Eos, Vol. 82, No. 16, April 17, 2001
V O L U M E 82
N U M B E R 16
APRIL 17, 2001 EOS, T R A N S A C T I O N S , A M E R I C A N GEOPHYSICAL
PAGES 185-192
UNION
Gauging Short-term Volcanic Hazards at Popocatepetl PAGES 1 8 5 , 1 8 8 - 1 8 9
Eruption History
During late D e c e m b e r 2000, the giant volcano Popocatepetl near Mexico City exhib ited violent explosions. About 20,000 people evacuated their h o m e s for a week to 10 days before returning. On January 2 2 , 2 0 0 1 , an even larger explosion occurred.This article explores the short-term hazards that are prob able at this volcano. Popocatepetl, which means "smoking moun tain" in the language of the Aztecs, stands at the southern end of an 80-km-long chain that trends north-south and divides the basin of Mexico to the west from the basin of Puebla to the east."Popo" is only 60 km southeast of Mexico City and 4 0 km west of the city of Puebla.The c o m b i n e d population of these two metropolitan areas e x c e e d s 30 million, so the D e c e m b e r 2000 activity has justifiably received intense public scrutiny. The current d o m e growth and explosive activity present volcanologists and civil protection authorities with vexing problems that stem from our insufficient understanding of how eruptions evolve at Popo. Large Plinian eruptions have occurred at Popo with intervals ranging from 1000 to 3000 years and their ages are fairly well known. In contrast, the historic and geologic record of more frequent, small-to-moderate eruptions is not as clear, and it may b e difficult to reconstruct their o c c u r r e n c e and characteris tics with accuracy. Important questions now facing public safety officials revolve around prudent decisions based on the perceived effects of expected short-term events. What is the prognosis for the next few months and years? Volcanic activity at Popo is likely to slowly evolve as the crater fills with lava, unless the final event (1919-1927) proves to b e the end of its activity Rock avalanches and pyroclastic flows could produce source materials for lahars.The maximum possible lahar, based on the size of the glacier, is about 10 rn.Our models (Figure 1) show that future pyroclastic flows and lahars could threaten the same general areas affected by lahars in the past sev eral hundred years. However, a catastrophic event does not seem likely in the short term.
Little is known about Popo's early geologic history The oldest rocks found at Popo so far have not b e e n dated, but they are stratigraphically younger than rocks from Iztaccfhuatl volcano, which lies immediately to the north. This suggests that the locus of magma production has migrated southward over time. Popo's present c o n e is not the first huge volcanic edifice to evolve at this site, as evi d e n c e d by at least three older debris avalanche deposits that fan out toward the south [Siebe et al., 1995]. The most recent Mount St. Helens-type collapse of the c o n e occurred - 2 3 , 0 0 0 years ago, and the resulting debris avalanche trav eled more than 100 km to the south.The present c o n e started to grow at that time. Activity during the past 20,000 years included at least 7 large Plinian eruptions that produced extensive pumice-and-ash fallout, pyroclastic flows, and lahars. Each of these eruptions produced - 5 - 1 0 km of fragmented material.The most recent of these occurred 3
within the period of human settlement, about 5 0 0 0 , 2 1 0 0 , a n d 1100 years BP [Siebe et al, 1996],with devastating effects,as evidenced by numerous archaeological remains buried by pumice, ash, and lahars. People have repeatedly repopulated the area b e c a u s e of the volcano's long repeat time and the availability of water and productive soil. R e c u r r e n c e of such a cataclysmic Plinian eruption in the near future would certainly represent a volcanic disaster of unprecedented dimensions. The stratigraphic record of volcanic activity between cataclysmic eruptions is poorly pre served and difficult to date radiometrically. Popo has erupted several times s i n c e the Spanish conquest in the early 16th century, but documentation of these events by witnesses is fragmentary and varies in quality [Waitz, 1921].These historic eruptions s e e m to have a c o m m o n characteristic: energy release was relatively gentle, with repeated formation of small d o m e s inside the summit crater. Related volcanic explosions produced 1-10 km-high ash plumes with a c c o m p a n y i n g ashfall.Such activity lasted for several years to a few d e c a d e s and no major damage or casualties were reported. The pattern of activity during these smaller eruptions is insufficiently understood to c o n n e c t them with cataclysmic eruptions.
