Do Now:

• How can or does a volcanic eruption or earthquake occur? What forces on this planet are responsible for them? Explain your answer in complete sentences.

• T and T

Aim: How do volcanoes and earthquakes change our

planet?

Volcanoes & Volcanoes & Earthquakes Earthquakes

Unit 2.1bUnit 2.1b

VolcanoesVolcanoes• are mountains formed when plates meet

• magma from asthenosphere rises through the lithosphere to erupt on the surface as lava

1. if internal pressure is high 1. if internal pressure is high enough…enough…

• Lava, ash, and gases can be ejected into the atmosphere or flow over land

Fig. 14-6b, p. 351

Extinct volcanoes

Eruption cloud

Ash Acid rainAsh flow

Lava flow

Mud flow

LandslideCentral ventCentral vent

Magma conduitMagma conduit

Magma reservoirMagma reservoir

2. Volcanic Activity2. Volcanic Activity• Active volcano- has/can erupt

– Magma has a direct line to the volcano and pressure exists within the volcano

• Dormant volcano- not known to erupt– Moving plates can connect magma to it

activating it

• Extinct volcano- wont erupt again – Magma line cut off due to moving plates

Volcano leading to islandsVolcano leading to islands

3. Types of volcanoes3. Types of volcanoes• Rift volcano- when plates move away from

each other and magma creates new ocean crust

• Subduction volcano- when plates collide and slide over each other exposing magma

• Hot spot volcano- place within a plate where magma upwelling causes magma to rise to the surface– not at plate boundaries– Ex: Hawaiian Islands

F. Earthquakes (EQ)F. Earthquakes (EQ)• Result of vibrations deep in the earth that

release energy– Usually at transform boundaries where plates

grind past each other and friction builds up when they get stuck in one spot until the point where they slip past each other releasing all the energy from the friction being released

• Focus- where the EQ begins inside Earth• Epicenter- where the EQ reaches surface

Major Features and Effects of an Earthquake

Fig. 14-7, p. 351

Fig. 14-7a, p. 351

Liquefaction of recent sediments causes buildings to sink

Two adjoining plates move laterally along the fault line

Earth movements cause flooding in low-lying areas

Landslides may occur on hilly ground

Shock waves

FocusEpicenter

1. Measuring EQ1. Measuring EQ• Seismograph- measures size (magnitude)

of EQ

• Richter Scale- measures the amplitude of the highest S-wave of an EQ– Each # = 33x the energy compared to the

previous #

Earthquakes Are Geological Rock-and-Roll Events (2)

• Richter scale – Insignificant: <4.0– Minor: 4.0–4.9– Damaging: 5.0–5.9– Destructive: 6.0–6.9– Major: 7.0–7.9– Great: >8.0

• Largest recorded earthquake: 9.5 in Chile in 1960

2. Major EQ features2. Major EQ features

Earthquake Risk in the United States

Figure 16, Supplement 8

3. Global EQ Risk3. Global EQ Risk

Earthquakes on the Ocean Floor Can Cause Huge Waves Called

Tsunamis

• Tsunami, tidal wave

– Travels several hundred miles per hour

• Detection of tsunamis

– Buoys in open ocean

• December 2004: Indian Ocean tsunami

– Magnitude 9.15 and 31-meter waves at shore

– Role of coral reefs and mangrove forests in reducing death toll

4. EQ Effect: Tsunami Formation4. EQ Effect: Tsunami Formation

Ex: Indonesia Tsunami 2004Ex: Indonesia Tsunami 2004

• In December 2004, a great EQ with a magnitude of 9.15 on the seafloor of the Pacific Ocean created a large tsunami that killed 168,000 people in Indonesia.

Indonesia shorelineIndonesia shoreline June 23, 2004 before tsunami June 23, 2004 before tsunami

December 28, 2004 December 28, 2004 aftermath from the tsunamiaftermath from the tsunami

Shore near Gleebruk in Indonesia before and after the Tsunami on

June 23, 2004

Fig. 14-9, p. 353

Summary:

• How do volcanoes and earthquakes impact society?