weathering? A) conglomerate C) sandstone B) shale D) limestone 8)
The cross section below shows residual soils that developed on rock outcrops of metamorphic quartzite and sedimentary limestone.
Which statement best explains why the soil is thicker above the limestone than it is above the quartzite? A) The limestone is less resistant to weathering than the quartzite. B) The quartzite is older than the limestone. C) The limestone is thicker than the quartzite. D) The quartzite formed from molten magma. Page 59 of 62
9)
The diagram below shows a residual soil profile formed in an area of granite bedrock. Four different soil horizons, A, B, C, and D, are shown.
10)
11)
3048 - 1 - Page 3 On the Earth's surface, transported materials are more common than residual materials. This condition is mainly the result of A) folding B) recrystallization C) erosion D) subduction The best evidence that erosion has taken place would be provided by A) tilted rock layers observed on a mountain B) faulted rock layers observed on a plateau C) deep residual soil observed on a hillside D) sediment observed at the bottom of a cliff
Which soil horizon contains the greatest amount of material formed by biological activity? A) A C) C B) B D) D 12)
In the cartoon below, the mountain climber's remarks show that he is aware of which pair of Earth processes?
A) folding and faulting B) weathering and erosion
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C) compaction and uplifting D) deposition and sedimentation
13)
Which factor has the least effect on the weathering of a rock? A) exposure of the rock to the atmosphere B) composition of the rock C) the number of fossils found in the rock D) climatic conditions
14)
At high elevations in New York State, which is the most common form of physical weathering? A) alternate freezing and melting of water B) abrasion of rocks by the wind C) oxidation by oxygen in the atmosphere D) dissolving of minerals into solution
15)
Which is the best example of physical weathering? A) the formation of a sandbar along the side of a stream B) the reaction of limestone with acid rainwater C) the cracking of rock caused by the freezing and thawing of water D) the transportation of sediment in a stream
3048 - 1 - Page 4 Questions 16 through 18 refer to the following: The diagram below represents the dominant type of weathering for various climatic conditions.
16)
Why is no frost action shown for locations with a mean annual temperature greater than 13DC? A) Large amounts of precipitation fall at these locations. B) Large amounts of evaporation takes place at these locations. C) Very little precipitation falls at these locations. D) Very little freezing takes place in these locations.
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17)
Four samples of the same material with identical composition and mass were cut as shown in the diagrams below. When subjected to the same chemical weathering, which sample will weather at the fastest rate? A)
19)
C) 20)
B) 18)
D)
3048 - 1 - Page 5 A large rock is broken into several smaller pieces. Compared to the rate of weathering of the large rock, the rate of weathering of the smaller pieces is A) less B) greater C) the same The diagram below represents a sedimentary rock outcrop.
Assume that the rate of precipitation throughout the year is a constant. Which graph would most probably represent the chemical weathering of most New York State bedrock? A)
Which rock layer is the most resistant to weathering? A) 2 C) 3 B) 4 D) 1
B)
C)
21)
D)
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Which erosional force acts alone to produce avalanches and landslides? A) gravity B) winds C) sea waves D) running water
Name: __________________
Weathering & Soil Vocabulary Primer Directions: Use your TB and BFRB to define each term in the second column. If neither has the definition, look it up on the Internet. When we study the concept in class, draw pics, make additional notes, record memory aids, etc. in the third column. Vocab Word: Definition: Additional Notes/Pics/Memory Aids/Etc.
Weathering
Bedrock
Outcrop/Outcropping of Rock Physical (Mechanical) Weathering
Frost Action/ Frost Wedging
Abrasion
Exfoliation (as in a type of Physical Weathering) Chemical Weathering
Hydrolysis/Chemical weathering of granite feldspars
Oxidation
Acid Rain
Surface Area
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Soil
Residual Soil
Transported Soil
Soil Horizon
Humus
Leaching
Regolith
pH
Mass Movement/Mass Wasting Creep (as it relates to erosion) Slump (as it relates to erosion) Landslide (as it relates to erosion) Lahar/Mudflow (as it relates to erosion)
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What are the Agents of Physical & Chemical Weathering?
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Weathering and Erosion
Chapter 8
• Weathering - Def. - the break down of rocks that have been exposed to the atmosphere. • Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion. • Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity. • VIF - Most erosion that takes place on Earth is caused by moving water
Weathering, Soils and Mass Movement BFRB Pages 95 - 101
What is W.E.D.?
