Late Pleistocene subglacial caldera formation at Cerro las Cumbres

Late Pleistocene subglacial caldera formation at Cerro las
Cumbres. eastern Mexico
Armann IJoskuldsson
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INTRODUCTION
Trnrs l\lerlcrn !olcinic belr is chamcrer
r N :i nefdin: chr . ofvoLcx.oes. rlre Cofre
de |e.oie l'i.o de Orizrbx nrounrxi. r.re Ihe chai.
cons srs of fonr nu or lolcani. cdili..s xn.l o.c \ol
cxni..onr|le\. r!hi.h n!.r n.rh Lo !)uLh xr. alofrc dc
l'erct.. Lr ajlorjx complc\. Ccrro ix\ Cumbr.s. Pico
dc Orizrbr. dnd Sicrn (Figurc 1. Ncgcndank rr dl..
The e.rsrenr
Lzed by
Ccro lrs Cunrbrcs (]950nrl rr l9''1(l N an.l
97'lar \\j. qr liAr rccognizcd rs r calderr slr!clurc
lc 1198.1) alld Iarer ide|rilied as .r urcli!ul
ual slftlololcm.i b) Nege dark ./ a1 (1985) 11
$rs hLgel) co|srrucled dLrin: ihe earl) ro rniddlePleistoce.e epoch. Acri!ir\ de.lined in the llrte I'leis
tocene whe. extefsile .trxio. of thc edilice trrck
pl!.e l\egcndrnk.r dl. 1985r.
br- $rcr
Flm ironrneftrl eUecls of the lare Pleislocene \Yis
co.sin Slxciriio. i. N,lexlco rre not fulll u.derstood.
Whi(c (1987), Whit. and VaL$ttu I l{18.11 dd Heine
(
19E8) sLrtrliocl (hc gldcixl
co\.r o.
(hc hrge \n
rt.r'.r
ca ocs: ,\jusco. Nfalinchc, Popocrtafc(l rnd Pico.l.
Oriz.rbr. Thc\ coucluded Lhxt durins Lhc hLc Wiscon
sm. all yolcrnoes olcr.1.0(l0m allirudc wcn crpt.d
br Shciers. GlacieA e rcpo cd 10 havc r.achcd as
low rs 3.200m hilude during lhe glaci.rl r)ra\inun
(Whire, l(lE7: He.e, L9llitl.
Thi\ rr(iclc do\cibcs Lhc rnosL rcccnt.ruptions rt
C.no lrs CuDrbrcs !olcrDo. $hich wcr. rsvrcirlcd
rilh r \!rlnnil c.,llapsc lornring { crlclcrx 1.5 xl.5 km
i dia erer Crrbon l.l clariug ()1 chamd phDL/$1n)d
rernains tound in lhe eL!pled ptuducls }iclds an ngc ol'
16,980+N70yrB ll (srrnple CIF85l7. d,red al Gilsur
Y FIe \".,
. 't l-lL,
co.rpositi{rn lrcnr dxcile
I.
ee, r.r, ".,...
hi8h K drtolite (Table I).
JOKULL No.
50
49
Atnrtrtn tt
iis
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tI
ES
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Figurc l. Snnplilied geologi.xl mrp oi Ccnlral Nlexico showing thc main volcxno tectdric stru.rtrres includ
ifg thc Tlalls Nlexican volcanic bclL rud the location of thc rcsearch area. lnset to lhc righl. shos's the f(n '
volcrnocs and the lolcrnic conplcr lbrmtng the eNlcrnmosl parl ol lhe'lftns Nlcrica \blcnnic Belt Lrs
Cumbres is situxred rbouL ? km nonh ol Pico de Oizabt. O1 the iour lolcarrccs Pico de Orizabx is curcntll
nrosr aclile. i..luding tlrc prrasilic lent Sienr Ncgr^. Stuatttltitry tunnvjkndts\enititts. M,\t intil htt:!i
sitii) lrrr fj[qur at&it)]t s.nt t)trld arsta u hlutu t"t\ikarsLo cl.lfjalldhthis; s Los ( r"1hr?s .t \ntn\41 th1
df rklljdtlinuPitoDcOti.dhd,okalellltttll hefut t?tinlittunsagukqt ltth d Sutut ttJ Pit.)
7L t
".,th" t ?hlsti)lin
t,( 0tiltha
Siu ru
N(n r.n th.\tit
sd"Lt
Thc Cero Las Cumbrcs |hyolirc coolains abunddcc
ol rnacroscopic biotitc phcnocrysls that diitinguishcs
ir liolrl orher rh\llitc ptuducls in lhe reqion (Vcnnd
and Lope7, 1982) Ar rhe lilr1e ot'ihe erttion thc vol
cano was .a|pcd bl r glacier. which had imporLanl
eJlects on thc cruptiou mechrnics And frocluccd a unusLral deposiLid l pallern of tbe eruptivc producIS.
DISTRIBLITION OF THE DEPOSITS
Volcaniclasric dcposiLs lbmred rn lhe 16.980+810 yr
B.P eruttion rr. distribured as)'nnnetricalL) &mnd
Cerro lxs auml,ns (Figures 2a and ztr). Thc g!:ar
est volum.s ol clcposils irc observe.l on Lhc $,est
1lA.k, whcrc the) coler the slotcs
fnn
about
l.40ll
of rhe
altilrde do\rn lo lhe Basin Ori
.nrrl tFigure 2a). Brmncas cul irllo lhe
50
volcano
iOKULL \o. 50
deposits rc
k.tl
lcal coi^e boulder rich llu!ial sedinrenrs rt thc basc
ol lhe volca.icLastic clcposils On dre s.st flank ol
lhe volcano. in rcrs proximal io the lcDL (.'gknt
the Cem L$ Cun)bres deposits .onsisr ol .1 e
'p
ti!e units. Thc 1o$,esI Lrnrt of tlre dcposils is laharic
ard i\ ovcrldm bl pyroclastic llow dclosils (Figurc
ll l'hc plroclastic tlow defosils form r sheer thri
is drick in ropographic lorls and lhirrs oLrl ioward Io
pographic highs. These Jctosils are ore xin br r
puniice lill deposit, thdL Llrins regularll rwry lronr
rhc lolcano if lccoturncc $ilh a WNw oricnlcd dis
persion ixis (Pigurc 2a) Withur x distancc ol 9kn1
ro,.,l-.'dp
r"p.r ,..,lat
n
i'
Di
,ro
gc tDd ash-1all
lwounit! bv r scrics olpircclostic
deposirs. Dcposirs ol sir.ilM lithologic charncier caf
the sequcncc (FigLrre 31.
