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Geology

doi: 10.1130/0091-7613(1992)020<0299:GDAFTC>2.3.CO;21992;20;299-302Geology

Gary R. Stoopes and Michael F. Sheridanfor long-runout landslides (>100 km) and hazard assessmentGiant debris avalanches from the Colima Volcanic Complex, Mexico: Implications

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Giant debr is ava lanches f ro m the Co l ima Vo lcan ic C om plex ,

Mexico: Impl icat ions for long-runout landsl ides (>100 km)

and hazard assessment

Ga ry R . S too pe s Department of Geology, Arizona State Univers ity , Tempe, Arizona 85287-1404

M i c h a e l F . S h e r i d a n Department of Geology, State Univers ity of New York, Buffa lo, New York 14260

A B S T R A C T

At least two giant volcanic debris-avalanche deposits are associated with the Colima

Volcanic Complex located in the western part of the Trans-Mexican volcanic belt. One ava-

lanche originated from Volcán de Colima (3820 m), probably 4300 yr ago. A much larger

avalanche originated fro m Nev ado d e Colima (424 0 m) 18 500 yr ago; it traveled more than 12 0

km from its source and covered an area of at least 2200 km2, almost twice the area of any

previously described avalanche deposit. This older debris avalanche is the second largest (by

volume) known, has the longest travel distance yet reported, and has one of the lowest

height/length ratios (0.04). The avalanche material was probably hot during emplacement and,

after initial slope failure, may have behaved similarly to a pyroclastic flow. Such large long-

runout landslides from volcanic or nonvolcanic constructs present a serious geologic hazard

that must be considered in risk assessment.

I N T R O D U C T I O N

It is well recognized that debris avalanches

(landslides) are a common phenomenon from

many volcanoes (Siebert, 1984). These events

can be catastrophic and may greatly alter a vol-

cano 's morphology and perhaps change i ts sub-

sequent evolution. Large volcanic (or non-

volcanic) constructs that may produce giant

debris avalanches are of particular importance

because they present the most danger to citizens

living within the sphere of a volcan o's influence.

These factors led us to investigate the distribu-

tion, age, and mode of emplacement of two

debris-avalanche deposits from the Colima

Volcanic Complex, Mexico. One debris ava-lanche is very large and traveled more than 120

km from its source. This is the longest reported

travel distance for a volcanic debris avalanche

and adds additional stimulus to an already lively

debate concerning the mechanism of movem ent

of dry rock avalanches (Hsu, 1975; Davies,

2 4 W

Figure 1. Location map forwestern part of Trans-Mexi-can volcanic belt and asso-c ia ted p la te boundar ies .Open triangles are andesiticcones; patterned area is Lake 2l°30'

Chapala. Volcanoes of ColimaVolcanic Complex are la-beled. VC—Volcán Cantara,N d C — N e v a d o d e C o l i m a ,VdC—Volcán de Colima. Gen-eral fault pattern of Colima rift 0

also shown. Figure modified 1 9

from Luhr and Prestegaard(1988).

1 1 2 W

1981; Melosh, 1987; Campbell , 1989; McEw en,

1989). This new information also provides im-

portant factors for risk assessment and hazard

evaluation for many volcanoes and other large

constructs and emphasizes the need to study this

phenomenon in greater detail.

B A C K G R O U N D

Volcán de Colima and Nevado de Colima

Volcán de Colima (3820 m) and Nevado de

Colima (4240 m) are andesitic composite cones

located near the western edge of the Trans-

Mexican volcanic belt at the southern end of the

Colim a graben, which is a southern extension of

the Colima rift (Luhr et al„ 1985) (Fig. 1). The

main centers of volcanic activity have migrated

southward from Volcán Cantaro through Ne-

vado de Colima to the currently active Volcán

de Colima.

Nevado de Colima, located in the state of

Jalisco, has been a center of volcanism for about

108°00 ' lOfOO'

600000 yr (Robin et al., 1987), but is currently

dormant. The youngest dated activity from Ne-

vado de Colima was - 8100 yr ago (Robin et al.,

1990). This age was obtained fr om charcoal in a

paleosol overlying a pyroclastic flow, which in

turn directly overlies a debris-avalanche deposit

from this volcano. Thus, th is is a minimum age

for volcanic activity at this cone.

