1. Lesson 1: Weathering
Weathering acts mechanically and chemically to break down rocks.
Through the action of Earth processes such as freezing and thawing, mechanical weathering breaks rocks into smaller pieces.
Chemical weathering by agents such as water and acids change the materials in rocks into new materials.
Dr. Marli Miller/Getty Images
Key Concepts 1

2. Weathering and Its Effects
The chemical and physical processes that change objects on Earth’s surface over time are called weathering.
Weathering Processes
Break, wear, abrade, and chemically alter rocks and rock surfaces
Can break rock into smaller and smaller pieces – sediment
Can change chemical makeup of a rock
The mechanical and chemical processes that change objects on Earth’s surface over time are called weathering. Wind, water, and organisms constantly weather the rocks on Earth’s surface. While Earth’s surface does not usually change noticeably from day to day, weathering can completely rework the landscape over time.
Weathering also changes Earth’s surface. Earth’s surface today is different from what it was in the past, and what it will be in the future. Weathering processes break, wear, abrade, and chemically alter rocks and rock surfaces.
Over thousands of years, weathering can break rock into smaller and smaller pieces called sediments – sand, silt, and clay are examples of sediments
Weathering can also can change the chemical makeup of rock. Often chemical changes can make a rock easier to break down.

3. Mechanical Weathering
When physical processes naturally break rocks into smaller pieces mechanical weathering occurs.
When physical processes naturally break rocks into smaller pieces – mechanical weathering occurs. Mechanical weathering is a process in which only physical changes occur in rock materials. While there are many types and causes of mechanical weathering each results in the breakdown of rocks and sediments into smaller pieces.
The chemical makeup of a rock is not changed by mechanical weathering.
Question: How does the Launch Lab demonstrate the mechanical breakdown of rock?
Answer: The launch lab demonstrates a mechanical process in which the shape of candies changes.
Example: if a pieces of granite undergoes mechanical weathering, the smaller pieces that result are still granite.
Mechanical weathering does not change chemical makeup.

4. Causes of Mechanical Weathering
Abrasion
Grinding away of rock by friction or impact.
Fragments tumble and bump against one another
Fragments eventually grind themselves into smaller and smaller pieces
Caused by glaciers, wind, and waves
Another effective mechanical weathering process is abrasion – or the grinding away of rock by friction or impact.
Strong currents provide the best example of abrasion at work. A strong current in a stream can carry loose fragments or rock downstream. The rock fragments tumble and grind themselves into smaller and smaller pieces.
Glaciers, wind, and waves along ocean or lake shores can also cause abrasion.
Question: Which two substances cause abrasion of rocks when they flow?
Answer: Both air and water cause abrasion when rocks flow.

5. Causes of Mechanical Weathering
Ice/Frost Wedging
Water enters cracks in rocks and temps drop
Water freezes and expands
Expansion widens cracks and eventually breaks the rock
One of the most effective weathering processes is ice wedging – also called frost wedging.
Water enters cracks in rocks and when temps reach 0 C the water freezes. Water expands as it freezes and the expansion widens the cracks – repeated events eventually break the rock.
Question: In which type of climate would you expect to observe ice wedging?
Answer: Ice wedging occurs in cold, wet climates

6. Causes of Mechanical Weathering
Plant Growth
Plant grows into a crack in the rock.
Roots absorb minerals from the rock making them weaker
As plant grows – steams and roots get longer and wider
Growing plant pushes on the sides of the crack and the rock breaks
Plants can cause weathering by crumbling rocks. Imagine a plant growing into a crack in a rock. Roots absorb minerals from the rock, making it weaker. As the plant grows, it stem and roots not only get longer but they also get wider. The growing plant pushes on the sides of the crack – over time the rock breaks.

7. Causes of Mechanical Weathering
Animal Burrowing
Animals that live in soil create holes in the soil
Water enters the holes and causes weathering
They also burrow through loose rock and help break it down as they dig
Animals that live in soil create holes in the soil where water enters and causes weathering. Animals burrowing through loose rock can also help break rocks down as they dig.

8. Causes of Mechanical Weathering
Forest Fires
Intense temps of forest fire cause rock to expand
When over expanded rock breaks
When intense temperature of a forest fire causes nearby rocks to expand and crack.

9. Chemical weathering does change chemical makeup.
Chemical weathering changes the materials that are part of a rock into new materials.
Chemical weathering changes the materials that are part of a rock into new materials. Chemical weathering occurs when new substances form due to chemical interactions between rock materials and water, air, biota.
Question: Look at the two photos. What is the evidence that chemical weathering occurred?
Example: if a piece of granite weathers chemically, the composition and size of the granite changes.
Chemical weathering does change chemical makeup.

