Section 3: Earth’s Interior Chapter 12 Section 3: Earth’s Interior

Basic Layers of the Earth Crust Mantle Outer Core (liquid) Inner Core (solid)

Earth’s Crust Continental Crust: rock layer under continents made of mostly granite Oceanic Crust: rock layer under oceans made mostly of basalt Basalt is much more dense than the granite. Less dense continents ride on the denser oceanic plates.

The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the lithosphere. The crust of the Earth is broken into many pieces called plates. The lithosphere makes up Earth’s plates.

The Asthenosphere The asthenosphere is the part of the middle mantle that flows gently like melted plastic. The lithosphere, or Earth’s plates, ride on top of the asthenosphere.

Convection Currents The middle mantle or asthenosphere moves Earth’s plates due to convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again.

Outer Core Under the mantle lies the outer core of Earth. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the metals of nickel and iron.

Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together to create a solid.

Earth’s Magnetic Field Don’t forget: Earth’s magnetic field is caused by the spinning of the molten iron core!

Chapter 12 Section 1

Continental Drift In 1915, Alfred Wegner hypothesizes the continents were once part of a super-continent called Pangea. Over time, the continents drifted apart.

Proving Wegner Correct Over time, there were three pieces of evidence found that supported Wegner’s idea: Matching coastlines: South America looks like it fits with the coast of Africa Matching fossils: The same fossils from ferns and dinosaurs are found on multiple continents. Matching rocks and mountain ranges: When fitting continents into Pangea, it shows mountains were originally one large mountain range.

Matching Coastlines

Matching Fossils

Matching Mountain Ranges

Sea Floor Spreading Dr. Harry Hess used sonar to map the seafloor and revived Wegner’s ideas. Discovered a mid-ocean ridge, or MOR, wrapped around Earth.

MOR Magma from the mantle is forced upward due to its low density (convection currents). This causes the ocean crust to crack (fault) and move apart. This is sea floor spreading! New oceanic crust is created.

Mid-Ocean Ridge Around the Globe

Mountains and Rift Valleys The MOR creates a twin mountain range along the fault. A rift valley is also produced with the mountain range.

Which crust is older?

Theory of Plate Tectonics Plate tectonics- The theory that pieces of the Earth’s lithosphere are in constant motion, driven by convection currents in the mantle No plate can move without affecting the other plates surrounding it; they must bump, grind, or pass each other in order to move. Remember, the plates of the lithosphere float on top of the asthenosphere (the top layer of the mantle)

Divergent Plate Boundary Divergent Boundary: the spreading apart of two plates. Examples: MOR and in East Africa. Features: Rift Valley, mountain range for MOR, earthquakes

Transform Plate Boundary Transform Boundary: two plates that move past each other horizontally Examples: western US called the San Andreas Fault Features: Earthquakes

Convergent Plate Boundaries Convergent Boundary: two plates that collide. There are three ways these form: Oceanic crust collides with continental crust Oceanic crust collides with oceanic crust Continental crust collides with continental crust With convergent boundaries, subduction can occur. This is when the plate with more density sinks, melts from contact with magma, and can produce volcanoes.

Convergent: Oceanic and Continental Two features created: volcanic arcs and a deep sea trench, earthquakes Examples: Cascade and Andes Mountain Ranges

Convergent: Oceanic and Oceanic Two features created: deep sea trench and a volcanic island arc Examples: Japan, Alaskan Aleutian Islands, Ring of Fire

Convergent: Continental and Continental Features: Mountain range and plateaus Examples: Himalayas in Asia, Appalacian Mountains East US

Chapter 12 Section 2 Earthquakes

What is an earthquake? Earthquake- The shaking that results from the movement of rock beneath the Earth’s surface

Types of stress Shearing- stress that pushes a rock in two separate directions Tension- stretches rock, causing it to become thinner in the middle Compression- pushes the two plates together until they either fold or break

