Back to syllabus

              last updated: 02/28/98

(abbreviated versions of the overheads)

Earth processes are dynamic - internal changes must involve intense deformation.

A record of this deformation is found in the geological structures; especially in folds

and faults

Geologic mapping - geologists make maps based on the distribution of outcrops that include features such as the geographic distribution of outcrops, the type of rocks in the outcrops and the attitude of the beds or layers as measured by the strike (direction of a rock layer relative to the horizontal) and dip (the angle the layer is inclined relative to the horizontal).


Experiments on deformation of rocks show there are  several factors that influence rock deformation.

Ductile deformation = (the smooth, continuous,  "plastic" deformation) takes place at .

Brittle = deformation (sudden breakage) takes  place at

3 types of forces affect rock deformation


Folding implies a planar feature that has been bent. 

To characterize and interpret a fold, a geologist = typically looks at the surface information e.g. dip, strike, "younging" information, = etc.

Anatomy of a fold

Parts of a fold Types of folds


Joints - cracks in a rock with



Faults - a fracture in a rock with

(1) dip-slip - up/down  motion in    

(2) strike-slip (right  or left lateral) -

(3) oblique-slip -  combination of

Grabens (rift valley) - narrow valley bounded by one or more


Topographic expression of deformation - deformation  over the past few 10s of Ma produce the relief we see in most mountain ranges