Earth Science Ch. 11:Earthquakes and Volcanoes

Ch. 11-1: Earthquakes

Key Terms• Earthquake

• Epicenter

• Focus

• Richter Scale

• Seismograph

California Content Standards for Earth Science Addressed:

Earth Science3(d) Students know why and how earthquakes

occur and the scales used to measure their intensity and magnitude.

3(e) Students know there are two kinds of volcanoes: one kind with violent eruptions producing steep slopes and the other kind with voluminous lava flows producing gentle slopes.

9(e) Students know the principal natural hazards in different California regions and the geologic basis of those hazards.

Ch. 11-1:Why Do I Need To Know This?

1. Because earthquakes rock!2. Because earthquakes are a major

geological hazard in California.3. Because you need to be prepared for

a major earthquake.

Key Sections Ch. 11-1

• Seismic Waves– Primary Waves– Secondary Waves– Surface Waves

• The Seismograph– Seismologists

• Predicting Earthquakes

Earthquakes

• An earthquake is the shaking and trembling that results from the sudden movement of part of the Earth’s crust.

• Over 1,000,000 earthquakes happen every year (about 1 every 30 seconds).

• Most are so small that we do not feel them.

• Earthquakes happen along faults, or big cracks in the surface of the earth.

• Earthquakes can occur beneath the ocean causing giant waves called tsunamis.

Seismic Waves

• Most earthquakes occur between a depth of 0 and 70 km below the earth’s surface.

• Some occur as deep as 700 km below the earth’s surface.

• Where an earthquake occurs (and the rocks break and move) is called the focus. The spot on the Earth’s surface directly above the focus is called the epicenter.

• The energy released in an earthquake moves throughout the earth as seismic waves which are like sound waves.

Seismic Waves

• There are 3 main types of seismic waves:– Primary Waves– Secondary Waves– Surface Waves (R

and L waves)

Seismic Waves

• Seismic waves bounce off of any boundary that they hit and tell geologists a lot about what makes up the inside of the Earth.

Primary Waves

• Primary Waves (P-Waves) are the seismic waves that travel the fastest.

• P-waves can travel through solids, liquids and gases.

• P-waves have a push-pull motion.

Secondary Waves

• Secondary Waves (s-waves) do not travel as fast as p-waves.

• S-waves cause rocks to move in a vertical motion.

• S-waves can travel through solids only (not liquids and gases).

Surface Waves

• Surface originate at the Earth’s surface at the epicenter and travel the slowest of all the wave types.

• Surface waves cause the Earth’s surface to tumble up and down and side to side.– Therefore, surface waves cause the most damage

in an earthquake.

The Seismograph

• A seismograph is a machine that geologists use to measure seismic waves.

• Using a seismograph, geologists can determine where, when and how strong an earthquake was.

Seismologists

• Seismologists are geologists who study earthquakes.

• They use the Richter Scale to measure the strength of an earthquake.

• The Richter Scale goes from 0 to 10.

– A 2.0 earthquake is 10 times more powerful than a 1.0 earthquake.

– A 3.0 earthquake is 100 times more powerful than a 1.0 earthquake.

– A 4.0 earthquake is 1000 times more powerful than a 1.0 earthquake!

Seismologists

• Seismologists analyze the data from seismograms to determine the different waves and motions.

Predicting Earthquakes

• There is no guaranteed way to predict an earthquake.

• Geologists are continuing to research signs that an earthquake is coming.

Ch. 11-2: Formation of a Volcano

Key Terms• Magma• Lava• Volcano• Shield Volcano• Composite Volcano• Crater• Caldera

California Content Standards for Earth Science Addressed:

Earth Science3(e) Students know there are two kinds of volcanoes:

one kind with violent eruptions producing steep slopes and the other kind with voluminous lava flows producing gentle slopes.

3(f) Students know the explanation for the location and properties of volcanoes that are due to hot spots and the explanation for those that are due to subduction.

9(e) Students know the principal natural hazards in different California regions and the geologic basis of those hazards.

Ch. 11-2:Why Do I Need To Know This?

1. Because volcanoes are HOT!

2. Because volcanoes can and do cause tens of thousands of deaths.

3. Because California has many active, dormant and extinct volcanoes.

Key Sections Ch. 11-2

• Volcanic Eruptions

• Types of Volcanoes– Cinder Cones– Shield Volcanoes– Composite Volcanoes

• Craters

• Volcanic Activity

Formation of a Volcano

1. Deep within the Earth, rocks melt under tremendous heat and pressure.

2. The melted rocks, called magma, begins to rise toward the surface of the Earth.

3. As the magma rises, it stores up underground in magma chambers.

4. Eventually, the magma reaches the surface of the Earth. The opening through which the magma erupts is called a vent.

5. When magma reaches the surface of the Earth, it is called lava.

Volcanic Eruptions

• Not all volcanic eruptions are the same. – Some are extremely explosive and violent.– Others are slow and steady.

• The type of volcanic eruption that happens depends on the amount of dissolved gases (steam and carbon dioxide) and the type of magma being erupted.

Extrusive Igneous Rocks• These are igneous rocks that formed at the

Earth’s surface.• Extrusive rocks can have glassy, fine-grained or

porphyritic textures.• They may also show signs of lots of gas bubbles

in them.• The most common forms of extrusive igneous

rocks are basalt, andesite and rhyolite.

Types of Volcanoes

• There are 3 main types of volcanos that form. They are:– Cinder Cones– Shield Volcanoes– Composite Volcanoes

• The type of volcano that forms depends upon the type of lava that is being erupted.

Cinder Cones• Cinder cones are made up of lots

of volcanic ash, volcanic dust and other rock debris from a small eruption.

• Cinder cones have steep sides and are only a few hundred feet tall at most.

• Cinder cones last for about 100,000 years or so before eroding.

Shield Volcanoes• Shield volcanoes form from

basalt, which flows very easily.

• Consequently, they tend to form big, broad and smooth volcanoes.

• The Hawaiian Islands (and almost all other volcanic islands) are examples of shield volcanoes.

Composite Volcanoes• Composite volcanoes are formed

by alternating layers of rock particles and lava.

• Composite volcanoes have steep slopes.

• Composite volcanoes are formed by andesite and/or rhyolite.

• Composite volcanoes are the most common form of volcano on the Ring of Fire.

Calderas

• When a volcano is done erupting, there is usually a funnel-shaped hole in the ground from which the lava erupted. This is called a crater.

• Often, when a volcano is done erupting, the underground magma chamber is empty and collapses. This is called a caldera.

Volcanic Activity

• Volcanic eruptions are very difficult to predict.

• An active volcano is one that erupts either continually or periodically.

• A volcano that has been known to erupt within historic times, but is not now active is called a dormant volcano.

• A volcano that has not been known to erupt in historic times is considered extinct.

Ch. 11-3: Volcano and Earthquake Zones

Key Terms• Ring of Fire

Key Sections Ch. 11-3

• None.

California Content Standards for Earth Science Addressed:

Earth Science

9(e) Students know the principal natural hazards in different California regions and the geologic basis of those hazards.

Ch. 11-3:Why Do I Need To Know This?

1. Because we live in California, one of the most geologically active states in the country.

2. Because California is part of the Ring of Fire.

3. To better understand plate tectonics.

Volcano and Earthquake Zones

• Volcanoes and earthquakes tend to occur in the same parts of the world. This has to do with plate tectonics.

• These are:– The Ring of Fire– The Mediterranean Zone– The Mid-Atlantic Zone

Ring of Fire