Landforming Processes:

DIASTROPHISM

Stress and Strain

•Stress is force acting on rock•Strain is rock’s response to stress

When a rock is subjected to stress, it deforms and is said to strain. A strain is a change in size, shape, or volume of a material.

Uniform Stress – is a stress wherein all the forces act equally from all directions

Differential Stress – occurs when stress acting on the rock is not equal in all directions

Tensional stress (or extensional stress) – stress which stretches rock

Compressional stress – stress which squeezes rock

Shear stress – stress which results in slippage and translation

Three Kinds of Differential Stress

1. Folds2. Faults

Types of Deformation When Types of Deformation When Rocks are Subjected to StressRocks are Subjected to Stress

FOLDING• Compressional stress causes rocks to buckle

and fold

– Anticline: arch-shaped fold– Syncline: sink-shaped fold

Anticlines begin as ridges

Synclines begin as valleys

FAULTING

• Rock is strained beyond ability to remain intact; rock fractures; one side is displaced with respect to the other .

Fault plane: surface along which 2 sides move

Fault scarp: cliff formed along fault face

The two sides of a non-vertical fault are known as the hanging wall and footwall.

hanging wall occurs above the fault plane

footwall occurs below the fault

Types of FAULTS

1. Normal Fault - results from extensional stress

- vertical movement along an inclined fault plane

HORST and GRABENHORST and GRABEN(result of normal faulting)(result of normal faulting)

Graben

down-faulted block

Horst

up-faulted block

2. Reverse Fault- results from compressional stress- Vertical movement along inclined fault plane such that one side rides up over the other.- often creates landslides

3. Thrust fault

- reverse fault with very low angle

- more horizontal than vertical movement

4. Transform(Strike-slip) Fault

- horizontal movement; no fault scarp

5. Oblique-slip faults - have both a vertical and horizontal component of motion along the fault- adjacent points on different sides of the fault have moved up or down and back or forward relative to each other. They are essentially a combination of strike-slip and dip-slip motion.