8
Fig. 1. Computer simulation of potential pyroclastic flow and lahar distributions. Red lines trace promi nent pyroclastic flow paths. Filled areas represent potential inundation limits of lahars with volumes of 10 m (red zones) and 1(5 m (yellow zones). Original color image appears at the back of this volume. ?
Eos, Vol. 82, No. 16, April 17, 2001 Present Eruption and Prognosis for the Next 5 Years The present eruptive activity started on D e c e m b e r 21,1994, at 1.30 A.M. local time. A dense ash plume rose in pulses from the crater floor following initial vent-clearing explosions. Increased fumarolic and seismic activity during the prior 2 years led the news media and scientists to report increasing con cern [see Global Volcanism Network Bulletins, 1994].During the first hours,silt-sized ash reached several towns east and northeast of the volcano, including the city of Puebla. In the afternoon of D e c e m b e r 21, the govern ment evacuated - 5 0 , 0 0 0 people from towns in the State of Puebla for almost 2 weeks.The emission of ash abated and almost c e a s e d completely during the s e c o n d half of 1995. On March 5,1996, ash emissions resumed with renewed intensity. By March 29, a new lava d o m e appeared in the crater. Within o n e month, the lava covered the entire crater floor to a thickness of at least 50 m. On April 30, a small volcanic explosion from the d o m e blasted meter-sized boulders from the crater, killing five mountaineers. Gravel 3 - 4 c m in diameter fell 6 km away, clasts as large as 0.5 c m fell on the roofs of Xalitzintla 12 km away and sand-sized ash fell in Tlaxcala 45 km to the northeast. S i n c e then, a total of 9 domes have formed in the crater. Dome growth is normally p r e c e d e d and a c c o m p a n i e d by harmonic tremor and increased fumarolic activity. At the end of each dome-building phase, volcanic explosions partially destroy the d o m e and eject incandescent, ballistic boul ders from the crater. The strongest explosion so far occurred on J u n e 30,1997, and not on D e c e m b e r 18,2000, as reported by the media. On both occasions, wind was blowing in the direction of Mexico City, where a thin coating of ash was deposited. In this context, the recent order to evacuate more than 40,000 people, as well as the coverage provided by the media, seems disproportionate. The current eruptive episode began on D e c e m b e r 12,2000, and a large volcanic explosion occurred on D e c e m b e r 18.The pat tern of this activity roughly matched that of J u n e 1997. More than 40,000 inhabitants were requested to evacuate on D e c e m b e r 16. Initially, only 15% of the population followed this advice.The number of evacuees increased after the D e c e m b e r 18 explosion. The total number of evacuees in camps varies greatly according to different sources, but it hardly reached more than 20,000 individuals. On D e c e m b e r 26, all were allowed to return home, since the activity had decreased. On January 22,2001, a larger explosive event produced an eruptive column that reached at least 8 km above the crater and produced two small pyroclastic flows that affected the gla cier on its northeast slopes. Shortly afterward, a small lahar c a m e down the Huiloac barran c a and reached the outer limits of Xalitzintla. Considering current and past activity, it seems probable that domes will continue to grow until the crater is entirely filled with lava.This
roads drainage s San Pedro lahar San Nicholas lahar r~l
TMVB
^
Fig. 2. Map of two lahars generated in the past 1200 years. The San Pedro lahars (SP) flowed to the west toward Amecameca (AM), and the San Nicolas lahar (SN) to the east initiated at the Alseseca channel. Cities shown include Atlixco (AX), Xalitzintla (XA), San Baltazar (SB), San Pedro (SP), and San Andreas (SA). Inset shows location of Popo (PC) and other active volcanoes as triangles. Cities, such as Mexico City (M) and Puebla (P), are squares.
Table 1. Data for mapped lahars Deposit/locality
Date
Thickness ( m )
Xalitzintla
1997
1
Planimetric area (rn ) 3.3 x 10
Volume* ( m ) r
3.3 x 10 '
San Nicholas
1100-1300 years ago
2
2.5 x 10
7
5.0 x 10
7
San Pedro
1100-1300 years ago
2
5.9 x 10
7
1.2 x 10
8
* Based on average thickness x planimetric area
might take at least a few more years at the current rate of d o m e emplacement. O n c e the crater is filled, lava will spill over the rim to the east and northeast, where the rim is low est. The viscous lava will form short flows, the e m p l a c e m e n t of which will b e a c c o m p a n i e d by small block-and-ash flows, which will not reach much further than - 5 - 6 km from the rim.This material might then b e c o m e remobilized and form lahars similar in volume to the San Nicolas lahar (Figure 2 ) . A major eruption seems improbable at this time.
