Geology of Delta Systems.docx

8/9/2019 Geology of Delta Systems.docx

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Geology of Delta Systems

Sedimentary Depositional Environments:Delta Systems

The following tables provide a brief description of the typical characteristics ofdepositional environments found in Upper Paleozoic rocks of southwesternPennsylvania. it is summarized from Donaldson (1 !"b#.

LOWER ALLUVIAL PLAIN TO UPPER DELTA PLAIN

DEPOSITIONAL ENVIRONMENT

LITHOLOGIC DESCRIPTION

Meanderin !"annels $assive thick sandstones with point bar structures and wedge%to%trough type large scale cross beds with erosional basalcontacts& chute%bar structures. Plant and wood fragments. 'rainsize and bedding thickness decrease upward. ateral and basalcontacts sharp. )hale plugs occasionally occur within thesandstone unit.

Levee and !revasseSplay

*lternating thin beds of mudstone (variegated to brown# andfine%grained sandstones to siltstone with ripple bedding& root%disrupted parallel laminations& and plant fragments.

S#amp +oal& +arbonaceous clay probably deposited in well drainedswamps whereas peat in poorly drained swamps.

La$e imestones (dismicrites& pelmicrites& intramicrites# withshrinkage& laminated& or poorly developed algal structures.

imestones alternate with dark%gray calcareous shale.Spirorbis & fish parts& and ostracodes are most common fossils.

imestones are usually light colored and occur in rhythmicaldepositional se,uences.)ome lake facies consist of thin&discontinuous coals or dark laminated shales of limited e-tent.


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LOWER DELTA PLAIN



Distri%&tary !"annels *lternate%bar structures (minor lateral migration# with duneand ripple structures in massive sandstones basal scour.*bandoned channel deposits of siltstone and dark%gray shalewith abundant plant fragments. )iderite and ironstoneconcretions commonly in lag gravel deposit in channel.

Levee and !revasseSplay

*lternating thin beds of mudstone and fine%grained sandstonesto siltstone with ripple bedding& root%disrupted parallellaminations& and plant fragments. /ron o-ide concretions abovewater table.

S#amp +oal& pyrite& claystone%siltstone partings.

La$e' Interdistri%&tary%ay' and Interdelta (ay

0ay laminated shale& ironstone concretions& plant fragmentsand some ostracodes. imestones with ostracodes& spirorbis, and fish scales alternating with dark gray shale.

(ea)" Thin siltstone and fine grained sandstone beds. Transportedshell fragments rarely preserved. 'reater ,uartz content thane,uivalent grain size deposits of fluvial origin.

ADDITIONAL ENVIRONMENTS



Delta *ront'Distri%&tary Mo&t" (ars *lternating thin beds of siltstone& fine%grained sandstone andshale (mudstone# with gradational basal contact. )lightly


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arched bedding reflecting bar shape. ipple& dune& and parallel bedding with burrow mottled structures& especially at distalfringe.

Prodelta aminated silty shale& ironstone concretions& and plantfragments. 0edding can be burrow obliterated creating massivemudstone.

(ay $udstone and shale& dark gray to reddish gray. imestones&massive or shaly with brackish fossils.

Destr&)tive DeltaMar in and Interdelta+in)l&din tidal ,lat-

)andstones with slightly increased ,uartz content2 ripple& dune&flaser bedding and burrow%mottled structures. Tidal flatmudstone (some variegated#& flint clay& siliceous mudstone& ndiron carbonate. Tidal flat limestones (dismicrites& pelmicrites&intramicrudites# with shrinkage& laminated& or poorlydeveloped algal structures. imestone alternates with dark%graycalcareous shale. )pirorbis& fish scales& and ostracodes are themost common fossils.

The following diagrams are included here to provide the reader a guide to the kinds of

depositional systems in which the Pennsylvanian and Permian rocks of southwesternPennsylvania were deposited.


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This diagram& from 3isher and others (1 4 #& depicts the four main delta types and the kinds

of depositional environments associated with each. +lick on image for a larger version.


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5nvironments of deposition in a deltaic se,uence (from 6orne and others& 1 !7#.


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Development of a delta se,uence (from 3razier and 8sanik& 1 4 #.


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0ack 0arrier typical section (from 6orne and others& 1 !7#.


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0ack 0arrier /sland depositional environments (from 6orne and others& 1 !7#.


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Distributary 5nvironment (from 6orne and others& 1 !7#.

ower Delta Plain 5nvironment (from 6orne and others& 1 !7#.


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Typical )ections from the lower delta plain& bottom section with crevass splay (from 6orneand others& 1 !7#..


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Typical )e,uence from lower delta plain (from 6orne and others& 1 !7#.


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Upper Delta Plain 5nvironment (from 6orne and others& 1 !7#.

Typical )ection from Upper Delta plain (from 6orne and others& 1 !7#.


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*n e-ample of facies relationships in deltaic se,uences from the 9irgin and :olfcamp rocksof )tephens +ounty& Te-as (3rom 0rown& 1 4 #. ;ote the lateral variations in facies due tothe shifting positions of the delta lobes. Pennsylvanian and Permian rocks in southwesternPennsylvania e-hibit similar lateral relationships& although the paucity of outcrops usually

precludes such definition.


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$odel for the deposition of ad


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$odel for the deposition of adsguidebook by *. +. Donaldson (:est 9irginia University& retired#.