Remember the Rock Cycle Diagram? Page 6 of the “Handy Dandy” ESRT’s…
• Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes. • Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is called Erosion. • Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.
2 Types of Weathering Physical weathering – rocks are broken down into smaller pieces without changing their chemical composition (what they’re made of). AKA - mechanical weathering
Agents of Physical Weathering
Chemical weathering – rocks break down as their minerals change in chemical composition (they become different substances).
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Types of Physical Weathering • #1 - Frost action (aka Ice Wedging) – water enters small cracks in the rock. – when water freezes, it expands and forces the crack to open more. – the ice melts back into liquid water and fills the crack again. – the process repeats over and over again until the rock breaks apart.
Close up shows jagged rocks from FROST wedging!
Mt. Brewster – looks solid, right?
Types of Physical Weathering • #2 - Abrasion – It is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in streams and rivers, windy areas, or under glaciers. – It can also happen during rock slides (gravity)
This boulder has been split apart by frost action!!!
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Rocks that have undergone different kinds of abrasion look very differently! Rock weathered by a rockfall
Types of Physical Weathering • #3 Plant Roots
The roots of trees often wedge in between cracks in rocks and force apart rocks even further as they grow!
Rock weathered by a stream
Types of Physical Weathering
Types of Physical Weathering • #5 Wetting and drying – Breaks up rocks that are made from clay. – When they are wet they expand, and they shrink as they dry. – As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!
• #4 Animals Animals (worms, groundhogs, rabbits, etc.) burrow into the ground exposing more rock surfaces to the agents of weathering.
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Types of Physical Weathering • # 6 - Exfoliation – Soil and rock is removed (glaciers melting, rocks being uplifted, overlying rocks eroded), exposing rock that was found deep underground under tremendous pressure. – This releases the pressure causing the surface of the rock to expand and eventually crack and flake off.
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Exfoliation Dome
Exfoliation Dome
“onion skin” exfoliation
Exfoliation Dome
Agents of Chemical Weathering #1 - Plant Acids Lichen & Moss These plants live and grow on rocks and eventually break them apart by the weak acids that they secrete!
Agents of Chemical Weathering
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Lichen – light green/looks like bread mold
Moss – dark green
Agents of Chemical Weathering • #2 - Oxidation – oxygen reacts with some minerals, especially those containing iron to form rust (called iron oxide). – The rusty spots weaken the rock and it breaks apart. – Water is not needed for oxidation to occur, but it does speed up the process!
Chemical weathering of basalt - an iron rich (mafic) igneous rock! You see, it all comes together!!!
Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)
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Agents of Chemical Weathering
“Gnarled Rock” – a formation of limestone chemically weathered by acid rain
• #3 - Acids in rain water and groundwater – Carbon dioxide, nitrogen dioxide, and sulfur dioxide dissolve in water and create carbonic acid, nitric acid, and sulfuric acid. – This acidic water can cause rocks to dissolve, especially those containing calcite like limestone and marble! – Acids may be found in ground water (carbonic acid forms caves) or in rain water (sulfuric and nitric acid rain).
Pitted limestone from rainfall
• Carbonic acid forms when groundwater combines with decaying organic material. – When the acidic groundwater comes in contact with limestone, the limestone dissolves and caves and caverns are formed. – Howe Caverns in NY and Carlsbad Caverns in NM are examples of these beautiful geologic formations
Stalactites
Stalagmites Carlsbad Caverns – New Mexico
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Agents of Chemical Weathering • #4 - Hydrolysis – water (hydro) reacts with minerals such as feldspar and hornblende to form clay which weakens the rock and breaks it apart..
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Link to visualization
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What factors affect the rate at which rocks weather? Page 17 of 62
Factors that affect rates of weathering: • Rock’s resistance to weathering (HARDNESS) • Amount of surface area • Climate:
Rates of Weathering
– Chemical weathering occurs faster in warm, wet climates – Mechanical weathering occurs faster in cold or dry climates
Rock’s resistance to Weathering More resistant rocks will look different than less resistant rocks in a photo or diagram. Which rocks are the most resistant rocks in these pictures/ diagrams?
The central area of rock was less resistant to weathering…thus the “arch” was formed! This is differential weathering.
