Lahar Hazards at Agua Volcano, Guatemala - USGS · Lahar Hazards at Agua Volcano, Guatemala 1 ......

Lahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua Volcano, Guatemalaolcano, Guatemalaolcano, Guatemalaolcano, Guatemalaolcano, Guatemala 11111

U.S. Department of the InteriorU.S. Department of the InteriorU.S. Department of the InteriorU.S. Department of the InteriorU.S. Department of the InteriorU.S. Geological SurveyU.S. Geological SurveyU.S. Geological SurveyU.S. Geological SurveyU.S. Geological Survey

Open-File Report 01–432Open-File Report 01–432Open-File Report 01–432Open-File Report 01–432Open-File Report 01–432

Lahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua Volcano,olcano,olcano,olcano,olcano,GuatemalaGuatemalaGuatemalaGuatemalaGuatemala

22222 Lahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua Volcano, Guatemalaolcano, Guatemalaolcano, Guatemalaolcano, Guatemalaolcano, Guatemala

Cover photographCover photographCover photographCover photographCover photograph

Agua volcano viewed from the west. (Photo by J.W. Vallance).


Lahar-Hazards at Agua Volcano,Lahar-Hazards at Agua Volcano,Lahar-Hazards at Agua Volcano,Lahar-Hazards at Agua Volcano,Lahar-Hazards at Agua Volcano,GuatemalaGuatemalaGuatemalaGuatemalaGuatemalaByByByByBy S.P. Schilling, J.W. Vallance, O. Matías, and M.M HowellS.P. Schilling, J.W. Vallance, O. Matías, and M.M HowellS.P. Schilling, J.W. Vallance, O. Matías, and M.M HowellS.P. Schilling, J.W. Vallance, O. Matías, and M.M HowellS.P. Schilling, J.W. Vallance, O. Matías, and M.M Howell

U.S. GEOLOGICAL SURVEYU.S. GEOLOGICAL SURVEYU.S. GEOLOGICAL SURVEYU.S. GEOLOGICAL SURVEYU.S. GEOLOGICAL SURVEYOpen-File Report 01-432Open-File Report 01-432Open-File Report 01-432Open-File Report 01-432Open-File Report 01-432

Vancouver, Washington U.S.A.2001


U.S. DEPARTMENT OF THE INTERIORGale Norton, Secretary

U.S. GEOLOGICAL SURVEYCharles G. Groat, Director

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Any use oftrade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

:morf desahcrup eb nac troper siht fo seipoC:ot etirw noitamrofni lanoitidda roF

yevruS lacigoloeG .S.UegrahC-ni-tsitneicSsecivreS noitamrofnIyevruS lacigoloeG .S.U

68252 xoB .O.P01 .gdlB ,truoC lanidraC ES 003152208 OC ,revneD38689 AW ,revuocnaV

0124-202 )303(0098-399 )063(FAX: (360) 993-8980


CONTENTSCONTENTSCONTENTSCONTENTSCONTENTS

Introduction................................................................................................................................................ 1

Debris Avalanches, Landslides, and Lahars ............................................................................................... 4

Future Landslides and Lahars at Agua Volcano ......................................................................................... 5

Lahar-Hazard-Zonation Map ..................................................................................................................... 5

Proximal lahar-hazard zone.................................................................................................................. 5

Distal lahar-hazard zones ..................................................................................................................... 6

Hazard Forecasts and Warnings ................................................................................................................. 6

Protecting Communities and Citizens from Lahar Hazards ....................................................................... 6

References.................................................................................................................................................. 7

Additional Suggested Reading................................................................................................................... 8

End Notes ................................................................................................................................................... 8

PLATEPLATEPLATEPLATEPLATE [In pocket]

1. Lahar hazards of Agua volcano, Guatemala..Proximal and distal hazard zones from laharsat Agua volcano.

FIGURESFIGURESFIGURESFIGURESFIGURES

1. Locations of major cities and significant Quaternary volcanoes in Guatemalaincluding Agua volcano .................................................................................................................... 1

