$*!r,g"[x+nrp$wr
Z. Geomorph.N.P.
Suppl.-Vol.140
93- 102
Berlin .Stuttgart
Iulv 2005
Glacier melting and lahar formation during January 22,2}}Leruption,
Popocatépetlvolcano (Mexico)
PatriciaJulio Mi randa,Alberto E. G onzález-Huesca, Flugo Del gadoG ranados,
and AndreasKááb, Zirich
'rith 6 figures and2 tables
Summary. During an explosiveevent that occurred on January 22, 2001,at Popocatépetlvolcano,
small pyroclasticflows melted part of the glacierand generateda lahar.To evaluatethe volume removed
from the glacier,before and after the event,digital terrain models were compared.Total removed mass
was ñ 1.0x 106-', brrt a p^rt of it was incorporatedin the - 4 x 105*' 1.h.. asmeltwater( - 1.6x 105m3).
The - 2.4 x lOs m3 deposit included more than 500/oof pumiceous material. An important issue for
hazard assessment
at ice-cladvolcanoesis that not all meltwaterplaysa role in laharicevenrs.
Résumé. Pendantun événementexplosif au volcan Popocatép
eú le 22 janvier 2001,des écoulements
pyroclastiquesde volume modesteont fondu une partie du glacieret ont engendréun lahar.Pour évaluer
le volume du glacierperdu, des modélesnumériquesde terrain avantet aprésl?vénementont été comparés.Le volume de glacedisparueétait de - 1.0x 106m3, alorsque une partie de ce volume ( - 1.6x 1Osm3)
a été retenucomme eau de fonte dansle lahar de - 4 x 1Osm3.Le dépót de - 2.4x 1Osm3 contenaitpleus
de 500/ode ponces.Un élément important pour qui doit évaluerles risquessur les volcanscouverts de
glaceest le fait que toute l'eau de fusion desglaciersne participepasi la gendsedeslahars.
1, Introduction
Popocatépetl is a large stratovolcano (S+SZa.s.l) comprising an accumulation of lavas, alternating
with pyroclastic deposits of andesitic to dacitic composition. Laharic processeshave also been
present on the volcano even during episodes of quiescence (Fig. 1).The volcano started ro erupr
on December 21,1994,and has not yet ended.The eruption has consisted of an alternation of vulcanian explosions with dacitic lava extrusions (DErcaoo
et al. 2OO1).
During the last decade, the presence of a body of ice at the summit of the volcano has represented a hazard due to possible laharic events caused by ice-melting during eruptive events
(Drrcaoo
6¿ BnucrvrnN 1996).The endangered population of - 8,OOOinhabitants lives in towns
and villages on the northeastern flank of the volcano and, in particular, in those places located in
the vicinity of the glacier-related drainage sysrem. Santiago Xalitzintl a (2327 inhabitants) is a
village situated 14 km from the crater, at the outlet of the main drainage from the glacier area.
Since the beginning of the eruption several laharic events have occurred (Pnrncros er al. 1998).
Most of them have reached less than 4 km from the source (DErcalo
et al. 20OO),and some of
which are suspected to have been generated by eruptive activity-glacier interaction. Major lahar
events were registered inJune 1997 andJanuary 2001. Both traveled as far as 14 km from the summit, reached the outskirts of Santiago XalitzintlaVillage.
0044-279810410140-0093
s X.XX
O 2005 Gebrüder Borntraeger,D-14129Berlin . l)-70176Stutrgart
94
PatriciaJulioMiranda et al.
This study describesthe role of ice melt in the January 2001eruptive event by studying the
ice-bodysizeand the magnitudeof the laharicevent.This type of study seeksto evaluatehazards
that might occur on other ice-cladvolcanoesin Mexico and elsewhere.
9q"00'
98'30'
Fig. 1.Location rnap.Popocatépetl(5,+SZa.s.l)is an ice-cladvolcano located70 km southeasrof downtown Mexico City and 40 km west of the city of Puebla.It representsthe southern end of a north-south
volcanicchainknownasSierraNevada.
TV:Telapón
volcano;IZY:Iztaccíhuatl
volcano;PV:Popocatépetl
volcano;
MC: Mexico City; PC: PueblaCity.
Methodology
2.1 Glacier eaalwation
One way to determinethe amount of water presenton the volcanobeforeand afrcr an eruption is
by calculationof the volumeof ice.Juuo-MTnANDAE¿Dpr-cnoo-GnnN¡,Dos(2003)havetackled
this issueby applyingdigitalphotogrammetryto producedigitalterrainmodels(DTM) and orthophotos,astools to determinepreciselythe amountof massgainedandforlost over a time interval.
Ve haveusedthe @OrthoEnginesoftwareto processaerialphotographstaken two daysbeforethe
explosiveeventof January22,2001 (scale1:11000),
and a month after on February22,2OOl(scale
1:13000).