10. Causes of Chemical Weathering
Dissolving by Water
Most substances dissolve in water
Occurs when minerals in the rock break into smaller parts in solution
Water is important in chemical weathering because most substances dissolve in water. The minerals that make up most rocks dissolve very slowly in water. Sometimes the amount that dissolves is so small that it seems as though the mineral doesn’t not dissolve at all.
For a rock, the process of dissolving happens when minerals in the rock break into smaller parts in solution.
For example: Table salt is the mineral sodium and chloride. When table salt dissolves in water, it breaks into smaller sodium ions and chlorine ions.

11. Causes of Chemical Weathering
Dissolving by Acids
More powerful weathering agent than water.
Rain weathers rocks because it is slightly acidic
Volcanoes and pollutants add acid-forming chemicals to air which produces acid rain – causing more weathering than rain
Acids increase the rate of chemical weathering more than rain or water does. Scientists use measurement called the pH scale to tell how acidic something is. The scale ranges from Solutions that have a pH between 0-6 are considered acidic, 7 is considered neutral, and 8-14 is considered basic.
Normal rain is slightly acidic, around a 5.6 because carbon dioxide in the air forms weak acid when it reacts with rain. This means ran can dissolve rock. Acid forming chemicals enter the air from natural sources such as volcanoes. Pollutants in the air also react with rain and make it more acidic. Acid rain has a pH of 4.5 or less.
Scientists measure acidity using the pH scale – acids have a pH between

12. Causes of Chemical Weathering
Oxidation
Combines oxygen with other elements or molecules during oxidation
Most oxygen in oxidation comes from the air
Product of oxidation is oxide
Outer part of rock oxidizes most because it comes in contact with air most
Another process that causes chemical weathering is called oxidation. Oxidation is the process that combines oxygen with other elements or molecules – with most of the oxygen coming from the air. Most iron-bearing rocks and sediments will oxidize in the presence of atmospheric oxygen. Rust, or iron oxide is a product of chemical weathering.
When any element reacts with oxygen, a new substance called oxide forms – in other words, the addition of oxygen to a substance produces an oxide.
The outside of a rock has the most contact with oxygen in the air, therefore during oxidation, the outer part of the rock oxidizes the most.

13. Weathering is the breakdown of rock
Weathering Review
Weathering is the breakdown of rock
Water, wind, and ice are main causes of weathering
Physical Weathering
Breaks rock into pieces without changing its composition
Chemical Weathering
Alters mineral composition of rock
One type of destructive process that changes Earth’s surface is weathering, or the breakdown of rock.
Chemical weathering changes the composition of the rock, whereas physical weathering breaks the rock into pieces called sediment but it does not change the chemical composition of the rock. Gravel, sand, silt and clay are all types of sediment that range in size.
Water, wind, and ice are called agents or causes of weathering – water can dissolve minerals in rock, wind can grind and polish rocks by blowing particles against them, ice and plant roots can expand cracks in rocks and break them apart.
The mineral composition of some rocks makes them more resistant to weathering than other rocks. Weathering can break away less resistant parts of the rock and leave behind the more resistant parts.
Question: Why do some rocks break down faster than others?
Answer: some rocks are softer than others, so they weather more quickly.
A rock’s resistance to weathering is based on its mineral composition, different rates of weathering can create unusual landforms.

14. Lesson 2: The Erosion-Deposition Process
Erosion is the wearing away and transportation of weathered material. Deposition is the laying down of the eroded material.
Erosion tends to make rocks more rounded. Erosion can sort sediment according to its grain size.
Landforms produced by deposition are usually on flat, low land. Landforms produced by erosion are often tall and/or jagged.
Key Concepts 1

15. Reshaping Earth’s Surface
A combination of constructive and destructive processes produce landforms
Destructive Processes
Tear down features on Earth’s surface
Have you ever seen bulldozers, backhoes, and dump trucks at constructions sites? The bulldozer was probably smoothing the land and making a flat surface. The backhoe might have been digging trenches for water or sewer lines. The dumb trucks were probably dumping gravel or other building materials into small piles. The changes that people make to a construction site are small examples of the processes that happen naturally to Earth’s surface.
A combination of constructive processes and destructive processes produce landforms.
Constructive processes build up features on Earth’s surface – lava erupting from a volcano hardens and forms new land on the area where the lava falls.
Destructive processes tear down features on Earth’s surface – a strong hurricane can wash part of a shoreline into the sea.
Constructive and destructive processes continually shape and reshape Earth’s surface.
Constructive Processes
Build up features on Earth’s surface

16. Erosion
Erosion is the removal of weathered material from one location to another.
What happens to weathered material? This material is often transported away from its source rock in another destructive process called erosion. Erosion is the removal of weathered material from one location to another.
Agents of erosion include water, wind, glaciers, and gravity.
Water, wind, glaciers, and gravity are main causes of erosion.