Cald.ru fomdtion at Ceur las Cunbrcs, l\4eico
O
AShJNd6POSb
Q90
Figure 2a.A simplified geological map ofihe 16 ka las Cunbms deposits, sbowing the locatioD ofthe caldera
and nhe distribution of the deposits. the caldera is circumscribed by a zone devoid of deposits. Tbis zoDe is
interpreied to represent ihe extension of surnmit glacier al the tine ofthe erupnon. - EinJ'dHaA idt,tedikott df
rltbrei'sLu sosefna I A el.lsasitlu i Las Cunbres f)1rir un t6 bisund at un. Gosejnalausa lteain, ren ryndat
han, i kringln dskjund, et taliA e dunpegh hamdfts ttbreiAsluj()k Lhetuti lind gossins Goselnin sen lZIlu
n inkulinn bAust s{6an burt ned lqsingdrNatni begdr jdkullinn brdAndAi.
of crlden floor m lhe fi.alphase of the eruplion.
up
m
the
caldera
rim
is
cornplelely
frce
of
In distal a.eas, close to the aillage Ciudad Serdan
-3,200m
deposits liom the 16,980 B.P.eruption. The deposirs to fie souLhwest of the volcano. rhe punice falllayer
reappear within the caidera, wherc they are delbrned occurs belween two units of reworked homblende
because ofrhe dacile dome that exL.uded tbrough the daciie ash. The upperhomblende r]acirc unil is overA
circular zone extending from an altitude
rOKIn.L No
50
51
At
ntntt tt iiskrttlsvrt
4
.q'
/
/.q
:t|!.a
\
or5
N
mo- arer
Contour
orest
l,-igure 2b. t.ocrti(nr
\,alin
ol nratigrxphic scclions exinrined
etid t tintli
t1\|tl
i!
-/
iletua
co our
this sludy. Selectcd \lr.rli$aphic
aoac
s 500 m tlre
ne b€'nqal
se.ti'n\ rr: n'own
l
Tible l. Vrlurne calculrti(nr\ ol lhe volcrnic dcposils lbfned in thc l6 9U0+870 )r B P cruflion. Crlculations
only for rlre deposits withiD Lhe resenrch rct (FigLrre 2rl. Rtit n1l roscJra nd Yn n^ndua st i qotinu
Nilrtnfi tndt.nt.tnri;nq l\qrait nh.in4naltrenlin dsti na tttt)lttilrldt\twnisi sttin,l\ttl2d)
Arc lfldtuatrnl Thick.css (n /l^Lkl l,,l VoLumc, rtnnril DRL
kmr krrs
kmz nin ntr
Ash {low/,\-lrrlr,/.t"r!1i,
IDside caldera/.r,;
Calde.a deprcssio
t,rdr rrtr,,L,
/rrirjrtl<in
.! I Ilit t:\u2)!.nlt\rn
52
JOKULL No. 50
hrttt::tilrrl
5 200
299 l5
r0 5
5 500
r
t0.9rJ
500
100
2
E
100
90
100
6Ut)
1.0
r80
r.5
78
7-8
.d1d\ra lo"qaron at
c,..o
1a,
cu".h,/ . \,1t,;,.
LEGEND:
u
t4H
.+
a
lll !
l
w
kif|
7/As^
sbr-
etoended smqe aid rar
sbni0a66a3h sdqgd€p0s
s
Lllll
i"i.
fifll
lllt
Figure 3.Craplic logs showing the statigraphy oflhe las Cumbres deposits at selected seclions. Section locations are showr in Figres 2a^nl2b. Udlin snid i eegnun gasefninrt'ti el.lgosinu sen nJnduAinskiund 6 Las
Cunhres. StuAserling eliAa nd et sind A nJndun20 ag 2b.
T ll diicitic plinial teph.a f.om Pico de Oriz
(H6skuldssoD
and Robin. 1993). ID distal areas
abr
the
eastern
oD
slopes of Pico de Orizaba a tephra
layer less fian 1cm thick was observed in soil profiles. The Ceno Las Cumbres lephm is disdnguished
frotn those originating at Pico de Orizababy theirdis'
lain by
linguishing phenocrysts. Stratigraphically the Ceffo
Las Cumbres lephra layer is siruated berween the T t
T II
tepbrx layers derived from Pico De Oizaba
arJ Rob r . oo1 . Rr^orl.d p.r , ice
ricb iI biotiLe was observed on alluvirlphtus close to
the iown of Tierra Blanca. about 150km east of the
volcano. No primary pyrocla$c-flow deposils were
observed io ihe easi ofthe volcano, indicatinglhar the
distibution of the pyroclastic-flow deposits was 1imited ro the western slopes.
and
lHit"k
id*or
JOKULLNo.50 53
Aitnun
lliitltL^rrl
,'
fi!!rc 1. Sl-lNi fhobg(th ol lhe frc.ljum Lo lin. r:h lnirs lhrL mxkc !p rrro.e
posir\. The.lrcn.bing nrlLcl r..llh. roll shrfed pr11icLcs. chifs. rrrd !e!cle
ld
qt
l)i lritlat \.tu allistn lv<r hti" \t) lt\\t
'Ih.rc rrc 1$o frrin Lrhoii.i.\ thll frrk. rp tlr.
hhrric clcruril. Ih. lir\( lxcics L\ iefr.scnl.cl bl
coxrs. g(irled. non b.dlcJ. uln{ {Uflnt.d hr.c
cir !lc|osil!. lh. mxrrii col]!\ls ol hn. lo Dcdiurrl
gtui|ed rnr $i(h s.rl(.red rorLnd.d tunicc hpillL.
