Unit 4 Chapter 11

Deformation of the Crust

Section 1 Deformation of the crust

Mountain ranges are a visible reminder that the Earth is constantly changing. Some of the changes are a result of deformation, or bending, tilting and breaking of the crust.

IsostasyIt is a condition of gravitational and buoyant equilibrium between Earth’s lithosphere and asthenosphere. Which means, Earth stays in balance; when the crust uplifts, it will erode until a balance is reached.

Mountain and IsostasyWhen mountains form they start to erode, when they erode they

become lighter making the range appear to rise. It is called uplift due to the isostatic adjustment.

Deposition and IsostasySubsidence- It is the apparent sinking of the ocean floor due to

the deposition of mud, sand and gravel flowing from rivers. This deposition is occurring in the Gulf of Mexico at the mouth of the Mississippi River.

Glaciers and IsostasyThe weight of the ice makes the land sink the ocean floor rises

because the weight of the water is less. When the glaciers melt, the land rises and the weight of the newly added water makes the sea floor sink.

StressStressStress is the amount of energy exerted on an area. As Isostasy is Stress is the amount of energy exerted on an area. As Isostasy is reached, the force of an area shifts causing another area to have reached, the force of an area shifts causing another area to have stress.stress.

CompressionCompressionSqueezes and shortens the rock. Found at converging Squeezes and shortens the rock. Found at converging

boundaries.boundaries.

TensionTensionStretches and pulls the body apart. Found at divergent Stretches and pulls the body apart. Found at divergent

boundaries.boundaries.

Sheer StressSheer StressThis distorts a body by pushing parts of a body in opposite This distorts a body by pushing parts of a body in opposite

directions. Commonly found at transform boundariesdirections. Commonly found at transform boundaries..

StrainStrainAny change in the shape or volume of a rock that is the Any change in the shape or volume of a rock that is the result from stress.result from stress.

Some stresses on a rock may not be permanent if the pressure Some stresses on a rock may not be permanent if the pressure is done slowly and for a short time. However, longer is done slowly and for a short time. However, longer periods of stress can lead to physical changes.periods of stress can lead to physical changes.

Types of Permanent StrainTypes of Permanent StrainBrittle – breaking or fracturingBrittle – breaking or fracturingDuctile – bending or deformingDuctile – bending or deforming

Factors that Affect StrainFactors that Affect StrainThe composition of the rockThe composition of the rockThe temperature or pressure The temperature or pressure The types of stress or the length of timeThe types of stress or the length of time

FoldsA fold is when rock layers collide, the land bends up & down. It is caused by extreme stress.

Anatomy of a fold

Limb are the sloping sides of a fold

Hinge is where the limbs meet at the bend.

Axial plane occurs when both halves are identical.

Sizes of foldsThe sizes of folds vary with the type and the area that has been affected. They can be small areas, or as large as mountains.

Syncline - downward fold of rock

Anticline - uplifted area of rock

Monocline

Faults

A fault is a crack in the earth where movement has occurred.Fracture – a break along rock that has no movementFault Plane – is the surface where motion occurs.

Sizes of faultsThe sizes of the faults vary according to the area. One of the larges

faults is the San Andreas Fault.

Normal FaultsOne side of the land moves downward relative to the other side

Reverse FaultsWhen one side of the land moves upward relative to the land around it

Strike-slip faultWhen rock on each side of the fault move horizontally past each other

Section 2 How mountains form

Orogeny

It is the mountain building process through the movement of the crust or volcanism.

Many mountain ranges form this way due to extreme deformation. Mt Everest, whose elevation is more than 8km above sea level, is the highest mountain. Mt. St. Helen’s is a volcanic mountain that grows each year.

Mountain Ranges and systems

A mountain range is a group of adjacent mountains that are related to each other in shape and structure.Mt Everest is part of the Great Himalaya RangeMt. St. Helen’s is part of the Cascade Range

Mountain System - Is a group of mountain ranges The Great Smoky, the Blue Ridge, the Cumberland, the Green &

White ranges make up the Appalachian Mountain Range.

Mountain Belts – The largest mountain systems joined together Circum-Pacific belt Eurasian-Melanesian Belt

Plate tectonics and Mountains

Both the Circum-Pacific and the Eurasian-Melanesian belts are located along convergent plate boundaries. This is evidence that most mountains form as a result of

collision between tectonic plates.