Probable Hazardous Events In terms of the effects of the current eruptive episode on surrounding villages, the major
hazard must b e considered to b e lahar. Rela tively small, gravelly lahars occurred at Popocatepetl about 1,300 years ago [Siebe et al, 1997].These monolithologic debris flows took place at a time when Popo's crater was completely occupied by a dome. Contempora neous small lava flows and block-and-ash flows also spilled over the crater rim.This mod erate activity preceded by about 200 years the last major Plinian eruption, which occurred 1,100 years ago [Siebe et al, 1996]. These earlier lahars went down the Alseseca and Nexapa channels, which drain the upper c o n e and originate downstream from a glacier (Figure 2).The San Nicolas lahar [GonzalezHuesca et al, 1997],between 1,100 and 1,300
Eos, Vol. 82, No. 16, April 17, 2001 years old, is o n e debris-flow deposit that prob ably formed when lava flows and block-andash flows emitted from the summit d o m e interacted with ice or snow This flow traveled as far as 60 km from the source along a path down the Alseseca channel, currently inhabit ed by more than 30,000 people. Ceramic frag ments in beds beneath this deposit suggest that the region was inhabited at that time. On the night of June 14,1997, a debris flood was observed near the village of Santiago Xal itzintla, which is - 1 3 km from the summit in the previously dry Alseseca channel. The flood filled the stream channel with debris, but there were no important consequences for the town. On July 1,1997, the day following the largest eruption, an even larger debris flow reached Xalitzintla. Although some rainfall was report ed at A m e c a m e c a in the days prior to the flow, no rainfall apparently had b e e n seen in Xalitz intla. No precursory flooding occurred in the channel.The debris flow inundated cultivated areas and flooded a house on the channel margins. Both flows originated near the outlet tongue of the Ventorillo glacier at an elevation of 4800 m. At a January 1998 inspection, the glaciers showed noticeable ablation and lacked marginal ice cliffs that had b e e n observed in 1995. The 1997 deposits and erosional scars gener ally occupy the lower-most 2 - 1 0 m of the channel at distances to - 1 2 km from the gla cier terminus, except where the basal channel cross-section broadens. Most of the deposit occurs in many localities as levees at the highwater trimline approximately 10 m above the channel floor (Figure 3 ) and at a s e c o n d trimline several meters above the channel floor. Inboard of the trimlines, material has b e e n eroded.Twelve to 17 km from the glacier ter minus, the debris-flow deposit is mud-rich and fills a broad, rectangular channel to - 1 m depth. The available data are all consistent with the floods originating at least in part from melting of glacial ice by pyroclastic debris. How much water is available in the glacier for melting? Glacier surveys conducted in April 1995 showed that the ice then covered a surface area of 0.559 km .The western third of the ice mass has very few crevasses. A thick ness of 1 0 - 2 0 m was estimated using a digital elevation model of nearby bedrock contours intersecting the glacier; this is consistent with an estimate derived from glacier flow theory using an effective yield stress of 100 KPa for the observed glacier slope of - 2 5 ° . T h e central and eastern portion of the main ice mass is heavily crevassed, which suggests that the ice is thicker than 20 m on average. Ice motion of - 2 c m per day measured from ground surveys conducted with the total station is consistent with a glacier that is 30^10 m thick on average. Measurements of the ice thickness in the cen tral portion of the ice mass were taken using a monopulse radar. The ice thickness varies from about 10 m to 60 m,and the total volume of ice is 2.8 x 10 m . 3
Numerous observations from the 1985 Nevado del Ruiz eruption have shown that large amounts of meltwater can b e rapidly produced by mechanical erosion of a glacier
by pyroclastic density currents [Thouret, 1990]. Photographs taken after the eruptions clearly show the presence of 100-m-long furrows or grooves several meters wide and deep over parts of the glaciers. Other sections of the gla ciers showed evidence of smoothing by pyro clastic currents. The snout of o n e glacier, and hanging glaciers within another valley, were removed by ice avalanching that may have b e e n caused by the earliest pyroclastic currents. In other areas, there is evidence of energetic glacial drainage following the earlier pyroclastic flows. Mechanical ablation proba bly accounted for 1 0 - 1 5 m of glacier thinning in some localities, while up to 32% of the volume of the glaciers was removed, perhaps not all by pyroclastic erosion. A reasonable estimate of the amount of water in Popo's glacier available for melting during eruption might therefore b e - 1 x 10 m . ?
