Plate Tectonics, Earthquakes and Volcanoes.

How do Scientists Know what is inside the Earth?

• Scientists use indirect evidence to determine what is inside the Earth• earthquake waves (SEISMIC WAVES) help determine what is in the

Earth• Seismic waves change speed or stop when they enter different

materials• This shows that Earth is made of layers

Earth’s characteristics change as you travel toward her center.

• TEMPERATURE: increases with depth

• PRESSURE: increases with depth

Layers Within the Earth

• The Earth possesses three main layers:

• Crust, Mantle, and Core

The Crust• Earth’s outermost

layer • Made up of ocean

crust-Basalt• Made up of

continental crust-granite

• Rigid rocky layer of Earth

The Mantle• The second layer

within the Earth• Asthenosphere: upper

layer of the mantle that is “plastic” in nature

• The plates that carry the continents “float” on the asthenosphere

The Core

• Outer Core: liquid sphere of molten nickel and iron

• Made of two layers-the outer core and the inner core

Inner Core: solid ball of nickel and iron

Earth’s Magnetic Field

• Earth acts as a magnet in space

• It has both a North and South pole

• caused by fluid movements in Earth’s liquid outer core causing the solid inner core to spin

Convection in Earth’s Mantle

• Magma is heated by the core, rises to the crust, cools, then again sinks to be reheated

• This causes a Convection Current to form in the upper mantle as shown in the diagram below

CHAPTER 1; SECTION 3:The Theory Continental Drift

• all continents were once joined together in one single landmass scientists called: PANGAEA

“Continental Drift”

Evidence For Continental Drift

Landforms Fossils Climate

The continents fit together like

a puzzle

Mountain rangesare the same on

Different continents

The same rocks andminerals are found

at edges of continents

The same fossilsfound on several

different continents

Coal deposits fromtropical forests werefound in arctic areas

Continents “Drifted” to their current locations….

CHAPTER 1; SECT. 4:Sea-Floor Spreading: 1

• The ocean floors are not smooth and featureless as once believed

• Scientists now know that the ocean floor has a huge mountain range that encircles the globe called the MID-OCEAN RIDGE SYSTEM

Sea-Floor Spreading: 3-diagram-

Sea-Floor Spreading: 2-The Process-

– molten material rises from the mantle and erupts

– The lava creates new rock at the ridge and pushes old rock to both sides of the ridge

– Old Rock is destroyed (remelted) at trenches– This process is called SEA-FLOOR

SPREADING

Sea-Floor Spreading: 5-Evidence to support it-

• Volcanic activity has been observed at the ridge system

• Reversal of magnetic polarity are locked in rocks on either side of the ridge system at equal distances.

• Drill samples from the ocean floor are the same age at equal distances from the ridge system. They get older going away from the ridge too.

Subduction at Deep-Ocean Trenches

• Deep ocean trenches occur where ocean crust is thrust underneath continental crust

• Subduction occurs where dense ocean crust is pushed under less-dense continental crust to be re-melted in the mantle

• This process occurs over tens of millions of years

• This process allows new crust to be created at the ridge systems and old crust to be re-melted; keeping the Earth the same size

CHAPTER 1; SECTION 5: The Theory of Plate Tectonics

• Explains:–Formation of Earth’s Crust

–Movement of Earth’s Crust

–Subduction (destruction) of Earth’s Crust

Plate Boundaries• Edges of crustal plates• Transform Boundary:

– Plates slip past each other in opposite directions (side to side) Ex: San Andreas Fault

• Divergent Boundary:– Plates are moving away from each other– Forms Rift Valleys, mid-ocean ridge

• Convergent Boundary:– Plates move toward each other and collide– Forms trenches and mountains

Earth’s Plate BoundariesPrentice Hall, 2000

CHAPTER 2: SECT. 1:EARTHQUAKES

• EARTHQUAKE:–A VIOLENT SHAKING OR

TREMBLING OF THE EARTH’S CRUST THAT RESULTS FROM MOVEMENT OF ROCK BENEATH THE EARTH’S SURFACE

Types of Stress in the Crust:-Shearing Stress-

• Stress: a force that can cause rock to change it’s shape or volume

• Shearing Stress: pushes rock in two opposite, horizontal directions

• Example: San Andreas Fault in California– One plate moves South and the other one

moves North

Types of Stress in the Crust:-Tensional-

• A force that pulls on the crust, stretching rock so that it becomes thinner in the middle.

