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<br />"e.nhertng ca"stng the" ta erode readily "<ld form thick tal,," ,~"d eolllJvi~l
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<br />GEOLOGIC HAZARD
<br />AREA
<br />AERiAL. Vl~W
<br />
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<br />Coalescing
<br />Debris Fans
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<br />deposits a1008 the canyan ""Ltg. l)uring tntense thundcrstor::!>) or pr~lang"d
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<br />r"bstorm", this loo"" fMterL11 becomes satur"ted ca\lsing it to mobi1h~ ,~nd
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<br />fIo'" like freshly mLxed tOClcret~ do"" th~ Heel' "">untllirl canYOll'.
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<br />ThCFMjorityofthLs1!\()blU?edrMterl,,-ltscompo"edofsand-, silt-, and
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<br />elay-sh~d p~rtitles, but cobble- "nd b<luLdct-.hed p"rtLc1",Q ..,s "ell ,qg
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<br />significant amoo.mts of diaplaced soiL "nd vegctatLan are also pres"nt. .
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<br />WhiLe the larg'H constitu~nta of these fl""s are properly elaa.iEted a.
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<br />"debris", the aburldarlce of fine-grained panLcLes causeS th~"e flows to
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<br />hehave l1l<e ""'ud," Theretore, both "debris flow" and "mud no,," A'" v"Hd
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<br />term" d~scribing the flow_. along the Chntk Cutfs.
<br />
<br />Coalescing
<br />Debris Fans
<br />
<br />This visco,," ,,"'l~$ of mud nnd dd>rL5 OrigiMtin,o; In e.~d1 ""'311 ,nountain b....sin
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<br />(~ag" ~), the 'Mlrl ,1d>ris flow el\,lnn~t ''''11 lY38 to 1961 cr".""~d t~.. c~"tr,~1
<br />
<br />
<br />GROUND
<br />
<br />VIEW
<br />----
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<br />is del'oslt~J at the ""'''rltOltn frorlt, for",t~g ~ hroad, triangular-shaped
<br />
<br />feOl""re c.,lied "- ,-(ebrts hn. Through time. successi\1<'. debris flows h,-,ve
<br />
<br />Undulating Surface
<br />Characteristic of
<br />Debris Fans
<br />
<br />h"tlt"pL,rgeckhrls faI\swhicilhavemer;:edorcoalesced"Uhfa1\s"tt:he
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<br />"'''''ths ot adJ"""rlt """yo"s. T".lav, th"~,, fans form n contln"",," blanket of
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<br />debris .1lo~g the norcll "tde of Chalk Cr(!~k.
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<br />D"posLtloI\ uf ",,,d and debris on these {(If'. Is ao oogoi"!! proc~"". flows
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<br />r~,,~hio~ th" h,.n~ of rh" f~n~ nFt~n Fnll'", th.. ch~on..1 form"~ hv natural
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<br />lc'''~cs depoRltd by the pr~cedlng flow or flows. F.v~ntually, ho",ev.or, tl",~~
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<br />"or~ recent ehanrlels "ilt heco"", clogged ",ith debris, forcing the no~' over
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<br />th~ levees ..."d int<l adjacent "re,,-S. As Seerl In the ""rlel> of ?hcto"r,,-phs
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<br />ponion '" the t"n. Ibw~v"r. bet"een 19,,2 and l'Jti9, an ~'."nt oce"teed in
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<br />"htch the ~ebrls bitl~lly tollowed the "",In eh""",,l, b"t lAter, due to the
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