Devil’s Tower, Wyoming - An igneous intrusion (volcanic neck – the underneath of the volcano) surrounded by less resistant sedimentary rock layers. Erosion has exposed this monolith! This is an example of differential weathering!!! You may recognize it if you’ve ever seen “Close Encounters of the Third Kind”
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Surface Area • Greater surface area increases the rate of weathering • Surface area is the amount of rock surfaces (area) exposed to the atmosphere • Weathering creates more surface area • For 2 samples of rock that have the same mass and volume, the sample that has more surface area will weather faster.
Dry Climate = Mechanical Weathering
Climate
(via wind blown sediment)
• Different climates will affect the rates of physical and chemical weathering in different ways. • This is due to the factors that affect chemical reaction rates and how effective physical weathering agents are.
Wet Climate = Chemical Weathering!
Dry Climate = Mechanical Weathering!
Devil’s Marbles, Australia – Mechanical weathering from wind and sand!
(water speeds up chemical reactions)
Water runoff seeps into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away granite minerals such as feldspar and mica!
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Temperate Climate (alternating freeze and thaw) = Mechanical Weathering (via frost action)
Warm & Moist Climate = Chemical Weathering (heat & moisture speed up chemical reactions)
Parthenon – Athens, Greece
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How is soil created?
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What is soil made of?
Soil Formation
Soil has 4 components: • Weathered rock • Organic material (humus) • Air • Water
Cross section of soil layers
There are 2 types of soil….
Each layer is called a HORIZON
PARENT MATERIAL is the rock that the soil forms from When the parent material is the underlying bedrock of the area, the soil is called RESIDUAL SOIL (residual = what is left behind when the bedrock weathers – it still “resides” or lives with the parent material)
Horizon O/A = Topsoil (mostly humus, some weathered rock) Horizon B = Mostly weathered rock, some organic material (mineral rich zone)
If the soil was formed in one place and carried (transported) elsewhere (by wind, water, glaciers, etc…) then the soil is called TRANSPORTED SOIL
Horizon C = Broken Bedrock
VIF - MUCH OF THE SOIL IN NYS IS TRANSPORTED SOIL LEFT BEHIND BY GLACIERS!
BEDROCK
Leaching is the process in which precipitation entering the soil infiltrates downward, dissolves nutrients, and carries them and colloids to lower layers of soil where they are deposited. Excessive Leaching can remove the humus making the soil unfit for growing vegetation.
HORIZON A
HORIZON B
HORIZON C
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NAME
DATE
CLASS
Chapter 20
Text Pages 562–567
STUDY GUIDE
Acid Rain
Use the words in the boxes to fill in the blanks.
acidic basic cars
factories nitrogen gases Midwest
soil wind sulfur
The amount of acid rain in an area depends on the number of
and
in the area. This is because they are the sources of and
that become acid rain.
Does acid rain fall where the pollution starts? It depends on the
,
which sometimes carries the pollution away. When acid rain does fall, the damage it does depends partly on the kind of in the area. Some soils are already
,
and plants that grow in them can’t survive when more acid is added. Other soils are , and the damage is less when acid rain falls on these. As a rule, soils in the
are basic and soils in the northeastern states are acidic.
sulfur car exhaust cost nitric acid
coal-burning public transportation scrubber
jobs car pooling coal
Acid rain is created when moisture in the air combines with nitrogen oxide to form . Do you know what the main source of nitrogen oxide is? It comes from
. Two ways people can help to reduce nitric acid are by and using
.
Another source of acid rain comes from
power plants that release
into the air. Power plants can help this situation in two ways. They can wash the
, and they can run the smoke through a .
Why don’t people insist that power plants make their exhaust cleaner? Because the of electricity would increase and because many people could lose their .
80
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Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
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Name ____________________________________ Date __________ Class ___________________
SECTION 7-3
SECTION SUMMARY
Soil Conservation Guide for Reading
Why is soil one of Earth’s most valuable resources? ◆ What caused the Dust Bowl? ◆ What are some ways that soil can be conserved? ◆
Unit 2 Resources
Science Explorer Grade 7
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© Prentice-Hall, Inc.
