1. Destructive forces
Mrs. Daugherty

2. What are destructive Forces?
Get out a sheet of paper. We are going to POWER WRITE!!!! 
Weathering and erosion

3. Weathering
What is weathering? ______________________________________________ ______________________________________________
There are 2 types of weathering – Mechanical (physical) or chemical.
What is mechanical weathering? - ___________________________________________________________________________________________________________________________________.
Sediment – small pieces of rock

4. Mechanical weathering?
Let’s watch a quick video on mechanical weathering. Please make sure your sound is muted.
Weathering and erosion

5. Types of mechanical (physical) weathering
Ice
How does ice cause weathering? ___________________________________________________________________________________________________________________________________________________

6. Types of mechanical (physical) weathering
Air, water, plants and animals.
As sand and air hits the rocks, they weaken. Over time, they crack and crumble.
Plant roots can grow through cracks and break apart rocks.
Burrowing animals push against rocks and allow water to move deeper into rocks and soils, where freezing and thawing can weather rocks.

7. mechanical (physical) and Chemical weathering
Although mechanical weathering breaks rocks, it does not change the type of rock.
CHEMICAL WEATHERING – __________________________ __________________________ __________________________ __________________________ .
Limestone path, completely broken down and weathered.

8. Chemical weathering?
Let’s watch a quick video on chemical weathering. Please make sure your sound is muted.
Weathering and erosion

9. Chemical weathering
Water is the main factor that causes chemical weathering.
Water dissolves certain chemicals from the air and soil to for a weak acid.
The acidic water (water with acid in it) dissolves certain minerals.
Certain types of rock of more affected by this type of weathering…Such as limestone and marble.

10. Chemical weathering
Usually weathering in a particular area occurs because many different types of weathering.
Most weathering occurs near the earth’s surface; although some can occur below the surface.
CAVES
Water trickling underground can affect rock beneath the surface.
Caves are underground hollow areas created by weathering.
Large caves are called caverns.
Most caverns are made from limestone.

11. How caves are formed
First
Weak acids seep into the ground until they reach a zone soaked with water.
Second
The ground water becomes more acidic.
Third
The acidic water dissolves minerals in the rock
Fourth
Holes are produced in the rock. As the holes grow, passages, chambers and pits are formed, eventually becoming a cave.
Fifth
The water drains away from the cave.

12. Can you put these in order?
_____
Weak acids seep into the ground until they reach a zone soaked with water.
The ground water becomes more acidic.
The acidic water dissolves minerals in the rock
____
Holes are produced in the rock. As the holes grow, passages, chambers and pits are formed, eventually becoming a cave.
The water drains away from the cave.

13. Comprehension check…. Which type of weathering is a cave formation?
A. Mechanical
B. Chemical

14. Comprehension check…. True or False
Weathering usually happens below the earth’s surface?
A. True
B. False

15. Comprehension check…. True or False
A destructive force is one that builds up the Earth’s surface?
A. True
B. False

16. Comprehension check….
The correct definition for mechanical weathering is
A. breaking of larger rocks into smaller pieces of rock.
B. A destructive force that breaks something down.
C. Rocks changing into other materials.

17. Erosion
Erosion is the carrying away of sediments by moving water, wind, or moving ice.
Water is the most common agent of erosion.
How do you think this canyon was formed?

18. Erosion

19. How rivers cause erosion
Fourth
The process may carve out steeper or wider valleys. In some cases, rapid cutting of the valley floor may create a canyon.
Third
The rivers becomes wider and deeper and usually joins another stream or river. The increasing flow of water and tumbing of rocks further erode the river channel.
Second
Gravity moves the water down hill. As the water moves it erodes the ground, dissolving minerals and picking up sediments from the streambed (deposition)
First
The river begins as a shallow stream – often at high elevations.

20. Erosion
Click on this link for a virtual lab on erosion.

21. Erosion with frozen water - Glaciers
Gravity moves rivers of ice downhill toward the sea.
Glaciers are very large and weigh a lot – the force of the glaciers shapes the earth’s surface.
Glaciers can move enormous amounts of soil and rock on the bottom and sides of the ice.
As the glaciers move forward they grind out the surface below them.
Glaciers often carve out hollows in the land they erode.
When the glaciers melt, the hollows fill with water and form a lake.
10,000 such lakes are in Minnesota

22. Glaciers
Click on this link for a look at how glaciers cause erosion.

23. Erosion – with waves and currents
Waves crashing against the shore also break down rock along the coast.
These sediments are dragged back and forth creating sand.
Wind and waves from the ocean also batter the headlands.
Headlands are narrow sections of land that just out into the ocean.
Waves curve around the headland, throwing up salty water and pebbles.
This movement over time erodes cracks in the headlands, form caves.
Caves on both sides may form an arch.
Eventually the arch may collapse. – breaking down the earth’s surface.
Click arch to watch video on erosion.