2 Schematic map showing the areal extent of and two cross-sections for the Casita,Nicaragua, debris flow of 1998 ........................................................................................................ 3


INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONAt 3760 m, Agua volcano towers more

than 3500 m above the Pacific coastal plainto the south and 2000 m above theGuatemalan highlands to the north(figure 1). The volcano is within 5 to 10kilometers (km) of Antigua, Guatemala andseveral other large towns situated on itsnorthern apron. These towns have acombined population of nearly 100,000. Itis within about 20 km of Escuintla(population, ca. 100,000) to the south.Though the volcano has not been active inhistorical time [1] (numerals in bracketsrefer to end notes in the report), or about thelast 500 years, it has the potential toproduce debris flows (watery flows of mud,rock, and debris—also known as laharswhen they occur on a volcano) that couldinundate these nearby populated areas.

In late October and early November1998, torrential rains of Hurricane Mitchcaused numerous slope failures in CentralAmerica, the most catastrophic of whichoccurred at Casita volcano, Nicaragua on

Lahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua VLahar Hazards at Agua Volcano,olcano,olcano,olcano,olcano,GuatemalaGuatemalaGuatemalaGuatemalaGuatemalaByByByByBy S.P S.P S.P S.P S.P. Schilling, J.W. Schilling, J.W. Schilling, J.W. Schilling, J.W. Schilling, J.W. V. V. V. V. Vallance, O. Matíasallance, O. Matíasallance, O. Matíasallance, O. Matíasallance, O. Matías11111, and M.M Howell, and M.M Howell, and M.M Howell, and M.M Howell, and M.M Howell

Figure 1. Locations of major cities and significant Quaternaryvolcanoes in Guatemala including Agua volcano adapted fromVallance et al. (1995). Circles indicate major cities, solidtriangles indicate active volcanoes and open triangles indicatedormant volcanoes. Atitlán is a large silicic caldera.

1 Instituto sismología, vocanología, meteorología, y hidrología (INSIVUMEH), Guatemala.

ce n

92o W.

16o N.

14oN.

90o W.

MEXICO

GUATEMALA

go

Fuego

ua

San Pedro

Tacana

ific

l Pl

Guatem

Highlands

4

5

1

zaltenango


muertes y danos que sucedieron fue tantala tormenta de la piedra que trago pordelante el agua y la mucha madera yárboles que los que lo uimos estábamoseadmirados entro por la casa de la delAdelantado don Pedro Alvarado que ayagloria que llevo todas las paredes ytezado como esetaba mas de en tire deballesta…(Marroquín) [1].

El memorabilisimo [suceso] de 11 deseptiembre de 1541, que totalmentearruinó la ciudad vieja de Guatemala …continuándose por muchos días, que a noprevenir al aviso de un ruidoso estruendocomo por debajo de tierra, hubierancausado los terremotos, que hubo despuésde la ruina de la ciudad, aun másmuertas, que en las que en ella hubo,siendo en número de más de seiscientaspersonas. Bastantemente expresan lasjuntas, y funciones de Cabildo estatribulación; pues en todas las que setuvieron para conseguir mudar la ciudad,dicen, estar casi continuamentetemblando la tierra (Vázquez 1937:1:154)[1].

[English translation:]

This has been a year of much rain, andhaving been raining Thursday, Friday andSaturday, with strong winds and not muchwater, the mentioned “lavada” [wash,means heavy rain or the debris flow?]happened two hours into the night. Agreat storm of water came from atop thevolcano (Agua) which is above the city, itwas so sudden that [we] did not ... preventthe deaths and damages that happened;the stone storm [debris flow] was so hugethat it swallowed the water in front of it,and much wood and trees, those who sawit were impressed, it entered through thehouse of the “Adelantado” don PedroAlvarado, and it took away all the wallsand the roof …(Marroquín) [1].