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)ection running ;: % )5 across the Pittburgh 1?> ,uadrangle showing the relationships ofsandstone bodies. )ection covers the Upper *llegheny 'roup into the ower +onemaugh


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'roup. the $ahoning sandstone is at the top. 8riginal data from @ohnson (1 A7#. 3rom 3ermand +avaroc (1 47#.

eferences

0eerbower& @. .& 1 41& 8rigin of cyclothems of the Dunkard 'roup (Upper Pennsylvanian %ower Permian# in Pennsylvania& :est 9irginia& and 8hio2 'eological )ociety of *merica

0ulletin& v. p. 1=A %1=?=.

0rown& ). .& 1 4 & ate Pennsylvanian paralic sediments& in 'uidebook to the atePennsylvanian )helf )ediments& ;orth%+entral Te-as2 Dallas 'eological )ociety& p. A1%BB.

Donaldson& *. +.& 1 !"a& Pennsylvanian )edimentation of central *ppalachians2 in 0riggs&'.& ed.& +arboniferous of the )outheastern United )tates& 'eological )ociety of *merica)pecial paper1"7& p. "!%!7.

Donaldson& *. +.& 1 !"b& *ncient deltaic depositional environments recognized inPennsylvania rocks of northern 8hio iver valley2 in Doanhue& @.& and ollins& 6. 0.& eds.&+onemaugh ('lenshaw# $arine 5vents& 3ield 'uidebook& Pittsburgh 'eological )ociety& p.3%1 to 3%11.

Donaldson& *. +.& and )humaker& . +.& 1 71& ate Paleozoic molasse of the central*ppalachians2 in $iall& *. D. ed.& )edimentation and Tectonics in *lluvial 0asins& 'eological*ssociation of +anada )pecial Paper AB& p. %1A".

3erm& @. +.& and +avaroc& 9. 9.& @r.& 1 47& * nonmarine sedimentary model for the *lleghenyrocks of :est 9irginia in Clein& '. de9ries Clein& ed.& ate Paleozoic and $esozoic+ontinental )edimentation& ;ortheastern ;orth *merica& 'eological )ociety of *merica)pecial paper 1=4& p. 1%A=.

3isher& :. .& 0rown& . 3.& @r.& )cott& *. @.& and $c'owen& @. 6.& 1 4 & Delta systems in thee-ploration for oil and gas2 * research collo,uium2 0ureau of 5conomic 'eology& TheUniversity of Te-as at *ustin& *ustin& Te-as& *ugust A!%A & 1 4 .

3razier& D. 5.& and 8sanik& *.& 1 4 & ecent peat deposits % ouisiana coastal plain2 in Dapples& 5. +.& and 6opkins& $. 5.& eds.& 5nvironments of +oal Deposition& 'eological)ociety of *merica )pecial paper 11"& p. 4B%74.

6orne& @. +.& 3erm& @. +.& +aruccio& 3. T.& and 0aganz& 0. P.& 1 !7& Depositional models incoal e-ploration and mine planning in *ppalachian region2 *merican *ssociation ofPetroleum 'eologists 0ulletin& v. 4A& p. AB! %A"11.

@ohnson& $. 5.& 1 A7& 'eology and $ineral esources of the Pittsburgh uadrangle&Pennsylvania2 Pennsylvania 'eological )urvey 0ulletin * A!& AB4 p.


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River deltaFrom Wikipedia, the free encyclopedia

Sacramento Delta at food stage, spring 2009. Photo by Doc Searls

* river delta is a landform that is formed at the mouth of a river & where the river flows intoan ocean & sea&estuary & lake & or reservoir . Deltas are formed from the deposition of thesediment carried by the river as the flow leaves the mouth of the river. 8ver long periods oftime& this deposition builds the characteristic geographic pattern of a river delta.

Despite a popular legend to the contrary& this usage of the word delta was not coined by6erodotus .E1F

Contents [ hide ]

• 1 Formation

• 2 Types of deltas

o 2.1 Wave-dominated deltas

o 2.2 Tide-dominated deltas

o

2.3 Gil ert deltas

http://en.wikipedia.org/wiki/Doc_Searlshttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Oceanhttp://en.wikipedia.org/wiki/Seahttp://en.wikipedia.org/wiki/Seahttp://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Lakehttp://en.wikipedia.org/wiki/Lakehttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Deposition_(geology)http://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Herodotushttp://en.wikipedia.org/wiki/River_delta#cite_note-1http://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/River_delta#Formationhttp://en.wikipedia.org/wiki/River_delta#Types_of_deltashttp://en.wikipedia.org/wiki/River_delta#Wave-dominated_deltashttp://en.wikipedia.org/wiki/River_delta#Tide-dominated_deltashttp://en.wikipedia.org/wiki/River_delta#Gilbert_deltashttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Oceanhttp://en.wikipedia.org/wiki/Seahttp://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Lakehttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Deposition_(geology)http://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Herodotushttp://en.wikipedia.org/wiki/River_delta#cite_note-1http://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/River_delta#Formationhttp://en.wikipedia.org/wiki/River_delta#Types_of_deltashttp://en.wikipedia.org/wiki/River_delta#Wave-dominated_deltashttp://en.wikipedia.org/wiki/River_delta#Tide-dominated_deltashttp://en.wikipedia.org/wiki/River_delta#Gilbert_deltashttp://en.wikipedia.org/wiki/Doc_Searls


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o 2.! "st#aries

o 2.$ %nland deltas

• 3 &edimentary str#ct#re

• ! 'eltas and all#vial fans

• $ "(amples of deltas

• ) "colo*ical threats to deltas

• + 'eltas in the economy

• 'eltas on ars

• &ee also

• 1/ 0otes

• 11 eferences

• 12 "(ternal links

Formation[ edit ]Formation of delta-shaped river asin

The formation of a river basin at the mouth of the river is usually characterised by the shapeof a delta & thetriangular 'reek letter . The cause of this shape of the river basin may bee-plained by the theory of colloids .