24. Slow and fast changes
Erosion and weathering are gradual affects that take place over time.
However, some changes seems to occur very quickly.
Sinkholes – formed with a cave has formed and the rock above has little support causing the cave to collapse.
This collapse is called a sinkhole.
Sinkholes can form very quickly.

25. Slow and fast changes
Erosion and weathering are gradual affects that take place over time.
However, some changes seems to occur very quickly.
Landslides – occur suddenly as a result of erosion.
Landslides are large movements of land that tumble down a steep slope.
Mudslides, rock falls, and avalanches are all examples of landslides.
Gravity is the main cause of a landslide; although other destructive factors are at work.
Erosion from rivers, rain, glaciers, or ocean water may steepen a slope and loosen sediment.
The sediments become soaked with water and move more easily.
Any disturbance, such as a minor earthquake can create cracks, causing landslides.
Can volcanoes cause landslides? Click here to find out.

26. How much do you remember
Click on this link and let’s see what you remember!

27. Earthquakes and Volcanoes
There are other types of destructive forces that shape and reshape the Earth’s surface
Two of these forces are Earthquakes and Volcanoes.
While Earthquakes and Volcanoes are destructive – the can also be constructive (build up the Earth’s surface.

28. Earthquakes and Volcanoes
We have already learned about the plates that make up the Crust of the Earth. We also know that where those plates meet is called a boundary.
What are the three types of boundaries we learned about?
_____________________________________________ _____________________________________________

29. Earthquake Earthquakes Earthquakes usually happen at plate boundaries.
The earth’s surface is moving very slowly – so slowly we do not feel it.
Sometimes the earth’s surface moves suddenly and unexpectedly…This sudden movement is an
Earthquake

30. Earthquakes
Do you remember the different types of boundaries that exist on the earth?
Convergent – Plates put together
Divergent – Plates push apart
Transform – Plates slide past each other

31. Earthquakes
Faults – crack in Earth’s crust along which movement takes place.
At faults rocks often bend and fold.
Over time stress builds up on the rocks and the plates strain against each other – eventually the plates shudder and jolt - causing an earthquake.
As the crust shakes – seismic waves are sent out….

32. Earthquakes
Seismic waves – waves of energy sent through Earth’s crust when plates move suddenly.
A seismograph detects and measures vibrations in the Earth’s crust.

33. Earthquakes Faulting – movement of rocks along a fault.
Rocks crack or split into blocks
Blocks continue to move, sometimes causing more faulting.

34. Earthquakes – 3 types of faults
Faults at diverging boundaries – force stretches block.
Eventually rock breaks and the block moves down.
Mid-Ocean ridges are the most common locations.
Fault at converging boundaries
Forces squeeze the rock
Rock breaks
One piece moves up
one piece of the rock moves down – happens in subduction

35. Earthquakes – 3 types of faults
Fault at a sliding boundary
Blocks of rock move past each other
Common at sliding boundaries
San Andreas Fault is an example

36. Earthquakes What is an earthquake?
Earthquake – violent shaking of the Earth’s crust as built-up energy is released.
Earthquakes are measured on a scale
Richter scale – expressed in magnitude.
Anything magnitude 3.5 or less may not be felt
Anything higher than 7.5 is considered a major earthquake

37. Earthquakes How do they work?
How intense and what happens on the surface of the earth depends on how far from the focus you are.
The focus of an earthquake is the point underground where the faulting occurs.
The epicenter is the point on the surface directly above the earthquakes focus.

38. Earthquakes
The intensity of an earthquake is the strongest at the epicenter
Closest to the focus
Seismic waves strongest
Shaking is caused by energy from seismic waves
Long after earthquake is over – seismic waves continue –
aftershocks

39. Earthquakes – types of seismic waves
Body waves – waves that travel through the earth’s interiors
The deeper they extend the faster they travel
Body waves called P waves can travel through the earth’s interior in less than an hour.
Can pass through solid and liquids
As they pass through liquid core they change directions
When hit the earth’s surface make back-and-forth motion

40. Earthquakes – types of seismic waves
Body waves – waves that travel through the earth’s interiors
S body waves travel slightly slower than P waves. When S waves reach surface – it causes an up and down motion.
S body waves only travel through solids.
When S waves move from mantle to liquid core – they lost their energy and do not return to the surface.

