2-1 What causes earthquakes?
2-1-1
Pressure within the earth causes the rocks to bend and
stretch. When the rocks are pushed more than they are able
to withstand, they break and may move.
FAULT
 A crack or fracture within the earth
where rock movement occurs
 Faults can occur on top of the
earth’s surface (San Andreas Fault) or deep within the
earth
 Faults occur because of
1. tension – rocks pulling apart
2. compression - rocks pushing together
3. shearing – rocks sliding past each other
 See activity (page 54)
TYPES OF FAULTS
1. Normal faults
 Caused by tension
 The rock above the fault
moves downward
EX: Sierra Nevada mountains
2. Reverse fault
 Caused by compression
 The rock above the fault
moves upward
EX: Himalayan Mountains
3. Strike-slip fault
 Caused by shearing
 The rocks are pushed in opposite
horizontal directions.
EX: San Andreas Fault
Can you identify the type of fault?
1.
2.
3.
4.
5.
FORCES THAT CAUSE FAULTS
Complete the concept map using the following words:
Normal
Compression
up and over
tension
reverse
shearing
strike-slip
downward
opposite sides
vertical
Fault
a fracture within the
earth where rock
movement occurs
TYPES
Caused by
Caused by
Which is
pulling on
material from
opposite sides.
Which is rocks
on opposite
sides sliding
past each
other.
Caused by
Which is
pushing on
material from
Result: causes
rocks above fault
surface to move
Results: little
Results: causes
rocks above fault
surface to move
movement of
rocks on both
sides of fault
2-3
Volcanic
Eruptions ( p 67 – 74)
VOLCANOES
What causes
volcanoes to erupt?
Magma (melted rock below the earth’s surface) rises
to the surface because it is less dense than the rocks
around it.
Vent
- opening in
the earth’s
crust through
which magma
flows.
Eruption:
- magma
flowing through
a vent.
Lava
- melted
rock above the
earth’s surface.
TYPES OF ERUPTIONS
Explosive
THICK magma
(lots of silica)
Clogs vent
gases under high pressure
magma explodes forming
dust, ash, rock fragments
Quiet
THIN magma
(little silica)
gases (H 2 O and CO 2 )
escape gently
lava reaches surface and
flows
Types of Volcanoes
 SHIELD
1) Gentle eruption force
2) Hot , thin lava
3) Gentle sloped sides
Example: Mauna Loa, Hawaii
 Cinder Cone
1) Violent disruptive
force
2) Volcanic ash,
slightly cooled lava
3) Steep sloped sides
Example: Paricutin,
Mexico
 Composite
- alternate quiet and violent
- Flowing lava, then hardened lava and chucks of ash
-medium steepness,
between shield and
cinder
Example:
Mt. Shasta,
California
Science 7
HOMEWORK: 2-3 Volcanic eruptions
Name
Identify the type of volcano and fill in the chart:
________________
_______________
_________________________________
Type of Volcano
Nature of Eruption
(quiet or
explosive)
Degree of Slope
(gentle or steep)
Type of Magma
1.
Cinder Cone
2.
Composite
3.
Shield
Give a real world example of each type of volcano:
1. Composite
__________________
2. Shield
__________________
3. Cinder cone
__________________
EFFECTS OF VOLCANOES
POSITIVE
NEGATIVE
1. Production of _______________
and __________________
1. Immediate destruction of
____________________
_____________________
_____________________
2. Rocks formed by ___________
2. ______________________
are used in construction of roads.
3. Increases soil fertility after it
_______________
___________
3. ______________________