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P
rairie soil is among the most fertile soils in the world. It is rich with humus because of the tall grass. The thick mass of tough roots at the soil’s surface is called sod. It keeps the soil in place and holds onto moisture. Soil is one of Earth’s most valuable resources because everything that lives on land depends directly or indirectly on soil. Plants depend directly on soil to live and grow. Animals depend on plants for food. Fertile soil is valuable because there is a limited supply. Less than one eighth of the land on Earth has soils that are well suited for farming. A renewable resource is one that is naturally replaced in a relatively short time. Soil is a renewable resource that can be found wherever weathering occurs. But it can take hundreds of years for just a few centimeters of soil to form. Soil can be damaged or lost. For example, soil can become exhausted, or lose its fertility. This occurred in large parts of the South in the late 1800s in areas where only cotton had been grown. In the early 1900s, a scientist named George Washington Carver developed new crops and farming methods that helped restore soil fertility in the South. Soil can be lost to erosion by water or wind. Water or wind erosion can occur wherever soil is not protected by plant cover. Plants break the force of rain, and plant roots hold soil in place. Wind erosion, combined with farming methods not suited to dry conditions, was the cause of soil loss on the Great Plains in the 1930s. The Great Plains cover an area east from the prairies to the base of the Rocky Mountains, including parts of North and South Dakota, Nebraska, Kansas, Oklahoma, and Texas. By 1930, almost all of the Great Plains had been turned into farms or ranches. Plowing removed the grass from the Great Plains and exposed the soil. In times of drought, the topsoil quickly dried out, turned to dust, and blew away. Wind blew the soil east in great, black clouds. The problem was most serious in the southern Plains states. There, the drought and topsoil loss lasted until 1938. This area was called the Dust Bowl. Many people in Dust Bowl states moved away. Soil conservation is the management of soil to prevent its destruction. Two ways that soil can be conserved include contour plowing and conservation plowing. Contour plowing is the practice of plowing fields along the curves of a slope. This slows the runoff of excess rainfall and prevents rain from washing soil away. Conservation plowing disturbs the soil and its plant cover as little as possible. Dead weeds and stalks of the previous year’s crop are left in the ground to help return soil nutrients, retain moisture, and hold soil in place.
Name ____________________________________ Date __________ Class ___________________
SECTION 7-3
REVIEW AND REINFORCE
Soil Conservation ◆
Understanding Main Ideas
Complete the flowchart below by filling in the blanks.
_______________ exposed the soil of the Great Plains. ➞ A(n) _______________ , or lack of rain, turned the topsoil to dust. ➞ Wind blew the soil away, creating an area called the _______________ . 1.
2.
3.
Answer the following questions on a separate sheet of paper. 4. 5. 6.
◆
Why is soil valuable? What causes soil damage and loss? When and where did the Dust Bowl occur?
Building Vocabulary
Fill in the blank to complete each statement. 7.
8.
© Prentice-Hall, Inc.
9.
10.
The practice of plowing fields along the curves of a slope is called _______________ . _______________ is the management of soil to prevent its destruction. A method of planting crops that disturbs the soil and its plant cover as little as possible is called _______________ . The thick mass of tough roots at the surface of the soil in a grassland is called _______________ .
Science Explorer Grade 7
Unit 2 Resources
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What are mass movements?
What is the driving force behind mass movements?
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CREEP
(Slow Mass Movement)
MASS MOVEMENTS (aka Mass Wasting)
• Very slow downward movement of soil
MOVEMENTS OF SOIL, ROCK, AND LOOSE MATERIALS CAUSED BY THE FORCE OF GRAVITY They can be slow, fast or very rapid.
– Only noticeable by the results of trees, fence posts, telephone poles, etc… that are tilted downhill
CREEP
(Slow Mass Movement)
• In winter, the water soaked soil expands, then thaws in spring and summer, producing a rise and fall of the surface soil layer and thus, creep.
Slump
(Slow to Fast Mass Movement) – SLUMP – small areas of land moving downhill in a curved shape - especially along roadways that cut into the side of hills or on hills of loose not adhered together well.
