Plate Tectonics, Earthquakes, and Volcanoes
Earth’s Structure
• Crust – thin, rocky top layer
• Mantle – middle layer; 82% of Earth’s mass
• Core – innermost layer
– Outer Core – liquid layer
– Inner Core – solid layer
• Lithosphere – crust and upper mantle
• Asthenosphere – lower mantle; partially melted
• Moho is boundary between the crust and mantle
• Waves speed up
• P waves diffract (bend)
• P waves slow when passing through the outer core
• S waves can’t pass through the core
Continental Drift
• Continents float on the ocean and drift from place to place
• Created by Alfred Wegener in the 1920s
• First to theorize about Pangaea
• Theory was disputed by colleagues
Plate Tectonics
1. Continental Puzzle
2. Matching Fossils
3. Rock Types and Structures
4. Ancient Climates
Energy Source
• Convection Cells
Earthquakes
 The starting point of the earthquake – focus
 below Earth’s surface
 epicenter is the point directly above the focus on Earth’s surface
 Fault – a fracture in the crust where the movement has occurred
Plate Boundaries
• Divergent Boundary - creates mid-ocean ridges with rift valleys in the ocean
and rift zone on land
• Convergent Boundary – creates
mountains and volcanoes on land and
trenches in the ocean
• Transform Fault Boundary – creates cracks
Paleomagnetism
• Earth’s poles switch periodically
• Rocks formed are magnetic  point to magnetic North
• Rocks are found with reverse polarities
Cause of Earthquakes
 Elastic Rebound Hypothesis
 Rocks are stretched
 Energy accumulates
 Rocks are bent to their breaking point and will vibrate for a short time
(earthquake)
 Rocks return to their shape
Aftershocks and Foreshocks
 Foreshocks are vibrations or small earthquakes that are seen before the major earthquake.
 Aftershocks are vibrations or small earthquakes that are felt after an earthquake.
Damage Caused by Earthquakes
 Damages to buildings, streets, etc. (infrastructures).
 Liquefaction occurs when sediments are saturated with water and move, so that it can no longer support
buildings.
 Tsunamis is caused by the ocean floor is moved upward, creating large waves.
 Landslides are created when the ground subsides (sinks) from the vibrations, so that it can no longer support
buildings.

Fires are often created from broken gas and electrical lines under the city which are started on fire. Because of
the amount wooden structures, the fire can spread very quickly throughout the cities.
Measuring Earthquakes
 Seismographs measure earthquake vibrations
 Seismogram is the print-out
Determining Earthquake Distance
 S waves travel faster than P waves
 Differences in arrival time can be used to determine distance
from earthquake
 Draw circle around the city using the distance from
earthquake from 3 different centers
 Where the circles meet is the epicenter of the earthquake
Earthquake Waves
Anatomy of Volcano
•
Volcano – repeated eruptions of lava or pyroclastic materials that is separated by long inactive periods.
– Result in mountain building
– Crater – small, steep-sided depression at the top of the volcano (summit)
Shield Volcanoes
• Basaltic composition
• Slightly domed structure
• Grow up from the ocean
floor
• Hawaiian Islands and
Iceland
Cinder Cones
• Made mostly from ash,
lapilli, cinders
• Gas-rich basaltic lava
• Erupt mostly pyroclastic
materials with small
amounts of lava
• Formed through a single
eruption that may last a few
weeks to several years
– After the eruption,
the pipe solidifies
and blocks future
eruptions.
• Usually very small in
diameter and height
• Flagstaff, Arizona consists of
about 600 cinder cones
volcanoes
• Mt. Etna has dozens of
cinder cone volcanoes on
the sides of the mountain
1. List at least 10 new things that you learned from the video.
2. Write a summary (at least 4 sentences) about the video.
Composite Cones
• Also known as stratovolcanoes
• Found mostly in the Ring of Fire in
Pacific Ocean
– Includes the Andes of South
America, the Cascades of
North America (Mt. St.
Helens, Mt. Ranier, Mt.
Girabaldi), Aleutian
Mountains, Japan,
Philippines, and New
Zealand
• Composed of pyroclastic materials
and lava
• Gas-rich silica magma
• Can eject large amounts of
pyroclastic materials
• Steep summit with gentle flanks