Introduction

Colloidal orces

http://en.wikipedia.org/wiki/River_delta#Estuarieshttp://en.wikipedia.org/wiki/River_delta#Inland_deltashttp://en.wikipedia.org/wiki/River_delta#Sedimentary_structurehttp://en.wikipedia.org/wiki/River_delta#Deltas_and_alluvial_fanshttp://en.wikipedia.org/wiki/River_delta#Examples_of_deltashttp://en.wikipedia.org/wiki/River_delta#Ecological_threats_to_deltashttp://en.wikipedia.org/wiki/River_delta#Deltas_in_the_economyhttp://en.wikipedia.org/wiki/River_delta#Deltas_on_Marshttp://en.wikipedia.org/wiki/River_delta#See_alsohttp://en.wikipedia.org/wiki/River_delta#Noteshttp://en.wikipedia.org/wiki/River_delta#Referenceshttp://en.wikipedia.org/wiki/River_delta#External_linkshttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=1http://en.wikipedia.org/wiki/River_basinhttp://en.wikipedia.org/wiki/River_basinhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/Delta_(letter)http://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/River_delta#Estuarieshttp://en.wikipedia.org/wiki/River_delta#Inland_deltashttp://en.wikipedia.org/wiki/River_delta#Sedimentary_structurehttp://en.wikipedia.org/wiki/River_delta#Deltas_and_alluvial_fanshttp://en.wikipedia.org/wiki/River_delta#Examples_of_deltashttp://en.wikipedia.org/wiki/River_delta#Ecological_threats_to_deltashttp://en.wikipedia.org/wiki/River_delta#Deltas_in_the_economyhttp://en.wikipedia.org/wiki/River_delta#Deltas_on_Marshttp://en.wikipedia.org/wiki/River_delta#See_alsohttp://en.wikipedia.org/wiki/River_delta#Noteshttp://en.wikipedia.org/wiki/River_delta#Referenceshttp://en.wikipedia.org/wiki/River_delta#External_linkshttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=1http://en.wikipedia.org/wiki/River_basinhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/River_deltahttp://en.wikipedia.org/wiki/Delta_(letter)http://en.wikipedia.org/wiki/Colloid


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Delta ormation

The river basin does form due to the formation of bottom%set beds& consisting of finermaterials carried farthest seaward and laid down on the floor of the embayment & on which thedelta is formed. 3ore%set beds are somewhat coarser and they represent the advancing front of the delta and the greater part of its bulk. They usually have a distinctly steeper dip than the

bottom%set beds and are in reality a continuation of the alluvial plain of which the delta is theterminal position.

Application of Colloidal theory to delta–shaped riverasins[ edit ]

+olloids are such substances& which basically possess an outward force which e-pands in twoways2 % 1. 8rdinal (vertical pressure# A. *bscissal (horizontal#

The lattice spread around those particles controls these forces. /n the ordinal force the pressure is ma-imum at the two ape-es of the particle. /n the case of abscissal pressure& thema-imum pressure is at the verte- which depends upon the lattice.(fig 1# /n the formation ofdelta%shaped river basin& the abscissal pressure is much more than the ordinal pressure(fig A#Therefore the delta shaped river basin is produced.

+olloids are present in the river system due to the presence of suspended alluvial silt as wellas silica deposits from the seawater & which act as the lattice for the colloidal bed.

!"amples of delta shaped river asins[ edit ]The Delta (shaded area# of the )t. +lair iver in ake )t. +lair has the classic shape of thedelta (see fig B#

http://en.wikipedia.org/wiki/Embaymenthttp://en.wikipedia.org/wiki/Embaymenthttp://en.wikipedia.org/wiki/Alluvial_plainhttp://en.wikipedia.org/wiki/Alluvial_plainhttp://en.wikipedia.org/w/index.php?title=Formation_of_delta-shaped_river_basin&action=edit&section=2http://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Abscissionhttp://en.wikipedia.org/wiki/Abscissionhttp://en.wiktionary.org/wiki/Particlehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Apex_(geometry)http://en.wikipedia.org/wiki/Vertex_(geometry)http://en.wikipedia.org/wiki/Silthttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Seawaterhttp://en.wikipedia.org/wiki/Seawaterhttp://en.wikipedia.org/w/index.php?title=Formation_of_delta-shaped_river_basin&action=edit&section=3http://en.wikipedia.org/wiki/St._Clair_Riverhttp://en.wikipedia.org/wiki/St._Clair_Riverhttp://en.wikipedia.org/wiki/St._Clair_Riverhttp://en.wikipedia.org/wiki/Lake_Saint_Clair_(North_America)http://en.wikipedia.org/wiki/Lake_Saint_Clair_(North_America)http://en.wikipedia.org/wiki/Embaymenthttp://en.wikipedia.org/wiki/Alluvial_plainhttp://en.wikipedia.org/w/index.php?title=Formation_of_delta-shaped_river_basin&action=edit&section=2http://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Abscissionhttp://en.wiktionary.org/wiki/Particlehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Apex_(geometry)http://en.wikipedia.org/wiki/Vertex_(geometry)http://en.wikipedia.org/wiki/Silthttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Seawaterhttp://en.wikipedia.org/w/index.php?title=Formation_of_delta-shaped_river_basin&action=edit&section=3http://en.wikipedia.org/wiki/St._Clair_Riverhttp://en.wikipedia.org/wiki/Lake_Saint_Clair_(North_America)