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LANDSLIDE
(Rapid Mass Movement) • Sudden movement of soil, rocks or snow downhill (usually on a very steep slope) – AVALANCHE – landslide made of Ice & Snow as well as Soil
LANDSLIDE
(Rapid Mass Movement)
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MUDFLOW or LAHAR (Rapid Mass Movement)
• Very fast & dangerous movement of water saturated soil (MUD)
All around the world, people live in places where the threat of natural disaster is high. On the North Island of New Zealand, the Mount Ruapehu volcano is just such a threat. A towering, active stratovolcano (the classic cone-shaped volcano), snow-capped Ruapehu Volcano is pictured in this enhanced-color image. The image is made from topography data collected by the Shuttle Radar Topography Mission aboard the Space Shuttle Endeavour, launched on February 11, 2000, and imagery collected by the Landsat satellite on October 23, 2002. Ruapehu is one of New Zealand’s most active volcanoes, with ten eruptions since 1861. The eruptions aren’t the only threat from the volcano, however. Among the most serious threats is a volcanic mudflow called a lahar. In between eruptions, a lake forms in the volcano’s caldera from melting snow. If a previous eruption has deposited a dam of ash, rocks and mud in the lake’s natural overflow point, then the lake becomes dangerously full, held back only by the temporary dam. In this scene, the lake is nestled among the ridges at the top of the volcano. Eventually, the dam gives way and a massive flow of mud and debris comes down the mountain toward farmland and towns below. Scientists estimate that Ruapehu has experienced 60 lahars in the last 150 years. A devastating lahar in 1953 killed more than 150 people, who died when a passenger train plunged into a ravine when a railroad bridge was taken out by the lahar. The flank (side) of the volcano below the lake is deeply carved by the path of previous lahars; the gouge can be seen just left of image center. Currently scientists in the region are predicting that the lake will overflow in a lahar sometime in the next year. There is great controversy about how to deal with the threat. News reports from the region indicate that the government is planning to invest in a high-tech warning system that will alert those who might be affected well in advance of any catastrophic release. Others feel that the government should combat the threat through engineering at the top of the mountain, for example, by undertaking a controlled release of the lake.
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Here is the Crater Lake – very acidic water and temp usually around 60° C.
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The Dominion Post (daily newspaper, New Zealand) Tuesday 2 January 2007 Dam on the brink of bursting by Emily Watt Mt Ruapehu's crater lake is at a record high level, and the dam wall is beginning to erode. Scientists say if the lake keeps rising as predicted, the dam could blow by March. They say it is a case of "not if, but when" for the lahar, which is expected to burst the dam and flow down the Whangaehu River on the eastern side of the mountain to Tangiwai and out to the coast. Unlike the 1953 lahar that led to the Tangiwai rail disaster that killed 151 people, this one is unlikely to threaten residential areas but roads, bridges and rail lines could be affected. When a multimillion-dollar early warning system sounds, police will have 20 minutes to cordon off key roads, including State Highway 1. The system also triggers automatic road and rail barriers. A 300-metre concrete barrier has been built to prevent the flow entering the Waikato Stream and Tongariro River; the road bridge on State Highway 49 has been raised and strengthened; and riverbanks have been cleared of pine trees to lessen the risk of their being wedged against the bridge. Last Friday, Conservation Department staff measured the lake at a record high of 2.8 metres below the top of the dam, and there is evidence of the dam seeping at up to 10 litres a second. Department earth scientist Harry Keys said that marked the beginning of the dam's eroding. The lower the lake levels when this happens, the less water that escapes. "The sooner it happens the better," Dr Keys said. "This needs to be resolved. It's an issue hanging over the local community." The lahar warning level remains at two, with a 1 to 2 per cent chance of an immediate lahar. There is also a wave hazard as chunks of the ice cliff fall into the lake, causing water to slosh on to the top of the dam. A large wave could spill over the dam and flow down the mountain. The lahar threat becomes more significant when the lake rises another 0.8 metres, which could be in two weeks, but more likely by February.
