Chapter 7.4 Notes
Deformation of the Earth’s Crust
*Deformation: any stress (pushing or pulling) on the crust which changes the
volume/shape of crust
Two types of deformation
1.
tension: stress when forces stretch an object
2.
compression: stress when an object is squeezed
*Folding: bending of rock layers b/c of stress
Types of folding
1.
anticlines: a fold in rock that bends upward into an arch
2.
syncline: a fold in rock that bends downward in the middle
3.
monocline: folded rock layers where both ends of the fold are
horizontal
*Faulting: occur along plate boundaries where rocks break & slide past each
other
Three types of faults
1.
Normal Faults: occur when tectonic forces cause tension that pulls
rocks apart & hanging wall slips downward past the footwall
2.
Reverse Faults: happen when tectonic forces cause compression that
pushes rocks together & hanging wall slides up & over the footwall.
3.
Stike-Slip Fault: form when opposing forces cause rock to slip past
each other sideways with little up/down motion.
Ex. San Andres Fault in CA.
*When tectonic plates undergo compression or tension, they form
mountains several ways:
1.
Folded Mountains: form at convergent boundaries where
continents collide.
Ex. Appalacian Mts. formed when
N. Amer. & Africa collided.
2.
Fault-Block Mountains: occur when tension causes large blocks
of crust to drop down.
Ex. Tetons in Wyoming
3.
Volcanic Mountains: located at convergent boundaries where
oceanic plates sink at subduction zones & under the sea to
sometimes cause islands.
Ex. majority of volcanic mts. are formed around rim of Pacific Ocean
Ring of Fire.
*Two types of vertical movement in the crust:
1. Uplifting of Depressed Rock: -rising of regions of the crust to
higher elevations.
*Mountains form or areas rise or rebound when weight on it is
removed.
2. Subsidence of Cooler Rocks:
-sinking of regions of crust to lower elevations.
*when lithosphere is hot, it takes up more space at mid-ocean ridge
*lithosphere away from ridge is cooler, takes up less space, & is
denser, so oceanic lithosphere crust subsides.