Types of stress

Kinds of faults Strike Slip Faults- created by shearing Normal Faults- Footwall rises above hanging wall Reverse Faults- Hanging wall rises above footwall

Normal Fault Reverse Fault Strike-Slip Fault

Strike-slip faults

When there is a movement along a fault, the place where the movement starts is called the focus. The spot above where the focus is called the epicenter. Focus- The point beneath the Earth’s surface where rock breaks under stress and causes an earthquake Epicenter- The point on the Earth’s surface directly above an earthquake’s focus

3 Types of Earthquake Waves Primary waves- push pull type waves Secondary waves- side to side waves Surface waves- up and down waves

1. Primary waves (P-waves) – arrive first.   (fastest of the three)

2. Secondary Waves (S-waves) – arrive second after the P wave 2. Secondary Waves (S-waves) – arrive second after the P wave. (second fastest)

 3. Surface waves (L-waves) –  slowest moving seismic waves. Arrives last. Most destructive!

Seismographs We use a seismograph to measure/ detect seismic waves

Modern day seismographs

Triangulation to find the epicenter

Ways we measure earthquakes Mercalli scale- relies on eyewitness accounts Richter scale- measures ground movement Moment Magnitude scale- uses both eyewitness accounts and ground movement

How earthquakes cause damage Loose soil Can cause landslides or mudslides

Liquefaction Soil and the water that is in it become separated Because the soil is heavier, it sinks pushing the water to the surface

Mudslide and landslide

Earthquake damage

Crack in the surface

Faults in California

Aftershocks Movement along a fault that occurs after a larger earthquake along that same fault

Tsunamis Tidal waves that can reach upwards to 115 feet Caused by Earthquakes that happen deep under water

Earthquake Hazards

Volcanoes

What is a volcano? Volcano- A weak spot in the crust where magma has come to the surface Magma- The molten mixture of rock-forming substances, gases, and water from the mantle Lava- Magma that reaches the surface

How is magma formed? Decompression Melting and Wet Melting

Lava flow at Mount Etna, Sicily, Italy

So where might you find a volcano? Ring of fire- volcanoes that rim the Pacific Ocean Most volcanoes occur at convergent boundaries (subduction zones) and diverging plate boundaries (MOR) Many volcanoes are found underwater

Ring of Fire from space

Crater on a shield volcano

Side vent

Hot spot- An area of magma from deep within the mantle melts through the crust above it The only major hot spot is located in the middle of the Pacific Ocean on the main island of Hawaii Another is in Yellowstone National Park

So why does some lava flow while others don’t? The more silica present in the lava, the thicker it becomes. Lava low in silica will flow like water (low viscosity); called basaltic lava. Lots of IRON AND MAGNESIUM!!! Lava high in silica will tend to form into a moving wall of crumbly rocks (high viscosity)

Pyroclastic Eruptions Pyroclasts: Volcanic fragments hurled in the air during an eruption Watch here

The stages of a volcano’s life Active volcano- volcano that is erupting or has shown signs of erupting in the near future Dormant volcano- volcano that does not show signs of erupting in the near future Extinct volcano- volcano that is unlikely to erupt again

Active Volcanoes

Other features of Volcanoes Hot springs- where hot steam and water rises to the surface after being heated by magma Where you find hot springs, you will also find geysers

Hot springs in New Zealand

Geyser in Iceland and Old Faithful (Yellowstone National Park)

Geothermal Energy Pump water underground to heat it This makes steam We can use this as a renewable energy source!

There are three types of Volcanoes Shield Cinder Cone Composite

Shield Volcano Flat Short Broad (wide) Low viscosity lava

Kilauea in Hawaii is a shield volcano

Cinder Cone Volcano Larger crater Homogenous (one kind of rock) Tend to be tall, but not wide Eruptions are like fountains; violent!

Izalco in El Salvador is a cinder cone

Composite Volcano Has layers of alternating rocks Layers of stone High viscosity lavas VERY TALL!!! Eruption style varies

Mount Egmont in New Zealand is a composite volcano