Volcán de Colima, a much smaller cone, is

built on the southern slope of Nevado de Co-

lima. Robin et al. (1987) suggested that this vol-

cano may be 50000 yr old , but no precise age

for its first eruption is available. Volcán de Co-

lima has been historically active, with docu-

mented eruptions dating from A .D. 1560 to the

present (Medina-Martinez, 1983). Small, blocky

andesite flows have erupted from the summit in

1961-1962, 1975-1976, and 1981-1982 (Luhr

and Carmichael, 1990) and more recently in

March-April 1991 (Rodriguez-Elizarraras et al.,

1991; Komorowski et al., 1991).

Previous Work

The debris avalanche originating from Ne-

vado de Colima was f irs t identif ied by Robin

et a l . (1987) as a large "Mount St. Helens-type

event" that created an east-facing avalanche cal-

dera. According to Robin et al. (1987), this de-

bris avalanche first moved southeast and then

turned southward along the Tuxpan-El Naranjo

river drainage but extended no farther south

than the town of San Marcos (Fig. 2) . Robin

et al. (1987) suggested a date of "some tens of

thousands of years" for this event.

The large debris-avalanche deposit from Vol-

cán de Colima produced a 4-km-wide avalanche

caldera open to the southwest. As mapped by

Luhr and Prestegaard (1988), this debris-

avalanche deposit has a distribution south of the

cone and extended into the Armería , upper Rio

Salado, and Tuxpan -El N aranjo r iver drainages.

Luhr and Prestegaard (1988) proposed that this

avalanche reached a distance of at least 65 km

from its source and estimated its area to be 1 600

k m 2 and i ts volume to be 8-16 km 3 .

Initially, Stoopes and Sheridan (1989) identi-

fied a large debris-avalanche deposit that

reached to the present ocean shore as originating

from Volcán de Colima. However, subsequent

field work, dating of carbonized wood, and

other considerations, presented below, now lead

us to conclude that the much larger cone of

Nevado de Colima is the source for this giant

G E O L O G Y , v . 2 0 , p . 2 9 9 - 3 0 2 , A p r il 1 9 9 2 29 9






debris-avalanche deposit (Stoopes and Sheridan,

1990a, 1990b).

The Volcán de Colima debris-avalanche de-

posit is Holocene but the radiometric age is in

question. Luhr and Prestegaard (1988) obtained

an age of 4280 ±110 yr B.P., and Robin et al.

(1987 ) determined an age of 9370 ±40 0 yr B.P.

These ages are from charcoal sam ples from sepa-

rate exposures located near the western base of

Volcán de Colima (Fig. 2).

EVIDENCE FOR TWO

OVERLAPPING DEBRIS-

A V A L A N C H E D E P O S I T S

Starting with data from previous workers, we

mapped the areal extent of debris-avalanche

deposits around both volcanoes (Fig. 2). The

mapped deposits exhibit features characteristic

of volcanic debris avalanches: humm ocky topog-

raphy, closed depressions, debris-avalanche

blocks, and jigsaw cracks within blocks as out-

lined by Glicken (1986, 1991) and Siebert

(1984). The area covered by all debris-avalanche

deposi ts is -3 4 00 km2.

The evidence for at least two distinct, over-

lapping debris-avalanche deposits is found in

numerous road cuts along a new highway from

the city of Colima north toward Ciudad Guz-

man and from exposures in barrancas through-

out the overlap area. Figure 3 shows represen-

tative sections where two debris-avalanche

deposits are exposed. The upper (younger) de-

posit throughout the overlap area is generally

1-4 m thick, composed mostly (up to 80%) of

an unsorted, unstratified mix of angular brec-

ciated andesite clasts with small (0.5-1 m) in-

cluded debris-avalanche blocks of the same

lithology. This upper deposit thins and ends to

the east and south, thickens considerably (10-30

m) to the west, and can be continually traced

toward Volcán de Colima until covered by m ore

recent products from this volcano. The lower

(older) deposit is much thicker (1 0-1 5 m ) and is

composed of the same type of andesitic matrix

material as the upper deposit (-50%) but with

many more and larger (decametres) includeddebris-avalanche blocks. In many localities, a

distinctive reddish-brown to brown clay-rich

soil horizon separates these two deposits. In

some barrancas, pyroclastic products and debris-

flow deposits separate the units. The lower

deposit can be traced north of San Marcos

toward Nevado de Colima where it is overlain

by lava flows and other volcanic products and,

at one location, directly overlain by a 2-m-thick

tephra fall. To the south and east, this avalanche

deposit is exposed at the surface and can be

traced to the river drainages and downstream to

the Pacific Ocean.