The well remembered [event] ofSeptember 11th, 1541, that totallydestroyed old Guatemala City [this firstcapital is now named Cuidad Vieja] …

October 30, 1998. At Casita, five days of heavyrain triggered a 1.6-million-cubic-meter rock anddebris avalanche that generated a 2- to 4-million-cubic-meter debris flow that swept down the steepslopes of the volcano, spread out across thevolcano’s apron, destroyed two towns, and killedmore than 2500 people [2]. The avalanche did notdam the upper drainages or impound water.Rather, it appears that the Casita debris flowevolved directly as the avalanche moved downslope [2].

On October 30, 1998 between 10:30 and11:00 a.m., residents south of Casita heard aroaring noise like helicopters or thunder. Somethought an earthquake was occurring. Three tofive minutes thereafter, a wave of muddy debris1.0-1.3 km wide and an average of 3.5 m deepdestroyed all traces of two towns (figure 2).Observations by survivors record an enormousflood on the slopes of the volcano and a wall ofmud on the volcano apron. A person on thevolcano slopes saw a “black curtain of water withtrees.” On the apron of the volcano where the flowspread out, survivors describe the flow as—“aninfernal wave of mud, rocks, and trees,” or“enormous mass of mud.” [2]. The debris flowmoved about 10 km from its source. It alsogenerated floods that moved an additional 10 kmdownstream, destroying roads and bridges andinundating homes.

No large debris flows occurred at Agua volcanoduring Hurricane Mitch, but historical accountsindicate that such events have occurred there in thepast. On September 11, 1541, heavy rains causeda debris flow that inundated Cuidad Vieja (plate 1),killed more than 600 people, and destroyed thetown [1]. Cuidad Vieja was the capitol city ofGuatemala in 1541. After the destruction ofCuidad Vieja, the capital moved to AntiguaGuatemala. The following eyewitness accountsrecord this event.

Este año a sido de muchas aguas yhabiento llovido jueves y viernes y sábadocon mucho viento y no mucha agua eldicho lavada serían como es dicho doshoras de noche. Vino muy gran tormentade agua de lo alto del volcán (Agua) queesta encima de la ciudad fue tan súpitoque no … para poder remediar las


FLOW II

FLOW I

ROLANDO

RODRIGUEZ

EL PORVENIR

Santa Narcisa

Bella VistaArgelia

AA'

B

B'

700

600

500

400

300

80090

10001100

1 200

1300

Boulders >3mintermediatediameter

End of debrisflow

Runout ofhyperconcen-trated hlow and sediment-ladenstreamflow

Head scarp1998 collapse

Overflow toArgelia

Sites of previousflank collapses

Site of flowcross-sectionat right

Site of flowcross-sectionat right

0 1 2 Km

La Pelona Caldera

1405

La OlladaCrater

Versalles

Volcán Casita

El

Mon

o

Mue

rto

Cha

nn

el

Pre-flow land

surface

Deposit thickness diagrammatic

Channel filltree

15 cm levee

770

780

790

800

810

820

830

260

270

280

290

300

310

Alt

itu

de

, in

me

ters

ab

ov

e s

ea

le

ve

l

320

A

A'

B' B

FLOW I

FLOW I

FLOW II

FLOW II deposits

FLOW I deposits

FLOW I deposits

Horizontal Distance, in meters0 50 100 150 200 250 300

Horizontal Distance, in meters0 200 400 600 800 1,000 1,200 1,400 1,600

FLOW I

500 100 Km

NICARAGUA

V. MomotomboV. Casita

V. MasayaV. Mombacho

V. MaderasV. Concepcíon

200

Lake Minagua

Managua

V. Cosiguiña

Figure 2. Schematic map showing the areal extent of and two cross-sections for the Casita, Nicaragua debris flowof 1998 adapted from Scott et al. (in press).


