comparative lahar hazard mapping at volcan citlaltepetl mexico using srtm aster and dted 1 digital topographic data abstract in this study we evaluated and compared the utility of spaceborne srtm and aster dems with baseline dted 1 bald earth topography for mapping lahar inundation hazards from volcan citlaltepetl mexico a volcano which has had a history of producing debris flows of various extents in particular we tested the utility of these topographic datasets for resolving ancient valley filling deposits exposed around the flanks of the volcano for determining their magnitude using paleohydrologic methods and for forecasting their inundation limits in the future we also use the three datasets as inputs to a gis stream inundation flow model laharz and compare the results in general all three datasets with spatial resolution of 90 m or better were capable of resolving debris flow and lahar deposits at least 3 106 m3 in volume or larger canopy and slope related height errors in the aster and srtm dems limit their utility for measuring valley filling cross sectional area and deriving flow magnitude for the smallest deposits using a cross sectional area to volume scaling equation height errors in the aster and srtm dems also causes problems in resolving stream valley hydrography which controls lahar flow paths and stream valley morphology which controls lahar filling capacity however both of the two spaceborne dem datasets are better than dted 1 at resolving fine details in stream hydrography and erosional morphologies of volcaniclastics preserved in the valleys around the more humid eastern flanks of the volcanic range the results of laharz flow inundation modeling using all three dems as inputs are remarkably similar and co validate one another for example at citlaltepetl all lahar simulations show that the city of orizaba is the most vulnerable to flows similar in magnitude to or larger than one that occurred in 1920 many of the other cities and towns illustrated are built higher up on terrace deposits of older debris flows and are safe from all but the largest flows which occur less frequently finally asters 60 km swath width and 8 duty cycle presents a challenge for mapping lahar inundation hazards at e w oriented stream valleys in low latitude areas with persistent cloud cover however its continued operations enhances its utility as a means for updating the continuous but one time coverage of srtm and for filling voids in the srtm dataset such as those that occur along steep sided valleys prone to hazards from future lahars

understanding multi vent plinian eruptions at mt tongariro volcanic complex new zealand the andesitic tongariro volcanic complex in the central north island of new zealand comprises tens of vents along an actively extending graben past work has hypothesised that multiple vents may operate during a single explosive eruption episode providing an unprecedented hazard challenge for this region the stratigraphic record suggests an irregular clustering of eruption episodes over time including an unusual 200 year long period from 11 3 11 1 ka when several large explosive eruptions occurred we carried out new field mapping stratigraphy and sedimentology of the resulting pyroclastic deposits to identify seven episodes during this period locating the vent sites and calculating their climactic dynamic properties five of the episodes involved two or more vent locations that produced separate sub plinian plinian eruption columns eruption columns ranged between 16 and 24 km high and erupted volumes of 0 05 to 0 76 km3 indicating magnitudes of 4 to 5 each of these episodes show north to south unzipping of the tongariro graben with episodes beginning in northerly vents before being joined by vents south of these this included two scenarios northern edifice vents followed by central edifice ones or central edifice vents followed by southern ones in both cases the northerly vents generally display the greatest peak eruption magnitudes and the steadiest eruptions by contrast the southernmost vents formed along a fault controlled fissure like system these produced unsteady plumes and pyroclastic density currents the northward widening tectonic graben structure thus influences the pattern and style of these plinian style eruptions this study highlights a real possibility for an extreme hazard scenario involving successive large scale eruptions at volcanic systems in slowly rifting environments and sheds new light on the volcano tectonic interaction in such settings

the 1997 and 2001 lahars of popocatepetl volcano central mexico textural and sedimentological constraints on their origin and hazards abstract popocatepetl volcano is the most active volcano in central mexico and represents a high risk for more than 40 million people including mexico city in 1994 volcanic activity at popocatepetl renewed with the formation of ash rich plumes up to 7 km high in april 1996 lava emissions filled the crater and were accompanied by a series of explosions that produced eruptive columns up to 8 km high associated with explosive events in 1997 and 2001 two major lahars events occurred leaving debris flow deposits along huiloac gorge for as far as 15 km to the town of santiago xalitzinta the 1997 debris flow deposit originated after a prolonged emission of ash which caused glacier melt and a rapid release of water 1 107 m3 the amount of melting water was sufficient to gradually erode the river bed causing a flood that gradually transformed from a debris flow to a hyperconcentrated flow in contrast the 2001 debris flow that originated from a post depositional remobilization of a pumice flow deposit did not experience any flow transformation and carried 25 water at maximum the different behavior of these two lahars has important hazard implications both lahars reached xalitzintla town but at that point the 1997 lahar had already transformed into a sediment loaded stream flow the 2001 lahar by contrast maintained the characteristics of a debris flow being more competent and with greater destructive power what happened with these lahars demonstrates how important it is to take into consideration secondary volcanic phenomena even though they were not large flows they were capable of threatening populated areas even during periods of volcanic quiescence or reduced magmatic activity