A radiocarbon age of 18520 ±260 yr B.P.

(University of Arizona, Tucson, lab no. 5304)

was obtained for a large (50-cm diameter) car-

bonized tree trunk embedded in the lower ava-

lanche deposit, found 1 km southeast of

Cuauhtem oc (Fig. 2). This age is much older (by

at least 9000 yr) than either age ascribed to the

Volcán de Colima debris avalanche by Luhr and

Prestegaard (1988) or Robin et al. (1987).

In addition to stratigraphic and age evidence

for two partially overlapping avalanche deposits,

many surface boulders on the older deposit are

quite dark in appearance, in contrast to surface

boulders on the younger deposit. Luhr and Pres-

tegaard (1988) first mentioned the darkerboulders and noted their location in the southern

part (mainly the Rio Tuxpan-El Narranjo

drainage) of the deposit. Although dismissing

the possibility that the dark boulders were evi-

dence of two separate debris-avalanche deposits,

they stated that their interpretation was not con-

clusive. Our interpretation is that the darker

color of the clasts is due to longer exposure to

weathering processes, similar to the develop-

ment of a weathering varnish. The darkening of

surface boulders ends at ground level; over-

Figure 2. Map showing distribution of volcanic debris-avalanche deposits from Volcan de Colima

(VdC) and Nevado de Colima (NdC). Dashed l ines—rivers, solid l ines—roads. Partial ly inferred

avalanche calderas marke d for each cone. Sol id square m arks approximate sample locat ion for

age determinat ion of Luhr and Prestegaard (1988) . Sol id oval marks same for age determinat ion

of Robin et al . (1987). Solid tr iangle marks sample location for age ass igned to Nevad o de Colima

avalanche deposi t .

30 0 GEOLOGY, April 1992






turned boulders are not dark on their unexposed

surfaces, a common characteristic of varnished

material. The suggested age, 18500 yr, of the

older avalanche is much older than either age

suggested for the Volcán de Colima avalanche,

and the areal distribution of these boulders fits

well with the mapped extent of the Nevado de

Colima avalanche deposit shown in Figure 2.

Large boulders with cracks that closely re-

semble breadcrust texture are also present in the

older debris-avalanche deposit and may be

juvenile erupted material. Although scarce, they

have been found in five different localities.

These probably juvenile blocks have been noted

only in the older avalanche, and many are also

dark.

In addition to the two volcanic debris-

avalanche deposits on the east side of the vol-

cano, two debris-avalanche deposits occur in the

deep barranca at El Remote near the Rio Arme-

ría (A. L. Martin, 1991, personal commun.).

The upper one probably corresponds to the

4300-yr-old avalanche, and the lower one is an

older avalanche deposit.

The lithologies of both deposits are very sim-

ilar as all clasts are two-pyroxene andesites.

Whole-rock analyses of surface boulders and in-

cluded clasts from both deposits revealed the

monotonous nature of their chemical composi-

tions. These deposits cannot be differentiated on

the basis of petrography or whole-rock analysis

(exclusive of rare earth elements) of included

clasts or by comparisons to analyses of probable

source rocks (Stoopes, 1991).

D I S T R I B U T I O N A N D A G E

O F D E P O S I T S

Nevado de Colima Deposit

On the basis of the above evidence, we showtwo partially overlapping debris-avalanche de-

posits in Figure 2. One originated from Nevado

de Colima and one from Volcán de Colima.

Luhr and Prestegaard (1988) identified a debris-

avalanche deposit in the Tuxpan-El Naranjo

river drainage and traced it to Paso de Potreril-

los (Fig. 2), 65 km from Volcán de Colima,

which they concluded was the probable source

of this deposit. We traced this same deposit

south, through the El Naranjo and the Rio Sa-

lado river drainages, to the Pacific Ocean. H ow-

ever, we interpret this debris-avalanche deposit

as an extension of the avalanche first identified

by Robin et al. (1987) which originated from

Nevado de Colima. This debris-avalanche de-

posit, as we have mapped it, covers an area of

—2200 km 2 and has an estimated minimum vol-

ume of 22-33 km 3 , based on an average

thickness of 10-15 m.