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•

The )t. +lair Delta

iver deltas form when a river carrying sediment reaches either (1# a body of standing water&such as a lake& ocean& or reservoir& (A# another river that cannot remove the sediment ,uicklyenough to stop delta formation& or (B# an inland region where the water spreads out and

deposits sediments. The rivers velocity decreases rapidly causing it to deposit the mas%foot of the $ississippi or Ural

iver deltas#& pushing its mouth further into the standing water. *s the deltaic lobe advances&the gradient of the river channel becomes lower because the river channel is longer but hasthe same change in elevation (see slope #. *s the slope of the river channel decreases& it

becomes unstable for two reasons. 3irst& the water under the force of gravity will tend to flowin the most direct course down slope. /f the river breaches its natural levees (i.e.& during aflood#& it will spill out onto a new course with a shorter route to the ocean& thereby obtaininga more stable steeper slope. EAF )econd& as its slope gets lower& the amount of shear stress onthe bed will decrease& which will result in deposition of sediment within the channel and arise in the channel bed relative to the floodplain. This will make it easier for the river to

breach its levees and cut a new channel that enters the body of standing water at a steeperslope. 8ften when the channel does this& some of its flow can remain in the abandonedchannel. :hen these channel switching events occur a mature delta will gain a distributary network.

*nother way in which these distributary networks may form is from the deposition of mouth bars (mid%channel sand andGor gravel bars at the mouth of a river#. :hen this mid%channel bar is deposited at the mouth of a river& the flow is routed around it. This results in additionaldeposition on the upstream end of the mouth%bar& which splits the river into two distributarychannels. * good e-ample of the result of this process is the :a- ake Delta in ouisiana .

/n both of these cases& depositional processes force redistribution of deposition from areas ofhigh deposition to areas of low deposition. This results in the smoothing of the planform (ormap%view# shape of the delta as the channels move across its surface and deposit sediment.0ecause the sediment is laid down in this fashion& the shape of these deltas appro-imates a

http://en.wikipedia.org/wiki/Stream_channelhttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Deposition_(geology)http://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Slopehttp://en.wikipedia.org/wiki/River_delta#cite_note-SlingerlandSmith-2http://en.wikipedia.org/wiki/Distributaryhttp://en.wikipedia.org/wiki/Shoal#Harbour_and_river_barshttp://en.wikipedia.org/wiki/Shoal#Harbour_and_river_barshttp://en.wikipedia.org/wiki/Wax_Lake_Deltahttp://en.wikipedia.org/wiki/Louisianahttp://en.wikipedia.org/wiki/Stream_channelhttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Deposition_(geology)http://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Slopehttp://en.wikipedia.org/wiki/River_delta#cite_note-SlingerlandSmith-2http://en.wikipedia.org/wiki/Distributaryhttp://en.wikipedia.org/wiki/Shoal#Harbour_and_river_barshttp://en.wikipedia.org/wiki/Shoal#Harbour_and_river_barshttp://en.wikipedia.org/wiki/Wax_Lake_Deltahttp://en.wikipedia.org/wiki/Louisiana


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fan. /t is closer to an ideal fan the more often the flow changes course because more rapidchanges in channel position results in more uniform deposition of sediment on the delta front.The $ississippi and Ural iver deltas& with their bird>s%feet& are e-amples of rivers that donot avulse often enough to form a symmetrical fan shape. *lluvial fan deltas& as seen in their

name& avulse fre,uently and more closely appro-imate an ideal fan shape.

#ypes of deltas[ edit ]

o er ississippi iver landloss over time

http://en.wikipedia.org/wiki/Avulsion_(river)http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=2http://en.wikipedia.org/wiki/Avulsion_(river)http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=2


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'elta lo e s itchin* in the ississippi 'elta , !)// yrs 56 , 3$// yrs 56,2 // yrs 56, 1/// yrs 56, 3// yrs 56, $// yrs 56, c#rrent

Deltas are typically classified according to the main control on deposition& which is usuallyeither a river& waves & ortides .EBF These controls have a large effect on the shape of theresulting delta.

$ave%dominated deltas[ edit ]/n wave dominated deltas& wave erosion controls the shape of the delta& and much of thesediment emanating from the river mouth is deflected along the coast line. EBF Deltas of this

form& such as the ;ile Delta & tend to have a characteristic 'reek%capital%delta shape .

http://en.wikipedia.org/wiki/Mississippi_River_Deltahttp://en.wikipedia.org/wiki/Radiocarbon_datinghttp://en.wikipedia.org/wiki/Wind_wavehttp://en.wikipedia.org/wiki/Tidehttp://en.wikipedia.org/wiki/River_delta#cite_note-Galloway1975-3http://en.wikipedia.org/wiki/River_delta#cite_note-Galloway1975-3http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=3http://en.wikipedia.org/wiki/River_delta#cite_note-Galloway1975-3http://en.wikipedia.org/wiki/Nile_Deltahttp://en.wikipedia.org/wiki/Mississippi_River_Deltahttp://en.wikipedia.org/wiki/Radiocarbon_datinghttp://en.wikipedia.org/wiki/Wind_wavehttp://en.wikipedia.org/wiki/Tidehttp://en.wikipedia.org/wiki/River_delta#cite_note-Galloway1975-3http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=3http://en.wikipedia.org/wiki/River_delta#cite_note-Galloway1975-3http://en.wikipedia.org/wiki/Nile_Delta


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The Ganges Delta in ndia and !angladesh is the largest delta in the"orld and it is also one o the most ertile regions in the "orld.