DEBRIS AVDEBRIS AVDEBRIS AVDEBRIS AVDEBRIS AVALANCHES, LANDSLIDES,ALANCHES, LANDSLIDES,ALANCHES, LANDSLIDES,ALANCHES, LANDSLIDES,ALANCHES, LANDSLIDES,AND LAHARSAND LAHARSAND LAHARSAND LAHARSAND LAHARS

Slope failure on a volcano can generate arapidly moving landslide called a debrisavalanche. Small-volume debris avalanchestypically travel only a few kilometers from theirsource, but large-volume debris avalanches cantravel tens of kilometers from a volcano. Debrisavalanches destroy everything in their paths andcan leave deposits of 10 meters thick or more onvalley floors.

Lahars, also called mudflows and debris flows,are masses of mud, rock, and water that look muchlike flowing concrete. They occur when watermobilizes large volumes of loose mud, rock, andvolcanic debris. Commonly, landslides and debrisavalanches will incorporate enough water to formlahars. Lahars, like floods, inundate floodplainsand structures in low-lying areas. They can travelmany tens of kilometers down valleys at speeds oftens of kilometers per hour. Lahars destroy ordamage everything in their paths through burial orimpact. Lahars follow river valleys and leavedeposits of muddy sand and gravel that can beseveral meters thick. They are particularlyhazardous because they travel farther from avolcano than any other hazardous phenomenonexcept tephra, and they affect stream valleys wherehuman settlement is usually greatest. In someinstances, lahars clog channels or block tributariesso that water collects behind the blockage. Theimpounded water can spill over the blockage andgenerate floods that move down valley. Breachingof such blockages can occur within hours, months,or even years after impoundment.

Like floods, lahars range greatly in size. Thesmallest lahars occur most frequently (perhapsevery few years), whereas the largest recur on theorder of centuries to millennia. The amount ofwater and loose volcanic debris entraineddetermines lahar size. Eruptions, like historicalexamples at nearby Fuego Volcano, can depositmillions of cubic meters of sediment into channelsthat when mixed with water during subsequentrains causes lahars [3].

Landslides and lahars can cause problems longafter the original eruptive or other disturbance.

lasting many days. Were it not for thenoisy uproar underneath the earth that theearthquakes caused, many more deathswould have taken place than those thathappened there, a number greater than sixhundred people. The meetings andfunctions of the town Council state thistribulation, since during each meetingthey had to achieve the move of the City,they say, the earth was constantlytrembling. (Vázquez 1937:1:154) [1].

Although many have suggested that the 1541debris flow resulted from a crater-lake breakout theaccounts above and others in reference note [1]suggest that the 1541 debris flow at Agua wasremarkably similar to the 1998 debris flow atCasita. In each case, the event occurred in thelatter half of the rainy season, when the groundwas water saturated. In each case, several days ofheavy rain triggered a landslide, which in turngenerated a debris flow. In each case, survivorsreported that the ground shook immediately prior tothe arrival of the debris flow, and many peoplemistook the event for an earthquake. In each case,the debris flow destroyed population centers on theapron of the volcano.

In prehistoric time, Agua has eruptedexplosively to form widespread ash-fall deposits(called tephra), hot ash flows (called pyroclasticflows) and lava flows. Although the volcano haserupted numerous times during the past 80,000years, the most recent eruptions presently dated aremore than 10,000 years ago [1]. If such eruptionswere to occur now, many people and costlyinfrastructure would be at risk. In the aftermath ofa voluminous eruption of ash or pyroclastic flows,volcanic debris flows would certainly occur duringthe rainy seasons.

This report describes the hazards of landslidesand lahars in general, and discusses potentialhazards from future landslides and lahars at Aguavolcano in particular. The report also shows, in theaccompanying lahar-hazard-zonation map, whichareas are likely to be at risk from future landslidesand lahars at Agua. A broader volcano-hazardassessment of the volcano is in progress [1].


