1. Unit 3: Earth Science Lesson 3: Earthquakes and Volcanoes

2. Objectives: By the end of the lesson you should be able to:
Explain how earthquakes are caused
Distinguish between epicenter and focus
Explain the 2 ways of measuring earthquakes
Describe the 3 types of waves produced in an earthquake
Describe the 2 types of volcanoes and the 3 types of eruptions

3. Background Info on Earthquakes
Evidence of plate tectonics
Over 1 million occur every year (that’s 1 every 30 sec)
Most are too small to be felt
Not all occur on land – some occur in oceans causing tsunamis

4. Earthquakes
Can be shallow (40kms) or deep (700kms) depending on fault type
Deep EQ cause more damage
After shocks are renewed tremors that follow a major EQ – may continue for months afterwards!

5. Focus VS Epicenter Focus:
Actual physical location of the EQ below the surface
Epicenter:
Location of the EQ on the surface (directly above the focus)

6. Finding the Epicenter Use the speed of waves and 3 different locations
This is called TRIANGULATION (we will talk more about this later!)

7. Waves
Primary Waves: (P Waves) waves of compression – can travel through any material – Fastest!
Secondary Waves: (S Waves) move at right angle to direction of travel – can travel through solids only (not liquids) – half as fast as P waves
Surface Waves: (L Waves) travel along surface like ripples in a pond – these do all the damage - slowest

10. Measuring Earthquakes
Seismometer: records EQ waves that travel through the Earth
Richter Scale and Mercalli Scale are both used to determine the strength of an EQ

11. Earthquake Scales Richter Scale: Developed in 1935
Measures amount of motion
Open ended but anything greater than 10 is highly unlikely
Exponential scale (each step is 10X greater than the one below it)
Mercalli Scale:
Developed in 1902
Ranges from I – XII
Based on intensity (a human judgment of damage done)
Not used as often now

12. Richter Scale Magnitudes Effects
Less than Generally not felt, but recorded.
Often felt, but rarely causes damage.
Under At most slight damage to well designed buildings. Can cause major damage to poorly constructed buildings over small regions.
Can be destructive in areas up to about 100 kilometers across where people live.
Major earthquake. Can cause serious damage over larger areas.
8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

14. Results of Earthquakes
Liquefaction: soft wet sand get compacted together as it is shaken
If something solid is on top of the sand, the pressure breaks the surface and the sand comes erupting to the surface in a liquefied form
Ground ruptures: breaks in ground
Landslides: land slides down a slope
Tsunamis: enormous waves from EQ in ocean
Fires: problematic if EQ ruptures main water supply

16. Triangulation
We know the speed of the P and S waves – so by determining the time lag between their arrivals we can figure out how far away the epicenter is
We need at least 3 stations to do this
Complete the triangulation activity

17. Background Info on Volcanoes
Evidence of a still active Earth
Asthenosphere is very close to the melting point of rock and the friction due to moving plates finishes the melting producing magma
Magma is less dense and tends to rise = volcanoes!
Often release large amounts of gas (CO2, SO2 and H2O)

18. Magma VS Lava Magma = melted rock under the crust
Lava = melted rock on the Earth’s surface
- two types of lava:
1) Mafic: thin and fluid
2) Felsic: thick and viscous

19. Types of Volcanoes Shield: Mafic lava Gentle eruptions Rounded dome
Made of basalt rock
EX. Mauna Kea
Strato:
Felsic lava
Explosive eruptions
Very peaked shape
Formed of layers
EX. Layer Cake Mountain

20. Mauna Kea

21. Layer Cake Mountain
Mount Fuji; Japan

22. Volcanic Vents
Openings in the crust, usually within the crater of a volcano, where magma (molten rock) and volcanic gases escape from the volcano's interior.
Typically, a volcano's crater may contain several vents.
A single vent can consist of a single round opening, or a larger or smaller fissure or fracture.

23. Volcanic Vent

24. Types of Eruptions
1) Rift Eruptions: occurs at diverging plates; mafic lava that travels thousands of kms
EX. Mount Boucherie
2) Subduction Boundary Eruptions: felsic lava (so strato volcano)
EX. Mount St. Helens
3) Hot Spots: mafic lava that can follow a crack in a plate (shield volcano)
EX. Hawaii

25. Mount Boucherie
Hawaiian Islands
Mount St. Helens

26. Results of Volcanoes
Ash Fall = ash that has been deposited on the ground after a volcano
Global Climate Change:
Adding volcanic gas and ash into atmosphere can lead to lower temps and dimmer days
Mass extinctions
Global warming and cooling
Ozone destruction
Vog (volcanic smog)