#ide%dominated deltas[ edit ]

5rosion is also an important control in tide dominated deltas& such as the 'anges Delta & which may be mainly submarine& with prominent sand bars and ridges. This tends to producea HdendriticH structure. E"F Tidal deltas behave differently from river% and wave%dominateddeltas& which tend to have a few main distributaries. 8nce a wave% or river% distributary siltsup& it is abandoned& and a new channel forms elsewhere. /n a tidal delta& new distributariesare formed during times when there>s a lot of water around I such as floods or storm surges . These distributaries slowly silt up at a pretty constant rate until they fizzle out. E"F

Gil ert deltas[ edit ]* 'ilbert delta (named after 'rove Carl 'ilbert # is a specific type of delta that is formed bycoarse sediments& as opposed to gently%sloping muddy deltas such as that of the $ississippi.3or e-ample& a mountain river depositing sediment into a freshwater lake would form this

http://en.wikipedia.org/wiki/Ganges_Deltahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Bangladeshhttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=4http://en.wikipedia.org/wiki/Ganges_Deltahttp://en.wikipedia.org/wiki/Ganges_Deltahttp://en.wikipedia.org/wiki/River_delta#cite_note-Fagherazzi2008-4http://en.wikipedia.org/wiki/Storm_surgehttp://en.wikipedia.org/wiki/Storm_surgehttp://en.wikipedia.org/wiki/River_delta#cite_note-Fagherazzi2008-4http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=5http://en.wikipedia.org/wiki/Grove_Karl_Gilberthttp://en.wikipedia.org/wiki/Ganges_Deltahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Bangladeshhttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=4http://en.wikipedia.org/wiki/Ganges_Deltahttp://en.wikipedia.org/wiki/River_delta#cite_note-Fagherazzi2008-4http://en.wikipedia.org/wiki/Storm_surgehttp://en.wikipedia.org/wiki/River_delta#cite_note-Fagherazzi2008-4http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=5http://en.wikipedia.org/wiki/Grove_Karl_Gilbert


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kind of delta. E?F E4F :hile some authors describe both lacustrine and marine locations of'ilbert deltas& E?F others note that their formation is more characteristic of the freshwater lakes&where it is easier for the river water to mi- with the lakewater faster (as opposed to the caseof a river falling into the sea or a salt lake& where less dense fresh water brought by the river

stays on top longer#.E!F

'.C. 'ilbert himself first described this type of delta on ake 0onneville in 177?. E!F 5lsewhere& similar structures can be found e.g. at the mouths of several creeks flowing into8kanagan ake in 0ritish +olumbia and forming prominent peninsulas at ;aramata (

! 73$83/90 11 73$83/9W : ! .$ 1)+70 11 .$ 1)+7W ;, mmerland <

! 73!82390 11 73+8!$9W : ! .$+3/)70 11 .)2 1+7W ;, or 6eachland <

! 7!+8//90 11 7!28!$9W : ! .+ 33370 11 .+12$/7W ;

!stuaries[ edit ]8ther rivers& particularly those located on coasts with significant tidal range & do not form adelta but enter into the sea in the form of an estuary . ;otable e-amples include the )aint

awrence iver and the Tagus estuary.

http://en.wikipedia.org/wiki/River_delta#cite_note-maine-5http://en.wikipedia.org/wiki/River_delta#cite_note-6http://en.wikipedia.org/wiki/River_delta#cite_note-maine-5http://en.wikipedia.org/wiki/River_delta#cite_note-chidsey-7http://en.wikipedia.org/wiki/Lake_Bonnevillehttp://en.wikipedia.org/wiki/River_delta#cite_note-chidsey-7http://en.wikipedia.org/wiki/Okanagan_Lakehttp://en.wikipedia.org/wiki/British_Columbiahttp://en.wikipedia.org/wiki/Naramata,_British_Columbiahttp://en.wikipedia.org/wiki/Naramata,_British_Columbiahttp://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_35_30_N_119_35_30_W_http://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_35_30_N_119_35_30_W_http://en.wikipedia.org/wiki/Summerland,_British_Columbiahttp://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_34_23_N_119_37_45_W_http://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_34_23_N_119_37_45_W_http://en.wikipedia.org/wiki/Peachland,_British_Columbiahttp://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_47_00_N_119_42_45_W_http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=6http://en.wikipedia.org/wiki/Tidal_rangehttp://en.wikipedia.org/wiki/Tidal_rangehttp://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Saint_Lawrence_Riverhttp://en.wikipedia.org/wiki/Saint_Lawrence_Riverhttp://en.wikipedia.org/wiki/Tagushttp://en.wikipedia.org/wiki/River_delta#cite_note-maine-5http://en.wikipedia.org/wiki/River_delta#cite_note-6http://en.wikipedia.org/wiki/River_delta#cite_note-maine-5http://en.wikipedia.org/wiki/River_delta#cite_note-chidsey-7http://en.wikipedia.org/wiki/Lake_Bonnevillehttp://en.wikipedia.org/wiki/River_delta#cite_note-chidsey-7http://en.wikipedia.org/wiki/Okanagan_Lakehttp://en.wikipedia.org/wiki/British_Columbiahttp://en.wikipedia.org/wiki/Naramata,_British_Columbiahttp://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_35_30_N_119_35_30_W_http://en.wikipedia.org/wiki/Summerland,_British_Columbiahttp://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_34_23_N_119_37_45_W_http://en.wikipedia.org/wiki/Peachland,_British_Columbiahttp://tools.wmflabs.org/geohack/geohack.php?pagename=River_delta&params=49_47_00_N_119_42_45_W_http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=6http://en.wikipedia.org/wiki/Tidal_rangehttp://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Saint_Lawrence_Riverhttp://en.wikipedia.org/wiki/Saint_Lawrence_Riverhttp://en.wikipedia.org/wiki/Tagus


