Mountains

Chapter 9

Stress and Strain• Stress is defined as force per unit area. It has the same units as pressure, and in fact pressure is one

special variety of stress. However, stress is a much more complex quantity than pressure because it varies both with direction and with the surface it acts on.

• Strain is defined as the amount of deformation an object experiences compared to its original size and shape.

• Compression Stress that acts to shorten an object.

• Tension Stress that acts to lengthen an object.

• Shear Stress that acts parallel to a surface. It can cause one object to slide over another. It also tends to deform originally rectangular objects into parallelograms The most general definition is that shear acts to change the angles in an object.

• Normal Stress Stress that acts perpendicular to a

surface. Can be either compressional or tensional

• Hydrostatic Stress (usually compressional) that is

uniform in all directions. A scuba diver experiences hydrostatic stress. Stress in the earth is nearly hydrostatic. The term for uniform stress in the earth is lithostatic.

Stress-Strain curve

Tensile Stress Test

Stress and Strain

Examples

In Geology Conditions

• Near Earths surface, Temp and Pressure are Low

• Temperature Higher Temp.Plastic manner

• Pressure • Time

9.1 Geologic Structures• Fold is a bend in a rock.

Five types of Folds

Dome and Basins

Examples

Examples

Faults

Faults

Joints • Joints a re fractures in the rock

Questions of the Day

Question ?

Question ?

Mountains• Orogeny refers to the process of mountain Building.

In a convergent plate boundary: Folding, faulting of rocks, earthquakes, volcanic eruptions, intrusion of plutons and metamorphism.

The motor of Orogeny is sudduction

Island Arcs

• Island Arc is volcanic mountain chain that forms where 2 plates carrying oceanic crust converge

The Andes

Himalayas • Continent-Continent Collision

Himalayas

The Wilson Cycle

Homework 5 Describe The Wilson Cycle Due: Monday 4/8/13