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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
How doscientist
knowabout the
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