Chapter

Mountain Building

11.1 Rock Deformation

Factors that influence thestrength of a rock and how it willdeform include temperature,confining pressure, rock type, and

Factors Affecting Deformation

confining pressure, rock type, andtime.

- Most crustal deformation occursalong plate margins.

•Deformation is a general term thatrefers to all changes in the originalshape and/or size of a rock body.

Factors Affecting Deformation

11.1 Rock Deformation

•Stress is the force per unit areaacting on a solid.acting on a solid.

•Strain is the change in shape orvolume of a body of rock as a resultof stress.

Factors Affecting Deformation

11.1 Rock Deformation

Temperature and Pressure

•Rocks deform permanently in twoways: brittle deformation andways: brittle deformation andductile deformation.

- Brittle deformation is the fracturingof an object once its strength isexceeded - glass, china plates andbones are examples

11.1 Rock Deformation

• Rocks deform permanently in twoways: brittle deformation and ductiledeformation.

- Ductile deformation is a type of- Ductile deformation is a type ofsolid state flow that produces achange in the size and shape of anobject without fracturing the object- modeling clay, bee’s wax, caramelcandy and most metals are examples

Factors Affecting Deformation

11.1 Rock Deformation

Rock Type•Mineral composition and texture ofa rock also greatly affect how it willa rock also greatly affect how it willdeform.• Granite and basalt usually fail bybrittle fracture• Sedimentary and metamorphicrocks are weak and deform byductile flow

Factors Affecting Deformation

11.1 Rock Deformation

Time

•Forces that are unable to deform•Forces that are unable to deformrock when first applied may causerock to flow if the force ismaintained over a long period oftime.

Types of Stress

11.1 Rock Deformation

The three types of stresses thatrocks commonly undergo arerocks commonly undergo aretensional stress, compressionalstress, and shear stress.

Types ofStress

Pulled

Squeezed or shortened

Distorted

Anticlines and Synclines

11.1 Rock Deformation

Anticlines

•Anticlines are most

Folds

•Anticlines are mostcommonly formed by theupfolding, or arching, of rocklayers.

Anticline

11.1 Rock Deformation

Synclines•Synclines are lineardownfolds in sedimentary

Folds

•Synclines are lineardownfolds in sedimentarystrata.

•Synclines are often found inassociation with anticlines.

Synclines

11.1 Rock Deformation

Monoclines•Monoclines are large step-like folds in otherwise

Folds

like folds in otherwisehorizontal sedimentarystrata.

Monoclines

Mexican Hat, Utah

Monoclines

Monocline

11.1 Rock Deformation

Normal Faults•Normal faults occur when thehanging wall block moves downrelative to the footwall block.

Faults

relative to the footwall block.•Most have steep dips of about 60o

•Result in the lengthening, orextension, of the crust

•Occur due to tensional stresses

Reverse Faults and Thrust Faults•Result from compressional stress•Reverse faults are faults in whichthe hanging wall block moves uprelative to the footwall block.

11.1 Rock Deformation

the hanging wall block moves uprelative to the footwall block.

•High-angle faults with dips greaterthan 45o

•Thrust faults are reverse faults withdips less than 45o.

Reverse FaultsReverse Faults

Thrust Faults

Folds

11.1 Rock Deformation

Strike-Slip Fault

•Strike-slip faults are faults in whichthe movement is horizontal and

•Strike-slip faults are faults in whichthe movement is horizontal andparallel to the trend, or strike, of thefault surface.

•Caused by shear stress.

Folds

11.1 Rock Deformation

Joints

•Joints are fractures along which no•Joints are fractures along which noappreciable movement hasoccurred.

•The result of large-scale regionalstresses.

Four Types of Faults

Joints

ArchesNationalNationalPark, Moab,Utah

Folded Mountains

11.2 Types of Mountains

Mountains are classified by thedominant processes that haveformed them.formed them.

•Orogenesis is the collection ofprocesses that result in the formingof mountains.

11.2 Types of Mountains

Folded Mountains

•Mountains that are formed primarilyby folding are called foldedmountains.mountains.

•A folded mountain is caused byextreme force pushing from bothsides of the plates. This greatpressure causes mountain to break,bend, and fold

Folded Mountains Mount Kidd, Alberta, Canada

11.2 Types of Mountains

Large-scale normal faults areassociated with structures calledfault-block mountains.

•Fault-block mountains are formed

Fault-Block Mountains

•Fault-block mountains are formedas large blocks of crust are upliftedand tilted along normal faults.