Once lahars fill stream channels with sediment, thestreams begin to erode new paths. The new streamchannels can be highly unstable and shift rapidly assediment is eroded and moved farther down valley.Also, because stream channels are clogged withsediment, they have less ability to convey waterand thus are more susceptible to smaller-magnitudefloods.

FUTURE LANDSLIDES AND LAHARSFUTURE LANDSLIDES AND LAHARSFUTURE LANDSLIDES AND LAHARSFUTURE LANDSLIDES AND LAHARSFUTURE LANDSLIDES AND LAHARSAAAAAT AGUA VOLCANOT AGUA VOLCANOT AGUA VOLCANOT AGUA VOLCANOT AGUA VOLCANO

Like neighboring Fuego and Acatenangovolcanoes, Agua can erupt explosively to producepyroclastic flows and widespread tephra falls,though the lack of historical volcanism of this typesuggests that the probability of explosive eruptionsat Agua is less than at Acatenango and much lessthan at Fuego [1, 3]. At Fuego such eruptionsoccur once every several years; at Acatenango theyoccur about once every thousand years; but atAgua none are documented in the last ten thousandyears. The ash and loose debris produced by aneruption would surely cause lahars when mixedwith water from rains during the rainy season.Small volcanic earthquakes, steam explosions anddeformation of the crater area would be likely toprecede pyroclastic eruptions at Agua volcano

Because eruptions are likely to be infrequent atAgua, landslides and debris flows during torrentialrainstorms are the most likely threats to nearbypeople and infrastructure [1]. Because there is lessloose, easily erodible volcaniclastic material on theslopes of Agua than on Fuego volcano, debrisflows having this origin are less likely than atFuego. These phenomena, like those at Casita,Nicaragua and at Agua in 1541, are most apt tooccur during unusually intense rain. They areespecially likely after long periods of rain towardthe end of the rainy season.

LAHAR-HAZARD-ZONALAHAR-HAZARD-ZONALAHAR-HAZARD-ZONALAHAR-HAZARD-ZONALAHAR-HAZARD-ZONATION MAPTION MAPTION MAPTION MAPTION MAPThe accompanying lahar-hazard-zonation map

(plate 1) shows areas that could be affected byfuture lahars at or near Agua volcano. Individuallahars typically affect only part of a hazard zone.

The location and size of an affected area willdepend on local conditions, like the volume ofmaterial involved, and the character of an eruption,if any.

Potentially hazardous areas around Aguavolcano include proximal lahar-hazard zones anddistal lahar-hazard zones. Distal lahar-hazardzones are subdivided further on the basis of theirrelative degree of hazard. Hazard-zone boundariesderive from three main factors. First, there are themagnitudes of lahars known to have occurred at thevolcano, as inferred from historical accounts andprehistoric deposits. Second, an empirical modelcalibrates lahar-inundation limits on the basis oflahars of known volume that have occurred at othervolcanoes. Third, we apply our experience andjudgment derived from past experience with eventsof a similar nature at other volcanoes.

Although sharp boundaries delineate eachhazard zone, the limit of the hazard does not endabruptly at the boundaries. Rather, the hazarddecreases gradually as distance from the volcanoincreases and decreases rapidly with increasingelevation above valley floors. Areas immediatelybeyond distal hazard zones are not free of riskbecause the hazard limits can only approximatelybe located, especially in areas of low relief. Manyuncertainties about the source, size, and mobility offuture lahars preclude precise location of thehazard-zone boundaries.

Users of our hazard map should be aware thatwe have not simulated all hazardous landslide andlahar scenarios. The edifice of Agua volcano issteep, incised, and partly affected by hydrothermalweakening of the rock. For this report, we selectedprominent channels directed toward populous areasin order to define the most significant zones ofinundation from lahars of various volumes. Otherchannels for which we have not modeled laharinundation are not necessarily devoid of laharhazard. Landslides and lahars from otherunmapped channels could also threaten life andproperty.

