CORE TOPIC 4
VOLCANOES, EARTHQUAKES AND
LANDFORMS
1. Volcanoes and earthquakes are located
where plates separate and collide
2. Earthquakes can also occur where plates
slide past each other
3. The remainder of earthquakes occur along
fault lines that are located away from plate
boundaries.
4. Most earthquakes and volcanoes occur along
the Pacific Ring of Fire because:
 Subduction occurs here
 As the plates sink into the mantle they
melt to form volcanoes and they get
stuck to form earthquakes
5. Why do earthquakes and volcanoes
regularly occur in similar locations?
Why has Plate tectonics revolutionized our
understanding of earthquakes and
volcanoes?
 Both occur at constructive and
destructive boundaries
 Only earthquakes occur at passive
boundaries – not volcanoes
Destructive boundary-where 2
ocean plates collide. Japan.
Diagram. Ocean plates are heavybasalt and saturated. One sinks under
the other. Can get stuck pressure
builds up until sudden release. If near
the sea bed-shallow earthquake. As it
sinks-melting-creates magma which
rises –explosive earthquakes. These
can create volcanic island.
Where the earthquakes occur along a
line of sinking plates-Benioff Zone
Destructive boundary-where ocean
plate meets continental plate.
Pacific Ring of Fire. Diagram. Ocean
floor is covered with heavy sediment.
As sinking occurs it is squeezed into
sedimentary and metamorphic rock
that is buckled to form fold
mountains. As plate sinks it gets
stuck-strain-rock snaps-earthquakes.
Sinking plate reaches 100km belowmelting-magma-rises through rockvolcanoes and earthquakes
When 2 continental plates approach
the intervening ocean plate sinks
under each until 2 plates collide
Constructive boundary-at a mid
ocean ridge Mid Atlantic Ridge.
Diagram. Ocean plates separateconvection currents bring magma to
surface to fill empty space. It
solidifies(cold water). New rock
splits-earthquakes(small)
Some places along the mid ocean
ridges are hot spots where large
volumes of magma pour onto the sea
bed-islands like Iceland
Passive boundary –where plates
slide past each other. Diagram. San
Andres Fault. Only earthquakes.
Plates become jammed. Strain. Plates
snap and jump forward-earthquakesforeshocks and aftershocks. Strain
transferred to next jamming point.
No subduction so no melting - no
magma –no volcanoes
5. Human cost of earthquakes is influenced by
socio-economic factors
In developed countries
a) Well Constructed Buildings
b) Education
c) Modern Technology
In developing countries
a) Poor buildings
b) Lack of information system
6. How earthquakes are predicted
Scientific instruments that measure
changes in movement or tilt of the earth
Seismic gaps haven’t had earthquakes for
along timebut are bordered by areas of
activity
Dating patterns
7. Effects of Earthquakes
Landslides
Destruction in cities
Tsunamis
8. Earthquake Facts
A seismologist studies earthquakes
A seismograph is an instrument that
measures earthquakes
Earthquake strength is measured on the
Richter Scale
Focus-point where the earthquake occurs
Epicentre-spot on earth’s surface directly
above the focus
9. Volcanic Prediction
Changes in types and amounts of gases
escaping from side of craters
Changes in local groundwater temperature
and composition
Numerous small earthquakes near a
volcano may suggest a large eruption
Dating of volcanic material can create a
time pattern
10. Effects of volcanic activity
Nuee Ardente-magma that has lots of silica
prevents gases from escaping-pressure
builds up-whole mountain top blastedgives rise to clouds of poisonous gases, hot
ash and rocks that cause destruction
Lahar- mud flows created by sudden
melting of snow on side of volcano
Study of past activity to plan for future