17. Sorting
Sorting is the separating of items into groups according to one or more properties.
Poorly Sorted
Sediment has wide range of sizes
Moderately Sorted
Sediment has a small range of sizes
Well-sorted
Sediment is all about the same size
Erosion also affects the level of sorting of sediment. Sorting is the separating of items into groups according to one or more properties. As sediment is transported, it can become sorted by grain size. Sediment is often well-sorted when it has been moved a lot by wind or waves. Poorly sorted sediment often results from rapid transportation, perhaps by a storm, a flash flood, or a volcanic eruption. Sediment left at the edges of glaciers is also poorly sorted.
Question: How can erosion sort sediment?
Answer: Sediment that is eroded over a short distance is poorly sorted, with grains of different sizes. As sediment erodes over a longer distance, it becomes moderately sorted (grains with small range of sizes) and then well-sorted (gains all about the same size).
If a pile of sediment erodes quickly, it is less likely to be well sorted than if the pile erodes slowly.

18. Deposition is the laying down or settling of eroded materials.
You have read about two destructive processes that shape Earth’s surface – weathering and erosion. After material has been eroded, a constructive process takes place – Deposition is that laying down or settling of eroded material. As water and wind slow down, they have less energy and can hold less sediment, therefore some the sediment is laid down or deposited.
Deposition is a constructive process in which sediment settles out of water or wind, or is laid down, and creates new landforms.
Running water, wind, glaciers, and gravity lay down sediments during deposition.

19. Landforms Created by Erosion
Landforms with tall jagged structures are usually formed by erosion
Can expose several layers of rock – leaving behind multicolored mounds
Leave more erosion resistant rocks behind
Produce ice-carved features in mountains
Produce picturesque landforms including sea cliffs, caves, and sea arches
Landforms are always changing, although you might not observe these changes in your lifetime. Landform characteristics can be observed to determine whether destructive forces such as erosion, or constructive forces, such as deposition, produced the landforms.
Landforms can have features that are clearly produced by erosion. These landforms are often tall, jagged structures with cuts in layers of rock.
Landforms formed by erosion can expose layers of rock – overtime erosion wore away parts of the land, leaving behind multicolored mounds.
Recall different rates of erosion can result in unusual landforms when some rocks erode and leave more erosion-resistant rocks behind.
Glacial erosion and coastal erosion also form unique landforms. Glacial erosion can produce ice-carved features in mountains. U-shaped valleys are often the result of glacial erosion.
Coastal erosion forms picturesque landforms such as sea cliffs, caves, and sea arches.
Question: Why do some types of rock erode more quickly than others?
Answer: some rocks are softer than other rocks. The softer rocks weather or erode more quickly than harder rocks.

20. Landforms Created by Deposition
Low and flat landforms are often formed by deposition.
Alluvial fan
Sandbars
Eskers and moraines
Landforms formed by deposition are often flat and low lying.
Wind depositions for example can gradually form deserts of sand. Deposition also occurs where mountain streams reach the gentle slopes of wide, flat valleys.
An apron of sediment – called an alluvial fan – often forms where a stream flows from a steep, narrow canyon onto a flat plain at the foot of a mountain.
Water traveling in a river can slow due to friction with the edges and the bottom of the river channel. An increase in the channel width or depth also can slow the current and promote deposition. Deposition along a riverbed occurs where the speed of the water slows – this deposition can form a sandbar.
The endpoint for most rivers is where they reach a lake or an ocean and deposit sediment under water. Wave action along shorelines also moves and deposits sediment.
As glaciers melt, they can leave behind piles of sediment and rock – glaciers can create long, narrow deposits called eskers and moraines.