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Inland deltas[ edit ]

#$a%ango Delta

/n rare cases the river delta is located inside a large valley and is called an inverted riverdelta . )ometimes a river will divide into multiple branches in an inland area& only to re


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• The foreset eds in t#rn #ild over the ottomset eds as the main deltaform advances. The foreset eds consist of the ed load that the river ismovin* alon* hich consists of lar*er sediments that roll alon* the mainchannel. When it reaches the ed*e of the form, the ed load rolls over theed*e, and #ilds #p in steeply an*led layers over the top of the ottomset

eds. The an*le of the o#termost ed*e of the delta is created y thesediments an*le of repose. ?s the foresets #ild o#t ard < hich make #pthe ma@ority of the delta; they pile #p and miniat#re landslides occ#r. Thisslope is created in this fashion as the edload contin#es to e depositedand the delta moves o#t ard. %n cross section, one o#ld see the foresetslyin* in an*led, parallel ands, sho in* each sta*e of the creation of thedelta.

• The topset eds in t#rn overlay the foresets, and are hori>ontal layers ofsmaller sediment si>e that form as the main channel of the river shiftselse here and the lar*er particles of the ed load no lon*er are deposited.?s the channels move across the top of the delta, the s#spended loadsettles o#t in hori>ontal eds over the top. The topset ed is s# dividedinto t o re*ionsA the #pper delta plain and the lo er delta plain. The#pper delta plain is #naBected y the tide, hile the o#ndary ith thelo er delta plain is deCned y the #pper limit of tidal in=#ence. [ ]

Deltas and alluvial fans[ edit ]Deltas are differentiated from alluvial fans in that deltas have a shallow slope & contain fine%grained sediment (sand and mud #& and always flow into a body of water. *lluvial fans& on theother hand& are steep& have coarse%grained sediments (including boulders#& and are dominated

by debris flows and large floods these floods are often flash floods . They can either flow

onto a land surface& or into a body of water in the latter case& they are called alluvial fandeltas.

!"amples of deltas[ edit ]The most famous delta is that of the ;ile iver & and it is this delta from which the term isderived. The 'anges G0rahmaputra combination delta spans most of 0angladesh and :est0engal & empties into the 0ay of 0engal and is the world>s largest delta. 8ther rivers withnotable deltas include& the 3ly iver & the Caveri & the ;iger iver & the Tigris%5uphrates & the

hine & thePo& the hKne& theDanube & the 5bro & the 9olga & the ena & the/ndus & the*yeyarwady (/rrawaddy#& the $ekong & the 6uanghe & the Langtze & the)acramento%)an@oa,uin& the$ississippi & the8rinoco & and theParanM.

!cological threats to deltas[ edit ]6uman activities& including diversion of water and the creation of dams for hydroelectric

power or to create reservoirs can radically alter delta ecosystems. Dams block sedimentationwhich can cause the delta to erode away. The use of water upstream can greatly increasesalinity levels as less fresh water flows to meet the salty ocean water. :hile nearly all deltashave been impacted to some degree by humans& the ;ile Delta and +olorado iver Delta aresome of the most e-treme e-amples of the ecological devastation caused to deltas by

damming and diversion of water.