After digitalphotogrammetricrestitution,DTMs were obtainedand the contoursof the icebodieswere digitized.Volumes
of icewereextractedby subtractingDTMs using@S.rrf.,software.
Glaciermelting and lahar formation
2
Labar estilnate
The January22,2001, explosiongeneratedseveralsmall-sizelaharsthat reacheddifferent distancesfrom the source,on the northern and northwesternflanks.The laharstravelledalong the
gorges:Tlamacas;Tenenepanco;
La EspineraandTetepeloncocone.
These are locatedon the northeasternflank of Popocatépetl(pig. z). Outcrops locatedin
(Ot) and Huiloac (Oz and 03) gorgeswere studied,and selectedsamplesfrom
theTenenepanco
thosedepositswere analyzed.At the outcrops,three sections(I, II and III) were constructedat
proximal, middle and distallocationsfrom the source.Thesesectionswere usedto estimatethe
areaand volume of the laharicdeposits.
The laharic volume was calculatedby measuringthe lahar travel distancealong eachgorge
and consideringthe crosssectionalareaat eachoutcrop(IvrnsoN et al. 1998).Grainsizeanalyses
Resultsfor the smallerlaharicdepositsarenot shown.
were carriedout by d.y sieveanalysis.
19" 06'
t9"04'
,,y_f/iri,l9
,'#
To*.rrs
@
ciorgcs
>
if
Proxirnalsector
)
i II j
\,lcdialscctor
'11111
Distalsector
t
t-
^
()utcrop
Sttttl¡ccl
I
Clacicrarea
ffi
ffi
0
98"38',
l
2
3
4
k
m
t9"32'.
Fig. 2. Map of Popocatépetl'snortheasternflank. Location of the lahar deposit outcrops (O1, 02, 03)
studied and secrors(I,It, tIt) inTenenepancoand Huiloac Gorges.
96
3
PatriciaJulioMiranda et al.
lce bodiesand eruptiveactivity
Two glaciersexistedon the northern flank of Popocatépetl(Ventorrillo and Noroccidental),
rogerherwith small permafrostfields.BeforeDecember1994,glacierswere inactive and showed
of the
a rerreattrend causedby regionaland globalclimatechange(DEI-cnoo 1997).By19964Oolo
of the glacierareawas lost (Huccrrwhile 1996-1999
period 22a/o
1958glacierare^disappeared,
8¿ DElcnoo 2000).After the eruption started,glacierretreatwas acceleratedby severalprocesses:
temporaland local heatflow increaseat glacierbed; pyroclasticmaterialaccumulationon
materialand pyroclasticflow generation,were among
glacier'ssurface;ejectionof incandescent
(DElcnoo et al., submitted).
The glaciersthinned and shrank.Differentialablathe main causes.
distribution of the tephra induced reduction of the glacier,leaving
tion due to heterogeneous
elongatedblocksof ice coveredby tephra and with frontal ice cliffs (f ig. ¡).
Fig. 3. Photographof the northern flank of Popocatépetlon February 22,2003.The white line indicates
the areacoveredby the ice blocks; the dark color is due to a pyroclasticlayer on top of the blocks.
A dome-destruction phase starting on December 11,2000 is of particular interest. l)uring this
explosive phase several high eruptive columns were generated and incandescent material was
ejected as far as 1 km from the summit. Ashes and blocks were deposited on the glacier's surface.
By December 16 the glacier was completely covered by tephra. The explosive activity continued
until early January 2001,.
On January 22, 2001.,at 15:15 (local time), a degassing event began and emission of ash
was observed an hour later. At16:23,the emission of gasesand ash continued and incandescent
fragments were ejected out the crater. Pyroclastic flows were emplaced on the northern flank,
reached 6.5 km from the crater (RouÁN-CASTTLLo et al. 2003). A flow moved down over the
glacierized area triggering a lahar. At 20:45, an army brigade, located 5 km from the volcano,
reported'h mud flood in the Huiloac Gorge" (CEXnpnED
reports).
97
Glaciermelting and lahar formation
4
Resuhs
4.1 Glacier cbanges
Thble 1 shows differencesin surfaceareal determinationsusing DTMs consrnrcredfor dates
beforeand after theJanuary222001,event.Theareallossreflectsthe retreatparrernobservedin
previousstudies(Dalcaoo 1997,Huccnr & Drrcloo 2OOO,
Julro-MTRANDA& DrlcnooGn¡Nnoos 2003).DTM subtractionallowedus to estimatea lost volumeof 1 109804m3 (t tto¡o),
equivalentto nearly 1.0x 106m3 of water.
Table1.Arealostatglaciers
on Popocatépetl
volcano.