As shown in Figure 2, the Neva do de Colima

avalanche initially moved southeast from its

source, filling and overflowing canyons of the

Rio Tuxpan-E l Naranjo and Rio Salado drain-

ages, and then moved down these two drainages

toward the Pacific Ocean. The separate lobes of

this debris avalanche converged near the pueb-

lo of Las Conchas, 90 km from its source, and

diverged a short distance farther. One lobe sur-

mounted an 80 m topographic barrier and

moved southwest through a gap in the surround-

ing hills toward the present site of San Miguel;

the other lobe continued down the main river

drainage. The two avalanche lobes then con-

verged again to the south near Cerro de Ortega

and flowed toward the Pacific Ocean along a 20

km swath. Sea level 18500 yr ago was at least100 m below its present height (Pinter and

Gardner, 1989), so the full extent of this large

avalanche is not known. Even at this great dis-

tance the deposit is an unsorted, unstratified

mixture of angular blocks in a pulverized rock

matrix. Debris-avalanche blocks are very rare at

distal locations in this deposit. This is a typical

characteristic of debris-avalanche deposits (Sie-

bert, 1984) as was noted for the Mount St.

Helens (Glicken, 1986, 1991) and the Mount

Shasta avalanche deposits (Crandell, 1989).

Numerous hummocks, many over 20 m high,

dot the landscape near the town of Cerro de

Ortega. Hummocks and andesitic bouldermounds are also evident only 3 km from the

present ocean shore, west of the town.

Volcan de Colima Deposit

This avalanche traveled 43 km south of the

old cone (Fig. 2), entering the Armeria river

drainage southwest of the volcano but not reach-

ing the Pacific Ocean. It did not enter the Tux-

pan-El Naranjo drainage as proposed by Luhr

and Prestegaard (1988), but it did reach loca-

tions ~ 10 km south of the city of Colima (popu-

VdC avalanche deposit

Paleosol overlain by

pyroclastic products

NdC ava lanche

deposit

Debris flows and

other fluvial deposits

lation 100000), which is built on this deposit.

The Volcán de Colima debris-avalanche deposit

covers a maximum area of 1200 km 2 and has an

estimated volume of 6-12 km3, based on an

average thickness of 5 -1 0 m .

D I S C U S S I O N

The fall-height to runout-length ratio (H/L) is

an index used to compare avalanche deposits

and other flow deposits (e.g., lahars, pyroclastic

flows) and to estimate a "coefficient of friction"

(F = H/L) for each deposit (Hsü, 1975; Siebert,

1984). The average F value for known volcanic

debris avalanches is 0.11 (Siebert, 1984). The

Volcán de Colima avalanche has an F value of

0.09, but the F value for the Nevado de Colima

avalanche is only 0.04. The low F value of the

Colima avalanche is consistent with other large-

volume deposits, but the 0.04 value for the Ne-

vado avalanche is one of the lowest ever

reported and in fact is similar to values reported

for some large pyroclastic flows (Sheridan,

1979).

The Nevado de Colima debris avalanche

flowed up various opposing slopes as it pro-

gressed southward in the Rio El Naranjo drain-

age. Velocities for this avalanche can therefore

be estimated using the relation v = (2gh)0-5,

where h = run-up height (Chester, 1979) and g =

gravitational acceleration. This equation as-

sumes no basal or internal friction; thus, v is a

minimum. Figure 4 shows calculated velocities

plotted against distance from source. At ~9 0 km

from its source, the avalanche was moving at an

estimated velocity of 44 m/s (about 100 mi/h).

Closer to the source, at about 42 km distance,

the estimated velocity is 78 m/s. For compari-

son, the estimated maximum velocity of the

Mou nt St. Helens debris avalanche was 70 m /s(Voight et al., 1983).

The breadcrust blocks found in the Nevado

de Colima avalanche deposit may be juvenile

material from a magma body that erupted simul-

taneously with the collapse of this volcano. The

log used for dating the avalanche was carbon-

ized by the deposit, testifying to the high

VdC avalanche deposit

Paleosol

NdC ava lanche

deposit

Cretaceous

sedimentary

bedrock

Figure 3. Representative sections of avalanche deposits in Barranca Rosario in town of San

Marcos, 16 km east of Volcan de Colima (A), and ~5 km southeast of city of Colima in Rio Salado

drainage (B). Bedrock is inferred here; i t is exposed in outcrop beneath Nevado avalanche ~ 5 km

downstream, but Volcan de Colima avalanche deposit is absent. Abbreviations as in Figure 2.