Lahar sweeps down New Zealand mountain Sunday 18 March 2007 4:59 GMT (1st Lead) Wellington, New Zealand -- A massive lahar, or volcanic mudflow, swept down New Zealand's 2,797-metre high Mount Ruapehu on Sunday after its steaming crater lake burst its banks releasing thousands of tonnes of rock-filled water. It had long been expected and police and civil defence officials said alarms and safety system installed after a similar lahar 54 years ago which killed 151 people on a train when a rail bridge was swept away, had worked perfectly. They said the lahar, confined by a new stopbank, had kept to its expected course down the mountain into the Whangaehu River valley and past the village of Tangiwai, near the rail bridge, without incident. Police, alerted by a series of automatic alarms monitoring the crater lake's temperature and level, closed all roads in the area, including the highway between the capital Wellington and the country's biggest city Auckland, and stopped trains on the main trunk line. Hundreds of motorists and train passengers were stranded but officials said the lahar had not reached the road, nobody was hurt and no settlements had been affected. The lahar kept to its predicted path eventually moving out to the sea. Civil Defence Minister Rick Barker said bad weather over the weekend had fortuitously kept hikers and climbers off the mountain, an active volcano that is the North Island's highest peak. Scientists had been closely monitoring the 17-hectare crater lake, which sits about 250 metres below the summit of Mount Ruapehu, since January when seeping water threatened to sweep away the rim. Weathermen said extremely heavy rain had fallen on the mountain for more than three hours which probably accounted for the rising lake level. The Department of Conservation had earlier predicted that a lahar would travel at about 21 kilometres an hour down the mountain and a spokesman described Sunday's event as 'moderate.' The National Crisis Centre in Wellington was activated and officials said the lahar emergency response plan had worked as expected.
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Even though rapid mass movement is more noticeable than slow mass movement, overall, more material is transported via creep than all others combined – because it is occurring in many more places and all the time!!!!
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Name ____________________________________ Date __________ Class ___________________
SECTION 8-1
SECTION SUMMARY
Changing Earth’s Surface Guide for Reading
What processes wear down and build up Earth’s surface? ◆ What force pulls rock and soil down slopes? ◆ What are different types of mass movement? ◆
Unit 2 Resources
Science Explorer Grade 7
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© Prentice-Hall, Inc.
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E
rosion is the process by which natural forces move weathered rock and soil from one place to another. Gravity, running water, glaciers, waves, and wind all cause erosion. The material moved by erosion is sediment. When the agents of erosion lay down sediment, deposition occurs. Deposition changes the shape of the land. Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface. Erosion and deposition are at work everywhere on Earth. Sometimes, they work slowly. At other times, they work more quickly. Erosion and deposition are never-ending. Gravity pulls everything toward the center of Earth. Gravity is the force that moves rock and other materials downhill. Gravity causes mass movement, any one of several processes that move sediment downhill. Mass movement can be rapid or slow. The different types of mass movement include landslides, mudslides, slump, and creep. The most destructive type of mass movement is a landslide, which occurs when rock and soil slide quickly down a steep slope. Some landslides may contain huge masses of rock, while others may contain only a small amount of rock and soil. A mudflow is the rapid movement of a mixture of water, rock, and soil. The amount of water in a mudflow can be as high as 60 percent. Mudflows often occur after heavy rains in a normally dry area. In clay soils with a high water content, mudflows may occur even on very gentle slopes. An earthquake can trigger both mudflows and landslides. In the type of mass movement known as slump, a mass of rock and soil suddenly slips down a slope in one large mass. It looks as if someone pulled the bottom out from under part of the slope. Slump often occurs when water soaks the base of a mass of soil that is rich in clay. Creep is the very slow downhill movement of rock and soil. It occurs most often on gentle slopes. Creep is so slow that you can barely notice it, but you can see its effects in objects such as telephone poles, gravestones, and fenceposts. Creep may tilt these objects at unusual angles. Creep often results from the freezing and thawing of water in cracked layers of rock beneath the soil.
Name ____________________________________ Date __________ Class ___________________
SECTION 8-1
REVIEW AND REINFORCE
Changing Earth’s Surface ◆
Understanding Main Ideas
Identify each of the examples below by writing landslide, mudslide, slump, or creep on the line beside it.
_________________ _________________ _________________ _________________ _________________ _________________ _________________ _________________
1.
2.
3.
4.
5.
6.
7.
8.
Watery clay soil slides down a mountain. A telephone poll leans downhill. Rock at the top of a cliff suddenly falls. As you step on the mountain path, bits of rock and soil fall downhill. After a heavy rainfall, soil on a desert hill slides to the bottom. After many years, a gravestone on a hillside falls over. Rock and soil suddenly slip downhill in one large mass. During an earthquake, rock and soil move down a slope.
Answer the following questions on a separate sheet of paper. 9.
© Prentice-Hall, Inc.
10.
11.
