Module 7: Earthquakes & Volcanoes

What causes stress in rocks? How does stress lead to faults?

• Stress is any force applied to a rock

• When the rock finally breaks, pieces move along a fault in response to the direction of the stress

What is strength in rocks?

Strength is a rock’s ability to resist stress

How do the three directions of stress compare to the types of plate boundaries?

• Tensional stress → divergent

• Compression stress → convergent

• Sheer stress → transform

What is a normal fault, and how does it compare to the direction of stress?

Vertical movement

What is a revers/thrust fault, and how does it compare to the direction of stress?

Vertical movement

What is a transcurrent/transform fault, and how does it compare to the direction of stress?

Horizontal movement

How does elastic rebound theory explain earthquakes? Why aren’t earthquakes predictable?

• When rocks accumulate stress and break, they result in earthquakes

• We don’t yet have the technology to accurately predict most earthquakes

Characteristics of P-waves (5)

• Fastest

• High frequency, low amplitude

• Travels through solids, liquids, and gases

• Ground motion is same as wave’s direction

• Length of p-wave is directly proportional to how far earthquake is

Characteristics of S-waves (4)

• Slower than p-waves

• Lower frequency, higher amplitude

• Travels only through solids → can’t travel through outer core

• Sheer — direction of ground motion perpendicular to wave’s direction

Characteristics of Surface waves (4)

• Slowest

• Causes damage

• Low frequency, high amplitude

• Limited to earth’s surface

How does Moment Magnitude measure the intensity of an earthquake?

It measures the amount of movement along a fault, which relates to the energy released

How do earthquakes reveal information about the interior of the earth?

Certain waves travel through certain states of matter, which can tell us what such states make up the interior of the earth

Why are each of the following three hazards associated with earthquakes?

• Fire — shaking can cause objects to catch fire

• Liquefaction — vibrations cause ordinarily-solid ground to flow like a liquid

• Tsunami — caused from the seafloor suddenly changing shape

At what kinds of locations does melting occur? (4)

• Mid-ocean ridge

• Subduction zone

• Continental rift

• Hot spot

What is viscosity, and what affects the viscosity of lava?

• Viscosity is how easily the lava flows

• The composition and temperature of the lava affect its viscosity

Characteristics of low viscosity lava (6)

• Pahoehoe

• High temperature

• More mafic

• Effusive eruptions

• Shield volcanoes

• Occasional cinder cone volcano

Characteristics of high viscosity lava (5)

• A’a

• Low temperature

• More felsic

• Explosive eruptions

  • Stratovolcanoes/composite volcanoes

Why was the eruption of Krakatau significant? (4)

• Because the effects felt were not limited to where the eruption occurred

  • Biggest explosion was loudest sound heard by human ears

  • Global av temps dropped 1.2 degrees Celsius

    • Unusual weather patterns for next 5 years

What are the following five volcanic hazards?

• Volcanic ash — tiny, sharp rock fragments that damage machinery & lungs

• Pyroclastic flow — superheated cloud of rock fragments

• Lahar — muddy mix of melted ice & rock fragments

• Volcanic gases — poisonous gases

• Tsunami