0 20 40 60 80 100 120

Distance (km) from Nevado de Colima

Figure 4. Graph showing velocities of Nevado

de Col ima avalanch e plotted against d istance

from source. Calculat ions based on runup

equation. Arrow points to calculated velocity

near vi l lage of San Miguel.

300 GEO LOG Y, April 1992







temperature of the avalanche. A thick tephra-fall

deposit directly overlies this avalanche deposit

closer to its source and suggests the possibility of

volcanic activity associated with this avalanche.

A magma body in the top part of Nevado de

Colima could have contributed substantial

energy to the movement and disaggregation of

the avalanche and may be one reason why it

traveled such a great distance. Hot gases and

fluids may have helped either mobilize part ofthe avalanche or buffer interparticle collisions,

reducing friction and energy dissipation within

the moving mass and extending its travel length

(Voight et al., 1983). The low F value of this

avalanche and the high velocities a great dis-

tance from its source may attest to this process.

The debris avalanche from Volcán de Colima

is very large, but its area and volume are less

than reported by Luhr and Prestegaard (1988).

The Volcán de Colima avalanche spread out

from its source like a fan because no large, con-

fining drainages or topography obstructions re-

stricted flow.

C O N C L U S I O N S

The Nevado de Colima avalanche deposit is

one of the largest known. The Mount Shasta,

California, avalanche deposit, with an estimated

volume of 45 k m 3 (Crande ll, 1 989) is the largest

know n. Active magmatic and hydrothermal sys-

tems may have influenced the collapse of Ne-

vado de Colima and may have been contribut-

ing factors to the long runout length of the

resulting avalanche. Thus, some long-runout

avalanches may act similarly to dense lithic py-

roclastic flows. An additional factor for long

runout w as the confinement of this avalanche to

river drainages for much of its travel distance.

Hum mocks fro m this deposit may be evident inthe submarine morphology and detectable by

seismic profiling or on detailed bathymetric

maps.

The debris avalanche from Volcán de Colima

is much smaller and traveled less distance than

the avalanche from Nevado de Colima. A repeat

avalanche event from this cone would be cata-

strophic to the population near this volcano

(Luhr and Carmichael, 1990). The possibility of

more than one avalanche deposit from Volcán

de Colima cannot be dismissed, and more map-

ping is required to resolve this question.

Earthquakes can initiate debris avalanches

(Keefer, 1984; Endo et al., 1989), and the asso-

ciation of the Colima Volcanic Complex with an

active rift along a subduction margin may be a

factor in the number of debris avalanches origi-

nating from these cones.

It is apparent that debris avalanches can travel

great distances and that water is not an essential

ingredient to long runout (McEwen, 1989). No

consensus has been reached on the mechanism

of movement of this phenomenon, b ut this work

illustrates the need for more research on grain-

flow theory and flow dynamics of large mass

movements.

Given the proper set of conditions—a large-

volume cone, steep proximal topography, a

great fall height (>3000-4000 m), and an ac-

companying eruption—primary avalanche mate-

rial can travel 120 km or more from its source.

Secondary lahars derived from avalanche mate-

rial could add substantially to the travel dis-

tance. Current hazard assessment techniquesregarding volcanic debris avalanches must take

these factors into account if accurate risk as-

sessment and hazard zonation maps are to be

developed.

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A C K N O W L E D G M E N T S

Partial funding for field work was provided by

National Science Foundation grant INT-89021 71. We

thank Norman Banks, U.S. Geological Survey, Cas-

cades Volcano Observatory, for financial support for

field work provided through OFDA/USGS Volcano

Early Warning and Disaster Assistant Program;

Austin Long, University of Arizona, Tucson, for the

carbon-14 date; Steve Anderson, Al Levine, Judy

Lopas Stoopes, and Mike Malin for reviews and co m-

ments on earlier versions of this paper; Thomas Pier-

son for a thorough and thoughtful review; and espe-

cially Claus Siebe and Jean Christophe-Komorowski.

Manuscript received October 7, 1991

Revised manuscript received December 11, 1991

Manuscript accepted December 23, 1991

30 2 Pr inted in U.S .A. GEOLOGY, April 1992




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