Earthquakes and Volcanoes

EARTHQUAKESPlate Tectonics

• Lithosphere – the crust and upper part of the earth’s mantle

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1. Inner Core

2. Outer Core

3. Mantle

4. Crust

EARTHQUAKESPlate Tectonics

• Plates – large pieces of the lithosphere• Theory of plate tectonics – the idea that the

earth’s crust is made of moving plates• Plate Boundaries – places where the plates meet

– Scientists think as the magma in the Earth’s mantle moves, it causes the plate boundaries to collide, separate or slide along each other.

EARTHQUAKESPlate Tectonics

• Scientists believe the Earth is made up of large plates that float on the partly melted rock of the Earth’s mantle.

• Pangaea – a large landmass that some scientists think may have existed at one time– No recorded observations

EARTHQUAKESCauses of Earthquakes

• Earthquakes often occur when rocks along the plate boundaries shift suddenly and release stored energy.

• Construction of large buildings and the movement of molten rock under a volcano can also cause earthquakes.

EARTHQUAKESCauses of Earthquakes

• Faults – breaks in the earth’s surface along which rocks can move– Three kinds of faults – determined by how the rocks

move against each other (thrust or reverse fault, normal fault, strike-slip fault)

• Reverse fault – rocks push together until a section of rock moves upward

EARTHQUAKESCauses of Earthquakes

– Three kinds of faults – determined by how the rocks move against each other (thrust or reverse fault, normal fault, strike-slip fault)

• Normal fault – rocks moving apart

• Strike-slip fault – rocks moving horizontally past each other

EARTHQUAKESEarthquake Waves

• Earthquakes occur below the surface of the earth.• Focus (A) – beginning point of an earthquake • Seismic waves – vibrations that flow out from the

beginning point of an earthquake• Epicenter (B) – the point on the surface of the

earth directly above the focus

EARTHQUAKESEarthquake Waves

• Body waves – seismic waves that occur beneath the surface of the earth– P Waves – primary waves; fastest moving; travel in a

straight path by a push and pull motion; these waves move back and forth

S Waves – secondary waves; move more slowly; move in an up and down zigzag pattern; causes the particles in the rock to vibrate to the direction in which the wave is moving

EARTHQUAKESEarthquake Waves

• Surface Waves: the slowest moving and most destructive waves– Can move back and forth in a zig zag pattern; fastest

moving land waves

– Can move in a circular pattern; rolling motion along the ground

EARTHQUAKESDetecting Earthquakes

• Seismograph – a machine that detects, times, and measures the movement of the earth

• Seismograms – records of the movements of the earth

• Seismologists – scientists who study the movement of the earth

EARTHQUAKESMeasuring Earthquakes

• Mercalli scale – based on the amount of destruction caused to man-made structures– Measures observable destruction

• Richter scale – measures the magnitude of an earthquake’s seismic waves and assigns it a number– Magnitude – strength of the seismic waves of an

earthquake, this is how much energy is released.

EARTHQUAKESBuilding for Earthquakes

• Features that help structures withstand earthquakes:– Concrete reinforced with steel rods– Foundation laid in rock– Steel framing

EARTHQUAKESRelated Disasters

• Tsunami – giant ocean waves triggered by earthquakes, volcanoes, or landslides

• Other catastrophic events associated with earthquakes:– Volcanic eruptions– Landslides

VOLCANOES

• Magma – molten rock under the earth• Volcano – are a form of a mountain, they occur when

a crack in the earth’s surface allows magma and gases to come to the surface

• Volcanologists – scientists who study volcanoes• Magma chambers – pockets of molten rock in the

earth’s lithosphere• Lava – hot molten rock that breaks through the

surface of the earth• Vent – opening in the surface of the earth through

which lava flows• Crater – the bowl shape at the top of a main vent

VOLCANOESCauses of Volcanoes

• Volcanic ash – jagged bits of crushed rock• Volcanic cone – funnel-shaped mound

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Draw this Diagram in your notes.

1. Side Vent

2. Vent

3. Lava

4. Magma Chamber

VOLCANOESLocations of Volcanoes

• Volcanic activity may occur under the ocean, at hot spots, along plate boundaries, and along the Ring of Fire.

• Ring of Fire – active volcanoes around the edges of the Pacific Ocean

• Under water eruptions (submarine eruptions) are 20x more frequent than eruptions on land

• Hot spots – places where a pool of very hot magma rises toward the surface and forms new land

VOLCANOES – ClassifyingBy Shape

• Shield volcano – large, gradually sloping sides; erupts continuous flowing lava; mild, continuous eruptions

• Cinder cone – resembles a hill; has a bowl-like crater; usually has more than one vent; made of cinders– Cinders – bits of ash and lava

• Composite cone – steep sides and layers of lava and tephra– Tephra – a mixture of cinders, ash, and rock emitted by

a volcano

VOLCANOES – ClassifyingBy How Often They Erupt

• Volcanoes can have more than one kind of eruption because one eruption can change the conditions inside a volcano, causing it to erupt differently the next time.

• Active volcano – one that has erupted at some point during a recorded time period and is expected to erupt again

• Dormant volcano – has erupted in the distant past but is currently inactive and not expected to erupt again

• Extinct volcano – does not have a recorded eruption and is not expected to erupt in the future– There is NO guarantee that it will remain extinct

VOLCANOES – ClassifyingBy The Type of Eruption

• Hawaiian eruption – runny lava and little or no cinder, ash or steam; quiet; may continue for long periods of time

• Strombolian eruption – fountain of lava that runs down the sides

• Vulcanian eruption – violent; causes a loud explosion that sends lava, ash, cinders, and gas into the air

• Pelean eruption – produces a pyroclastic flow (avalanche of red-hot dust and gases emitted by a volcano)

• Plinian eruption – most powerful; spews lava, blows gases, ash, and debris into the atmosphere

• Pyroclastic flow – a high-speed flow of very hot gases and dust

VOLCANOESEffects of Volcanoes

• Vog – volcanic gases; volcanic fog; pollutes the air and can cause acid rain and respiratory problems

• The gases, ash, and dust of volcanoes can cause cooling in the weather.

• Dangers of Volcanoes– Debris flow – when part of the mountain collapses and

mud and rock fragments surge down the mountain

• Products of Volcanoes– Soil rich in nutrients, valuable gems– Igneous rock – formed as magma and lava cool and

harden

VOLCANOESEffects of Volcanoes

• Other thermal eruptions– Hot spring – a heated pool of warmed ground water

• Geyser – a hot spring that blows steam and water into the air

• Mud pots – a hot spring that contains more mud than water

Review for CFA #11 Earthquakes & Volcanoes 1. Earthquakes occur along breaks in the earth surface, these breaks are

called___________. List and Describe the 3 types.

2. The _________is the beginning part of an earthquake & the ____________is the point on the surface of the earth directly above the focus.

3. ________ ________ are the vibrations that flow out of the beginning point of an earthquake. List and Describe the 3 types.

4. What are the 2 scales used to measure the strength of an earthquake? How do they differ?

5. What is magnitude?

6. What is a volcano?

7. Where can volcanic activity occur?

8. What is the ring of fire?

9. What are some of the effects of a volcanic eruption?

10. What types of geological events occur at plate boundaries?