Earthquakes and Volcanoes!

Oh my!

Stress

• Stress: a force that acts on rock to change its shape or volume

• 3 Types of Stress (happens in the crust):– Tension: pulls on the crust– Compression: squeezes until folded or

breaks– Shearing : pushes rocks in opposite

directions

Faults

• Faults: the point where rocks break Ex. San Andreas fault

• 3 Types of faults:– Normal faults: form where rocks are angled with

each other; one block or rock lies below the other – Reverse faults: are like normal faults but move in the

opposite direction– Strike-slip faults: form when rocks slide past each

other

Faults

Faults: What kind am I?

Earthquake

• Earthquake: shaking & trembling that results from the movement of rock below Earth’s surface

• Forces of the plates causes earthquakes.• Most start in the lithosphere.• Focus: area beneath the Earth where the stress

occurs & rock breaks• Epicenter: point on the surface directly above

focus

http://www.google.com/url?sa=i&rct=j&q=focus+and+epicenter+of+japan+earthquake&source=images&cd=&cad=rja&docid=3O7mAAS4hFS7AM&tbnid=172_WqiZ6horZM:&ved=0CAUQjRw&url=http%3A%2F%2Fearthquakesandplates.wordpress.com%2F2008%2F05%2F12%2Fdifference-between-earthquake-focus-and-the-epicenter%2F&ei=ZioEUfrUJYaI8QTZwIHoDg&bvm=bv.41524429,d.eWU&psig=AFQjCNE7D2HOpJNMidgn43e-KpySa8Ahug&ust=1359313895101689

Seismic Waves

• Seismic waves: vibrations that travel through Earth carrying energy released during an earthquake

• Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

Types of Seismic Waves

• P Waves- compress & expand (back & forth) the ground like an accordion, can damage buildings, travels through solids and liquids

• S Waves- the crust vibrates from side to side & up and down, shake the ground back and forth, travels through solids

• Surface Waves- P and S waves that reach the surface. Move very slowly in a wavelike motion

http://www.google.com/url?sa=i&rct=j&q=seismic+waves&source=images&cd=&cad=rja&docid=WXBThJqmwWRQNM&tbnid=wMjnW6PE4DBlZM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.education.com%2Fstudy-help%2Farticle%2Fearthscience-help-seismic-waves%2F&ei=qC8EUfiUMJPy8ATB2IGAAw&bvm=bv.41524429,d.eWU&psig=AFQjCNHCh3LLSLRrCNbq82F-ArPAmmVHCA&ust=1359315240933578

Measuring Earthquakes

• Mercalli Scale-based on level of damage (slight damage, moderate damage, great damage)

• Richter Scale-based on magnitude based on the size of the earthquake’s seismic waves, good for small, near-by quakes

• Seismograph- instrument that records the size of the seismic waves

• Moment Magnitude Scale-estimates total energy released

seismograph seismograph

http://www.google.com/url?sa=i&rct=j&q=earthquake+damage&source=images&cd=&cad=rja&docid=VuI_598RZfnS7M&tbnid=5PEkDrutT681_M:&ved=&url=http%3A%2F%2Fwww.wilderspin.net%2FSchool%2520stuff%2FScience%2FSpace%2FEarthquakes.html&ei=TzMEUZS_CYrm8gT-1YDQBQ&bvm=bv.41524429,d.eWU&psig=AFQjCNEXyhCE8wJHRV1pVsOUa5aZKfL_xQ&ust=1359316175435203

http://www.google.com/url?sa=i&rct=j&q=earthquake+damage+in+japan&source=images&cd=&cad=rja&docid=lGPigzuNBftJlM&tbnid=6_VSGM8sQM83DM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.newswise.com%2Farticles%2Fearthquake-structural-engineering-expert-available-to-discuss-haiti-earthquake2&ei=0jMEUfXZK4ig9QSKooHoDA&bvm=bv.41524429,d.eWU&psig=AFQjCNFXVujdw34FaRifvfZcHtXSzUvF1Q&ust=1359316307231179

http://www.sanandreasfault.org/Quake_7.jpg

Volcano

• Volcano: weak spots in the crust where molten rock (magma) comes to the surface

• Magma: molten mixture of rock, gases & water from the mantle

• Volcanoes form when plates converge &

diverge (on land & on ocean floor)

Island Arcs

• Island arc: a string of islands formed by the volcanoes along a deep ocean trench (oceanic plates converge) Ex. Japan, New Zealand

Hot Spot Volcanoes

• Hot spot: an area where material from deep inside the mantle rises & then melts

• A volcano forms above a hot spot when magma erupts through the crust & reaches the surface. Ex. Hawaii

Viscosity

• Viscosity: the resistance of a liquid to flowing (a property of magma)

– The greater the viscosity, the slower it flows (ex. honey)

– The lower the viscosity, the faster it flows (Ex. water)

• Viscosity of Magma depends on: silica content & temperature

• Silica-compound made of silicon & oxygen

• More silica, higher the viscosity

• Silica produces light colored magma that is sticky

• Viscosity increases as temperature decreases

• Pahoehoe (pah Hoh ee hoh ee):fast moving, hot lava with low viscosity. Produces lava mass with ripples & wrinkles when it hardens

• Aa (AH ah): slow moving, cooler lava with high viscosity. When it hardens, it forms huge, jagged chunks.

Pahoehoe Pahoehoe

Aa Aa

Parts of a Volcano

• Magma chamber-collection of magma under a volcano

• Pipe-long tube in the ground that connects the surface to the magma chamber

• Vent-opening that magma exits through

• Lava flow-area covered by lava

• Crater-bowl-shaped area at the top

http://www.google.com/url?sa=i&rct=j&q=volcano+with+all+of+its+parts&source=images&cd=&cad=rja&docid=Gp-SY8lqL3Fv5M&tbnid=K18EiAAcV_B5OM:&ved=0CAUQjRw&url=http%3A%2F%2Famsroom8.edublogs.org%2Fpage%2F8%2F&ei=aJAFUZHFGoTc8wTsw4DYBA&psig=AFQjCNGVYF_CYL6aoHYzfZgLRiCKuX-wtA&ust=1359405544726752

Types of Eruptions

• Quiet eruptions -magma has low silica content, high viscosity, slow moving

• Explosive eruptions -magma has high silica content, low viscosity, fast moving– Pyroclastic flow-eruption which hurls hot

gases, ash, cinder, and bombs

Volcanic Landforms

• Caldera-huge hole left by the collapse of a volcano (the magma chamber collapses)

• Volcanic neck-when magma hardens in a volcanic pipe (soft rock wears way exposing the hard rock)

• Dike-rock layer forming vertically• Sill-rock layer forming horizontally• Batholith-a large body of cooled, exposed

magma

Caldera (Crater Lake) in Iceland Caldera (Crater Lake) in IcelandDevil’s Tower in WyomingDevil’s Tower in Wyoming