Earthquakes and Volcanoes Chapter 10 - Quia · Earthquakes and Volcanoes Chapter 10 Objectives: 1)...

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Earthquakes and Earthquakes and

VolcanoesVolcanoesChapter 10Chapter 10

Objectives: 1) Describe the cause of earthquakes. 2) Identify the difference between p and s waves. 3) Explain how p and s waves are used to identify the location of the earthquake. 4) In what ways are the Richter Scale and the MM scale different?


EarthquakesEarthquakes

• One of most destructive forces on Earth

• Natural rapid shaking of the ground due to friction from sliding faults (ex rubbing your hands)– Results in displaced rocks

– Causes energy to dissipate outward

– Energy travels through Earth in seismic waves

– When reaches the surface, moves the ground

– On ocean floor, forms tidal waves—tsunamis





Seismic WavesSeismic Waves

• Seismic Waves can be detected using a seismograph– Uses series of springs and weights

• Types of seismic waves:– 1) P-waves (compressional primary wave)

• Move like sound waves

• Fastest type of seismic wave

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Seismic Waves Seismic Waves ((continuedcontinued))

• 2) S-waves (secondary waves)– Travel in an up-and-down pattern

– Can only travel through solid material

• Surface wave—interaction of P- and S-waves– Results in a rolling motion of the ground

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Source of waves is called the focus

Area directly above focus called epicenter


Epicenter LocationEpicenter Location• Determined by arrival of P- and S-waves

– Using a seismograph

– Locates the distance to the epicenter

– Use difference in arrival times

– Data from three seismograph stations needed


Earthquake MeasurementEarthquake Measurement

Strength measured using:

– Richter scale—measures equivalent energy produced

• Scale of 0 to 9

• Every increase in number means tenfold increased magnitude

• 5 is equivalent of medium-sized atomic bomb



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EarthquakeEarthquake

MeasurementMeasurement

• Or the MM scale, which measures destruction.

• The Modified MercalliIntensity (MM) scale is a means of categorizing the effects of shaking on people, structures and the environment.

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Objectives: 1)Uder what conditions do volcanoes often occur? 2) list and provide a one-sentence description for the 6 types of volcanoes discussed in class.


Formation of a VolcanoFormation of a Volcano

• Where molten rock flows from beneath crust– Molten rock is called lava

• Location associated with convergent tectonic plate boundaries– Where subducting plate begins to descend underneath another plate.

– Sinking plate brings in seawater making steam





Quiet Eruption VolcanoesQuiet Eruption Volcanoes

• Volcanoes are classified by type of eruption

• Eruption—release of lava, ash, steam, and gases

• Quiet eruptions from volcanoes called shield cones– Formed when lava flows from a central vent

• Lava cools at surface and solidifies forming a shield

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Quiet Eruption Volcanoes Quiet Eruption Volcanoes ((continuedcontinued))

• Fissure eruption

– Long crack in Earth’s crust

– Produces large amounts of lava

– Cool to form huge sheets or plateaus

– Deccan lava flows in India

– Columbia River plateau


Explosive Eruption VolcanoesExplosive Eruption Volcanoes

• Much more violent• Greatest threat to human life and property

• Composite cone—mountain-like structures– Fire-broken rocks that were blasted apart– Usually surround one central vent– Near subduction zones with convergent plate boundaries


Explosive eruption with lightning at

Sakurajima Volcano

Cinders were issued up to >2,500 m high

(23:03 on18 May 1991; taken by SVO)


Explosive Eruption Volcanoes Explosive Eruption Volcanoes ((continuedcontinued))

• Caldera—volcanic crater (a small canyon)– Left behind after composite cone is destroyed

– Crater Lake in Oregon

– One of world’s largest in Yellowstone Park

– Heats water • Produces geysers, mud pots, and hot springs


Caldera A large, usually circular depression at the summit of a

volcano formed when magma is withdrawn or erupted from a

shallow underground magma reservoir.


Geyer in Yellowstone

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• Lava dome – Smaller mounds, hardened lava covering a vent

– Grow slowly

– Build up great pressure

– After Mount St. Helens in 1980• Formed small lava dome in its crater




• Cinder cone– Small mound of lava, ash, and pyroclastic material

– Smallest type of volcano

– When lava breaks through for first time

– Resulting eruption spews lava into air

– Forms a volcanic bomb• Lava hardens before hitting the ground



Size and Shapes of VolcanoesSize and Shapes of Volcanoes


Volcanic HazardsVolcanic Hazards

• Most dangerous result is pyroclasticflow– Moves at speeds of more than 100 mph

– Contains hot gases, water, ash, and debris

– Destroys everything in its path

– Mount Vesuvius in A.D. 79• Destroyed Pompeii and Herculaneum

– Volcanic ash enters atmosphere and travels miles

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Volcanic Hazards Volcanic Hazards ((continuedcontinued))

• Ash mixes with water, causes mudflows• Mount Pinatubo in 1991

– Mudflow 650 feet deep

• Release of toxic gas– Sulfur dioxide and water forms sulfuric acid

• Debris flows called lahars– When snow melts suddenly at high elevations

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