Tlie cor*e hl.cls s ilhrir the br.c.ir xr. xnguhr lLlhLc
lrrs e.t. lrom t|c ca rice. lh. s.cotcl li(ie! \ n..
5:l
ihd lllri ol lh' rnr llo$ (le
\rll lrrgm.nlsrt i.di.rred
Ia)Kr
r r- \o.
i(J
grinrcd rllr $irh .ns.\ ol hpilli punrLces r.d Li(hics
Th. !n r erhibils tli\ti.cli\c inle rrl srfutilicxri.. xnd
dcpo\Lllonrl slrrcturcs such ,t\ dunes rnd mc.lrrclucs
Abunddr lirgmcnt5 01 !rrchu erl woo(l occtr irr thn
r nlr nr:!.sli.g r rclali!el\ lo$ entLrcc.rcnl lcD'pcr
rilure lloth lircics rre !llle\ .oniin.d \hcrc th.t oul
dop on rhc $csre r \lop.s ol (hc \olQro. \ellhe'
rri r hr\ hc.f l.urd ro rh. cxsr ol Lhc lolcrno.
Cdl,lera fomLatiott dt Cerro Lds Crnbrcs,
Figurc sr.Thc dsh flo* dcposits shoilmg lcn\es of
pumicc rnd lithics. Thc mcgaduncs al rhc basc oithc
seclion are fiee of charred \food liagnenls indical
ing low ernplaceme|t temperatures, whereas charred
wood occurs just above rhe rippled zore withln the
pyroclastic-l']ow deposii. Gjiskull'Aasetin n1.a
tinytt 4 tikti os Iand\dsteinm, sm1 Inurnat
betula ,i tftrLL garuruir ebst i opluntti ttu titt koLd,
sc Lbendr'tilhess aa hetd sl e inskonar jnkulhlaupa
set lt nii* rarl\ hladdn. Il,1s ielo etu knla"nl
at nlii;B dkensu i efii hlutd aTu ndr, t;tt ofdn til
sitdswtnin
4
sent
end
aukiun hila leinna
tsp.sk ni tkandi lr
i g1sinu.
asn
Mc\ito
Figure 5b. Close trp of the basal zone in Figure 5a.
Norc inchrcd lcDses md accumnlxtior ofpumice and
lithics \liLhin lhis pxrt oldrc defosit, iDdicatins trans
por1 and deposiLion bl lraction iD a LobulcDt iolv
regine. A contacr can be seen al lhc locdtion ol dre
scale. abole whlch carbonized deLtiLus is abuDdaDt.
Below the contacr onLv roiten wood liagnents were
obseNed. This reiects two iypes ol pyroclastic llow
detosilr. a hot flow on top of a cold (laharic) one.
Nam1.\'n.l df bo ii opnu u d nLvtd 5t1 Hollantii
1-.. .'. ...?t..-o..1. "/t, aa- \..-.,..
al \ehirndunit hefv it tlr \tdt i itusrc\nti nJ(likratni ntdtkdt skil
l1?itd oS kaldd ltlutd
selitis. Koltnknot
fn
un hans, i
kaldl
hhrtd
dst oldn
hafidnt
gj6tk14 ta
en
ekki
ed
flin\iits.
JoKULL No.
5ri
-55
AD
n
Hii\LLl\v,l
Pumice from Las Cunbres
Figure6.Ase.ondar,,-crtlosi(mcratcrwithin(hcashllovdetosrts.Thecl'|Lteri\rbout50mindilmclcr. In
the back.lrtr)und r sccLi(lr rhtuugh rhc plrocl.rsric lalldeposiis crn be obseNed. lhe.rrt.r $rs bh\led lhro!gh
the fytr)cldsLic hll doposils. Nhich shows lhal dre they serc \rill hor when the tyr)claslic lill Iaycrs rcc!
nrulrLcd on rof o1 rhcrn. Gt)\iristrr.r"t 501tt i ltcnrkil t.n Mr i qtrnDr qtl)J1ldlin lii tldlasin turt
!ttitkuluqrtttt)trtn .n futa tiutlir til h(tt dl setn|nLIm hdl tetin ,tii)e htin
Thc ash fio$ deposils
posiG lronr the lvlt. PelEe voLcoo in
.iF.r-.
1.,.
Lr.
\ .,. . .. r.J
\'ldrLiriquc
Dcl
fios depsits .ovcr thc rvo\tcm llxnk ol Ccno
rlrxining x n \inrurn thickness ol l6 rn
$i(hi. ropogriphic lo$s cloie lo lhe dispersrl !ris of
Lhc p!oclasric lillour !niI (Figure la)
The rlh fiow d.tosiL is llnc grrincd. $ilh nrorc
thxn 7(l% ol thc mrLcrirl hciDg Dlcdiutn Lo line ash
(lri3ur. ll IL lornrs a singlc corrinuous unit be-
tiecrnse they lerturc.l dcposiLid l slnrclures i diculin-! trrbulcnL ioN. Thc r.nn ".rsh llow is pretered
lor thc Ccro las Cu brcs deposic becr[se r]rev rre
ldll dcrosi(s rb.,ve (Figure 3). The upper nrxin frt
ol lhc rsh llo$ deposrG is nrxssive, with oc.rsionrl
Icnscs ol pujrice lapilli rnd lithics (Fisures 5r xnd
5b). This rnrssive pal] of ilre depsit is rich in car
bonized derfitui ltnd logs. lt\ blsrl hr'cr i\ s(rrliilcd
slrowing onridunes rnd mcgrdurcs similar Lo thosc
tou.d in drc L$r! dcposirs tFigurc ll. Srnirh .rnd
Roobol {1991) dcscribcd snnilrr sntall !.,lurne de-
Nere rlso distrjbut.d b) rhc crtlosions. nnplying lhat
Ash
L!s Cumbrcs.
