Volcanoes and Earthquakes

For two-column notes, underlined titles are main ideas

Volcanoes• Volcanoes

– A mountain that forms in the Earth’s crust when magma (molten material) reaches the surface and cools to form solid rock.

– When magma reaches the surface, it is called lava

Where volcanoes form• At plate boundaries

– At divergent plate boundaries– At convergent plate boundaries

• where a continental and an oceanic plate meet and the latter is subducted

– Example: Ring of Fire: a belt of volcanoes along the edges of the Pacific plate

• where two oceanic plate meet– These often form island arcs, a string of islands– Examples: Japan, New Zealand, Caribbean

islands

Where volcanoes form• Where volcanoes form

– At hot spots• Places where material from the mantle rises

through the crust and melts to form magma• Hot spots stay in the same place while a plate

moves above them– Example: The Hawaiian islands formed from a

hot spot under the Pacific plate– Example: Yellowstone National Park is under a

hot spot in the state of Wyoming

Inside a volcano• Inside a volcano

– Magma chamber• Pocket where magma collects

– Pipe• Tube that extends from magma chamber to

top of volcano– Vent

• Opening in volcano (central vent on top; may be several on sides)

Inside a volcano• Inside a volcano

– Lava flow• Spread of lava as it pours from vent

– Crater• Bowl-shaped area that may form around

central vent

Inside a volcanoDraw this and label the diagram

Classwork 1

1. At what types of plate boundaries do volcanoes form?

2. What is the difference between magma and lava?3. What is a hot spot?4. What is a magma chamber5. What is a vent?6. What is a pipe?

Volcanic eruptions• Dissolved gases in magma expand, forcing

magma to flow through pipe and out vent• Eruption factors

– Silica is a mineral composed of the elements oxygen and silicon and is found in magma

– Temperature determines whether lava is thick or thin

• Types of Eruptions– Quiet Eruptions– Explosive Eruptions

Volcanic eruptions• Quiet eruptions - hazards

– Lava sets fire to or buries everything in its path

• Explosive eruptions - hazards– Pyroclastic flow of hot gases, volcanic ash,

cinders and bombs can move quickly down the sides of the volcano

– Landslides of mud, melted snow and rock can occur

– Volcanic ash can be thrown high into the atmosphere, where it can damage jet plane engines

Volcanic activity• Volcanic Activity

– Active• Erupting or shows signs that it may erupt in

near future– Dormant

• “Sleeping” volcano expect to erupt again one day

– Extinct• Unlikely to ever erupt again

Volcanic landforms• From Ash and Lava

– Types of landforms• Shield volcano – gently sloping lava flows• Cinder cone volcano – from explosive eruptions• Composite volcano – alternating layers of lava and

layers of ash, cinders, bombs• Lava plateau – Forms from repeated lava flows along

long cracks in an area• Caldera – hole left if magma chamber collapses after

eruption

Volcanic landforms – Ash and lava

Lava plateau

Volcanic landforms

How a caldera forms

Volcanic landforms• From Magma

– Types of landforms• Volcanic necks – Magma hardened in pipe, softer rock

around pipe eroded• Dikes and sills – Across rock layers, dike; between

rock layers, sill• Dome mountains – uplift pushes a hardened mass of

magma toward the surface• Batholith – Large body of magma forms inside crust

Volcanic landforms• From Magma

Batholith

Classwork 2

1. What are the two types of volcanic eruptions?

2. What are the three types of volcanic activity?

3. Describe the three types of volcano4. How does a lava plateau form?5. How does a caldera form?

EarthquakesForces in Earth’s Crust

• Stress– Tension

• Force that pulls crust and thins rocks in the middle

– Compression• Force that squeezes rocks until they fold or

break– Shearing

• Force that pushes mass of rock in two opposite directions

Earthquakes• Stress

Draw these three types of stress

EarthquakesForces in Earth’s Crust

• Faults– A fault occurs when enough stress builds up in

rock to break it– Types of faults

• Normal– Fault cuts through rock at an angle– One block of rock sits over fault (hanging wall)– Other block sits under the fault (footwall)– During movement, hanging wall move

downward, footwall moves upward

Forces in Earth’s Crust• Faults

– Types of faults• Reverse

– Same structure as normal fault– During movement, hanging wall moves

upward, footwall moves downward• Strike-Slip Faults

– Rocks on either side of fault slip past each other

– Little up or down motion

Forces in Earth’s Crust• Faults

Draw this normal fault and label the footwall and hanging wall

Forces in Earth’s Crust• Faults

Draw this reverse fault and label the footwall and hanging wall

EarthquakesForces in Earth’s Crust

• Faults

Draw this strike-slip fault

Forces in Earth’s CrustCreating new landforms• Folding Earth’s crust by compression

