Transcript Earthquakes & Volcanoes

Earthquakes & Volcanoes
Objectives
1. Given information on Earthquakes, you will be able to describe,
in writing:
a) what an earthquake is;
b) what the elastic rebound theory is;
c) how earthquakes are measured;
d) how earthquakes are related to plate tectonic theory;
e) hazards associated with earthquakes; and
f) the significance of studying earthquakes.
2. Given information on Volcanoes, you will be able to describe, in
writing:
a) what a volcano is;
b) what types of volcanoes there are;
c) how volcanoes are measured;
d) how volcanoes related to plate tectonic theory;
e) hazards associated with volcanoes; and
f) the significance of studying volcanoes
Earthquakes
Definition:
An earthquake (also known as a tremor or
temblor) is the result of a sudden release
of energy in the Earth's crust that creates
seismic waves.
Earthquakes
Elastic Rebound Theory
• explanation for how energy is spread during earthquakes
• plates/blocks of earth shift on opposite sides of a fault
• these are subjected to force (Time 1)
• they accumulate energy (Time 2)
• they slowly deform until their internal strength is exceeded
• a sudden movement occurs along the fault
• accumulated energy is released
• rocks snap back to their original undeformed shape (Time 3)
Earthquakes
Measurement
1. Magnitude scale
a) measures energy released;
b) an earthquake one number higher is
approximately 30 times more powerful (e.g. a
7.0 vs. a 6.0); (the scale is logarithmic)
d) an earthquake one number higher produces
approximately 10 times more ground shaking
e) examples = Moment Magnitude, Richter
Earthquakes
Measurement (cont.)
2. Mercalli intensity scale
a) measures intensity or damage of an earthquake;
b) quantifies the effects of an earthquake on the Earth's
surface, humans, objects of nature, and man-made
structures
d) scale ranges from I through XII, with I denoting a
weak earthquake and XII one that causes almost
complete destruction
e) based on the amount of resulting physical damage
received
f) data is gathered from individuals who have
experienced the quake
Earthquakes
Plate Tectonics
• Earthquakes are NOT randomly distributed
across the globe
• They are concentrated along narrow zones
• Most earthquakes (~80% or more) occur along
plate boundaries
• Interior of plates are mostly earthquake free
• Earthquakes define plate boundaries
• Some also occur at Hot Spots
Earthquakes
Hazards
1. Ground motion
2. Liquefaction
3. Landslides & mass wasting
4. Tsunamis
Earthquakes
Significance
• It is important to study earthquakes due to
the loss of life and damage to property
they can cause
• Human population continues to grow and
many cities are cited along plate
boundaries
• Education is the key to being prepared for
earthquakes
Volcanoes
Definition
A volcano is an opening, or rupture, in a
planet's surface or crust, which allows hot,
molten rock, ash, and gases to escape
from below the surface. Volcanic activity
involving the extrusion of rock tends to
form mountains or features like mountains
over a period of time.
Volcanoes
Types
There are 5 general types of volcanoes:
1. Caldera volcanoes
2. Cone volcanoes
3. Lava Dome volcanoes
4. Shield volcanoes
5. Strato volcanoes
Volcanoes
Types of Eruptions
1. Effusive (Hawaii)
2. Explosive
a) Pyroclastic Flow
b) Phreatic Eruption
c) Plinian Eruption
d) Strombolian Eruption
e) Vulcanian Eruption
Volcanoes
Measurement
The Volcano Explosivity Index (VEI)
provides a relative measure of the
explosiveness of volcanic eruptions. The
scale is based on:
• Volume of products erupted
• eruption cloud height
• qualitative observations
Volcanoes
Plate Tectonics
• Volcanoes are NOT randomly distributed across
the globe
• They are concentrated along narrow zones
• Most volcanoes (~80% or more) occur along
plate boundaries
• Interior of plates are mostly volcanoe free
• Volcanoes help to define plate boundaries
• Volcanoes form Hot Spots
Volcanoes
Hazards
1. tephra (ash fallout)
2. pyroclastic flows (Mt. Unzen, Japan)
3. tsunamis (Krakatau)
4. mass wasting (landslides)
5. lahars (volcanic mudflows)
6. lava flows (Hawaii)
7. gas emissions (Mammoth Lakes)
8. directed blast (Mt. St. Helens)
9. pyroclastic surge (less dense than pyroclastic flows)
Volcanoes
Significance
• It is important to study volcanoes due to the loss
of life and damage to property they can cause
• Human population continues to grow and many
cities are cited along plate boundaries
• Education is the key to being prepared for
volcanoes
Summary
• Earthquakes occur due to the elastic rebound theory;
they are measured using the magnitude scale; they
occur along plate boundaries; they cause ground motion,
tsunamis, mass wasting, and liquefaction all of which
may cause loss of life and damage to property
• Volcanoes occur due to molten rock reaching the earth’s
surface; they are measured using the VEI scale; they
occur along plate boundaries; they cause pyroclastic and
lava flows, ash fallout, lahars, mass wasting,
earthquakes, and may cause tsunamis, all of which may
cause loss of life and damage to property