Unit 3: Earth Science Lesson 3: Earthquakes and Volcanoes

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

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

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!

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)

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

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

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

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

Richter Scale Magnitudes Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4 Often felt, but rarely causes damage. Under 6.0 At most slight damage to well designed buildings. Can cause major damage to poorly constructed buildings over small regions. 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

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

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

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)

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

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

Mauna Kea

Layer Cake Mountain Mount Fuji; Japan

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.

Volcanic Vent

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

Mount Boucherie Hawaiian Islands Mount St. Helens

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)