Weathering and Soil Formation

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Weathering and Soil Formation

• Ch. 10

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Section 10.1 Rocks and Weathering

• Standard S6E5.c Describe processes that change
  rocks and the surface of the earth.
• Objectives
• Describe how ice, water, wind, gravity, plants,
  and animals cause mechanical weathering.
• Describe how water, acids and air cause chemical
  weathering of rocks.

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Engage/Explore

• How would you describe the the difference between
  a new headstone and one that is a hundred years
  old?

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Headstones
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Headstones
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Introduction

• P. 212
• John Muir Trail - Sierra Nevada mtns. - 640 km
• Appalachian Trail - 2000 km - Alabama to Maine

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Which one is older?

• Sierra Nevada mtns. - 10 million years old
• Appalachian Trail - 250 million years old

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Weathering

• Weathering is the process by which rock materials
  are broken down by the action of physical or
  chemical processes.

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Weathering

• Two kinds of weathering mechanical and chemical.
  

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II. Mechanical Weathering

• Mechanical weathering is breakdown of the rock
  into smaller pieces by physical means. This type
  of weathering in which rock is physically broken
  into smaller pieces. It breaks rock into pieces
  by ice, wind, water gravity, plants,and even
  animals.

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• Abrasion - refers to the grinding away of rock by
  rock particles carried by water, ice, wind, or
  gravity.
• Mechanical weathering works slowly but can wear
  away whole mountains.

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Ice

• The alternate freezing and thawing of soil and
  rock is frost action.
• One type of frost action is ice wedging. Ice
  wedging starts when water seeps into cracks
  during warm weather, then temperatures drop,
  water freezes and expands, the ice pushes on the
  sides of the crack,the crack widens.

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Ice Wedging
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Abrasion

• Abrasion is the grinding and wearing away of rock
  surfaces through the mechanical action of other
  rock or sand particles.

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Wind, Water, and Gravity

• Three forms of abrasion
• Water flowing river rocks bump and scrape
  against each other.
• Wind Wind blows sand against exposed rock.
• Gravity Rocks fall on one another.
• P. 279

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Demonstration

• 2 pieces of sandstone, newspaper
• P. 213
• Rub two pieces of sandstone together over
  newspaper.
• What kind of mechanical weathering does this
  model?
• Abrasion

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Demonstration

• How could such abrasion occur in nature?
• Water or wind could carry sand particles into
  rock, grinding part of it away.

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Plants

• Plants send their roots into existing cracks in
  rocks. As the plant grows, the force of the
  expanding root becomes so strong that the crack
  widens. Eventually, the entire rock can split
  apart.

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Animals

• Believe it or not, earthworms cause a lot of
  weathering!
• Ants, worms, mice coyotes, rabbits, moles,
  gophers, prairie dogs are some of the animals
  that contribute to weathering.

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The process by which rock materials are broken
down by the action of physical or chemical
processes.
iRespond Question
Multiple Choice
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4AABB00C-B194-714F-ACDE-26C568B4B2CB
A.) mechanical weathering
B.) weathering
C.) abrasion
D.)
E.)
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The breakdown of rock into smaller pieces by
physical means.
iRespond Question
Multiple Choice
F
FD058DC1-EB98-C742-A1A7-4646FF74A914
A.) mechanical weathering
B.) weathering
C.) abrasion
D.)
E.)
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The grinding and wearing away of rock surfaces
through the mechanical action of other rock or
sand particles.
iRespond Question
Multiple Choice
F
3959FD66-705D-2947-BCDB-E6EB48084864
A.) mechanical weathering
B.) weathering
C.) abrasion
D.)
E.)
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Which of the following is a type of frost action?
iRespond Question
Multiple Choice
F
8BE2BB5E-39AB-B84E-83F9-C277F9E92B32
A.) abrasion
B.) oxidation
C.) ice wedging
D.) gravity
E.)
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Chemical Weathering

• The process by which rocks break down as a result
  of chemical reactions is called chemical
  weathering.
• The agents of chemical weathering include water,
  weak acids, and air.

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Water

• Water can break down many rocks even granite.

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Acid Precipitation

• Rain, sleet, or snow, that contains a high
  concentration of acids is called acid
  precipitation.
• Caused by volcanoes, and burning fossil fuels
  (coal oil)

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Acid Rain

• What do you and your family do to contribute to
  the problem of acid rain?
• How could you reduce your contribution to this
  problem?

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Acids in Groundwater

• Groundwater contains weak acides, such as
  carbonic or sulfuric acid. They chemically react
  with the rock such as limestone. Karst features
  such as caverns form.

