Mountain Building Chapter 11

WHERE MOUNTAINS FORM 11.1

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

HOW MOUNTAINS FORM 11.2

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

TYPES OF MOUNTAINS 11.3

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