Date
Surface area (mt)
o1/20/2001
280357
02/21/2001
252262
Lost surface area (m')
28095
4.2 Lahar cbaracteristics
The January22,2001,lahariceventwas associated
with the explosiveactivity and generatedpresumablyby a pyroclasticflow that flowed over glacier'sarea.The lahar had the characteristicsof
a debrisflow asshown by the depositsstudiedat three different locations(pig. Z).
At the proximal zone (SectionI), gravelsize clastsare the main componenrar the river bed
and border,but sandincreasesasthe main componentin the centralpart of the river bed (Fig.+,
sectionI). The histograms(Eig. 5) mostly show bimodal distributions,rhe principal modes are
-5Qto 3Qanda meangrainsizebetween-1.770
and1.19Q.
Thelargest
clastsizeis 1.10
m.Thedepositexhibits very poor sorting,which are a characteristic
of laharicdeposits.The skewnessof the deposit
reflectsfine asymmetryat the border of the river bed and high coarseasymmerryin the centerof
the river bed.Platikurtic valuesindicatethe broad size distribution of the sediments(Fig. 6).
In the middle zone (SectionII) gravelsize clastsare the main componentat the centreand
marginsof the river bed (Fig. +),the sand is the main componentin the centralchannelof the
river bed and in the lobate zone.A bimodal distribution (Fig. 5); showsmain modesvarying from
-5Qto 3Q,and a mean sizebetween-2.775and lQ. Field observationsshow that the largestclast
size was 40 cm. Valuesshow poor sorting (fig. e).The skewnessof the middle zone does not
establisha cleartrend.Platikurticvaluesreflectthe broadsizedistributionof sediment(nig.O).
In the distalzone (SectionIII) gravelsizeclastsform the principalcomponent,but in the centre of the channelsandis the main component(Fig.a).The histogramsindicatea bimodal distribution (Fig. S),at the proximal and middle zones,but in the small central channelof the river the
distribution is unimodal. The principal modesvary from -2Q to aQ.The mean grain size values
are in a rangeof 0.2Q- 3.430. A maximum size of.2 cmwas observedin the field.The sorting varies from very poor to poor. The skewnessreflects fine asymmetry in the deposit and a high
coarseasymmetry in the small centralchannel.The platikurtic valuesshow a broad size distribu-
98
PatriciaJulioMiranda et al.
Proximal section I
,.5(nr)
i
l
- Samples
Stratigrlph¡"
S;ti¡ ti;¡¡i;;i"i. iuuingut."r,,trountlctj chsts of purniccrnti rndcsitc.nrcansizc 1.5 c'nr.
Saritlirrpporiü'suhingirLir-súlrr.runtlid.:iastJ,;ipunric;'.üil;linü iirit an¡ciit.:
gl$!,','.lu'..*
'.. Santlsupportr'd.subangul:rr-suhrounrlctl
clasfsof punrice.gmy ¡nt-lrctl antlcsitc.
.:
¡ncansizr-I c'n¡.-c-lírsts
_I :-¡|.
__
'. (llast supported.subangular-subroundccl
clastsof pumicc lvith olivine xenoliths.
',,.qlI'19i::!lld::I::l::lll1,:li5il::,t$Ii_l_j9l_
Substlate.
't\r
S
i\
lledial section lI
5 (m)
0
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S
Distal scction lll
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''" -l'1-ji!¡-u-¡tL,yi*lt.g
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n i c a ns i z c0 . 5 c n l . c l a s l s . ,I c r n .
(s,,lrrt.ot..
Fig 4. Sectionsstudiedon the northeasternflank of Popocatépetlvolcano,
ar 5.5km,10 km and 17km from
the vent area.The stratigraphyof the outcropsis describedin detailper unit. Seelocationmap in Fig. 2.
99
Glaciermelting and lahar formation
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100
PatriciaJulioMiranda et al.
tion of the deposit and a leptokurtic vaiue in the small central channel of the river bed, reflect
a restricteddistribution (fig. e).
The sectionsindicatedin Fig. 4 were usedto obtain the volume of the laharicdepositof January 22,2007,accordingto the parametersshown in Fig. 5. Consideringan averagesediment
contentof nearly60%in debrisflow volume,we obtaineda volumeof sedimentof - 2.4 xTOsm3
(Table2).The main componentsof the flow depositare pumice, gray and red andesite.Among
all thesecomponents,pumice representsmore than 500/o
of the total volume as both clastsand
matrix. This fact supportsthe idea that most of the materialparticipatingin the laharic event
correspondedto a pumice-richpyroclasticflow that triggeredmeiting of the ice and transported
them togetheras a debrisflow. Andesiteand daciticclastswere alsoincorporatedin the debris
flow.
Thble2.Laharvolumeestimate.
