Diastrophism Results of plate tectonics 1 volcanism 2

Diastrophism Results of plate tectonics: 1. volcanism 2. diastrophism 3. earthquakes

diastrophism: n Deformation of crust due to tectonic stress: • Folding (bending) • Faulting (breaking and displacement)

Types of Stress and Strain (Stress is force acting on rock; strain is rock’s response to stress) n Compression (shortening) n Extension (stretching)

EXTENSION COMPRESSION

Folding n Compressional stress causes rocks to buckle and fold • Anticline: arch-shaped fold • Syncline: sink-shaped fold

n Anticlines begin as ridges ; synclines begin as valleys.

n Differential erosion leads to: • Anticlinal ridges and valleys • Synclinal ridges and valleys n Differential erosion: less-resistant types of rock strata will weather and erode more rapidly than more-resistant rock strata

Anticlinal mountain/ridge Synclinal valley

What’s this? Synclinal mountain/ridge

Faulting n 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

Fault from Hebgen Lake, Montana earthquake, 1959 What’s this? Fault scarp

Types of Faults 1. Normal Fault: from extensional stress Vertical movement along an inclined fault plane

normal

Horst and Graben (result of normal faulting) Horst : upfaulted block Graben: downfaulted block

Block mountains

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

reverse

reverse

reverse

3. Overthrust fault n n Reverse fault with very low angle More horizontal than vertical movement

overthrust

3. Transcurrent (Strike-slip) Fault horizontal movement no fault scarp

Transcurrent

Transcurrent HEY! Who moved my wood pile? !@*

Transcurrent

San Andreas