1. Unit 4 The Restless Earth Part II Lessons 4, 5 & 6
The Big Idea: The movement of tectonic plates accounts for important features of Earth’s surface and for major geologic events.

2. Unit 4 Lesson 4 Volcanoes
Magma Magic
Volcano- any place where gas, ash, or melted rock come out of the ground
Magma -melted rock is less dense than solid rock, so it rises to the surface.
Lava - magma that has reached Earth’s surface. Lava and ash erupt from a vent, or an opening of a volcano.
Many volcanoes are dormant, meaning an eruption has not occurred in a long period of time.
Volcanoes form as rock below Earth’s surface melts.
The location of a volcano and composition of magma determine the type of volcanic landforms created.
Volcanic landforms include shield volcanoes, cinder cones, composite volcanoes, lava plateaus, craters, and calderas.

3. Volcanic Flow
Viscosity- resistance to flow; shape and explosiveness of a volcano depend on the lava’s viscosity.
Pyroclastic material- hot ash and bits of rock, may also be ejected into the atmosphere.
Volcanic mountains are built from materials ejected from a volcano.

4. Unit 4 Lesson 4 Volcanoes
Volcanic Landforms
Shield volcanoes -broad bases and gently sloping sides.
They are the result of mild eruptions.
Cinder cones -small volcanoes with steep slopes.
They form from ash and pieces of solidified lava that fall around a small vent.

5. Lava plateau-fissure eruptions produce flattened layer of cooled lava
Unit 4 Lesson 4 Volcanoes
Volcanic Landforms continued
Composite volcanoes- built from alternating layers of hardened lava flows & pyroclastic material.
They generally develop into large, steep mountains. Have violent eruptions
Lava plateau-fissure eruptions produce flattened layer of cooled lava
Fissure eruptions happen when lava flows from giant cracks, or fissures, in Earth’s surface.
Because fissures have no central opening, lava flows out the entire length of the fissure.

6. Magma chamber-expanded area of magma
Unit 4 Lesson 4 Volcanoes
Volcanic Landforms continued
Caldera – magma chamber empties, the roof of the chamber can collapse, leaving a large basin-shaped depression
Magma chamber-expanded area of magma
A volcanic crater is an opening or a depression at the top of a volcano.
A crater is caused by eruptions.
Inside the volcano, molten rock can form an expanded area of magma called a magma chamber.

7. Eruption! Where do Volcanoes come from?
Unit 4 Lesson 4 Volcanoes
Eruption! Where do Volcanoes come from?
Tectonic plates -giant sections of lithosphere on Earth’s surface. Volcanoes can form at plate boundaries or within the middle of a plate.
Divergent boundaries-creates fissure eruptions & shield volcanoes, crust stretches & gets thinner. Most occur on ocean floor, creating undersea volcanoes, long underwater mtn range known as mid-ocean ridge. On land the crust stretches until a rift valley is formed.
At divergent plate boundaries, where two plates are moving away from each other, fissure eruptions are likely to occur.
As a result, the pressure on the mantle rock below decreases, and magma rises through fissures in the lithosphere.
Most divergent boundaries are on the ocean floor. When eruptions occur in these areas, undersea volcanoes develop.
These volcanoes and other processes lead to the formation of a long, underwater mountain range known as a mid-ocean ridge.
When a divergent boundary is located in the middle of a continent, the crust stretches until a rift valley is formed.

8. Unit 4 Lesson 4 Volcanoes
Convergent boundaries- composite volcanoes or calderas can occur. Magma has high concentration of fluids, which form gas bubbles
Hot spots-far from any plate boundary, shield volcanoes, fissure eruptions & cinder cones can occur.
Ring of Fire –numerous explosive volcanoes that form on convergent boundaries surrounding the Pacific Ocean.
Hot spots are locations far from plate boundaries where a mantle plume, a column of extremely hot mantle rock, rises and produces volcanoes.
Hot spots are caused by convection b/c it transfers energy by the movement of matter.
At convergent boundaries, one plate usually sinks beneath the other. The mantle above the sinking plate can melt to form magma.
Because the magma has a high viscosity, the bubbles cannot escape easily. As the bubbles expand, the magma rises faster.
Eventually, the magma erupts explosively, forming composite volcanoes or calderas.
The magma rises to the surface and forms volcanoes.