The lengths(Eig.2) weremultipliedby the corresponding
section
al area
(Fig.+)to obtainthelaharicvolumeof everysector.
Sector
Distance (m)
Section area (-')
Laharvolume (mr)
I
3571
59.21
211439
II
5710
34.54
197223
III
2860
0.34
972
Total
12141
94.09
409634
(r¡)
SORTINCi
i
(Sk) i
SKEWNESS
¡' KURTOSIS
(Kg) l
t
I
L
^
a
t
3
t
h
a
r
a
a
I
a
e
t
.
.
o
t
tDr lD2 2A 2ts 2Cl 2Cl
;
)
a
3Bl 382383
SAMPLE
Fig.6. Sorting, skewness,and kurtosisvaluesfor everysample.Explanationin the text.
Glacier melting and lahar formation
5
101
Discussion
Description and characterizationof the lahariceventof January22,2001.,
and resultingdeposit
were important for identification of the role of the glacier's meltwater and the interactions
between the glacier and volcanic activity.Clast size, sorting, skewnessand kurtosis indicate
that the studied laharic depositsare debris flow related.The contentsof the deposit indicate
that more than 500/o
of the clastsare madeof pumice as a consequence
of the pumiceouspyroclasticflows.
The estimatedlaharicvolume in this study differs from those of other authors.CapnR et
al. (zoo¡) estimateda flow volume of 2.3x 1Osm3.In this study a laharicvolume ofl4 x105m3 is
reported.The differencesin volume are explainedin terms of the delineationof proximai zone
of the deposit.A day afterJanuary22nd eruptive event an important depositwas recognized
upstreamof the Huiloac Gorge in the feedingTenenepancoGorge.This was consideredthe
proximal area in this stud¡ whereasCnpnn et al. (ZOO3)
consideredthe proximal areato be in
the Huiloac Gorge.
The total volume of meltwater releasedduring eruptions does not fully participate in the
generationof lahars.During the November 13,1985,eruption of Nevado del Ruiz (Colombia)
the meltwater releasedwas estimatedin 43 x 106m3 (THounEr 1990),but nearly 5Oo/o
of that
water did not contribute to lahar generation.The water was incorporated to snow avalanches,
sediment-ladenavalanches,
phreaticexplosions,sublimationgeneratedby pyroclasticflows or
it was stored in the glacier.Similar processes,including percolation,might have occurred at
Popocatépetlvolcanowhere total massremoved( - 1.0x 106*') *", larger than the water in
t he lahar(-1 .6 x 1 0 5m 3 ).
Calculatedremovedmassinclude melted ice and tephra.During the volcanicactivity that
took placesinceDecember112000,was accumulatedon the glacier'ssurface.The earlyJanuary
DTM representsa surfacemodified by deposition of volcanic materials.The February DTM
showsa landscapetransformedby the removalof both volcanic debrisand ice.
The massdifferenceamongDTMs ascomparedto the volume of the laharic depositand particularly to the sediment(lessthan 1.2x 1Osm3of tephra)and water ( - 1.0x 105m3) allow us to
establishthat - 8.1x 1Osm3 of ice were removedfrom the glacierbut did not participatein the
laharicevent.The resultingmeltingwater was sublimatedby the pumiceouspyroclasticflow or
percolated.
6
Conclusions
The subtractionof DTMs allowed the calculationof the total massremovedfrom the glaciated
(-1.0 x 106m3)by the explosiveeventof January22,2OOl.The
slopesof Popocatépetlvolcano
meltwater and pumice from the collapsingexplosivecolumn, together with volcanic materials
accumulatedon the glacierin December2000,participatedin a lahar (a debrisflow) that rraveled
alongthe northern gorgesof the volcano.The lahariceventleft behind a depositof - 2.4x 10sm3,
consistingof more than 50%of pumiceousmaterial,and - 1.6x 105m3 of meltwater (t.7 x 105m3 of
removedice)was incorporatedin the lahar.This representsñ 170/o
of the total ice massremoved.
102
PatriciaJulioMiranda et al.
Acknowledgements
The National Center for Disaster Prevention and the Ministry of Communications and Transport provided aerial photographs. We thank Isaac A. Farraz, Carrlos Linares, Patricio Chicati,
Demian Schneider and F. Graffe, for field, laboratory and abstract translation assistance.This
study was funded by CONACYT (grants 074-PÑ and 32527tr).
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Authors'addresses:P. Julio-Miranda, A.E. González.-Huescaand H. Delgado-Granados,Instituto de
Geofísica,UNAM, Ciudad Universitaria,04510,Coyoacán,México, D.F.,México.
A. Kááb, Department of Geography, lJniversity Zürich-Irchel, \{intherturerstrasse 190, 8057 Zúrich,
Switzerland.