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I-5 Notes Dynamic Planet
The Nature of Earthquakes
Fault
• A fracture or fracture zone along which
there has been displacement of one mass
of rock relative to another, parallel to the
fracture
• Fracture may extend for tens of kilometers
• When rocks break, the rocks on either side
of the fracture plane slide past one
another producing strong vibrations (felt as
Earthquakes)
• Over time fractures may heal
Earthquakes and Plate Movements
• Largest earthquakes occur along
subduction zones
• Earthquakes range from shallow to as
deep as hundreds of kilometers
• Earthquakes also occur at continentcontinent collision zones
Earthquakes along a transform
boundary
• If fault locks for a long time & suddenly
slips, it will produce a major earthquake
• If fault slips continuously, produces a very
minor earthquake
• The San Andreas Fault is locked in the
vicinities of Los Angeles and San
Francisco
The Nature of Volcanoes
• Rock deep in the Earth melts to magma
• Magma rises because it is less dense than
surrounding rock
• Rising magma may crystalize to rock
again OR rise to surface forming a volcano
• The most important factor in how
volcanoes erupt is the gas content of the
magma
• Low gas content – magma flows
peacefully down the sides of the volcano
without a violent eruption
• High gas content – powerful explosion
Volcanoes and Plate Movements
• Volcanoes are formed along the midocean ridges
• These volcanoes are very numerous
• Most are deep in the ocean
• If activity is strong enough, may build an
island above sea level (Example –
Iceland)
• Most large volcanoes occur along
subduction zones
• Scientists think this is caused by parts of
the subducting ocean crust reaching a
certain depth & melts OR
• At a certain depth down, water is released
from the rocks rising up above the
subducted plate (water lowers the melting
point of the mantle rock)
Hot Spot Volcano
• Hot spots in the mantle generate magma
for a long period
• The hot spots don’t move
• Plates move over the hot spot
• The orientation & age of a line of hot spot
volcanoes reveal the direction and speed
of plate movement
• Volcanoes may occur far from plate
boundaries
• The Hawaiian Islands & Yellowstone Park
The Association of Earthquakes
and Volcanoes
• Subduction Zones – major earthquakes,
large volcanoes
• Most of the Pacific Ocean is rimmed with
subduction zones
• The Ring of Fire
Continent-Continent Collision
• Earthquakes are common
• No volcanoes are formed
• Examples, Southern Asia (China, India,
Iran, & Turkey)
Mountain Building
• Most of the world’s large mountain ranges
are where two plates collide
Subduction Zone
• Magma from deep rises to feed volcanoes
on the plate that is not subducting
• Crust near subduction zone grows in
volume
• Example – Andes Mountains
Two Continents Collide
• Lithosphere becomes thicker, so rises up
to form mountains
• Himalayas
• Use your notes to fill in the following chart:
Earthquake Volcano
Divergent
Boundary
Subduction
Zone
ContinentContinent
Collision
Transform
Boundary
Mountain
• Volcanoes are caused by the rise of
magma formed within the Earth. Magma
rises because it is less dense than the
surrounding rock. The rising magma does
not always reach the surface, but when it
does, it forms a volcano.
• If the gas content of the magma is low, the
magma erupts gently. If the gas content of
the magma is high, an explosive and
violent eruption can occur.
• Volcanism at a hot spot can occur far from
a plate boundary, whereas volcanism at a
mid-ocean ridge occurs at a plate
boundary (a divergent boundary). Both
types of volcanism involve the production
and release of magma.