21. Lesson 3: Landforms Shaped by Water and Wind
A young stream moves quickly down steep slopes. A mature stream moves more slowly and develops meanders. An old stream is wider and moves slowly.
Water erosion forms V-shaped valleys. Longshore currents reshape beaches. Deposition of sediment from water can form deltas.
Wind abrasion can alter the shape of rock. Wind deposition can form a dune or loess.
Key Concepts 2

22. Erosion depends on streams energy
Water Erosion
Stream Erosion
Erosion depends on streams energy
Young stream in mountainous area has most energy
As stream matures it gets slower and develops curves
Old stream flows slowly when it reaches flat land
If you have ever had a chance to wade into an ocean and feel the waves running toward shore, you know that moving water can be incredibly strong. Moving water causes erosion along streams, at beaches, and underground.
Stream erosion
Streams are active systems that erode land and transport sediment – with the amount of erosion caused dependent on the stream’s energy.
This energy is usually greatest in a steep mountainous area where young streams flow rapidly downhill – waterfalls and rapids are common and add to the erosion.
When water slows as it reaches gentler slopes – it is said that the stream is now mature. Slower moving water erodes sides of the stream channel more than its bottom, and the stream develops curves. This creates meanders – or broad C-shaped curves in a stream.
When a stream reaches flat land, it moves even slower and is called an old stream. Over time, meanders change shape. More erosion occurs on the outside of bends where water flows faster – more deposition occurs where water flows slower. Over time, this changes the meander, increasing its size.
Meander is a broad, C-shaped curve in a stream.

23. Strong or long-lasting winds can significantly change the land.
Wind Erosion
Strong or long-lasting winds can significantly change the land.
As wind carries sediment along, the sediment cuts and polishes exposed rock
Abrasion
If you think about a gentle wind that blows leaves in the autumn, it seems unlikely that the wind can cause land erosion and deposition, but a strong or long-lasting winds can significantly change the land.
As wind carries sediment along, the sediment cuts and polishes exposed rock. Abrasion is the grinding away of rock or other surfaces as particles carried by wind, water, or ice scraping against them.
Question: In what type of place would you expect to see the most wind erosion?
Answer: You would expect to see the most wind erosion in a place that has long lasting strong winds and soft rocks.
Abrasion the grinding away of rock or other surfaces as particles carried by wind, water, or ice scrape against them.

24. Two common types of wind-blown deposits are dunes and loess.
Wind Deposition
Two common types of wind-blown deposits are dunes and loess.
Dune – pile of windblown sand
Loess – crumbly, windblown deposit of silt and clay
Two common types of wind-blown deposits are dunes and loess (luhs).
A dune is a pile of windblown sand. Overtime entire fields of dunes can travel across land as wind continues to blow sand.
Loess is a crumbly, windblown deposit of silt and clay – one type of loess forms from rock that was ground up and deposited by glaciers. Wind picks up the fine grain sediment and redeposits it in think layers of dust.

25. Lesson 4: Mass Wasting and Glaciers
Gravity can shape Earth’s surface through mass wasting. Creep is an example of mass wasting.
A glacier erodes Earth’s surface as it moves by carving grooves and scratches into rock.
Key Concepts 3

26. Glacier Erosion and Deposition
A glacier is a large mass of ice that formed on land and moves slowly across Earth’s surface.
Two types of Glaciers
Alpine glaciers
- Form in mountains, flow downhill
Ice sheets
- cover large areas of land and move outward from central locations
Glaciers can also cause erosion and deposition. A glacier is a large mass of ice that formed on land and moves slowly across Earth’s surface.
Glaciers form on land in areas where the amount of snowfall is greater than the amount of snowmelt. Although glaciers appear motionless, they can move several centimeters or more each day.
There are two main types of glaciers:
Alpine glaciers – form in mountains and flow downhill. More than 100, 000 alpine glaciers exist on earth.
Question: Where do you think it common to find glaciers today?
Ice Sheets – cover large areas of land and move outward from central locations. Continental ice sheets were common in past ice ages but only exist today in Antarctica and Greenland
Form where amount of snow fall is greater than amount of snow melt

27. Glacial Deposition
Glaciers slowly melt as they move down from high altitudes or when the climate in the area warms – sediment that was once frozen in the ice eventually gets deposited.
Till
Mixture of various sizes of sediment deposited by glacier
Poorly sorted
Moraines
Mound or ridge of unsorted sediment deposited by a glacier
Outwash
Layered sediment deposited by streams of water that flow from a melting glacier
Well sorted sand & gravel
Glaciers slowly melt as they move down from high altitudes or when the climate in the area warms. Sediment that was once frozen in the ice eventually is deposited in various forms.
A till is a mixture of various sizes of sediment deposited by a glacier. Deposits of tills are poorly sorted. They commonly contain particles that range in size from boulders to silt. They often pile up along the sides and fronts of glaciers.
Tills can be shaped and streamlined into many features by the moving ice.
Moraines are mounds or ridges of unsorted sediment deposited by a glacier.
Outwash is layered sediment deposited by streams of water that flow from melting glaciers. Outwash’s are generally well sorted sand and gravel.