◆
What causes mass movement? Describe how three processes act together to wear down and build up Earth’s surface. What is the difference between a mudflow and a landslide?
Building Vocabulary
Fill in the blank to complete each statement. 12.
13.
14.
15.
The agents of erosion lay down sediment in new locations in a process called _______________ . The material moved by erosion is called _______________ . The process by which natural forces move weathered rock and soil from one place to another is called _______________ . _______________ includes several processes caused by gravity that move sediment downhill.
Science Explorer Grade 7
Unit 2 Resources
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Test what you know about weathering, soil and mass movements
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Name ____________________________________ Date __________ Class ___________________
SECTION 7-1
SECTION SUMMARY
Rocks and Weathering Guide for Reading
What causes mechanical weathering? ◆ What causes chemical weathering? ◆ What determines how fast weathering occurs? ◆
Unit 2 Resources
Science Explorer Grade 7
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© Prentice-Hall, Inc.
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W
eathering is the process that breaks down rock and other substances at Earth’s surface. The forces of weathering break rocks into smaller and smaller pieces. The forces of erosion carry the pieces away. Erosion is the movement of rock particles by wind, water, ice, or gravity. Weathering and erosion work together continuously to wear down and carry away the rocks at Earth’s surface. The type of weathering in which rock is physically broken into smaller pieces is called mechanical weathering. These smaller pieces have the same composition as the rock they came from. Mechanical weathering breaks rock into pieces by freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion. Rock particles carried by wind, water, and ice can wear away rocks in the process called abrasion. Water expands when it freezes, and acts as a wedge. This process is called ice wedging. As a rock surface erodes, pressure on the rock below is reduced, and this pressure release can cause rocks to crack. Plant roots can pry apart cracked rocks. Chemical weathering is the process that breaks down rock through chemical changes. The agents of chemical weathering include water, oxygen, carbon dioxide, living organisms, and acid rain. Chemical weathering produces rock particles that have a different mineral makeup from the original rock. Chemical and mechanical weathering often work together. As mechanical weathering breaks rock into pieces, more surface area becomes exposed to chemical weathering. Water is the most important agent of chemical weathering. Water weathers rock by dissolving it. The oxygen in air is an important cause of chemical weathering. Iron combines with oxygen in the presence of water in a process called oxidation. Rock that contains iron oxidizes, or rusts. Another gas found in air, carbon dioxide, combines with rainwater to form carbonic acid. Carbonic acid easily weathers marble and limestone. Plant roots produce weak acids that slowly dissolve any rock around the roots. Lichens also produce a weak acid that weathers rock. Acid rain causes very rapid chemical weathering. The most important factors that determine the rate at which weathering occurs are type of rock and climate. Some types of rock weather more rapidly than others. For example, some rock weathers easily because it is permeable, which means that it is full of air spaces that allow water to seep through it. Both chemical and mechanical weathering occur faster in wet climates. Chemical weathering occurs more quickly where the climate is both hot and wet.
Name ____________________________________ Date __________ Class ___________________
SECTION 7-1
REVIEW AND REINFORCE
Rocks and Weathering ◆
Understanding Main Ideas
Fill in the blanks in the table below. Type
Agent
Mechanical Chemical
1. 2.
Freezing and thawing Carbon dioxide
3. 4.
Chemical Mechanical
5. 6.
Plant growth Living organisms Oxygen
7. 8. 9.
10.
Mechanical
Description
Rock particles wear away rock Forms from coal, oil, and gas burning Breaks rock by ice wedging Forms carbonic acid in water Weathers marble and limestone Burrowing in the ground breaks rock Roots pry apart cracks in rock Produce weak acid that weathers rock Causes rust on some rock Causes rock to flake off in layers
Answer the following questions on a separate sheet of paper. 11.
© Prentice-Hall, Inc.
12.
◆
How does erosion differ from weathering? What factors determine the rate of weathering?
Building Vocabulary
Fill in the blank to complete each statement. 13.
14.
15.
16. 17.
_______________ is the movement of rock particles by wind, water, ice, or gravity. _______________ means that a material has spaces that allow water to seep through it. The process that breaks down rock and other materials at Earth’s surface is called _______________ . The grinding away of rock by other rock particles is called _______________ . The process by which ice widens and deepens cracks in rocks is called _______________ .