41. Earthquakes – types of seismic waves
Surface waves – travel along the earth’s surface.
L waves (surface waves) travel more slowly than body waves
Do not travel too far from the epicenter
Cause the most damage
They make the ground swell and roll like the waves of an ocean
Damage is extensive- roads buckle, building fall down, glass breaks, rivers change course, tree topple, cliffs crumble – out at sea MASSIVE waves are set in motion.
Click here for a demonstration of earthquakes!

42. Comprehension Check Which type of waves are the most destructive?
A. surface waves
B. body waves

43. Comprehension Check
True or false? Seismic waves measure the intensity of the earthquake?
A. true
B. false

44. Comprehension Check True or false? Faults occur at boundaries? A. true
B. false

45. Comprehension Check
True or false? The focus is the point underground where the earthquake occurs.
A. true
B. false

46. Volcanoes
A volcano is an opening in the Earth’s surface through which melted rock, hot gases, rock fragments, and ash burst forth – or erupt.
The word volcano comes from the ancient Roman god of fire – Vulcan. Why?

47. Volcanoes How do volcanoes form?
miles below the earth’s surface.
Rock is so hot it is melted
Magma – melted rock BELOW the earth’s surface
When rock melts – it releases gases.
gas mixes with magma making it lighter than solid rock
Slowly, the gas-filled magma rises toward the surface
As it rises it melts the rock around it, gradually forming a large chamber - may be only a few KM below the surface

48. Volcanoes How do volcanoes form?
Under pressure from surrounding rock, the magma is forced to escape
It melts or forces a channel in weak or cracked rock
Once near the surface, gas and magma burst through a central opening or vent.
The erupting material builds up, forming a volcanic mountain – or volcano

49. Volcanoes
After an eruption, the volcano usually collapses into a bowl-shaped mouth – called a crater.
Most volcanoes have multiple eruptions
Later eruptions may push lava out through side vents and not just through the top

50. Volcanoes Volcanic material-3 types
Magma – called lava once it reaches the surface.
May be fast-flowing and liquid-like
May be thick and slow-flowing
Lava may be as hot as 2,000 degrees
As it cools it forms:
boulders
Domes
Tubes
Smooth or jagged sheets

51. Volcanoes Volcanic material-3 types Rock fragments
forms when gas in sticky magma cannot escape
Pressure builds up and the gas blasts the magma apart
Fragments will erupt into
Dust
Ash
Large chunks called bombs
Small bombs may be no large than a baseball
Large bombs can be 1m wide and weigh 100 tons

52. Volcanoes Volcanic material-3 types Gases Mostly in the form of steam
Contain poisonous chemicals
Mix with ash to form deadly black smoke

53. Volcanoes Classes of volcanoes and volcanic cones Shield volcano
Lava flows smoothly form a vent and spreads out to cover a wide area
Creates a broad, low, dome-shaped volcano

54. Volcanoes Classes of volcanoes and volcanic cones Cinder Cones
Formed when rock fragments erupt and are deposited around the vent
Cone shaped volcano with steep sides.

55. Volcanoes Classes of volcanoes and volcanic cones Composite Volcanoes
Also cone shaped
Sides are steeper than a shield
Sides are not as steep as a cinder cone.

56. Volcanoes
Click here for a volcanic activity!

57. Ring of Fire An area where a lot of earthquakes and volcanoes occur
Outlines Earth’s subduction zones (places where one of Earth’s plates is forced under another)
Pacific plate converges with several continental plates

58. Ring of Fire

59. Ring of Fire
Faulting during subduction causes earthquakes and volcanoes
As the subducting plate sinks into the mantle, it melts to form magma
Magma may later rise to the surface as a line of volcanoes

60. Ring of Fire
Faulting at diverging boundaries also causes earthquakes and create volcanoes
Usually located near the middle of ocean basins
Magma rises to the surface between separating plates
Creates volcanic mountain ranges known as ocean ridges
Faulting at the ridges leads to earthquakes

61. Comprehension Check The origin of the word volcano comes from
A. The latin root volcos
B. The Roman God of Fire – Vulcan
C. The Greek word for mighty mountain - Volca

62. Comprehension Check
Which type of Volcano has a broad, dome-shaped cone?
A. Shield
B. Composite
C. Cinder

63. Comprehension Check
True or False – The ring of fire occurs at subduction zones?
A. true
B. false