• This occurs when two plates move apart

• Example: North East African Rift Zone

Types of Stress in the Crust:-Compressional-

• Stress that squeezes rock until it folds or breaks

• This occurs when one plate collides with another

• Example: India and Eurasia; the Himalayan Mountains are continuing to grow due to compressional stresses

Faults• Breaks in the

Earth’s crust where movement occurs

• Usually occur along plate boundaries

Mountain Building• Over millions of years, stresses can turn

flat land surfaces into towering mountains

Mountains from Folding• Compressional stresses cause rocks to

bend upward or fold

• These folds can create alternating hills (anticlines) and valleys (synclines)

Mountains from Faults• Faults can cause areas to be uplifted

thousands of feet• Fault-Block Mountains:

– Areas where paired normal faults uplift blocks of rock forming mountains

– Ex: plateaus

CHAPTER 2: SECT. 2:EARTHQUAKES

• EARTHQUAKE:–A VIOLENT SHAKING OR

TREMBLING OF THE EARTH’S CRUST THAT RESULTS FROM MOVEMENT OF ROCK BENEATH THE EARTH’S SURFACE

Chapter 2: Sect. 2: Measuring Earthquakes

• Earthquake Focus: – The location within the Earth where rocks break

releasing earthquake energy

• Earthquake Epicenter: – The point on the Earth’s surface directly above the

Focus; greatest damage here

• Seismic Waves: – Three types of shock waves that are emitted from the

focus of an earthquake; used for study

Types of Seismic Waves

• Primary Waves (P-waves): – First waves to arrive at a seismograph; compress

and expand like a sound wave; travel through solids and liquids.

• Secondary Waves (S-waves):– Second waves to be recorded; move up and down

like a water wave; – Travel through solids only

• Surface Waves: – Very slow; P and S waves on the ground. Cause

severe ground movement; most damaging form of seismic waves

Detecting Seismic Waves

• Seismograph: – Device that records ground movements

caused by seismic waves

From Prentice Hall 2000

Rating Earthquake Strength

• Richter Scale– Most widely used

method for public reporting

– Scale of 1 - 10

• Moment Magnitude Scale– Used most often by

geologists– Much more accurate

Locating an Epicenter• Collect P and S-wave data from three

seismic monitoring stations

• Calculate the difference in arrival times between P and S-waves

• Determine the distance to the epicenter

• Draw circles around all three stations with those distances

• They will intersect at the epicenter!

Earthquake Hazards

• Liquefaction:– Ground shaking is amplified by loose soil;

buildings sink

• Aftershocks:– Smaller quakes that occur after a larger one

• Tsunamis:– Tidal waves that occur when earthquakes

occur under the ocean

Inside Earth Chapter 3

Volcanoes

Chapter 3: Sect 1: What is a Volcano?

• A weak spot in the crust where molten material, magma, comes to the surface

• Magma: underground liquid rock

• Lava: liquid rock at the Earth’s surface

Where are volcanoes found?

• Ring of Fire: – A geographic region that rings the Pacific

Ocean– Many volcanoes occur due to the many plate

boundaries that exist in this region– Plate boundaries provide a weak spot in the

crust that is necessary for volcano formation

Hot Spot Volcanoes

• A special volcano that is not located on a plate boundary, but in the center of a plate

• Magma melts through the Earth’s crust to spill out onto the Earth’s surface

• May be causes by a super-heated plume of magma (scientists are not sure)

• Hawaii

Chapter 3: Sect 2

Volcanic Activity

What makes a Volcano Erupt?

• Magma rises toward the Crust because it is hot and less dense than the solid rock around it, however, it gets trapped under the crust

• Gases dissolved in the magma build up• Eventually, the gas must escape; and an

eruption occurs• The escaping gas pushes the magma

out

Types of Eruptions:Quite Eruptions

• Quiet Eruptions occur with a very fluid, low silica, low gas magma

• Example: Mt. Kilauea, Hawaii

• Lava slowly oozes out of the volcanic vent

Types of Eruptions:Explosive Eruptions

• Explosive eruptions occur with a more viscous (thicker), higher silica, high gas magma

• Example: Mt. St. Helens, Washington; May 18, 1980

• Gas cannot escape the thick lava so it builds up and eventually explodes violently

Mt. St. Helens after 1980 eruption

Other Volcanic Activity

• Hot Springs