J p i ro r-l'
56
JOKLr-r- No. 50
oln
ch 9..ucr !ol! rehboutIIknrr.Tablel)rhrn
Lh. 'ash huricr e deposiis menrioned rb.!e A
rcorless cralel. prcduced bv r se.onddy fhrclLic cx
plosion. occLrs in rhe distrL sc.t(n ol thc rsh lldl
lt-
,.re.
')\" 1.i' t, ,:. Ll 'p.
I
the rwo units wcrc d.posilcd wilhil r sho lirne of
each other. l'hc unlcss craLcr rnr) hrle lbrr ed dur
ing d.hydr aLi(nr ol uDderl) mg lih.rric deposits.
A Scrnning Elec$or Nli.nscofc (SENII srucly ()1
rr l,.\r
- 'r ". .t
order ro underslx.d lhc intcnsc lrrgmcnlaLiou ol llre
r
Filurel Iihrplini.rn frrni.c lrll
Borti r
i ,ir !tnltr t)ivltXrt
Iit
phrse !ho\ingcrudc bcddingofrlr. pu.rice. The.r\lr tlow tlcfosir
t:r^l'tlttatt\r
x
mrguu .di.rlccl b\ ils line gi!incL1 chxrrclcrL\lrcs
Sc\errl nud L\pcs {cre ,e..grircd rnd nr o ei of
rbundrncc rr. phle like r.d rngrlxr blocky shrds.
'I
lr.rl,'.
(Lin.. plrgiocLrse. o..r\io.rl biotilc tr.d hon]blc.fc.
Adhcrcncc 01 dusr si/c pr iclcs orlo lhe nrrlirccs ol'
!rr:cr g(ins is...rnron Vcsicle\ l.e xbundor. .\cll
jn rhc {nrllesr grrins rFie!rc.1)
Thc pr'r'oclasti(-f ll dcposits
.rrf i..1i l.s r tred nendin.! rris li)Ilhe
nriir p)mclxstic lrll !ri(5. $llh x lotrL Lhickrrcs! ol
-15 rl l0knr disrrrc. lr'tnn lh. trldcn rirn (Fi!
lhc isoprch
r.
'r''
ll .'l.r IuI
corsist.l t$o.rudell bedded. plnrirrr PU rLce lif.rs.
seprrl.d hI plur.rr lo .roisb.dd.cl !ulcrnir. rsh dc
r'
!I
l r l
rr
r'rll dctosil orcLLrs fs r \j..1rlc unil ie.g. \e.tion Ctl S.r
trll
dcposil co.sL(s ol LtLo dis
Li.c1i\ c lilhol,r.i.s: fliniur r d \'trl.rrir. (lri\hcr rnd
Thc plroclxsric
Sclnni|cke.
l9Slr Thc
nroie \oluminols
lor r!
.urd
$iLlcsprcrd
lilhoti.ie\ i\ c.Dfriscd ol lwo nrr\\'!c
o| cn cl) (.rfilicd plinirn h)eI\ iF:rrc l) thr(
r".r L l..^': 'l Lf r,
xih.rnd llrhi. 1rr.lrn.rls (Figurc ll Al -9knr li,r r
thc \enr rhe mr\inn n cLtal
dec.ersing to rboul 5cr)] lI
dirfret.r is rboul l0cnr.
r dirr.cc ol l5krr. li
(-9k.rl
rhc l$o prDricc lull lr\
pro\l.rrL out.rofs
ers ric scp!tulcd b) los l..'rlc io\s nrllilled blsc
clcposils o. rhe .n \crlc in(.rbcdded Nirh rhlLh
micxll,- l.rr-ered uLl.!nix. r\h llrll nlrs (l'igurc l).
Thc rh) (lnnicrllf hlcr..l !nils ate te\ersc.!rxdcd rr
{r.!.
xr. olien detumc.l h) bxllisrrc
blocls lomring
\.ll
dclnrcd
obsid
Lo b
rn an| lilhn
sxg\ $irhnr llkl
\Irc|'
$crr obrairl!'rl rLsl.S rhc m.rhod oi Fier\Iein rnd NN
thcn\ol 11991). in{licrring r b!lk lollln]e ot' I I kmr
lorrhcdeposirs shich xnroulslo -lk.rI $h.ncrlcr
ldLcd rs dense nr.k .qriurlcrl. l)RE llNblc i).
Ii
thin s.cticrr pu]1rLces sbo$ foThlrilic l'ltLidril
rexrur. \iLh \rnidine 10.5 I nrm). qur r ( |.r nlfr).
bi{xi(c i0.l l nrl ir.d rlic orlhop}ro\ene irnd rnl
TOKULL
\o.
:o 5l
Amldnn Haskuldsson
8. Final phase of the eruptioD: base suBe layers inierbedded with vulcanian-like ash- and scoriae fall
deposiLs. Nole lolv xngle cmssbedding. bomb sags of ballisijc ejecta. and plastic delbnnation ot' rhe underly-
Figure
ingbedsGcaleis25dn). G sthtaupdtet ri\|al ned lolborituti sj'sku dlvulcanian sera nrndaa i bka|asa
el.lgossins TakiA e|iir- hshana sk'ilLisun, honh sekktun og plasti.rkti unnrndu u]tdr'liggjandi laga (seht
hend tilbL(luts unht?tlis). KtatAinn6 nyt nlniet-25.n ldnsut.
lithic
phibole (0.1 0.5 n1m). The phcnocrysts a.c subhedral
in
1o euhedral. The glassy groundnlass contains cuhedr al
zircon, apatite and titanomagneine microlites
intra{alder{
The pyroclastic-surg€ d€posits
The Dome
Pyroclastic-surge deposits are interbedded with the
vulcanian ash-fall deposits in seciions from the west
flank of Cello Las Cumbres (Fisure 3). The surse
deposits consist of coarse to medium grained ash
(Md=1.5 nm) anaDged in sets of low angle cross
bcds (Figure 8). Ballistic bomb impacts hrve cansed
plastic dcfomaLion of the surge beds .ts lvell as dre
ash fall layers (Figure 8). In the caldera, the sLrxti
graphical equivalenl ofthese surge deposiLs consist of
The caldera of Ce(o las Cumbres was partly Jilled
by the el Cumbre Grande lava dome. tiom which the
lapilli-tephra (2-6.1 mlrl). Ieaixring sandwave struc
iures wiih amplitudes up to 1 n. These coarse grained
lurae sequences arc intercalated wirh layers ofcoarse
sGjned (100 1000 mm) aifall breccia deposits rich
58
.roKrn-r. No 50
and obsidian blocks (Figure 3, Q78). The
se.tneDces arc deformed and uplifted by
later dome extrusioD oDto the caldem noor.