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Acids in Living Things

• Lichens consist of fungi and algae living
  together, contribute to chemical weathering.
  They produce acids that can slowly break down
  rock. The can grow in deserts, in arctic areas,
  and timberline.
• Animals produce weak acids.

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Air

• This car is under going chemical weathering due
  to the air. The oxygen in the air is reacting
  with the iron in the car, causing rust or
  oxidation.

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Rain, sleet, or snow that contains a high
concentration of acids
iRespond Question
Multiple Choice
F
875E0CE0-C6A0-A54F-AEFB-E815ED6B78A8
A.) oxidation
B.) acid precipitation
C.) abrasion
D.) chemical weathering
E.)
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The process by which rocks break down as a result
of chemical reactions.
iRespond Question
Multiple Choice
F
D5F906CF-8B96-F94E-A002-4C0F6CDFF34C
A.) oxidation
B.) acid precipitation
C.) chemical weathering
D.)
E.)
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A chemical reaction in which an element, such as
iron, combines with oxygen to form an oxide.
iRespond Question
Multiple Choice
F
CED9D92B-9661-B942-9E63-6BED88D8EDDC
A.) oxidation
B.) acid precipitation
C.) chemical weathering
D.)
E.)
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Which of the following types of chemical
weathering causes a karst landscape, such as a
cavern?
iRespond Question
Multiple Choice
F
221B23B4-95C8-8B4E-99E4-4C4A33B97ABB
A.) lichens
B.) acid precipitation
C.) acids in groundwater
D.) water
E.)
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How do lichens slowly break down a rock?
iRespond Question
Multiple Choice
F
D2398728-7CDF-134A-87F6-D3E2BE312167
A.) by abrasion
B.) by mechanical weathering
C.) by ice wedging
D.) by chemical weathering
E.)
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Which of these is most likely to experience
oxidation?
iRespond Question
Multiple Choice
F
A26FAE23-D546-C549-A8FC-35F24DF9A700
A.) tennis ball
B.) aluminum can
C.) wooden fence
D.) bicycle tire
E.)
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Weathering Field Trip

• Field trip (15 min)
• Look for examples of mechanical and chemical
  weathering caused by ice, abrasion, plants, and
  animals on or around the school grounds. Make a
  sketch of what you see and label what it is.

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Activity

• Make a compare/contrast table that includes every
  agent of mechanical and chemical weathering.

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Rate of Weathering

• 10.2

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Demonstration

• P. 215
• Materials - limestone and granite, 2 plates,
  dilute hydrochloric acid or vinegar, plastic
  dropper, gloves
• 5 minutes
• Add a drop to both rocks
• What does this demonstration model?

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Discover Activity

• How Fast Can It Fizz?
• P. 212
• Materials antacid tablet, water, beakers,
  stirrers, stopwatches

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Rate of Weathering

• Weathering is a process that takes a long time.
• The rate at which a rock weathers depends on
  climate, elevation, and the makeup of the rock.

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Differential Weathering

• In the experiment, we see that granite weathers
  slower than limestone.
• Differential weathering is a process by which
  softer, less weather resistant rocks wear away
  and leave harder, more weather resistant rocks
  behind.

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Differential Weathering
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Devils Tower in Wyoming

• About 50 million years ago, a mass of molten rock
  cooled and hardened underground to form igneous
  rock. The surrounding rock was softer than the
  igneous rock. Eventually, the softer rock wore
  away. This harder, more resistant rock of the
  tower is all that remains.

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The Shape of Rocks

• Weathering takes place on the outer surface of
  rocks.
• The more surface area that is exposed, the faster
  the rock will be worn down.
• Large rocks have large surface area but lots of
  volume, so it will take a long time to wear down.
  

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The Shape of Rocks

• Smaller rocks will weather much more quickly
  because it has more surface area and less volume.
  
• Figure 2, p. 285

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The Shape of Rocks
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Weathering and Climate

• The rate of weathering is greatly affected by the
  climate of that area.
• Climate is the average weather condition in an
  area over a long period of time.
• Look at Figure 3, p. 286 mailboxes

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Mailboxes
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Temperature and Water

• The rate of chemical weathering is faster in
  warm, humid climates.
• Oxidation happens faster in places that the
  temperatures are higher and when water is
  present.
• Water and temperature also increases ice wedging
  (mechanical weathering).

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Ice Wedging
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Weather and Elevation

• Mountains are exposed to air and water.
• The rocks on mountains at higher elevations are
  exposed to more wind, rain, and ice than the
  lower elevation rocks. This causes the peaks of
  mountains to weather faster.

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Weathering and Elevation

• Gravity affects weathering.
• Steep slopes cause rainwater to quickly run off
  the sides of mountains causing sediments to go
  down the slopes exposes fresh rock surfaces to
  weathering.

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