http://en.wikipedia.org/wiki/River_delta#cite_note-8http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=9http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/wiki/Slopehttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Mudhttp://en.wikipedia.org/wiki/Debris_flowhttp://en.wikipedia.org/wiki/Floodhttp://en.wikipedia.org/wiki/Flash_floodhttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=10http://en.wikipedia.org/wiki/Nilehttp://en.wikipedia.org/wiki/Gangeshttp://en.wikipedia.org/wiki/Brahmaputra_Riverhttp://en.wikipedia.org/wiki/Bangladeshhttp://en.wikipedia.org/wiki/West_Bengalhttp://en.wikipedia.org/wiki/West_Bengalhttp://en.wikipedia.org/wiki/Fly_Riverhttp://en.wikipedia.org/wiki/Kaverihttp://en.wikipedia.org/wiki/Kaverihttp://en.wikipedia.org/wiki/Kaverihttp://en.wikipedia.org/wiki/Niger_Riverhttp://en.wikipedia.org/wiki/Tigris%E2%80%93Euphrates_river_systemhttp://en.wikipedia.org/wiki/Tigris%E2%80%93Euphrates_river_systemhttp://en.wikipedia.org/wiki/Rhinehttp://en.wikipedia.org/wiki/Po_(river)http://en.wikipedia.org/wiki/Rhonehttp://en.wikipedia.org/wiki/Danube_Deltahttp://en.wikipedia.org/wiki/Ebrohttp://en.wikipedia.org/wiki/Ebrohttp://en.wikipedia.org/wiki/Volga_Riverhttp://en.wikipedia.org/wiki/Volga_Riverhttp://en.wikipedia.org/wiki/Lena_Riverhttp://en.wikipedia.org/wiki/Indus_Riverhttp://en.wikipedia.org/wiki/Ayeyarwady_Riverhttp://en.wikipedia.org/wiki/Ayeyarwady_Riverhttp://en.wikipedia.org/wiki/Mekonghttp://en.wikipedia.org/wiki/Mekonghttp://en.wikipedia.org/wiki/Yellow_Riverhttp://en.wikipedia.org/wiki/Yellow_Riverhttp://en.wikipedia.org/wiki/Yangtze_Riverhttp://en.wikipedia.org/wiki/Sacramento_%E2%80%93_San_Joaquin_River_Deltahttp://en.wikipedia.org/wiki/Sacramento_%E2%80%93_San_Joaquin_River_Deltahttp://en.wikipedia.org/wiki/Mississippi_River_Deltahttp://en.wikipedia.org/wiki/Orinoco_Deltahttp://en.wikipedia.org/wiki/Paran%C3%A1_Deltahttp://en.wikipedia.org/wiki/Paran%C3%A1_Deltahttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=11http://en.wikipedia.org/wiki/Damhttp://en.wikipedia.org/wiki/Damhttp://en.wikipedia.org/wiki/Hydroelectrichttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Nile_Deltahttp://en.wikipedia.org/wiki/Colorado_River_Deltahttp://en.wikipedia.org/wiki/Colorado_River_Deltahttp://en.wikipedia.org/wiki/River_delta#cite_note-8http://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=9http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/wiki/Slopehttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Mudhttp://en.wikipedia.org/wiki/Debris_flowhttp://en.wikipedia.org/wiki/Floodhttp://en.wikipedia.org/wiki/Flash_floodhttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=10http://en.wikipedia.org/wiki/Nilehttp://en.wikipedia.org/wiki/Gangeshttp://en.wikipedia.org/wiki/Brahmaputra_Riverhttp://en.wikipedia.org/wiki/Bangladeshhttp://en.wikipedia.org/wiki/West_Bengalhttp://en.wikipedia.org/wiki/West_Bengalhttp://en.wikipedia.org/wiki/Fly_Riverhttp://en.wikipedia.org/wiki/Kaverihttp://en.wikipedia.org/wiki/Niger_Riverhttp://en.wikipedia.org/wiki/Tigris%E2%80%93Euphrates_river_systemhttp://en.wikipedia.org/wiki/Rhinehttp://en.wikipedia.org/wiki/Po_(river)http://en.wikipedia.org/wiki/Rhonehttp://en.wikipedia.org/wiki/Danube_Deltahttp://en.wikipedia.org/wiki/Ebrohttp://en.wikipedia.org/wiki/Volga_Riverhttp://en.wikipedia.org/wiki/Lena_Riverhttp://en.wikipedia.org/wiki/Indus_Riverhttp://en.wikipedia.org/wiki/Ayeyarwady_Riverhttp://en.wikipedia.org/wiki/Mekonghttp://en.wikipedia.org/wiki/Yellow_Riverhttp://en.wikipedia.org/wiki/Yangtze_Riverhttp://en.wikipedia.org/wiki/Sacramento_%E2%80%93_San_Joaquin_River_Deltahttp://en.wikipedia.org/wiki/Sacramento_%E2%80%93_San_Joaquin_River_Deltahttp://en.wikipedia.org/wiki/Mississippi_River_Deltahttp://en.wikipedia.org/wiki/Orinoco_Deltahttp://en.wikipedia.org/wiki/Paran%C3%A1_Deltahttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=11http://en.wikipedia.org/wiki/Damhttp://en.wikipedia.org/wiki/Hydroelectrichttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Nile_Deltahttp://en.wikipedia.org/wiki/Colorado_River_Delta


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Deltas in the economy[ edit ]*ncient deltas are a benefit to the economy due to their well sorted sand and gravel . )and andgravel is often ,uarried from these old deltas and used in concrete for highways & buildings&sidewalks& and even landscaping. $ore than 1 billion tons of sand and gravel are produced in

the United )tates alone.E F

;ot all sand and gravel ,uarries are former deltas& but for ones thatare& a lot of the sorting is already done by the power of water.

*s lowlands often ad


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•

Probable delta in a crater to the ;5 of 6olden +rater& as seen by $ars 'lobal)urveyor. /mage in $argaritifer )inus ,uadrangle .

See also[ edit ]

• ?ll#vial fan

• ?v#lsion

). ( 5ernard 5i@#-'#val, I. "d in & e>ey. E&edimentary Geolo*yE.6a*e 1 3. %&50 2-+1/ -/ /2-1 . "ditions T"DH0%6, 2//2. 6artial te(t onGoo*le 5ooks.

