Download how mountains form

Mountain Building
Chapter 11
11.1
WHERE MOUNTAINS FORM
What is a Mountain?
• Large mass of rock
• Rises far above its base
A. Mountain Belts
• Most form in long belts that follow
convergent plate boundaries
• Some are old boundaries, some are
current boundaries
• Appalachians – OLD boundary
• Himalayas – Current boundary
Appalachians
Himalayas
B. Continental Margins
• Boundary between continental and ocean
crusts
• Active Margins
– Along plate boundaries
• Passive Margins
– Not at plate boundaries
Atlantic Continental
Margin
•Passive
•Creates Mountain
Building Materials
Active Continental Margin
•Mountain Building Happens
•Subducting Boundaries
•Usually Volcanically Active
•Earthquake Prone
How are these margins related?
• Passive margins contain a lot of sediment
• When that passive margin becomes
active, those sediments will become part
of the new mountains
11.2
HOW MOUNTAINS FORM
STRESS!!!!
• Stress within the earth causes rock to
break or fold
A. Types of Stress
• 1. Compression
– Rock layers are being squeezed inward
– Makes layers thicker and shorter
• 2. Tension
– Layers are stretched
– Makes rocks thinner and longer
.
• 3. Shear Stress
– Rocks are being pushed in opposite directions
– Distorts the rock along the plane
Where does this happen?
• Along plate boundaries
• Usually all occur together
• Different rocks respond differently to the
three types of stress
B. Folds
• Along continental margins
• Stress causes rocks to warp and crumple
• Over time, erosion exposes the rock
Anticlines
• An upfold in the rock strata
Synclines
• A downfold in rock strata
Limbs
• The sides of an anticline or syncline
C. Faults
• Fault plane – the plane along which
movement in earth’s crust occurs
• Above the Fault Plane: Foot Wall
• Below the Fault Plane: Hanging Wall
1. Normal Fault
• Hanging wall moves DOWN
• Tension is pulling crust apart
2. Reverse Fault
• Hanging wall moves UP
• Compression pushing crust together
3. Thrust Fault
• A type of reverse fault
• The major difference: the angle of the fault
plane
– 45 degrees or less from horizontal
4. Strike-Slip Fault
• Rocks on opposite sides of the fault move
past each other
5. Joints
• A break in the
bedrock – no
movement has
occurred
• Usually in the form of
a plane
• Gives a channel in
which fluids (molten
material, soil, water)
can move
11.3
TYPES OF MOUNTAINS
A. Folded Mountains
• Two colliding continental plates
• Rocks don’t break, they crumple
• Ocean between plates must disappear first
– Due to subduction
– Continues until crusts meet
Himalayas are Folded
B. Dome mountains
• A type of folded mountain
• Nearly circular
• Usually solitary
Plutonic Dome
• Made by plutonic intrusion
• Pushes up older rock
• Core of mountain is younger
Tectonic Dome
• Made by uplifted rock
layers
• Rocks at core are
older
– No new material
– Layers erode,
exposing older rock
C. Volcanic Mountains
• Different types of volcanoes form in
different areas (remember chapter 9)
D. Fault-Block Mountains
• Formed by Compression or Tension
• Blocks of crust are dropped (tension) or
lifted (compression)
• Form Normal or Reverse faults
Grabens and Horst
• Horst- formed by compressional forces
• Graben – formed by tension forces