1. FORCES THAT SHAPE THE EARTH

2. Forces that Shape Earth

3. Continental crust constantly changes over time due to plate tectonics
Continental crust constantly changes over time due to plate tectonics. Forces at plate boundaries are strong enough to break rocks or change their shape.

4. Stress Force that acts on rock to change its shape or volume
Three different kinds of stress can occur in the crust:
Tension
Compression
Shearing

5. Tension
Pulls on the crust, stretching rock so it becomes thinner in the middle
Landforms Created by Tension
Mid-ocean ridges – tension causes oceanic crust to spread allowing hot rock from mantle to rise creating high ridges
Continental rifts – when divergent boundaries occur within a continent, they cause enormous splits in the crust

6. Compression Squeezes rock until it folds or breaks
Landforms Created by Compression
Mountain ranges – collision between two continental plates
Ocean trenches – one plate goes under another during collision forming a deep trench where the two plates meet
Volcanic arcs – curved line of volcanoes that forms parallel to plate boundaries

7. Shearing Pushes a mass of rock in two opposite directions
Landforms Created by Shearing
Transform faults – when plates slide horizontally past each other they form a fault, or a break in the rock of the crust
Fault zones – an area of many fractured pieces of crust along a large fault

8. Strain – a change in the shape of a rock caused by stress
Elastic strain – change in rock that is NOT permanent; when stress is removed rock goes back to original shape
Plastic strain – creates a permanent change in the shape of a rock; usually occurs when rocks are weak or hot

9. Earthquakes

10. Earthquake
Vibrations in the ground that result from movement along faults, or breaks in Earth’s lithosphere
Three types of faults
normal
strike-slip
reverse

11. Seismic Waves
Waves that carry energy of an earthquake away from the focus focus – point beneath Earth’s surface where rock under stress breaks to cause an earthquake epicenter, or point on the surface directly above the focus

12. Three types of Seismic Waves
Primary waves
Secondary waves
Surface waves

13. Primary Waves
(P waves) – compression waves that travel through solids and liquids, compressing and expanding the material they pass through, temporarily changing volume

14. Secondary Waves
(S waves) – only travel through solids and temporarily change the shape, but not the volume of the material they pass through; move slower than P waves

15. Surface Waves
Move slower than P and S waves, but can produce severe ground movement with a wavelike motion

17. Locating an Earthquake’s Epicenter
Done using triangulating data from at least three different seismometers, or devices that measure and record ground motion and helps determine the distance seismic waves travel.

18. Steps to Locating an Earthquake’s Epicenter
1. Find the arrival time difference between the first P-wave and S-wave which is called lag time.
2. Find the distance to the epicenter by using a graph of lag time vs. distance, then go from y- axis to line and read down to x-axis
3. Locate the epicenter by using a map scale to mark radius on a compass then draw a circle around each seismometer location to find intersecting point.

19. Volcanoes

20. Volcano
Weak spot in earth’s crust where molten material, or magma, comes to the surface magma – molten mixture of rock-forming substances, gases and water from the mantle; when magma reaches Earth’s surface it is called lava

21. At plate boundaries the crust often fractures due to the diverging (pulling) or converging (pushing) plates. As a result, these fractures allow magma to reach the surface forming volcanic belts along the boundaries of Earth’s plates.

22. Ring of Fire
Major belt is the Ring of Fire, formed by many volcanoes that rim the Pacific Ocean.

23. island arc – string of islands created by volcanoes near boundaries where two oceanic plates collide and one sinks beneath the other
hot spot – area where material from deep within the mantle rises then melts, forming magma; a volcano forms above a hot spot when magma erupts through the crust (ex. Hawaiian Islands)

24. Inside a volcano is a system of passageways through which magma move
Inside a volcano is a system of passageways through which magma move. This system includes a magma chamber, pipe, vent, lava flows and a crater.
crater
vent
magma chamber
pipe

25. Geologists classify volcanic eruptions as quiet or explosive:
quiet eruption – magma has low silica content, flows easily and erupts quietly with gases bubbling out gently and lava oozing quietly producing both pahoehoe (fast moving hot lava) and aa (lava that is cooler and slower-moving) explosive eruption – has magma high in silica with trapped gases building up pressure until they explode with incredible force creating a pyroclastic flow, or an eruption that hurls out ash, cinders and magma bombs.

26. dormant volcano – not active, but may become active extinct volcano – unlikely to erupt again

27. Volcanic Landforms

28. Landforms from Lava and Ash

33. Landforms From Magma
1. Volcanic necks – forms when magma hardens in a volcano’s pipe; softer rock around pipe wears away exposing hard rock

34. Landforms From Magma
2. Dikes – formed when magma forces itself across rock layers and hardens

35. Landforms From Magma
3. Sill – formed when magma squeezes between horizontal layers of rock

36. Landforms From Magma
4. Batholiths – mass of rock formed when a large body of magma cools inside the crust

37. Landforms From Magma
5. Dome mountain – forms when an uplift pushes a batholith or smaller body of hardened magma toward the surface

38. Geothermal Activity
Occurs when magma, a few kilometers, beneath Earth’s surface, heats underground water and forms:
Hot springs
Geysers

39. Hot Springs
Formed when groundwater is heated by a nearby body of magma or hot rock and eventually rises to the surface to collect in a natural pool.

40. Geyser
Fountain of water and steam that erupts from the ground when buildup of pressure is released.

41. Geothermal Energy
Water heated by magma can provide an energy source called geothermal energy which can heat homes and make electricity.

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