Mountain Building By Bhavani Sridhar Internship I Lesson

What are Mountains? A mountain is a large mass of rock that rises a great distance above its base. Where do mountains form? Forms at the convergent plate boundaries. Continental Margins – boundary between the oceanic crust and continental crust. Two types: 1.Active continental margin 2.Passive continental margin

Active continental margin 1.Mountain building takes place here. 2.Occurs at the plate boundaries. E.g. Nazca plate in South America. Passive continental margin 1.Do not occur at the plate boundaries 2.Found in stable areas 3.Has large sediment deposit

How Mountains form? Just like a sculptor uses a hammer to chisel a rock and the rock breaks at a specific area where the sculptor concentrated the force of the hammer. STRESS is a measure of the amount of force applied over a given area. During mountain formation Stress is applied to rocks at converging plate boundaries. The rocks respond to the stress by “fracturing” whereas stress applied to rocks deep within the lithosphere causes the rocks to fold or stretch without fracturing.

Types of Stress 1.Compression Stress 2.Tension Stress 3.Shear Stress NOTE: Three stress contribute to mountain building at plate boundaries. They all occur together

Compression Stress The rock layers are being squeezed inwards Compression makes rocks thicker and shorter

Tension Force The rocks are being stretched and pulled Called TENSION It makes the rock thinner and longer

Shear Stress The rocks are pushed in the opposite direction Called SHEAR STRESS.

FOLDS When plates collide, compression stress can cause rock layers along continental margins to crumple into FOLDS. These occur deep in the earth, but may be exposed after long periods of time by uplift due to erosion and weathering.

Types of Folds Anticline – Up fold in the rock layers Syncline – Down fold in the rock layer The two sides of the fold is called the LIMB

FAULTS Faults – is break in the Lithosphere along which the movement occurred. Remember: Fault Plane – surface between the two moving crust Footwall – Part below the fault Plane. Hanging wall – Part above the fault plane

Types of Faults 1. Normal Fault 2. Reverse Fault 3. Thrust Fault 4. Strike-slip Fault

NORMAL FAULT Occurs when the hanging wall moves down due to pulling of the crust

REVERSE FAULT 1. Occurs when the hanging Wall moves up. 2. Caused by compression due to plate collision

THRUST FAULT It is also a reverse fault, where the fault plane dips 45 0 or less from the horizontal.

STRIKE-SLIP FAULT The rocks on opposite side of the fault plane move slide horizontally. Example: San Andreas fault

Types of Mountains 1.Folded Mountains 2.Dome Mountains 3.Volcanic Mountains 4.Fault-block mountains

Folded Mountains When two continental plates collide, rocks crumple and fold into Folded mountains E.g. Himalayas, Ural mountains in Russia.

Dome Mountain Dome mountain is circular, isolated structures found in flat region. E.g. Rocky mountains Volcanic Mountain Formed because of the volcanic activity. E.g. Cascade Mountains

Fault – Block Mountain Earth’s crust which has been uplifted due to compression tension, undergoes stretch and the whole block of crust is pushed into fault-block mountains E.g. Sierra Nevada, CA

Graben and Horst Graben - When the crust drops between two normal faults Horst – When the crust thrust upwards, between two normal faults

Faults and Folds