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.
- Faults can occur on top of the earth’s surface (San Andreas Fault) or deep within the earth
- Faults occur because of
- tension – rocks pulling apart
- compression - rocks pushing together
- shearing – rocks sliding past each other
- See activity (page 54)
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: HimalayanMountains
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.
Complete the concept map using the following words:
Normal up and overreversestrike-slipopposite sides
Compression tensionshearingdownwardvertical
2-3 Volcanic Eruptions ( p 67 – 74)
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.
ExplosiveQuiet
THICK magmaTHIN magma
(lots of silica) (little silica)
Clogs ventgases (HO and CO)
escape gently
gases under high pressurelava reaches surface and
flows
magma explodes forming
dust, ash, rock fragments
- 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,
slightlycooled 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 7Name
HOMEWORK: 2-3 Volcanic eruptions
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______
POSITIVENEGATIVE
1. Production of ______1. Immediate destruction of
and ______
______
______
2. Rocks formed by ______2. ______
are used in construction of roads.
3. Increases soil fertility after it3. ______
______