Horizontal distance, m Fig. 3. Cross-section through the 1997Xalitzintla lahar at section 7 (see asterisk in Figure 2 for location). A
SanS&ftazarPotentSallnundatSon V.E~8
£>
3
sac
Computer Simulations of Hazardous Areas Simulation of pyroclastic flows and rock ava lanches used the FLOW3D c o d e [Sheridan and Kover, 1996], which provides velocity his tories of particle streams along flow paths in three dimensions. The algorithm for the flows uses parameters for basal friction and viscosity similar to those of McEwen and Malin [1990]. FLOW3D simulations were used to create the hazard map at Popocatepetl [Macias et al, 1995]. Figure 1 models the Merapi-type blockand-ash flows that might o c c u r at Popo using a model basal friction coefficient of 0.09 and a viscosity parameter of 0.01. Bit-mapped and color-coded overlays of multiple themes, including the flow paths and velocities, were used to produce a realistic image useful for non-professional observers. The interactive platform of FLOW3D allows the observer to adjust the perspective and distance for the desired view. The use of cities and towns as a layer in the model allows the estimation of sites of potential loss of life and property Volcanic debris flows related to various sources eventually follow major river systems. For Popo, the Alseseca and Nexapa channels constitute these systems. Iztaccihuatl and rem nants of the ancient Popo edifice block flows from the upper flanks that are then diverted to the east or west at the Paseo de Cortez down the two major channels (Figure 1). Assuming likely source areas, particularly on the northern flank, inundation zones for lahar volumes of 10 and 10* m were simulated with Arclnfo using the LAHARZ model developed by Iverson et al. [1998] .Their GIS code calculates flow cross-sec tional areas to plot the width of the peak flow in the river valleys and uses planimetric area to map the flow extent. Figure 4 shows inundation wave heights at San Baltazar computed by this code. The source areas for the debris flows were based on energy c o n e models using FLOW3D code. The smaller-volume model lahar represents the water available from glacier abla tion by pyroclastic flows and the larger volume represents the water from complete melting of the current glaciers. Compare these volumes to the size of the prehistoric lahars of Table 1.
1000
15O0
2308
2«»
itm
ssos
«m
Distance |mj)
Fig. 4. Cross-section at San Baltazar (see Fig ure 2 for location) showing the inundation levels for lahars predicted by LAHARZ.
Recommendations Interpretation of small events such as Merapi-type block-and-ash flows and short-term expected lahars requires a much better topo graphic data set than is currently available. In this regard, SRTM data would be particularly useful in model construction, visualization, and analysis. New models are needed that can better simulate small flows of 10 to 10 m . These models should include erosion and deposition from the flows and should respond to topographic elevation differences of 10 m or less. Animated visualization of the simulated hazards is needed to help civil protection authorities and the general public understand the risk involved in specific inhabited areas. 6
8
3
Acknowledgments This work was partially funded by NASA grant NAG57579 and NAG53142.Work by Siebe and Macias was funded by grants to C. Siebe from Consejo Nacional de CienciaYTechnologia (27993T and 27994-T) and UNAM-DGAPA-Universidad Nacional Autonoma de Mexico] (IN 101199). Information on the glaciers and 1997 events was collected in conjunction with Melinda Brugman and Hugo Delgado. Facilities at the US. National Center for Geographic Information Analysis were used for GIS analysis. The Center for Compu tational Research at the University of Buffalo helped to develop the visualization models.
Authors Michael FSheridan, Bernard Hubbard, and Marcus I. Bursik, University at Buffalo, N.Y,USA; Michael Abrams, Jet Propulsion Laboratory Pasadena, Calif., USA; and Claus Siebe, Jose Luis Macias, and Hugo Delgado, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico. For additional information, contact Michael Sheridan, Department of Geology 876 Natural
Eos, Vol. 82, No. 16, April 17, 2001 S c i e n c e Complex, University at Buffalo, Buffalo, NY 14260 USA; E-mail:
[email protected]
References Gonzalez-Huesca,A. E., H. Delgado, and J. UrrutiaFucugauchi.The San Nicolas lahar at Fbpocatepetl vol cano (Mexico): A case study of a glacier-ice-melt-relat ed debrisflov^triggered by a blast at the outset of a Plinian eruption,/toc. IAVCEI, Puerto Vallarta, p. 94,1997. Iverson, R. M., S. PSchilling, and J.WVallance, Objec tive delineation of lahar-inundation hazard zones, Geol. Soc.Am. Bull, 110,972-984,1998. Macias, J. L., G. Carrasco-Nuriez, H. Delgado, A. L. Mar tin, C. Siebe, R. Hoblitt, M. FSheridan, and R. I.Tillmg, Mapa de Peligros delVolcdn Popocatepetl.