volcanic hazard zonation of the nevado de toluca volcano mexico abstract the nevado de toluca is a quiescent volcano located 20 km southwest of the city of toluca and 70 km west of mexico city it has been quiescent since its last eruptive activity dated at 3 3 ka bp during the pleistocene and holocene it experienced several eruptive phases including five dome collapses with the emplacement of block and ash flows and four plinian eruptions including the 10 5 ka bp plinian eruption that deposited more than 10 cm of sand sized pumice in the area occupied today by mexico city a detailed geological map coupled with computer simulations flow3d titan2d laharz and hazmap softwares were used to produce the volcanic hazard assessment based on the final hazard zonation the northern and eastern sectors of nevado de toluca would be affected by a greater number of phenomena in case of reappraisal activity block and ash flows will affect deep ravines up to a distance of 15 km and associated ash clouds could blanket the toluca basin whereas ash falls from plinian events will have catastrophic effects for populated areas within a radius of 70 km including the mexico city metropolitan area inhabited by more than 20 million people independently of the activity of the volcano lahars occur every year affecting small villages settled down flow from main ravines

hydrogeochemical surveillance at el chichon volcano crater lake chiapas mexico abstract el chichon volcano has an eruptive record of at least 12 major eruptions in the holocene the latest one in march april 1982 causing the worst volcanic disaster in the history of mexico after about 6 centuries of quiescence this eruption destroyed a large dome and opened a 1 km wide crater a lake formed within the crater shortly after the eruption has been an important source of information about the evolution of the post eruptive processes the fluctuations of the crater lake water physicochemical parameters observed since 1983 have allowed in identifying hydrothermal waters and h 2 s rich gases influenced by tectonic and meteorological effects as the main contributors to its composition here we propose some methods to help in assessing the state of the volcano derived from the relative contribution of these factors as an easy to implement volcanic surveillance method in potentially active volcanoes with crater lakes or other volcano influenced water sources

the orange tuff a late pleistocene tephra fall deposit emplaced by a vei 5 silicic plinian eruption in west java indonesia a vei 5 dacite eruption emplaced the orange tuff about between 34 3 cal kbp and 17 2 cal kbp gunung salak is the unit s source and the orange tuff represents the most recent such eruption from any of the volcanoes southwest of bogor indonesia the orange tuff is the region s first such documented tephra fall deposit whose characteristics and phenocryst geochemistry make it readily identifiable over at least 1250 km2 magnetite compositions and temperature and fo2 estimates inferred from fe ti oxide compositions are particularly useful for identifying the unit deposit characteristics suggest that the eruption lasted 1 11 h with mass eruption rates of 1 0 8 3 108 kg s and a column height of 31 40 km the eruption s column height and the deposit s 2 5 11 km3 volume suggest that the unit was dispersed over a much wider area than mapped the unit is a marker bed throughout its mapped distribution and has potential to be applied over a much broader area as a regional marker bed the large population and infrastructure proximal to salak suggest that the unit should be considered in hazards assessments despite its age and the lack of subsequent similar eruptions

paleohydrology and sedimentology of a post 1 8 ka breakout flood from intracaldera lake taupo north island new zealand sudden releases of impounded water from lakes in volcanic regions constitute a major and frequently repeated hazard an outburst flood from taupo caldera new zealand released 20 km 3 of water within decades following an ignimbrite emplacing eruption ca 1 8 ka paleohydrologic reconstruction of the taupo flood provides estimates of peak discharge at the outlet in the range 17 000 35 000 m 3 s dimensionless analysis demonstrates that 1 failure of the barrier was essentially instantaneous 2 the event may be treated hydraulically as a dam break and 3 the peak discharge was a function of outlet geometry rather than lake volume or breach formation rate paleohydraulic reconstructions based on empirical relations derived from historic dam breaches yield only order of magnitude estimates of peak discharge calculations based on the physical dimensions of the outlet channel and hydraulic principles are likely to be more accurate and are in close agreement with computer implemented dynamic flow routing models the latter give peak discharges and maximum stage levels similar to constraints imposed by field evidence and estimates of flow depth and velocity the long duration of the taupo flood and the relatively narrow confined flood route resulted in minimal attenuation of the flood wave compared with modern dam breach events and flood deposits can be traced as far as 232 km downstream caldera lake breakout floods may be among the most far reaching hazards associated with volcanism