•Grabens (ditch or trench) areformed by the downwarddisplacement of fault-boundedblocks.

11.2 Types of Mountains

•Horsts are elongated, upliftedblocks of crust bounded by faults.

Fault-Block Mountains

•A block fault mountain is createdwhen a mountain rises from theearth. When the mountain risespressure causes the rock to crackand slide. This creates sharp anddistinctive faces on the mountain.

Fault-Block Mountains

Large-scalefolding isapparent inthis satelliteimage of theAppalachianAppalachianMountains,Pennsylvania.

The Andes from space

Himalayan Mountains from space

Domes and Basins

11.2 Types of Mountains

When upwarping produces acircular or elongated structure, thefeature is called a dome.feature is called a dome.

•Uplifted mountains are circular orelongated structures formed byuplifting of the underlying basementrock.

Domes and Basins

11.2 Types of Mountains

•A dome mountain is formed whenmelted rock is pushed up throughthe earth's crust without folding orthe earth's crust without folding orfaulting creating a dome like shapeof the mountain

•Erosion is believed to be a majorfactor in the shaping of most domeformations.

DomedMountains

Black Hills of SD

Michigan Basin

Volcanic Mountains

11.2 Types of Mountains

A volcanic mountain is formed whenmelted rock rises from the earth andbuilds up over time on the earth’sbuilds up over time on the earth’ssurface. This is how Mount St.Helens was formed.

MOUNTAIN FORMATION DATE TYPE CONTINENT

Himalayas around 75 mya folded/block AsiaUrals around 300 mya folded EuropeAppalachians around 500 mya folded N AmericaRockies around 140 mya block/fault N AmericaAlps around 25 mya folded EuropeAlps around 25 mya folded Europe

Mount Shasta

Mount St. Helens

Mount Hood

Mountain Building at ConvergentBoundaries

11.3 Mountain Formation

Most mountain building occurs atconvergent plate boundaries.convergent plate boundaries.Colliding plates provide thecompressional forces that fold,fault, and metamorphose the thicklayers of sediments deposited atthe edges of landmasses.

Mountain Building at ConvergentBoundaries

11.3 Mountain Formation

Ocean-Ocean Convergence

•Ocean-ocean convergence mainlyproduces volcanic mountains.

11.3 Mountain Formation

Ocean-Continental Convergence•The types of mountains formed byocean-continental convergence arevolcanic mountains and folded

Mountain Building at Convergent Boundaries

volcanic mountains and foldedmountains.

• An accretionary wedge is theaccumulation of differentsedimentary and metamorphicrocks with some scraps of oceancrust.

Ocean-Ocean Convergence

Ocean-Continental Convergence

11.3 Mountain Formation

Continental-Continental Convergence

•At a convergent boundary betweentwo plates carrying continental

Mountain Building at Convergent Boundaries

two plates carrying continentalcrust, a collision between thecontinental fragments will resultand form folded mountains.

• India and the Eurasian plate

Continental-Continental Convergence

Mountain Building at DivergentBoundaries

11.3 Mountain Formation

The mountains that form alongocean ridges at divergent plateboundaries are fault-block typemountains.

Mid-Atlantic Ridge

Mountain Building byContinental Accretion

Non-Boundary Mountains

11.3 Mountain Formation

Not all mountains are formed byplate boundaries. Some areplate boundaries. Some areformed by hot spots or regionalextension or stretching.

Hawaiian Islands

Continental Accretion

11.3 Mountain Formation

Accretion is a process that occurswhen crustal fragments collidewhen crustal fragments collidewith and stay connected to acontinental plate. Many of the mountains along thePacific

Continental Accretion

11.3 Mountain Formation

Terranes•Terranes are any crustal fragments•Terranes are any crustal fragmentsthat have a geologic history distinctfrom that of the adjoiningfragments.

•Terranes occur along the PacificCoast.

Accretion inWestern NorthWestern North

America

11.3 Mountain Formation

• Isostasy is the concept that Earth’scrust is floating in gravitational balanceupon the material of the mantle.

Isostatic Adjustment for Mountains

• Because of isostasy, deformed and

Principles of Isostasy

• Because of isostasy, deformed andthickened crust will undergo regionaluplift both during mountain buildingand for a long period afterward.

• Isostatic adjustment is the process ofestablishing a new level ofgravitational equilibrium.

Isostatic Adjustment

Isostatic Adjustment in Mountains