Mapa e Informe tecnico al Comite Cientifico Asesor de la Secretaria de Gobernacion (map with expla nation booklet), 14 pp.,Universidad Nacional Autonoma de M e x i c o - Centro Nacional de Prevencion, Mexico City Mexico, 1995. Siebe, C , M. Abrams, J. L., Macias, and J. Obenholzner, Repeated volcanic disasters in Prehispanic time at Popocatepetl, Central Mexico: Past key to the future?, Geology, 24,399-402,1996. Siebe, C , J. L. Macias, M. Abrams, M., S. RodriguezElizarraras, R. Castro, and H. Delgado, Quaternary explosive volcanism and pyroclastic deposits in east central Mexico: Implications for future hazards, in Guidebook for the 1995Annual Meeting of the Geolog ical Society of America, pp. 1^47, New Orleans, Louisiana, 1995.
Conference Focuses Attention on Sun-Earth System PAGES 1 8 5 - 1 8 6 The International Council for Scientific Unions' (ICSU) Scientific Committee on SolarTerrestrial Physics (SCOSTEP) has organized several scientific programs in the area of solar-terrestrial physics. One such program is the STEP-Results, Applications, and Modeling Phase (S-RAMP).Scheduled to run from 1998 through 2002, it is capitalizing on the vast data sets and powerful modeling techniques that were developed under STEP its predecessor. S-RAMP has three main goals: to enable detailed understanding of Sun-Earth coupling mechanisms; to facilitate effective information transfer between experimentalists, theoreticians, and modelers; and to demonstrate the successful benefits of the STEP endeavor to funding agencies, the media, and the general public. For more information about S-RAMr? see the program's Web site (http://www.ngdc. noaa.gov/stp/SRAMP/sramp.html). S-RAMP's first c o m p r e h e n s i v e c o n f e r e n c e was held in the beautiful northern J a p a n e s e city of Sapporo halfway through its 5-year international program. Besides enabling the effective flow of data and information throughout the wide S-RAMP community, the c o n f e r e n c e also emphasized the importance of conveying exciting s c i e n c e findings to the general public and to the media, as well as to funding a g e n c i e s . In so doing, we e x p e c t to maintain current support and generate new support to e n h a n c e our scientific pro grams, cross-disciplinary studies, and the practical applications of this knowledge of the Sun-Earth system to areas important to society. Over 800 papers were presented at the conference, and s o m e 590 scientists attended. There were 19 separate scientific symposia, three tutorial lectures, three workshops, and numerous affiliated side and splinter meetings. Clearly the c o n f e r e n c e covered all aspects of solar-terrestrial physics.
The First S-RAMP Conference Extreme solar, geomagnetic, and solar wind conditions were observed during April-May
1998 by an impressive international array of satellites and ground-based sensors. (This period was designated by the S-RAMP Steer ing Committee as a Special Analysis Interval.) Multiple coronal mass ejections, large solar flares, and high-speed solar wind streams led to a powerful s e q u e n c e of solar wind drivers of magnetospheric processes on Earth. One result of the combination of solar wind disturbances was the production of a deep, powerful, and long-lasting e n h a n c e m e n t of the highly relativistic electron population throughout the outer terrestrial radiation zone. A new radiation belt was formed and its characteristics were recorded by the Solar, Anomalous, and Magnetospheric Particle Explorer satellite. Scientists associated with the Solar and Heliospheric Observatory collected impressive images of solar eruptions spread ing out into s p a c e . Japan's Yohkoh satellite and NASAs Transition Region and Coronal Explorer satellite also recorded images of these disturbances. At geostationary altitude, NOAAs GOES-8 and -9 satellites measured solar X ray flare emissions and monitored the influx of energetic electrons, protons, and heavier ions into the magnetosphere. They also recorded magnetic storms in s p a c e as a c o m p l e m e n t to magnetograms recorded at ground observatories. The S-RAMP program also c o n c e i v e d and coordinated S p a c e Weather Month, which was held in S e p t e m b e r 1999, to study s p a c e weath er and events from their initiation on the Sun to their impacts at the Earth, including effects on space- and ground-based worldwide assets and the a c c u r a c y of forecasting techniques. Through broad international cooperation, the event provided as c o m p l e t e as possible cover age through worldwide coordinated spaceand ground-based observations. Three sched uled Incoherent Scatter Radar world days held S e p t e m b e r 1 5 - 1 7 , 1 9 9 9 , encouraged involvement of the user communities and participation of the forecasting community. A campaign Web site has been set up at http:// aoss.engin.umich.edu/intl_space_weather/ sramp/. The campaign is now moving into the post-event analysis phase.
