A Changing Earth

Earthquakes and

Volcanoes

EARTHQUAKES Plate Tectonics

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

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3

4

1. Inner Core

2. Outer Core

3. Mantle

4. Crust

EARTHQUAKES Plate 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.

EARTHQUAKES Plate 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– Genesis 7:11 says “the fountains of the

great deep were broken up, and the windows of heaven were opened.”

EARTHQUAKES Causes 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 cause earthquakes.

EARTHQUAKES Causes 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

EARTHQUAKES Causes 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

EARTHQUAKES Earthquake Waves

• Earthquakes occur below the surface of the earth.

• Focus – beginning point of an earthquake

• Seismic waves – vibrations that flow out from the beginning point of an earthquake

• Epicenter – the point on the surface of the earth directly above the focus

EARTHQUAKES Earthquake 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, somewhat like

a slinky.

S Waves – secondary waves; move more slowly; move in an up and down zigzag pattern

EARTHQUAKES Earthquake Waves

• Land Waves – surface waves; the slowest moving and most destructive waves– Love waves – back and forth in a zig zag pattern;

fastest moving land waves

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

EARTHQUAKES Detecting 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

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layersof the earth?

EARTHQUAKES Measuring 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

EARTHQUAKES Building for Earthquakes

• Features that help structures withstand earthquakes:–Concrete reinforced with steel

rods–Foundation laid in rock–Steel framing

EARTHQUAKES Related 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 – occurs where 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

VOLCANOES Causes of Volcanoes

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

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5

1. Crater

2. Side Vent

3. Vent

4. Lava

5. Magma Chamber

VOLCANOES Locations 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 – Classifying By 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

Types of Volcanoes

VOLCANOES – Classifying By 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