Chapter 5: Earthquakes and Volcanoes Section 1 - Earthquakes

What causes earthquakes? When sudden energy is released from Earth’s crust breaking or moving which cause vibrations. If the vibrations are large enough they are felt as earthquakes.

What is a Fault? A fault is a large fracture in rock along which movement occurs. The type of fault that forms depends on the forces applied to the rock.

What are the three main types of faults? Normal Fault Reverse Fault Strike-Slip Fault

What are Normal Faults? When rocks are pulled apart under tension forces. Along this fault, rock above the fault moves DOWN compared to rock below the fault

What are Reverse Faults? Created when compression forces squeeze rocks together and rock above a fault moves UP compared to the rock. Reverse Fault Animation

What are Strike-slip Faults? Shearing forces cause rock to move past each other in opposite directions along Earth’s surface. Strike Slip Fault Animation

Where do earthquakes begin? Inside the earth at the FOCUS.

What is a focus? What is an epicenter? The focus is the point INSIDE Earth where movement first occurs and energy is released. What is an epicenter? The epicenter is the point on Earth’s SURFACE located directly above the focus.

What are Seismic Waves? Waves of energy that travel away from the focus in ALL directions.

What are the three main types of seismic waves? Primary waves (P-waves) Secondary waves (S-waves) Surface waves

What are Primary Waves (P-waves)? The first waves. Travel the fastest through rock material. The rock particles move back and forth in the same direction as the waves are moving. Primary Waves Animation

What are Secondary Waves (S-waves)? Next waves to occur after P-waves. Jiggle the rock through which they pass up and down and from side to side. Secondary Waves Animation

Surface Waves Animation What are Surface Waves? Slowest and largest. Cause the most destruction. Can vibrate side to side, sway or like “waves of water” across land. Surface Waves Animation

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How are Earthquakes Measured? By a seismologist who is a scientist that studies earthquakes and seismic waves. Using a seismograph which is the instrument used to measure seismic waves.

How do seismologists locate the epicenter? They look at the distance between the seismic waves arrival times. Data from at least three different seismograph stations. Where the points meet is where the epicenter is located.

The measure of an earthquake’s strength. Earthquake in Japan, 1923 What is magnitude? Before After The measure of an earthquake’s strength.

How is earthquake strength (magnitude) measured? Using the The Richter Scale which measures the earthquake’s magnitude. The scale ranges from 1-10; 1 = weakest; 10 = strongest As each number goes up, the strength increases by 10 and it releases 32 times more energy.

How is earthquake damage measured? By the Modified Mercalli intensity scale which measures how much damage an earthquake creates. The range of intensities is represented by Roman numerals. The range is from I (1) to XII (12); I = least damage, XII = most damage

Earthquakes with Tim and Moby!

What are Tsunamis? Powerful seismic sea waves. Occur when an earthquake occurs on the ocean floor. Can travel outward from the epicenter in ALL directions. When they approach land, the waves slow down and the height increases.

Tsunamis with Tim and Moby!

What is seismic safe? When a building will be able to stand up against earthquake vibrations.

How can we be seismic safe? Retrofitting buildings Installing underground pipes that can bend Buildings standing on steel and rubber supports Keep away from all windows; avoid anything that may fall on you

Can earthquakes be predicted? Earthquakes are unique – no single change happens to the Earth before an earthquake strikes which is why they are almost impossible to predict.

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Chapter 5 Section 2 - Volcanoes

What is a volcano? A cone shaped hill or mountain formed when hot magma, solids and gases erupt onto Earth’s surface through a vent.

What is magma? Molten rock material under the Earth’s surface. Magma can be pushed upward by rocks that surround it.

How do volcanoes form? Layers of cooled, hardened lava Hot spots

What is lava? What is the difference between lava and magma? Magma is INSIDE the Earth and lava is OUTSIDE of the Earth. Molten rock materials above Earth’s surface.

What is a crater? Circular hole at the top of a volcano where lava and other volcanic materials are released.

Bits of rock or solid lava that falls from the air after an eruption. What is tephra? Bits of rock or solid lava that falls from the air after an eruption.

What is subduction? When two plates collide and the heavier plate sinks below the lighter plate causing it to melt which forms a chamber of magma. Occurs when an oceanic plate collides with a continental plate or when two oceanic plates collide.

What is a hot spot? Weak spots in the crust that allow magma to rise upward. Hot spots are NOT located on plate boundaries. The Hawaiian Islands formed because of a hot spot.

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What determines HOW a volcano will erupt? Some eruptions are violent and some have just slow flowing lava quietly down its slopes…. The “ingredients” of the magma determines what type of eruption will occur! Lava that has more silica (oxygen and silicon) is thicker and slower. Lava that has more iron and magnesium and LESS silica flows easier and faster. Water vapor and other gases can also affect eruptions.

Types of Volcanoes There are three major types of volcanoes: Shield volcanoes Cinder cone volcanoes Composite volcanoes or stratovolcanoes

Shield Volcano Largest type of volcano Gentle, hilly slopes Formed by the build up of basaltic lava layers Slower lava flows

Shield Volcanoes (cont.) Forms where magma is forced up from deep in the Earth OR where plates are diverging (separating) EXAMPLE: Mauna Loa, Hawaii which is the largest active volcano on Earth.

Cinder Cone Volcanoes Relatively small volcanoes usually less than 300 meters tall. Often form in a group near other larger volcanoes.

Cinder Cone Volcanoes (cont.) Formed by medium force of explosion of tephra Once gas is released the eruption stops Can have short powerful eruptions or high eruptions EXAMPLE: Sunset Crater, Arizona

Composite Volcanoes (Stratovolcanoes) Steep-sided volcanoes made of alternating layers of lava and tephra. Sometimes erupting violently, releasing large amounts of ash and gas, which forms a tephra layer of solid materials.

Composite Volcanoes (cont.) Then a “quieter” eruption forms a lava layer. Forms when one plate subducts beneath another. Most common type of volcano EXAMPLE: Mount St. Helens, Washington

Fissure Eruptions Fissure – cracks in Earth’s surface Magma that is highly fluid (watery) can ooze from fissures and form lava plateaus.

Chapter 5 Section 3 – Earthquakes, Volcanoes, and Plate Tectonics

Pacific Ring of Fire The Pacific Ocean is almost completely surrounded by volcanoes. This ring is thousands of miles long and contains hundreds of volcanoes. 80% of all earthquakes and volcanoes happen in the Ring of Fire.

Ring of Fire

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