9. Unit 4 Lesson 5 Earthquakes
Let’s Focus
Earthquakes are ground movements that occur when blocks of rock in Earth move suddenly and release energy.
The energy is released
as seismic waves that
cause the ground
to move.

10. What Causes Earthquakes?
Unit 4 Lesson 5 Earthquakes
What Causes Earthquakes?
Faults -release of energy that accompanies the movement of rock along a fault causes an earthquake.
Deformation-process by which the rock becomes deformed and changes shape caused by stress
As the stress on rock increases, the energy stored in it increases.
When the stress is released, the rock may return to its original shape.
When rock returns to nearly the same shape after the stress is removed, its called elastic deformation.
Elastic rebound- return of rock to its original shape after elastic deformation
The movement of tectonic plates breaks Earth’s crust into a series of faults, which are breaks in Earth’s crust along which blocks of rocks move.

11. Unit 4 Lesson 5 Earthquakes
What is an Earthquake?
Focus-place w/in Earth along a fault where the first motion of an earthquake occurs. Seismic waves flow outward in all directions
Epicenter- place on Earth’s surface directly above the focus
Seismic waves flow outward from the focus in all directions.
Most earthquakes occur near a tectonic plate boundary, which is where two or more tectonic plates meet.

12. Where do Earthquakes happen?
Unit 4 Lesson 5 Earthquakes
Where do Earthquakes happen?
Divergent boundaries- tension stress causes normal faults to form. Earthquakes tend to be shallow because the crust is thin.
Convergent boundaries- rock is squeezed, & the stress is called compression. Reverse faults are formed, and earthquakes can be strong and deep.
Transform boundaries- shear stress pushes tectonic plates in opposite directions. Earthquakes tend to be relatively shallow.
Most earthquakes happen at or near tectonic plate boundaries.
At tectonic plate boundaries, stress builds up from tectonic plates colliding, separating, or grinding past each other.
There are three main types of tectonic plate boundaries: divergent, convergent, and transform.
Most earthquakes do not cause damage, but some strong earthquakes can cause major damage and loss of life, especially in areas closest to the epicenter.
When the shaking of an earthquake is more than structures can withstand, major destruction can occur.
Much of the injury and loss of life after an earthquake is caused by structures that collapse.
An earthquake under the ocean can cause a vertical movement of the sea floor, displacing an enormous amount of water and generating a tsunami.
A tsunami is a series of extremely long waves that can travel across the ocean at speeds of up to 800 km/h.
As the waves reach the shoreline, the height of the waves increases. The huge waves can cause major destruction.
In 2004, an earthquake generated a tsunami that wiped out half the population of Banda Aceh, Indonesia.
The tsunami traveled outward from the epicenter in the Indian Ocean. Banda Aceh was very close to the epicenter.
The destruction to parts of Asia was so massive that geographers had to redraw the maps of some countries.

13. Shake, Rattle & Roll
Unit 4 Lesson 6 Measuring Earthquake Waves
Seismic waves -vibrations that cause different types of ground motion. Their speed depends on what they travel through
Surface waves- travel along Earth’s surface
As plates of the lithosphere move, the stress on rocks at or near the edges of the plates increases. This stress causes faults to form.
A fault is a break in a body of rock along which one block moves relative to another.
When rocks along a fault break and move, energy is released into the surrounding rock in the form of waves, causing earthquakes.
When rocks along a fault slip, the energy released travels away from the focus and through Earth in all directions as seismic waves.
The strength of an earthquake is based on the energy that is released as rocks break and return to an undeformed shape.
There are two kinds of seismic waves: body waves and surface waves. Each kind travels through Earth in different ways and at different speeds.
Seismic waves carry energy, and their speed depends on the material through which they travel.
Seismic waves that travel along Earth’s surface are called surface waves.
Body waves travel more rapidly than surface waves do, but the latter, being focused on Earth’s surface, cause more damage.
Surface waves produce two types of ground motion: up-and-down and back-and-forth.

