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. ______

______