1. Earthquakes and Volcanoes
Unit D Chapter 1 Lesson 3
Pgs D22-D29

2. 95% of earthquakes occur near faults, cracks in the earth’s crust.
When plates grind past each other they lock up, bend and stretch, and eventually snap releasing the energy.
This sudden jolt releases energy as vibrations that are felt as Earthquakes.
Overpasses are not the ideal place to be during an earthquake.
Earthquakes

3. The focus is the point inside earth’s crust where the movement starts.
The epicenter is the point on the surface directly above the focus.
A seismograph is an instrument that detects earthquake waves.
A seismogram is the recording of the earthquake on paper or in a computer.
Earthquakes

4. The energy from an earthquake travels away from the focus in waves.
The P-Wave or “Primary Wave” is the first wave. It is the fastest wave and causes push-pull motion.
The S-Wave or “Secondary Wave” is second. It is an up and down, slower wave in the earth.
The last wave is the “Surface Wave.” It travels on the surface and makes the ground roll and sway. The most damaging wave.
Earthquakes

5. Measuring Earthquakes
Scientists measure earthquakes in different ways.
The Richter Scale measures the amount of energy released during an earthquake.
The largest earthquake recorded was 9.5 on the Richter Scale in Chile, 1960.
An earthquake in Indonesia in 2005 measured 9.1 on the Richter Scale. The resulting tsunami killed 230,000 people.
The 2005 Indonesian Tsunami
Measuring Earthquakes

6. Measuring Earthquakes
The Mercalli Intensity Scale measures the amount of damage done.
The Mercalli scale goes from I to X11.
An earthquake with an intensity of I is hardly felt. An intensity of XII means complete destruction.
There are more than 900,000 earthquakes with a magnitude less than 2.5 each year.
Measuring Earthquakes

7. A volcano is a mountain that forms around openings in earth’s crust where lava builds up.
Volcanoes are earth’s chief land builders.
The Ring of Fire is a 30,000 mile long chain of volcanoes that surrounds the Pacific Ocean.
School bus vs. lava…..lava wins.
Volcanoes
House vs. lava…..lava wins

8. Shield Volcanoes- have a broad and slightly domed shape.
They are the world’s largest volcanoes.
They may erupt for over 1 million years.
They typically have “gentle” eruptions of runny lava.
Mauna Loa in Hawaii is the world’s largest active volcano.
Types of Volcanoes

9. Cinder Cone Volcanoes are built up of ashes, cinders and rocks from violent eruptions.
Most erupt for a short period of time and end up no taller than 1000ft.
They are typically steep sided with a flattened top.
A cinder cone volcano…it’s made of cinders…..and it’s a cone shape…..brilliant.
Types of Volcanoes

10. Composite or Stratocone Volcanoes switch between quiet eruptions of flowing lava and violent gas explosions.
This type of volcano has the most powerful eruptions of all.
Like shield volcanoes, composite volcanoes may erupt for up to one million years.
Types of Volcanoes
Mt. St. Helens is a Stratocone Volcano

11. Hot Spot Volcanoes Not all volcanoes form at the edges of plates.
Sometimes a single column of magma called a hot spot punches through the middle of a plate.
If this happens under the ocean, the build up of lava can get high enough to form islands.
The Hawaiian islands were formed by a hot spot.
Hot Spot Volcanoes