g oodvolcanoes folding faulting

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Crustal DeformationProcesses – Volcanoes,

Folding and Faulting

Results of Plate Movements



Volcano - conical or dome-shaped landformbuilt by the emission of lava, gases and solidfragments from a narrow vent in the surface.Volcanic materials : include: lava, gases and solidparticles - tephra : particles of all sizes, ash,volcanic bombs .



Volcano

The nature of eruption and the resultingvolcanic landforms depend on the nature oflava:

FELSIC LAVA - high degree of viscosity, resistsow = violent, often explosive eruptions

causing steep composite cones.

!ruptions of felsic lava typically create stratovolcanoes , also "nown as compositevolcanoes#eatures of a strato volcano: – steep slopes, - lots of tephra, - violent e$plosions, -

e$plosive discharge of gases.

Examples of composite volcanoes are !t"



!AFIC LAVA - highly uid = relatively%uiet eruptions causing lava ows

&a'c lava (basaltic) produces e*usiveeruptions that create s+ield volcanoes

it+ gentle long slopes ( e.g. +awaii )

lava often ows from 'ssures - crac"s -on the sides of the volcanic dome toform e$tensive deposits of plateau

basalts, or ood basalts

Landforms of Extrusive Volcano --2



o can cCone



Volcanic !ountains -Islands

Submarine volcanoes sometimes formIslands (Hawaii, Philippines, Japan, Sicily).

Some of the highest mountains in the world were formed by volcanoes –a) Mt. u!i"ama in Japan,b) Mt. #oto$axi in Ec ador, So th !mericac) "t. %iliman!aro in #an$ania, !frica,d) Mount Shasta in %alifornia and Mt.

Rainier in &ashin'ton state, S!.



Eruption of !t" Pinatu*o,P+ilippines, (une .//.



!agma

!agma is a molten orpartially molten roc"beneath the !arth ssurface. hen magma

erupts onto the surface,it is called ava.

&agma typicallyconsists of a li%uidportion . &agma collectsinside a volcano smagma chamber before

it erupts (see diagram).



Lava Flo Lava is the word formagma when it eruptsonto the !arth s surface.

/eologists also use theterm to describe thesolidi'ed deposits of lava

ows and fragments

hurled into the air bye$plosive eruptions (e.g.,lava bombs or bloc"s).

ava is derived from the0talian word for stream,which is derived from theverb lavare -- to wash.

Left 1 fast-moving lavaow from &t. !tna in

2icily.



Volcanic Vent Vents are openings inthe !arth s crust fromwhich magma andvolcanic gases escapeonto the ground or intothe atmosphere.Vents may consist of asingle, circular-shapedstructure, a largeelongated 'ssure andfracture, or a tiny

ground crac".2team rises from a venton &ount 1sahida"e , avolcano on +o""aido,

3apan (see picture onleft).



4aldera1 caldera is a large,usually circular depressionat the summit of a volcanoformed when magma iswithdrawn or erupted froma shallow undergroundmagma reservoir.

Calderas are di*erent

from craters, which aresmaller, circulardepressions createdprimarily by e$plosivee$cavation of roc" during

eruptions.Left &ount 1so vents alarge cloud of steam at

3apan s 1so 5ational 6ar".

The mountain s caldera isone of the world s largest.



Tephra Tephra is a general term forfragments of volcanic roc"and lava that are blasted

into the air by e$plosions orcarried upward by hot gasesin eruption columns or lavafountains.

Tephra includes large,dense bloc"s and bombsand small, light roc" debrissuch as scoria, pumice and

ashPicture ! fo ntain of hot lavaand tephra er pts from a craterin Hawaii*s +ila ea East ift in

- /0



0ntrusive 7 !$trusive Volcanic#eatures



8y"e: thin vertical veins of igneous roc" that form inthe fractures found within the crust. 9ecause theseintrusive features cool %uic"ly their roc"s are

dominated with 'ne mineral grains.Sill horizontal planes of solidi'ed magma that runparallel to the grain of the original roc" deposit9atholith: large plutonic masses of intrusive roc" withmore than ;; s%uare "ilometers of surface area.

Volcanic Pipe if a dy"e reaches the surface of the!arth it is then called a volcanic pipe .

I n t

r u s

i v e

v o

l c a n o e s



&istribution of Volcanoes



Compressionalforces s%ueezesedimentary depositsthat lie between theconvergingcontinental platesand folds them intos$nclines andanticlines

!$treme stress andpressure can causeroc"s to shear alonga plane of wea"nesscreating a fault" Lateral forces pullcontinental plates

apart to form riftvalle$s

Folding and faulting



olding 2tress and strain causes roc" tobuc"le and fractureor crumple intofolds.

#olding of initially

at layers (typicallyof sedimentaryroc"s) creates foldbelts consisting of:

– anticlines - arcli"eupfolds, and . . .

– s$nclines -troughli"e downfolds



#olding

1 fold is a bend inroc" that is theresponse tocompressional forces.

#olds are most visiblein roc"s that containlayers (strata)



S"nclinal folds in bedroc1, near Saint23odard2de24e5e ne,%anada. ( Source'(atural Resources #anada - )errain Sciences &ivision - #anadian Landsca$es "ore comple6 fold types can develop in sit ations where lateralpress res become 'reater. #he 'reater press re res lts in

http://sts.gsc.nrcan.gc.ca/landf.htm






0ormal fault 5ormal faults occur when tensionalforces act in opposite directions and cause one slab ofthe roc" to be displaced up and the other slab down.1ranform or stri2e3slip faults are produced +eret+e stresses are exerted parallel to eac+ ot+er" A

ell32no n example of t+is t$pe of fault is t+eSan Andreas fault in California"



1 gra*en isproduced whentensional stressesresult in thesubsidence of abloc" of roc". <na large scalethese featuresare "nown as 4iftValle$s

* horst is thedevelo$ment oftwo reverse faultscausing a bloc+ ofroc+ to be $ushed

u$ over the otherbloc1s.

A gra*en and a +orst



#he 7888 miles East *frican Rift Valle"

9ormed the ed Sea,and several rift valle"la+es in East !frica(#an'ayi1a, :yansa,# r1ana etc.)

Several bloc+mountains ,horsts rise within the riftvalley ("t. wen$ori)



Transcurrentfault zones onand o* the

est coast of5orth 1merica .

(Source .2./eological2urvey)

g oodvolcanoes folding faulting

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