Proximal laharProximal laharProximal laharProximal laharProximal lahar-hazard zone-hazard zone-hazard zone-hazard zone-hazard zoneThe proximal lahar-hazard zone includes areas

immediately surrounding Agua volcano, and


extends about 5 kilometers outward from thesummit depending upon local topography (plate 1)[4]. This zone delineates areas where laharsoriginate. During periods of volcanic unrest orduring an eruption, this area should be evacuatedbecause events can occur too quickly for humans toescape harm. Avalanches and lahars will originatein the proximal area, and deposits from small slidesand flows may be restricted to this zone. However,large debris avalanches and lahars will travel awayfrom the volcano and flow onto adjacent slopes.The extent of inundation from these larger lahars isthe basis for defining distal lahar-hazard zones.

Distal laharDistal laharDistal laharDistal laharDistal lahar-hazard zones-hazard zones-hazard zones-hazard zones-hazard zones

An automated empirical technique calibratedwith data from other volcanoes [5] estimatespotential areas of inundation from lahars of variousvolumes. For each channel analyzed, we definefour nested hazard zones that depict anticipatedinundation by hypothetical “design” lahars havingdifferent volumes. The largest design lahar reflectsour estimate of the largest probable lahar generatedon the steep slopes of Agua volcano (plate 1) [5].The intermediate and smallest design lahars aremore typical lahar volumes. Lahars of the largestsizes have occurred historically at Agua and wouldbe likely after an eruption or during severerainstorms.

Large lahars are less likely to occur than smalllahars. Thus, the nested lahar-hazard inundationzones show that the likelihood of lahar inundationdecreases as distance from the volcano andelevation above the valley floors increases. Laharsof all designated sizes could form on the volcano’sslopes if unusually intense rainstorms occur. Thelargest design lahar (plate 1) is based on the size ofthe largest lahar that occurred during HurricaneMitch at Casita, Nicaragua. An intense storm, likeHurricane Mitch, would not invariably triggerlahars as large as the one at Casita. Smaller laharsmay occasionally result from heavy rains thatnormally occur each year during the rainy seasonof May to November.

In general, lahar-hazard zones extend 10 to 25kilometers from the summit crater (plate 1). Localtopography plays a large role in controlling lahartravel distance. Lahars of a given volume will

move considerably greater distances southwardfrom the volcano than northward because thesouthern flank of the volcano drops steeply downto the coastal plain whereas northern slopesintersect the Guatemalan Highlands. Despite theirrelatively short runout distances, even the smallestlahars moving northward can be devastatingbecause of nearby large population centers in thatdirection.

HAZARD FORECASTS ANDHAZARD FORECASTS ANDHAZARD FORECASTS ANDHAZARD FORECASTS ANDHAZARD FORECASTS ANDWARNINGSWARNINGSWARNINGSWARNINGSWARNINGS

It is difficult, if not impossible, to predict theprecise occurrence of landslides and laharstriggered by earthquakes or torrential rains.However, generally hazardous conditions that favorformation of landslides and lahars can berecognized. Forecasts for very heavy rainfall,which commonly trigger flood warnings, can serveas indicators of conditions favorable for landslidesand lahars. When Agua volcano erupts again, it islikely to disperse tephra fall on its flanks.Subsequent erosion of that tephra can generatelahars similar to or larger than those that haveoccurred in historical time. In this case, theeruption of the volcano can serve as a warning thatconditions are favorable for lahar formation, andthe distribution of tephra fall can indicate whichflanks are more likely to be affected. However,government officials and the public need to realizethat potentially lethal events can occur in the laharhazard zones with little or no warning.