Collisions between continental and oceanic crusts

When ocean and continental crusts collide, the ocean crust being denser will subduct under the continental crust. This drives mountains upward. Areas of frequent earthquakes & volcanoes because pressure is built up and needs to be released either through eruptions and earthquakes.

Collisions between oceanic and oceanic crusts

The Mariana Islands in the North Pacific are volcanic mountains caused by ocean to ocean collisions. One oceanic plate subducts below another. The denser one sinks, partially melts and breaks through the crack causing an arc of volcanic mountains.

Collisions between two continental crusts

The leading edge of a continental crust is oceanic so when it collides with another continental crust, it will subduct and continue to subduct until it reaches the continental edge. Then the two continental crusts will thrust each other upward forming mountains. The Indian plate collided with the Eurasian one in the same manner and the result was the Himalayan Mountains.

Types of MountainsFolded Mountains and PlateausWhen tectonic movement squeezes rock layers together like an

accordion-like fold. Parts of the Alps, the Himalayas, the Appalachians and Russia’s Ural mountains are folded.

Plateau

They are large, flat areas of rock high above sea level which were formed when thick, horizontal layers of rock are slowly uplifted. The Tibetan Plateau by the Himalayas and the Colorado Plateau by the Rockies are plateau.

Fault Block Mountains and Grabens

Parts of the crust are stretched and broken into large blocks, faulting may cause them to tilt and drop relative to other blocks. Sierra Nevada range of California is this type of mountain.

Graben- a long narrow valley usually found opposite a fault block mountain.Death Valley and the Basin and Range Province of Western U.S. are Grabens.

Dome Mountains

They are circular folded mountains resulting from uplifting forces (magma). They are gently sloping away from the centers.

Plutonic dome mountains-1. Result of underground volcanism2. Rock layers are pushed up because of an igneous intrusion3. Colorado Plateau, Rocky Mountains, Henry Mountains (Utah)

Tectonic dome mountains-` 1. Resulting from uplifting forces

2. Adirondack Mountains, Black Hills of S. Dakota

Volcanic Mountains

Are mountains that form when magma erupts. They are common along convergent plate boundaries. The Cascade Range of Washington, Oregon and Northern California are this type of mountains, the Azores in the North Atlantic Ocean.

Hot Spot

Hot Spots are active areas that lie in the middle of a tectonic plate. Hawaiian mountains are among some of the tallest in the world and are made from hot spots; 10 km above sea level and 1160 km wide.

Tallest Mountains of the worldTallest Mountains of the world Mount Everest 8850m (29035 ft) Nepal Mount Everest 8850m (29035 ft) Nepal

Qogir (K2) 8611m (28250 ft) India (Kashmir) Qogir (K2) 8611m (28250 ft) India (Kashmir) Kangchenjunga 8586m (28169 ft) Nepal Kangchenjunga 8586m (28169 ft) Nepal Lhotse 8501m (27920 ft) Nepal Lhotse 8501m (27920 ft) Nepal Makalu I 8462m (27765 ft) Nepal Makalu I 8462m (27765 ft) Nepal Cho Oyu 8201m (26906 ft) Nepal Cho Oyu 8201m (26906 ft) Nepal Dhaulagiri 8167m (26794 ft) Nepal Dhaulagiri 8167m (26794 ft) Nepal Manaslu I 8156m (26758 ft) Nepal Manaslu I 8156m (26758 ft) Nepal Nanga Parbat 8125m (26658 ft) Pakistan Nanga Parbat 8125m (26658 ft) Pakistan Annapurna I 8091m (26545 ft) Nepal Annapurna I 8091m (26545 ft) Nepal

  TALLEST MOUNTAINSTALLEST MOUNTAINS (On Each Continent)(On Each Continent)

Mount Everest 8850m (29035 ft) Asia Mount Everest 8850m (29035 ft) Asia Aconcagua 6959m (22831 ft) S. America Aconcagua 6959m (22831 ft) S. America Mount McKinley 6194m (20320 ft) N. America Mount McKinley 6194m (20320 ft) N. America Mount Kilimanjaro 5963m (19563 ft) Africa Mount Kilimanjaro 5963m (19563 ft) Africa Mount Elbrus 5633m (18481 ft) Europe Mount Elbrus 5633m (18481 ft) Europe Mount Willhelm 4509m (14789 ft) Oceania Mount Willhelm 4509m (14789 ft) Oceania Vinson Massif 4897m (16066 ft) AntarcticaVinson Massif 4897m (16066 ft) Antarctica