Siebe, C , P Schaaf, and J. Urrutia-Fucugauchi, Mam moth b o n e s e m b e d d e d in a Late P l e i s t o c e n e lahar from Popocatepetl volcano, near Tocuila, Central M e x i c o , G e o l . S o c . A m . B u l l , 111, 1550-1562,1999. Sheridan,M.F,andT.Kover,FLOW3D.A computer code for simulating rapid, open-channel volcanic flows, P r o c , Workshop on the T e c h n o l o g y of Dis aster Prevention Against Local Severe Storms, pp. 1 5 5 - 1 6 3 , Norman, Okla., 1996 Thouret, J.-C, Effects of t h e November 1 3 , 1 9 8 5 eruption o n t h e snow p a c k a n d i c e c a p of Nevado del Ruiz Volcano, Colombia, J.Volcanol. Geotherm.Res., 4 / , 177-201,1990. Waitz, P, Popocatepetl again in activity ,4m. i Sci., 5th Ser.,1,S\-SS,\92\.
Origins of S-RAMP S-RAMP is the latest in a long line of interna tional programs developed under ICSU aus pices, and many have been begun through SCOSTEP The Comite Scientifique pour l'Annee Geophysique Internationale (CSAGI),a precursor ICSU body to SCOSTEP organized the International Geophysical Year (IGY) of 1957-1958 and created the World Data Center (WDC) system to preserve the data and prod ucts arising from IGY This was the first globally coordinated observing program of modern times, and it documented the first large-scale picture of Sun-Earth connections. The Interna tional Quiet Sun Year (IQSY) in 1964-1965 followed IGY and contained many of the STP observing networks, data processing plans, and archiving and dissemination systems devel oped for IGY In 1966, the STP part of CSAGI evolved into the Inter-union Commission on SolarTerrestrial Physics (IUCSTP). ICSU then created SCOSTEP from the IUCSTP activity in 1972 in recognition of the increasing scien tific importance of STP activities within the various ICSU bodies. The International Magnetospheric Study (IMS),SCOSTEP's main program from 1976 to 1979, was the first globally coordinated STP program to integrate satellites, airborne, ship, and ground-based observing platforms to study the forces that form and affect the mag netosphere. During IMS, ICSU recognized that solar-terrestrial physics topics were likely to remain important among many other ICSU bodies. This led to the designation of SCOSTEP as a "Scientific Committee." Such committees continue indefinitely, although they undergo periodic review by the ICSU. Two other SCOSTEP programs followed the IMS. Solar Maximum Year (SMY) was a small program from 1979 to 1981 focused specifically on solar physics. The Middle Atmosphere Pro gram (MAP) was a major, broad STP program coordinated by SCOSTEP from 1982 to 1985. Both IMS and MAP produced a good scientific picture of the physics of Sun-Earth connections in particular regions. The Solar-Terrestrial Energy Program (STEP) was SCOSTEP's umbrella program from 1990 to 1995 and was later extended through 1997 to take advantage of satellite arrays that were delayed in launching during STEP One of STEP'S goals was to build and operate models
Eos,Vol. 82, No. 16, April 17, 2001
Page 185
Fig. 1. Computer simulation of potential pyroclastic flow and lahar distributions. Red lines trace prominent pyroclastic flow paths. Filled areas represent potential inundation limits of lahars with volumes of 10 m (red zones) and 10 m (yellow zones). 7
s
Eos,Vol. 82, No. 17, April 24, 2001
Fig. 1. Dredging
operations
in pack
ice
conditions.
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