PROTECTING COMMUNITIES ANDPROTECTING COMMUNITIES ANDPROTECTING COMMUNITIES ANDPROTECTING COMMUNITIES ANDPROTECTING COMMUNITIES ANDCITIZENS FROM LAHAR HAZARDSCITIZENS FROM LAHAR HAZARDSCITIZENS FROM LAHAR HAZARDSCITIZENS FROM LAHAR HAZARDSCITIZENS FROM LAHAR HAZARDS

Communities and citizens must plan ahead tomitigate the effects of future landslides and laharsfrom Agua volcano. Long-term mitigation effortsmight include using information about lahar andother volcano hazards contained in plate 1 whenmaking decisions about land use and siting ofcritical facilities and development. Futuredevelopment should avoid areas judged to have anunacceptably high risk.


Depending on the distance from the volcano,the hazard zones depicted on the map are areas thatwill be affected within a few minutes to about onehour after the onset of a lahar. Beyond 10kilometers from the volcano’s summit escape maybe possible if people are given sufficient warning.Within 10 kilometers of the volcano lahars mayhappen too quickly to provide effective warning.Therefore, citizens must learn to recognize forthemselves hazardous conditions that favorformation of landslides and lahars.

Because landslides and lahars can occurwithout warning, suitable emergency plans fordealing with them should be made in advance.Although it is uncertain when landslides and laharswill occur again at Agua volcano, public officialsneed to consider issues such as public education,communications, and evacuations as part of aresponse plan. Emergency plans already developedfor floods may apply to some extent, but may needmodifications. For inhabitants in low-lying areas amap showing the shortest route to high groundwould be helpful.

Knowledge and advance planning are the mostimportant items for dealing with landslide andlahar hazards. Especially important is a plan ofaction based on the knowledge of relatively safeareas around homes, schools, and workplaces.Lahars pose the biggest threat to people living orrecreating along channels that drain Agua volcano.The best strategy for avoiding a lahar is to move tothe highest possible ground. A safe height aboveriver channels depends on many factors includingthe size of the lahar, distance from the volcano, andshape of the valley. For areas beyond about 8kilometers from the summit of the volcano, all butthat largest lahars will rise less than about 10meters above river level. Landslides and laharsfrom Agua volcano will happen again, and the bestway to cope with these events is through advanceplanning in order to mitigate their effects.

REFERENCESREFERENCESREFERENCESREFERENCESREFERENCESBonis, S.B. and Salazar, O, 1973, The 1971 and 1973

eruptions of Volcán de Fuego, Guatemala, andsome socio-ecoonomic considerations for thevolcanologist: Bulletin Volcanologique, v. 37,p. 394-400.

Davies, D.K., Querry, M.W. and Bonis, S.B., 1978,Glowing avalanches from the 1974 eruption of thevolcano Fuego, Guatemala: Geological Societyof America Bulletin, v.89, p. 369-384.

Feldman, L., 1993, Mountains of Fire Lands thatShake: Labyrinthos, Culver City, CA, 295 p.

Iverson, R.M., Schilling, S.P., and Vallance, J.W.,1998, Objective delineation of lahar-hazard zonesdownstream from volcanoes: Geological Societyof America Bulletin, v. 110, p. 972-984.

Kerle, N., in press, Volume estimation of the 1998flank collapse at Casita volcano, Nicaragua–acomparison of photogrammetric and conventionaltechniques: Earth Surface Processes andLandforms

Kerle, N., and van Wyk de Vries, B., 2001, The 1998debris avalanche at Casita volcano, Nicaragua–investigation of structural deformation as thecause of slope instability using remote sensing:Journal of Volcanology and Geothermal Research,v. 105, p. 43-63.

Scott, K.M., Vallance, J.W., Kerle, N, Macías, J.L.,Strauch, W., Devoli, G., in press, Catastrophic,precipitation-triggered lahar at Casita volcano,Nicaragua—Flow transformations, flow bulking,and future mitigation stratigies.

Sheridan, M.F., Bonnard, C., Carreno, R., Siebe, C.,Strauch, W., Navarro, M., Calero, J.C., andTrujillo, N.B., 1999, Report on the 30 October1998 rockfall/debris avalanche and breakout flowof Casita volcano, Nicaragua, triggered byHurricane Mitch: Landslide News, n. 12, p. 2-4.