+. a b EGeolo*ical and 6etrophysical Dharacteri>ation of the Ferron&andstone for 3-' &im#lation of a Fl#vial-deltaic eservoirE. 5y Thomas D.

http://en.wikipedia.org/wiki/Margaritifer_Sinus_quadranglehttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=14http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/wiki/Avulsion_(river)http://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Formation_of_delta-shaped_river_basinhttp://en.wikipedia.org/wiki/Mega_deltahttp://en.wikipedia.org/wiki/Regressive_deltahttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=15http://en.wikipedia.org/wiki/River_delta#cite_ref-1http://www.jstor.org/pss/228368http://www.jstor.org/pss/228368http://en.wikipedia.org/wiki/River_delta#cite_ref-SlingerlandSmith_2-0http://en.wikipedia.org/wiki/River_delta#cite_ref-Galloway1975_3-0http://en.wikipedia.org/wiki/River_delta#cite_ref-Galloway1975_3-1http://en.wikipedia.org/wiki/River_delta#cite_ref-Fagherazzi2008_4-0http://en.wikipedia.org/wiki/River_delta#cite_ref-Fagherazzi2008_4-1http://en.wikipedia.org/wiki/River_delta#cite_ref-maine_5-0http://en.wikipedia.org/wiki/River_delta#cite_ref-maine_5-1http://en.wikipedia.org/wiki/River_delta#cite_ref-maine_5-2http://www.maine.gov/doc/nrimc/mgs/explore/surficial/facts/dec03.htmhttp://web.archive.org/web/20061012185632/http:/www.maine.gov/doc/nrimc/mgs/explore/surficial/facts/dec03.htmhttp://en.wikipedia.org/wiki/River_delta#cite_ref-6http://en.wikipedia.org/wiki/Special:BookSources/2710808021http://books.google.com.au/books?id=2txTeLt5MXgChttp://en.wikipedia.org/wiki/River_delta#cite_ref-chidsey_7-0http://en.wikipedia.org/wiki/River_delta#cite_ref-chidsey_7-1http://en.wikipedia.org/wiki/Margaritifer_Sinus_quadranglehttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=14http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/wiki/Avulsion_(river)http://en.wikipedia.org/wiki/Estuaryhttp://en.wikipedia.org/wiki/Formation_of_delta-shaped_river_basinhttp://en.wikipedia.org/wiki/Mega_deltahttp://en.wikipedia.org/wiki/Regressive_deltahttp://en.wikipedia.org/w/index.php?title=River_delta&action=edit&section=15http://en.wikipedia.org/wiki/River_delta#cite_ref-1http://www.jstor.org/pss/228368http://www.jstor.org/pss/228368http://en.wikipedia.org/wiki/River_delta#cite_ref-SlingerlandSmith_2-0http://en.wikipedia.org/wiki/River_delta#cite_ref-Galloway1975_3-0http://en.wikipedia.org/wiki/River_delta#cite_ref-Galloway1975_3-1http://en.wikipedia.org/wiki/River_delta#cite_ref-Fagherazzi2008_4-0http://en.wikipedia.org/wiki/River_delta#cite_ref-Fagherazzi2008_4-1http://en.wikipedia.org/wiki/River_delta#cite_ref-maine_5-0http://en.wikipedia.org/wiki/River_delta#cite_ref-maine_5-1http://en.wikipedia.org/wiki/River_delta#cite_ref-maine_5-2http://www.maine.gov/doc/nrimc/mgs/explore/surficial/facts/dec03.htmhttp://web.archive.org/web/20061012185632/http:/www.maine.gov/doc/nrimc/mgs/explore/surficial/facts/dec03.htmhttp://en.wikipedia.org/wiki/River_delta#cite_ref-6http://en.wikipedia.org/wiki/Special:BookSources/2710808021http://books.google.com.au/books?id=2txTeLt5MXgChttp://en.wikipedia.org/wiki/River_delta#cite_ref-chidsey_7-0http://en.wikipedia.org/wiki/River_delta#cite_ref-chidsey_7-1


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Dhidsey, Thomas D. Dhidsey, Ir


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The Fraser River delta

0at#reOs ne *ro#nd

Where iver eets &ea

8ver the last 1=&=== years& a great pile of sediment has accumulated as a delta where the3raser iver flows into the )trait of 'eorgia. 0efore the construction of dykes in the 1 ==s&floods regularly deposited silt and clay on the flat 3raser delta plain. )and that reaches theriver mouth occasionally slumps into deep water along submarine canyons. $ud accumulatesin tidal marshes and on the seafloor off the delta front. There are many competing pressuresfor the use of the delta land2 it is an important agricultural area it is e-periencing dramaticurban and industrial growth centered in ichmond& adner& and Delta and the tidal flats andmarshes are vital habitats for salmon fry and migratory waterfowl.

'rowth of 3raser iver delta and floodplain (shown in yellow# over the last1=&=== years.

DanOt stop G NW%0G -- or can itP

The 3raser delta began to develop at what is now ;ew :estminster about 1=&=== years agoand has since advanced about A? km seaward. 6owever& today sand is dredged to maintainthe shipping channels below ;ew :estminster& dykes strait


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to the coal port& ferry terminal& or submarine electric cables that supply much of the power to9ancouver /sland.

What Happens When %t &H?K"&P

5arth,uakes pose special problems for the 3raser delta. )evere shaking turns loose& water%saturated sediment into a fluid (li,uefaction#. :hen sediments li,uefy& the ground maysubside irregularly& causing buildings that are not properly anchored to tilt or collapse. Thethick delta sediments can locally dampen or intensify earth,uake shaking areas withintensified shaking e-perience greater damage.

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