mountaiD takes its name. Ernplacement of this dome
complci was the last episode oflhe eruption.
heronero.L hospoQl)ri iclLiddl
rl rr
re.rio|rd.on.
e{r
Ie
r
n roJndcn. g-oun.lrna.. Tl .g o
clxse and pyroxene. Phenocrysts ofresorbed anhedml
quartz (0.5
lmm). subhedral resorbed biotite (0.5I mm). zoDed srbhedml !o euhedraL plagioclase displaying rcaction rims (l 2 mm), snbhedral to anhedral
sanidine wilh rcacLion rims (l 2mm). subhedml id
dingsitized olivine (0. 1 1 nm), subhedml clnDpy.ox
ene r0.l- I nrn\. dn.l - rh-,i. al rirpnorr.gr crir" /FrgJr,
t .l rl
. '
o
n
l. '
V.
,
Figure 9.l'hoLdricrograph of the dome rocks. The se*ioD i\ '1 5 n]m ocrrss The three lhcnocrlns present
are pyro\.Dc absofbed on irs edges. rouDdc.l qLrartz and sanidine feldlpar: Croundnrass is made up oftlt
gioclase. clnropyroxenc aDd lirrno rnagnctire. - Li1sry-n.l d bu tls,lcin lit h.4 hn ng lsins Ljisn) di tt
Gtxn
ns\i et
ir
t)laRn')klos.
Llini|ibt.n rs til.tnl
taRnetili
9). This is thc sune phenocry\t assembloSe obscrred
in the ptrmiccs. bur ibe domc pherocrysts clilir in
lhat rhey rc subhedrll to uhedral. In lddilion. the
dome hva contajns lrltrcctral oLi!ine lnd clnropyro\
ene. 'lhc rolume of thc la\a dome is calcuLated as
1.5 km3 DRE (Table I).
in3 volcano Pico de Orizaba and surouDdiDg saielitic
coDcs (Hajskuldlson. 1992). a.d dcPicrs lhe Se.e.xl
gcochenicil len.1 ol nagNas frun rhe region 'lh.
ploLs show! drc cloh,ed nature ol lhe rhyolite\ Il
rhe nineral asscmblage ollhe domc lava, is relatcd lo
the nlLxing of L\vo magnras. thcn the basaltic magn
$,oLrld probrbly be within ihis corrpositionrl rrnge.
GEOCI.IEMISTRY
$Jlrole rock composilio. of sorples liom the donle
aDd ash
flow dcposils.
dd
Lhree pumi.es
fun
lhe
rumice fal! dcposils wer. malyzed by ICP MS rr
Clennonr Fcrraid (Table II).
Accolding to Lhe anhydrous tolal alkxlis silica
chcrnical classincaLion \ystcm, (Figure l0) (Le
lvlailre, 1989). Llre ash iow dcposils and thc done
ar€ dacitic. whereas the tumice lall deposits ue rh)'
olLric (lablc II) The bulk conposition ofthc rhe ash
now deposits na), have bccn nodified by Lhe loss ol
line lighr components such as glass or lcldspar etc ,
ihe conce iraiio. ofdcnse mi.enls, or Lhe incorpora
tion ot hhic clasts (Luhr. pts.nal.o,t" nicntt t)
Fisurc 10 slrows mdllses of lavas Irom the neiShbor
RECONSTRUCTION OF EVENTS
In reconstmcting e t6ka Ccros las Clunrbrcs crup'
tior rt is ncccssar) to considcr Lhe et!iltnrnrcnlal
'or
h rre r'e|n l ' , of:1,950Ir1 at the highc( peak
l ro,' Lrl rc
bres has dD ahitude
on th. caldera rinr. JusL
.1. . ol rn<
trior to
the cruplion and
nr. I
o.d'o
dnmghr 10 bave bccn conside'ably hisher, perhrps
-.:.n<.1,'1,,.li,, rI -l. A t.
r. r.o,,r'r'.
m Nlexicoreachnrg lhis altitude. such as Popocat6|cll,
Izraccihuatl rnd Pico de OriTxba, are all capped b)
smaLl glacicrs. Paleoclimatic (udies lrom thc Gulf
ofllexico show thal during thc late Wisconsinan. fie
cLinrate w$ nuch colder Lha il is todar (Kennett
JOKULL
No.50
59
Atn
i
t
n
"
H t^ I
t.r
I tl
| )n
\
lubLe 2 Vqor elemenL anahsis ol rhc frmice from ihe pyroclastic ful1 dcposit. dome mcks rnd \holc rock
samfLe frorr rhe pvroclanic llo$ dcposit. All rn!l\'ses s,ere canicd ouL oD an lCl, al3o. plasma specLtumclcr
in Clc.no.t Irena.d. The
ikin
,1 ht"nFl|lnr"t
nttttt ialt,"t)nt
t
og
t a,.l
etror is abou( 2% for Sioj and 5t. ibr olher elcmcnLs. Al).//d7rrr,?,rnrrdr dJ
ri,isl'tlbndsatin /\lLo tlndqrcinirgdt uuronat,tnICP dtlortlnsttkr!rllli
2 s
rrAt8 PA96(I)
qill pumice/rjl,r
BCl
(I)
PA96
lonclhtuu
sio!