Science Explorer Grade 7
Unit 2 Resources
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3048 - 1 - Page 1 Weathering & Erosion by Mass Wasting Pre-Test Name: ____________________________________________ 1)
2)
As a particle of sediment in a stream breaks into several smaller pieces, the rate of weathering of the sediment will A) increase due to a decrease in surface area B) decrease due to an increase in surface area C) increase due to an increase in surface area D) decrease due to a decrease in surface area
3)
Which graph best represents the chemical weathering rate of a limestone boulder as the boulder is broken into pebble-sized particles?
A)
Which substance has the greatest effect on the rate of weathering of rock? A) hydrogen C) water B) argon D) nitrogen
B)
C)
D)
4)
Chemical weathering of rocks occurs most rapidly in a climate that is A) hot and arid B) cold and arid C) cold and humid D) hot and humid
5)
A landscape having which climate would be influenced by the fewest types of weathering and erosional agents? A) arid B) glacial C) humid tropical D) subarctic
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3048 - 1 - Page 2 6)
Solid bedrock is changed to soil primarily by the process of A) erosion C) infiltration B) transpiration D) weathering
7)
The diagram below represents a geologic cross section of a portion of the Earth's crust. The rock layers have not been overturned.
Which type of rock appears to be most resistant to weathering? A) conglomerate C) sandstone B) shale D) limestone 8)
The cross section below shows residual soils that developed on rock outcrops of metamorphic quartzite and sedimentary limestone.
Which statement best explains why the soil is thicker above the limestone than it is above the quartzite? A) The limestone is less resistant to weathering than the quartzite. B) The quartzite is older than the limestone. C) The limestone is thicker than the quartzite. D) The quartzite formed from molten magma. Page 59 of 62
9)
The diagram below shows a residual soil profile formed in an area of granite bedrock. Four different soil horizons, A, B, C, and D, are shown.
10)
11)
3048 - 1 - Page 3 On the Earth's surface, transported materials are more common than residual materials. This condition is mainly the result of A) folding B) recrystallization C) erosion D) subduction The best evidence that erosion has taken place would be provided by A) tilted rock layers observed on a mountain B) faulted rock layers observed on a plateau C) deep residual soil observed on a hillside D) sediment observed at the bottom of a cliff
Which soil horizon contains the greatest amount of material formed by biological activity? A) A C) C B) B D) D 12)
In the cartoon below, the mountain climber's remarks show that he is aware of which pair of Earth processes?
A) folding and faulting B) weathering and erosion
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C) compaction and uplifting D) deposition and sedimentation
13)
Which factor has the least effect on the weathering of a rock? A) exposure of the rock to the atmosphere B) composition of the rock C) the number of fossils found in the rock D) climatic conditions
14)
At high elevations in New York State, which is the most common form of physical weathering? A) alternate freezing and melting of water B) abrasion of rocks by the wind C) oxidation by oxygen in the atmosphere D) dissolving of minerals into solution
15)
Which is the best example of physical weathering? A) the formation of a sandbar along the side of a stream B) the reaction of limestone with acid rainwater C) the cracking of rock caused by the freezing and thawing of water D) the transportation of sediment in a stream
3048 - 1 - Page 4 Questions 16 through 18 refer to the following: The diagram below represents the dominant type of weathering for various climatic conditions.
16)
Why is no frost action shown for locations with a mean annual temperature greater than 13DC? A) Large amounts of precipitation fall at these locations. B) Large amounts of evaporation takes place at these locations. C) Very little precipitation falls at these locations. D) Very little freezing takes place in these locations.
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17)
Four samples of the same material with identical composition and mass were cut as shown in the diagrams below. When subjected to the same chemical weathering, which sample will weather at the fastest rate? A)
19)
C) 20)
B) 18)
D)
3048 - 1 - Page 5 A large rock is broken into several smaller pieces. Compared to the rate of weathering of the large rock, the rate of weathering of the smaller pieces is A) less B) greater C) the same The diagram below represents a sedimentary rock outcrop.
Assume that the rate of precipitation throughout the year is a constant. Which graph would most probably represent the chemical weathering of most New York State bedrock? A)
Which rock layer is the most resistant to weathering? A) 2 C) 3 B) 4 D) 1
B)
C)
21)
D)
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Which erosional force acts alone to produce avalanches and landslides? A) gravity B) winds C) sea waves D) running water
