Chapter 11: Deformation of the Crust

Section 1: How Rock Deforms Mountain ranges are constantly changing in a process called deformation – the bending, tilting and breaking of Earth’s crust.

Isostasy Deformation sometimes occurs because the weight of the Earth’s crust changes. As the lithosphere becomes thicker it sinks into the athenosphere and when it thins it rises higher in the athenosphere. When the two forces are balanced they are in a state of isostasy. As the adjustments occur the crust bends up and down which causes it to break.

Stress As the lithosphere moves the rock in the crust is squeezed, stretched and twisted. Stress is the amount of force that is exerted on each area. Compression – squeezes and shortens a body Normally occurs at convergent boundaries. Tension – is stress that stretches and pulls a body apart. Occurs at divergent boundaries Sheer stress – pushes parts of the body in opposite directions and distorts it Occurs at transform boundaries.

Strain When stress is applied to the rock, the rock will deform which is called strain. Rocks will fracture, crack, bend or deform based on the type of rock present.

Folds Is a bend in rock layers due to stress. Sometimes cracks form but mainly they stay intact Scientists study the ages of the relative rocks to determine the types of folds. Anticline – fold in which the oldest layer is in the center of the fold. Syncline – youngest layer in the center Monocline – both limbs are almost horizontal.

Faults Fracture – a break in which there is no movement of the surrounding rocks. Fault – a break in which the surrounding rocks moves Normal faults – the hanging wall moves downward relative to the footwall. Example – Great Rift Valley of East Africa Reverse faults – hanging wall moves upward to the footwall. Occurs in the Rockies and Alps. Strike-slip faults – rock on either side moves horizontally.

Section 2 – How Mountains Form Mountain range- a group of adjacent mountains that are related to each other in shape and structure Mountain system – a group of adjacent ranges Mountain belt – bunch of mountain systems together

Types of Mountains Scientists classify mountains according to the way in which the crust was deformed and shaped.

Folded Mountains Form when tectonic movements squeezed rocks together in accordion – like folds.

Fault-Block Mountains Faults cause blocks to tilt and drop relative to other blocks.

Also occur when tectonic forces gently uplift rock layers Dome Mountains Magma rises through the crust and pushes up the rock layers above the magma Also occur when tectonic forces gently uplift rock layers

Mountains form when magma erupts onto Earth’s surface Volcanic Mountains Mountains form when magma erupts onto Earth’s surface Form along convergent plate boundaries Part of mid-ocean ridges along divergent plate boundaries Form at hot spots which are volcanically active areas that lie far from tectonic plate boundaries.