Tiol
61.8
0.2
61.5
0.58
70.:1
Alro,l
r5.88
15.81
t:.8
FerOr
0.19
0.07
1.12
X{nO
MgL)
Tordl/\n,,ur,
1.28
3.18
0.1:l
.15
:1.i9
t)2
t.-15
35
1.03
.t.3
L82
H"OPF
t.27
l) 07
2.11
1.65
0.08
o.22
1.).
.1.:ll
L)9.1',]
99l l
{).t8
:1.2
!9.9.1
Figurc
l0 lbtrl
r6
t. t]
0.07
0.29
l,42
3.94
3.71
0.19
0.
l].87
0.07
0.38
Nar(l
Kro
69.8,1
02
0.21
0.06
3.61
99. r5
xlk!11 silica classiiicrLjon
of
the
nagmr cxtrtrclcd during the las C\ brcs crupL(D (open
sqlarcsl. Thc.lots lre rcck rn.rllsis lionr (hc nejgh
bouring volcano Fico de Orizrba and nrargm{l cmlcr
cones (HiiskulclssoD, 19921.
ro u
..,r.lu' -l
il
All !nalyses normrlizccl
rc
I
brslliic tield ol rhe clidglrm indi.rres those Locks
co.Lrming (ol) and (cpi) phcnocrysts (Robin. l98l:
Gourgrud 1985) AlLuli kisil ltakkn h?rytc.qrndtl
Lhc
T
55
60
65
TA
75
so"
.tnd Huddlcsrun. 1972). Glx.ially derived sedineDLs
on.rnd arouncl Nlcxico volcx.oes suggesl tucrcascl
glicial aclivily duing thc Wisco.!in (Whlte, 19871
ulre ,.1 \.'J.||o.,uql. rl . o..r lr..
der.e n'ggesr thal al aboul 16ka. Lh. Ceno lxs Cum-
60
JOKI-ILL No 50
.....
4nasu,tsthti"!" irftn,ltLUi0ll\irs Pi( o Llt Oti.h.t,
os snlLi!isa Ll slltt n i u,tl\.t.llt (llljalli . Alldt tlttl
!ftining[ tN leilit r'rk'd rilliti t)l rtt s
bres cone Nas colered by an jce .rp. This high
altitrde srte/ice reseryoir ha.l a strone innuence on
rhc pmSress of the 16 ka enrtlion as indicated by the
occun ncc of phrextomagnralic dcposiis in the Ce o
Lrs Cumbrcs cNFion succession.
Ca,d, ra
E\oldio ol*E
lrCmha
top
Jt.ut, dt
.e' ro ta\
Cu,. h ?,. \'14:. o
c[@a
:ltf-T*r,:i"'"*
5L-_
I,e
I
ltf!r,iT#'ni:$;".
''
h i, d,!{m..dr6
's8q,m.!r- t5l!
Figure I L schematic illustration ofihe evolutioD of the Las Cumbres caldera MaiD stages are explained in fie
frglne. TnLkun hdlund d gangi eklg.,ssins i Las Cunbres. l) Liklegt i I edfiakins AA t e sosiA h6!\t 2)
peg krikdn steig til )ththL,t's komst hin i snetinguri6 gtunnwtn og is sen lei.dni til nJn.lunar pl1rcatisktut
sjnsku. Oskul6A urduIgff bfteAsbatuha itjkuthexuvli bldnrtdai Easefnttn ti' haa aa sosndkkutinn Jatl
sanan. 3) peg Bosktdftur i1111 j6kst, ninnkuAu Ahtif wtns d krikukd ag gosid vtd fLiniskt. TopPUfjallsins
fe siaan sanan os brcnsdi baA aa sostdsinni. Gosidwtn brf alur phrct6nasnatkkt Eftn ad soe.^in InJAi
hteinsdstNard gosia enn dftut pliniskt. Pttliskufasatnn etun dkenndit nen PI oEP2d3.nind 4) Aa lokunl
ia Phreat6ma7mdt{skllr sprengingar pesril lasar etu autken nd t ncil Shl
.hb nt gosinu os tdrA bd aftut
og Tsb2 n 3.
nfnd.
'dft
JOKULLNo.
s0
61
Atnan !tnsk
ldsson
The openingfhase olLheeruption is markcd by la
,epo i \-., r... rp J,..'r i.
capped voLcanoes hale been known 1l] generare srnall
nrud Aows or lah.r's (Major and Neivhall, 1989). La'
hals of this iype occu ed during the beginmng ofthe
1947 eruption ofHeklq sherew.rler-rich low iempe.
atue curents conlined to cor8es and valle)s (Kjar-
LicrlJl-llo
rmssoD, l95l) Ash flo$, dnd lahar deposi$ nonr
Cero las Cunbrcs arc b! lrr Lhc ilDc\L crrincd de
posils in the sLrccession. indicaling lhrL lhcy wcrc
lornred by jntense lrlagna liagmenlalion. As demon
srmted by ihe :jEX{ srudy or partlcles fion the ash
r rJr 'o.c.e.rrJg,er . o,
by magnra w.rter interacrio. (oval shaped vesicles
lo
,eqr- c',:
rnd dust wclding) rs ivell as volatile laruration (tabular grrin! rD.l vcsiclcs). Thc co+xistence of tabtr
lar and ovdl lcsiclcs m Lhc chst populrtion suggests
fiaI liagmenlalion ol
lhe rnagna bcgan rL dcpdr nr thc
condLu (magmatic). generaling rod and chip likc td
ticles with labular lesicles. This ge eraled an opcD
venr srtuatior where the lieeLy expanding nagna wrs
fr,rgrnented as ir cane lnto coNact wlth abundanl sur
face water (liiguE ll) to lbm Y shaped plaiey and
bl{rcky frricles $,ith olrl ve!i.les (Heike. a.d Who-
lcrz, I985). Ilowcvcr, occurrence of tumice lapilli
in lhe deposils shows thal Lhc mrgmr was not totally
Lr.r Lr'
rhan one (Sell aicl Spdks, l9l8! Fishcr
rigr c,r
was less
J. , ,.*ri,'-
and
Schnrincke. i9E4l.
bI
Thc iDiLirl phrcatomrgn tic phase wr! Senemled
an extlosivc inlcmclion bctwccn Lhc ghcial melt
valerand lhe nagma. The early labrB Ll Ldcsccndcd
down the 1lanks of the volcano $,ere lbmrecl by an
eruptive mixrure ot neltwater. ash and coarse liLhic
tiagments. The accompanyrng erLrprion column con
sisted ofrsh
lnd
superheated steanr. The steancooled
md condensed duri.3 as.ent rcduci.g ihe bLroyarcy
ol thc column and prcmoting its .ollapse to geneF
aLc thc ash llo\ lhaL follorcd the floods and laha$.