– Anticlines• Fold that bends upward into an arch

– Synclines• Fold that bends downward like a V

– Folded mountains• Himalayan mountains in Asia• Alps in Europe• Process requires millions of years

Forces in Earth’s CrustCreating new landforms

Draw this diagram, label the syncline and anticline and draw in the arrows showing the direction of force

Forces in Earth’s CrustCreating new landforms• Stretching Earth’s Crust

– Fault block mountains• Two normal faults cause valleys to drop down

on either side of a block of rock• As hanging walls of each fault drop down, block

in between stands above surrounding valleys

Forces in Earth’s CrustCreating new landforms

Draw this diagram

Forces in Earth’s CrustCreating new landforms• Uplifting Earth’s Crust

– Plateaus• Large area of land elevated high above sea level

Classwork 31. Describe the three types of stress2. What is a fault?3. Describe the three types of faults4. Describe three types of folds in the Earth’s

crust5. How is a plateau formed?

EarthquakesEarthquakes and Seismic Waves

Seismic Waves• Waves produced by earthquakes that travel

through the Earth

EarthquakesTypes of Seismic Waves

– P Waves• Seismic waves that compress and expand ground

like an accordion (longitudinal)• Fastest waves of the three

– S Waves• Seismic waves that can vibrate side-to-side or up

and down (transverse)• Arrive after P waves

– Surface Waves• Similar to waves in water; can make ground roll

like ocean waves (also transverse)

EarthquakesEarthquakes and Seismic Waves

Draw and label these P, S and surface wave diagrams

Anatomy of an earthquake• An earthquake is the shaking and trembling

that results from movement of rock beneath the surface

• The point beneath Earth’s surface where rock breaks under stress and triggers an earthquake is called the focus

• The point on Earth’s surface directly above the focus is called the epicenter

Measuring earthquakesMonitoring Earthquakes

How do seismographs work?

Measuring earthquakes

Monitoring EarthquakesReading a Seismogram

Measuring earthquakes

Earthquakes and Seismic WavesHow is an epicenter located

Measuring earthquakes • Modified Mercalli Scale

– Rates the amount of shaking from an earthquake

– Done by observation (no instruments)• Richter Scale

– Measures earthquake magnitude (size)– Measure small earthquakes using

seismographs– Take distance into account

• Moment Magnitude Scale– Measure total energy of an earthquake using

seismographs

Measuring earthquakes

Earthquakes and Seismic WavesHow are earthquakes measured

Modified Mercalli Scale

Moment Magnitude Scale

Measuring earthquakes

Monitoring EarthquakesEarthquake risk in the United States

Earthquake Hazards• Ground Shaking

– Buildings can be damaged by the shaking – Buildings can be damaged by subsidence (the

ground beneath them settling to a different level

– Soil liquefaction (mixing of sand or soil and groundwater) causes ground becomes very soft and acts similar to quicksand. 

• Ground Displacement – Land on sides of fault moves in different

directions•

Earthquake Hazards• Flooding

– Dams or levees break– Tsunamis (huge wave caused by an

earthquake under the ocean) 2004 Indian Ocean tsunami killed over 230000 people

– Seiches (occur on lakes shaken by earthquakes)

• Fires– Broken gas lines and power lines– Tipped over wood or coal stoves.

Pacific Ring of Fire Mid-Ocean Ridge Eurasian-Melanesian

Earthquake risk in the world

Where Earthquakes Occur

• Most Earthquakes occur on plate boundaries– Some earthquakes can occur on plate boundaries that

aren’t active anymore (like in Missouri, US or in central China)

• There are three zones:– Pacific Ring of Fire (mostly subduction but some transform

plate boundaries)– Mid-Ocean Ridges (diverging ocean plates)– Eurasian-Melanesian (continental plates colliding)

• If there are several faults in an area they can form an interconnected fault zone

Classwork 4

1. How does a seismograph work2. How do you read a seismogram?3. What is the risk of an earthquake in Florida?4. What part of the United States has the highest

earthquake risk?5. Where do most earthquakes occur?