Vallance, J. W., Siebert, L., Rose, W. I., Girón, J, andBanks, N. G., 1995, Edifice collapse and relatedhazards in Guatemala: J. Volcanol. andGeotherm. Res., v. 66, p. 337-355.

Vessel, R.K. and Davies, D.K., 1981, Nonmarinesedimentation in an active fore arc basin, SEPMSpecial Publication no. 31, p. 31-45.


ADDITIONAL SUGGESTED READINGADDITIONAL SUGGESTED READINGADDITIONAL SUGGESTED READINGADDITIONAL SUGGESTED READINGADDITIONAL SUGGESTED READINGBlong, R.J., 1984, Volcanic hazards: Academic Press,

Orlando, 424 p.

Tilling, R.I., ed., 1989, Volcanic hazards: Shortcourse in geology, v. 1, American GeophysicalUnion, Washington, D.C., 123 p.

Vallance, J.W. 2000, Lahars: in Sigurdsson, H.,Houghton, B., McNutt, S., Rymer, H., and Stix,J., Encyclopedia of Volcanoes, Academic Press,San Diego, p. 601-616.

END NOTESEND NOTESEND NOTESEND NOTESEND NOTES[1] Information about the 1541 debris flow that

destroyed Cuidad Vieja derives from Feldman(1993). Other geologic data upon which thisreport is based come chiefly from theunpublished work of Otoniel Matías.

[2] Information about the Casita flow derives fromSheridan et al. (1999), Kerle and Van Wyk deVries (2001), Kerle (in press), and Scott et al.(in press).

[3] Eruptions of Fuego are described in Bonis andSalazar (1973), Davies et al. (1978), and Vesseland Davies (1981).

[4] The maximum extent of the proximal lahar-hazard zone derives from the formula H/L ≈ 0.5,in which H is the elevation difference betweenthe summit of Agua and the hazard boundaryline and L is the horizontal distance from thecenter of the summit crater to the hazardboundary line (see, for example, Iverson et al.,1998). The steep slopes within the proximalzone are the likely source of future lahars.More gentle slopes outside the proximal zoneare areas where lahars will funnel into valleys,travel downstream, and spread out on alluvialfans.

[5] We constructed lahar-hazard zones by choosingdesign-lahar volumes of 500,000; 1,000,000;2,000,000; 4,000,000 cubic meters. We thenmodeled a lahar for each volume using therepeatable empirical model and digitalcartographic technique described in Iverson etal. (1998). The model requires the choice of areasonable range of volumes for each volcano.It then uses these volumes to compute averagecross-sectional areas and areas of inundation foreach modeled lahar. The GIS based computerprogram, LAHARZ (Iverson et al., 1998) thencalculates the extent of inundation downstreamin each drainage that heads on the volcano.


Shilling and others — LA

HA

R-HA

ZARD

S ALA

HA

R-HA

ZARD

S ALA

HA

R-HA

ZARD

S ALA

HA

R-HA

ZARD

S ALA

HA

R-HA

ZARD

S AT AG

UA

VOLCA

NO

, GU

AT A

GU

A VO

LCAN

O, G

UA

T AG

UA

VOLCA

NO

, GU

AT A

GU

A VO

LCAN

O, G

UA

T AG

UA

VOLCA

NO

, GU

ATEMA

LATEM

ALA

TEMA

LATEM

ALA

TEMA

LA —

U.S. Geological Survey — Open-File Report 01-432

Printed on recycled paper

Lahar Hazards at Agua Volcano, Guatemala - USGS · Lahar Hazards at Agua Volcano, Guatemala 1 ......

Documents

Transcript of Lahar Hazards at Agua Volcano, Guatemala - USGS · Lahar Hazards at Agua Volcano, Guatemala 1 ......