Thc rsh flow blankclcd Lhc wholc castenr side of the
. lc ,o lJ l
| .lr A rlee
rp
.J ."... i - ir .l: 'r l:i",o, r F ir. r,. Lr, .tr '{
raie (hence the magmatic pressure) increased cnough
to prele.t eriernal water iionl comlng inro
conLacl
wirh the maSrna. a.d ihe eruptjon siyle changed fiom
62
.r()KUr.r. No 50
phrcat(rnr8matic to pli.irn. This is indLcaied by the
lowcr plinirD lrnmicc fril (Pl o. FiSures i, and ll
l). AD csLimaLc for the lolume of nra8Dra erupred
by lhe llrsr pliiirn thasc is rbour 4km3 (2.!kmir
DRE, Table I). E\acuarion oi Lhis .ragma volume
ron.h. lo.l r .lJlbrii,r
rp,' lr' 'r.'
rr
tiaied caklera collapse ol lhe cenLftl conLral block.
The slrarp tlansirion fiom plinian lrll (Pl) Lo vul
crnir. fall md surye (SB l) deposits in oulcrcps clos
csL to thc calderr (e.9. F_i8ure 3) suggesis that exre.
nal waLcr rcgriDcd acces! to the ven!\ ro initirte the
seconcl phrcrtdn.tgm.ttic thasc
i lLel ldr L rb,J.
of the
erption
Ii
r
ol mrgmr $,ithi. the
.ondrir lier.r p he 'r rT o,. .o ..i, \r'J'. r.
the magma ellusion rates liom the nagnasralic prcs
nne in lhe co.duits ard thus allowing exlenal \alcr
'i. $: - Jrd.r g.Jrdu,,e . o rlov I e-l) r,
the vent svstem x.d re initiote phreatomagmatic activity (Figurc I Sbl and lrigurc I l -1).
Thc sccond pliniaD layer is interpreted to have
posed rcsrictions oD lhc now
I , J..r''r
. r .' ".cJ: i.rd
i-.'e,
etlusion rale ard extcn l warcr \as rgain isolated
irom the vent (Figure 3. P2 aDd Figurc 1l l). As
ihe eruption declined. ihe eliLrsion.alc dccrtasccl, wa
ter rcgained access ro the lrlaglrla and !ulcanian dc
posirs we€ produced (Figure 3. Tsbz and Figun i 1
4). Strch x tmnsirion, lion plLrian io vulcania . hrs
bccn rcported for other euptions Bond and Sparks
(1976) showcd thrt strch { trrnsi!io. took place du.
i
g the Nlinoan crupLidr of Santdini, xs a result of
At alero las
Clulr1bres. glacirl nell\aler rnd guurdwatcr phyed
rhe same role. Al presenl therc is a rcgion in Lhc ufpcr
reaches ofthe volcano and circunscrib;ng Lhe cal.lcrr
seawaler g.rining acccss to lhc vcnLs.
LrJr
r'ro l
e'.dol .epor ro, hr'-rpu,.
This area rctresents the exieni of rhe glacie. on rhe
volcaDo at the time of the eruption (Figure 2a). All
mrLcirlLhat fcllupon the glacier wa! lvashed away as
Lhe glacicr nrcltcd. lcavirg r defosit free Tone arou.d
Lhe caklcra. This matcrial is lound rs resedirne.ted
epiclanic lephft unirs on rlltrvial flains to the exsi of
the volcano. The actniry ot Cero lrs Cunrbrcs cDdcd
with exlrusion of a dacnic dome conrplex (Tablc I and
lisurc I0) on the caldera lioor (Fieure 11 5).
(:altlcrd
fl,t
atd1ut Ctt to
Lds L
u,1ht.s, MavLo
d&it. 6jrln\rgi i kristallrsrmsctDiDgu kom iiatr !i6
CONCLUSIONS
cm Mexico- at 16.980+810 yr B.P, led to thc lornd
sm,Lsjir sko6un ii dasiti.u sem myDdar hraungnl inni
i itskiunni. Hraur:irllinD cr si6asla kvika se'n upp
Uton co.t.rct with lhe nagma. gla.ier icc nrcllecl, im-
lrrerja kvikublondun hrfi !cri6 aa rieda skommu lyrir
gos i boini kvikuh6llsins Ri6lir likurinn fii cld
'lhc crutlion in ihe (--cro
las Cumbres vol.ano. casL
LurorJ.JdP :< ,.'knr" 'rJr rPP \r I rrc
o rle<1 ,r nr rl. .o..nou, , 1.Jl .'o 1i'liating expl$i\c interaclions bet$ecn thc mrgnla and
\r,e1. .p'r.. onJ!r,r
.
deposits. Subsequently. thc cruplion st,!le became
fliniu \hen
$,nier was frcvcnted lionr acces!ing thc
cruprive vent. resulting in c.lldera collaPse. Collatsc
ol lhe ceotllLl block obstrucled the conduit tDd lhe
crullion st,!le wrs LrrDslbrmed to vnlcrnirn xs $'aLer
rcganred occess Lo lhe renl. lncreased cllusion lale
and/or clerring ol Lhe \enl revetted drc cruplion sl,!le
.o ti ,.,r .'PoL lo Jr. F erJ. r '
' or.or .rer
sitl declmcd and plinian rcti!iLy moderaled to !ulca
nio
oDcc more. The
eN|tion cnded whh the extr
sion 01 a d.icitic donre complcr onlo lhe calderr floor.
