Essential of Geology , 2 ed.

(9.1) Development of Strain (pure and simple shear)

This animation illustrates the development of two types of strain: simple shear and pure shear.

(9.2) What a Geologist Sees: Offset Stream Channel Along San Andreas Fault

An oblique air photo shows the San Andreas Fault displacing a creek flowing from the Tremblor Range (background) into the Carizzo Plain, California. The sketch shows what a geologist sees looking down on the San Andreas Fault.

(9.3) What a Geologist Sees: Fault Offsetting

A road cut in the Rocky Mountains of Colorado shows a fault offsetting strata in cross section. Note that the fault is actually a band of broken rock about 50 cm wide. The sketch shows what a geologist sees looking at the Rocky Mountain road cut.

(9.4) What a Geologist Sees: Thrust Fault

The photo shows a thrust fault, on which a distinct layer has been offset. A geologist’s sketch emphasizes the offset.

(9.5) What a Geologist Sees: Horsts and Grabens

The photo shows horsts and grabens cutting through marble exposed in a quarry wall in Brazil. A geologist’s sketch of the quarry wall indicates the positions of the faults.

(9.6) Process of Folding

Layers of rock can wrinkle or contort into a series of wave-like curves that geologists call folds. Not all folds look the same—some look like an arch, some like a tough, and some have other shapes. This animation examines how two types of folds are formed. View 1 illustrates the formation of a flexural-slip fold, and View 2 shows the formation of a passive-flow fold.

Created by: Stephen Marshak

(9.7) What a Geologist Sees: Fold Trains in Ireland

What a geologist sees looking at a train of folds exposed in sea cliffs in eastern Ireland. Note that the axial planes of these folds are not vertical.

(9.8) What a Geologist Sees: Flexural Fold

What a geologist sees looking at a small fold formed by flexural slip. Note that the sedimentary beds maintain the same thickness around the fold.

(9.9) What a Geologist Sees: Flow Fold

What a geologist sees when looking at a small flow of folds exposed in northern Scotland. Note how rock flowed into the hinge zone of the fold.

(9.10) What a Geologist Sees: Cleavage in an Anticline

A stream cut shows axialplanar cleavage; a geologist’s sketch of the stream cut.

(9.11) What a Geologist Sees: Shear Movement

The photo shows schistosity oriented at a low angle to the direction of shear. Note how large grains are all parallel to each other. A geologist’s sketch of the outcrop shows shear movement.

(9.12) Development of a Collisional Mountain Belt

When two continents collide, the resulting compression shortens and thickens the continental crust so that a large mountain range develops. This animation is a continuation of the 1e “Process of Subduction” animation.