14. Seismic Waves continued
Unit 4 Lesson 6 Measuring Earthquake Waves
Seismic Waves continued
Body waves- travel through Earth’s interior
P waves – pressure waves or primary waves are the fastest
S waves- shear waves secondary, move side to side
Body waves are seismic waves that travel through Earth’s interior. They are further divided into P waves and S waves.
P waves, also called pressure waves or primary waves, are the fastest body waves.
P waves can travel through solids, liquids, and gases. They cause rock to move back and forth in the direction the wave is traveling.
S waves, also called shear waves or secondary waves, move rock from side to side. They cannot travel through completely liquid parts of Earth.
Do the human P wave and S wave: P wave= people hit shoulder to shoulder; S wave= people move up and down time both and we should see that the P wave moved faster.
Slinky demonstration.

15. Wave Action!
Unit 4 Lesson 6 Measuring Earthquake Waves
Seismogram -tracing of earthquake motion. It also records the arrival times of seismic waves at a seismometer station.
Page 259 to see triangulation.
Scientists use instruments called seismometers to record seismic waves. When seismic waves reach a seismometer, it produces a seismogram.
Seismograms are plotted on a graph, which is then used to pinpoint the earthquake’s epicenter.
In the S-P time method, scientists use the lag time between P and S waves to determine how far the waves have traveled from the epicenter.
In a process called triangulation, the epicenter can be located by drawing circles around at least three seismometer stations on a map.
The radius of each circle equals the distance from that station to the earthquake’s epicenter. The point of intersection of the circles is the epicenter.

16. Earthquake Measurement
Unit 4 Lesson 6 Measuring Earthquake Waves
Earthquake Measurement
Magnitude- measure of the energy released by an earthquake, larger magnitude = stronger earthquake
Richter scale-measures ground motion from an earthquake to find the strength
Moment Magnitude scale-more accurate for large earthquakes, based on area of moving fault, avg distance the fault moves & rigidity of rocks in the fault.
The height of the waves on a seismogram indicates the amount of ground motion.
Ground motion can be used to calculate magnitude, the measure of energy released by an earthquake.
The larger the magnitude, the stronger the earthquake.
An increase in the magnitude by one unit corresponds to a ten-fold increase in ground motion.
Earthquake strength is also measured by the Moment Magnitude scale, which is more accurate for large earthquakes than the Richter scale is.
It is based on the size of the area of the moving fault, the average distance that the fault moves, and the rigidity of the rocks in the fault.
The moment magnitude of an earthquake is expressed by a number. The larger the number, the stronger the earthquake.

17. Effects of an Earthquake
Unit 4 Lesson 6 Measuring Earthquake Waves
Did you feel that?
Intensity-effects of an earthquake and how the earthquake is felt by people
Effects of an Earthquake
Magnitude
Local geology
Distance from the epicenter
Type of construction used
Magnitude measures how much energy is released by an earthquake. Intensity measures the effects of an earthquake at Earth’s surface.
The Modified Mercalli scale is used to describe an earthquake’s intensity. Intensity values are usually highest near the epicenter.
Four factors determine the effects of an earthquake: magnitude, local geology, distance from the epicenter, and type of construction used.
An earthquake’s magnitude is directly related to its strength. Stronger earthquakes cause more damage than weaker earthquakes.
As an earthquake’s magnitude increases, the earthquake’s intensity is commonly higher.
When water-saturated soil or sediment is shaken by seismic waves, the soil and sediment particles become completely surrounded by water.
This process is called liquefaction.
It can intensify ground shaking or cause the ground to settle. Settling can cause structures to tilt or collapse.
The more energy a surface wave carries, the stronger the ground motion will be and the more damage the wave will cause.
However, surface waves decrease in size and energy the farther they travel from the epicenter.
Therefore, the farther an area is located from the epicenter, the less damage it will suffer.
The materials with which structures are built also determine the amount of earthquake damage.
Flexible structures are more likely to survive strong ground shaking.
Taller buildings are more susceptible to damage than shorter buildings.
Special technologies control how much tall buildings sway during earthquakes.