Tephra thaL fcll upon the ice cat wrs hLer lrashed
away a! ihc ghcier nlelted, lerving r zoDc around lhe
r.:
r'!ul ep^| nl.JU'r rurlee-rf
or
The total rolume of mrgru cltimled to be extNded
by Lhc cruplion is on the ordcr ol7-9 km:r (DRE.-lrblc
I). Olrhis lolume,,1km3 (2.2 kmr DREI wxs.xtr udccl
during the 1i$t ph$c ol lhe eruption.
ACKNOWLEDCMENTS
lwoulcl like ro thdnk drc lollowing persons
that
nrg ns prcp.r'atidr:Dr. G. Camus. Dr. E. Aydar aDd
Dr. O. Sigmarsson. D. R. B. waitt. Dr..1. Luhr and Dr
G. Ablo) rrc grcrrly rcknowiedged for rcvicwing this
naruscrbt. for logisric and lranspor mpPorL cluring
tield work I (hank Dr J. Nlayer at thc CcnL!: d Eludes
Mexicai. ct Cenro Anrericain in Mcrico Ciry. por
rJ
1..,or
:0 "e. JJJl'r
Lr\iJ.rl-.^..r .1 .ll rr ,. , rr
gjdskunr mjtjg ruakennilega. I Dessxri grcin cru leidd
ad bvi rijk aa cLdljallid hafi verid huli6 jdkulhettu i
rin n cklgossins. Jcjkulhettan brndDadi i gosinu og
olli lcysingarvatnia Dvi aa.ldgosi6 lari phreaiomxS
mdLiskr i byrjun goss nEddu nidur veslur ljallshliainr
i\rr.po.to.,FI'
undir lotibornu rj6skunDi. I'eg.lr gosia haf6i einogr
ad sie tri brensluvaLDhu lal. Dad pliniskt. 6skiu
myidunin h6fst bcgar i niaju gosi oS lci.ldi til bess
ad ioppur fjallsins ltll srnran. vi6 sig fitllsnrs lepplist gosraLsnr timrbundia og gosi6 !rd aliur phrearo
magmrLiskr. Fegar gosrdsi. hrfai hrcnrsast ni6i gos
id rfL'rr pliniskurn eiginleikum. I iok eldgossjns d'69
r11 vcrulega nr k!ikusireymi scnr Iciddi enn ifiur til
thrcrtomagmatiskro sf €nginga. Gosiru Lauk salxn
ned f\i ad hr.rungnllmn EI Cunbre Gmnde mln
claiiist inni toskjunni. Ilrmglrgr kans ikringum dskj
una getin til kynnd hain1.lrksntbrc i6s lu .i.iktrlhcLtonnar
a tnnum cldgossins. HeiLdar tummatl gosclna er Lrpp
kon,u er i krmsum 7 9km:r(DRB), rffcsu konu Lrpp
,-\ ' ':..|r
grcarl! contrlbuted to this paper by discussions dur
\ ! Iur) r'or...r'1lPll1.'
l.-,, r..ro r.o.rI
DRL,,l). r' Lrr ,, go..r.
REFERENCES
1 .3 re". ,nl' . ! ,
'. ,n.r5.A
srer ind hvr A'ar,,? 2.1.:1. ji2 55.1.
.,. '.
Co\ K. G.- J D Bell .nd R.J I'a*huNl 1979. 711 r,/fr
Fditnrr .ftl| irnar^ k\'kr.
*D, Londoi. pp.450.
Gc.rge Allen dnJ Ur
Bond A..nd R. S. J. Sprk\ l976 lhe Minoin cruption.l
S.florlni. Crccce. / a;2,/. S,. L. .laa | 3), 1 - t 6
F.r{.in I rn,l Nr Nilhens.n
1991. Arothcr look rr lhe
calculirion of falloul lcDhra !olunres. A!11 Ii)/.arrl.
AGRIP
Eldtj,llid Ccrc Las Cumbres iM€xik6 grus ntjijg ofl'
ugtr gosi lylr un 16980 nrum. I cldgosnN mynda6
isr a,kia sell) er unr 3,5 til 4.5km i b\enndl. Kvik
an scm upp ko'r i eldgosmu \ar hi-K rhi6lit og
5.1. 156
l6l.
Fisher R. v. and H. U. Schnircke 19E4 Pl,'.1dlrn
Nc$ Y{trk, Sp.iiger lerlae. p| 471
,i. l.-,l .\. aSr r/,,.
.....
r,.lJ
1-....,
JOKLLLNo.50 6]
At
rxnl Haslrklsrt
r
lt\ ltr.: nrttr tllidjtr\ tt ltut itrflr.r.. D l.\ nn,
tx ti t:; Auttil:. L,vnll^ tti\ ldn\ lr Mt!;ilCt tat! Fnt\ti:lUrt! datr.a t1(ik l(: Pu\s).n l Mdt
1i1i4r. lMrna!r. Ptltt t'isiln Brt!.s DiLndt!)
tt tr ttt.ti.tr( (Pit. lt Orillrrl. Thisc dc do.ror.ir
Ncecndrnk J.F
d atxL. LJni!c.nL] ol Clcirnorl Fcnxf(l II. pp.5l2.
Rt
odK
\\irhlctz l9$5 hl,?Jir drl I-o\Arec
les. Urne.\Lt) ol Cnhioirir P.ess tp.l.1al
llcikcn.C
.h..r.logl oi
Lhe \1eric.n \ol..noes Di. Gtu\'i\t rh4nr 6th
Hene. K. 19811 Lrtc Qrxleirnil glacnl
Jrln.sang 1. 197 105.
Hil.lrerh W 1981. Gradiedrs nr
(,:
i.r' .
o
siLici. rgDi chdr
L 'i
t-.
l0l5.l lll92.
dr\on. ,\.1991. /,. Canit)lc\1 \bl.drnttt Pnr Dt
J C..rtt-\s Rts
Hnsku
.
S6,
(r'i:tl Sn nt li.ltlt ( t|t) l.t\ (, tht.s lS r.st
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