integrating multidisciplinary science modelling and impact data into evolving syn event volcanic hazard mapping and communication a case study from the 2012 tongariro eruption crisis new zealand abstract new zealand s tongariro national park volcanoes produce hazardous eruptions every few years to decades on 6 august 2012 the te maari vent of tongariro volcano erupted producing a series of explosions and a fine ash of minor volume which was dispersed rapidly to the east this manuscript presents a summary of the eruption impacts and the way these supported science communication during the crisis particularly in terms of hazard map development the most significant proximal impact was damage from pyroclastic surges and ballistics to the popular and economically important tongariro alpine crossing track the only hazard to affect the medial impact zone was a few mms of ashfall with minor impacts field testing indicated that the te maari ash had extremely low resistivity when wetted implying a very high potential to cause disruption to nationally important power transmission networks via the mechanism of insulator flashover this was not observed presumably due to insufficient ash accumulation on insulators virtually no impacts from distal ashfall were reported post event analysis of pm10 data demonstrates the additional value of regional air quality monitoring networks in quantifying population exposure to airborne respirable ash while the eruption was minor it generated a high level of public interest and a demand for information on volcanic hazards and impacts from emergency managers the public critical infrastructure managers health officials and the agriculture sector meeting this demand fully taxed available resources we present here aspects of the new zealand experience which may have wider applicability in moving towards improved integration of hazard impact information mapping and communication these include wide use of a wiki technical clearinghouse and email listservs a focus on multi agency consistent messages and a recently developed environment of collaboration and alignment of both research funding and technical science advice hazard maps were integral to science communication during the crisis but there is limited international best practice information available on hazard maps as communication devices as most volcanic hazard mapping literature is concerned with defining hazard zones we propose that hazard maps are only as good as the communications framework and inter agency relationships in which they are embedded and we document in detail the crisis hazard map development process we distinguish crisis hazard maps from background hazard maps and ashfall prediction maps illustrating the complementary nature of these three distinct communication mechanisms we highlight issues that arose and implications for the development of future maps

recent lahars at volcan de colima mexico drainage variation and spectral classification abstract volcan de colima is the most active volcano in mexico and represents a high risk for more than 500 000 people in 1998 the volcano renewed its activity with the extrusion of a lava dome and subsequent lava and block and ash flows during the recent period of activity pyroclastic products did not directly affect villages around the volcano however several lahars did we used lidar topographic coverage aster and landsat images for the recognition of morphological changes in the drainage system and lahar detection for lahar delineation we applied principal components analysis and canonical classification tasseled cap in order to perform a supervised image classification using the maximum likelihood rule algorithm laharz objective delineation of distal debris flow hazard zones has been used and tested using two topographic datasets with different resolutions which provided evidence of the importance of high resolution topographic coverage in hazard assessment finally a hazard map for lahars is presented showing that several villages and ranchos can be affected in contrast due to morphological changes produced by products of the intense explosive activity other populated areas such as la yerbabuena are outside of the high risk zone they could be affected by lahars only in case of cataclysmic eruptions such as the 1913 plinian event

the 26 may 1982 breakout flows derived from failure of a volcanic dam at el chichon chiapas mexico the eruptions of el chichon between 28 march and 4 april 1982 produced a variety of pyroclastic deposits the climactic phase on 3 april at 07 35 4 april at 01 35 gmt destroyed the central andesitic dome and fed pyroclastic surges and flows that dammed nearby drainages including the magdalena river by late april a lake had formed 4 km long and 300 400 m wide containing a volume of 26 10 6 m 3 of hot water at 01 30 on 26 may the pyroclastic dam was breached and surges of sediment and hot water soon inundated the town of ostuacan 10 km downstream this hot flood was finally contained at penitas hydroelectric dam 35 km downstream where one fatality occurred and three workers were badly scalded stratigraphic and sedimentologic evidence indicates that the rapidly draining lake initially discharged two debris flows followed by five smaller debris flows and water surges the main debris flows became diluted with distance and by the time they reached ostuacan they merged into a single hyperconcentrated flow with a sediment concentration of 30 vol deposits from this hyperconcentrated flow were emplaced for 15 km as far as the confluence with another river the mas pac below which the flow was diluted to sediment laden streamflow the minimum volume of the breakout flow deposits is estimated at 17 10 6 m 3 from high water marks flow profiles and simulations utilizing the dambrk code from the national weather service we calculated a maximum peak discharge of 11 000 m 3 s at the breach this maximum peak discharge occurred 1 h after initial breaching the calculations indicated that 2 h were required to drain the lake

a 550 year old plinian eruption at el chichon volcano chiapas mexico explosive volcanism linked to reheating of the magma reservoir 1 some 550 years ago 1320 1433 a d a powerful plinian eruption at el chichon volcano in southern mexico produced a widespread pumice fall deposit we subdivided the deposit into three parts on the basis of structural and textural characteristics pumice lithology and density granulometry and petrologic geochemical attributes the deposit covers an area of 1500 km2 within the 1 cm isopach and has a minimum estimated bulk volume of 2 8 km3 1 1 km3 dense rock equivalent dre its eruptive column reached an altitude of 31 km consideration of field evidence the presence and nature of mafic enclaves and chemical data strongly suggest that the 550 year b p eruption is linked with the intrusion of a high temperature basaltic magma into preexisting but stagnated trachyandesitic magma beneath el chichon thorough mixing of the two magmas produced a compositionally uniform hybrid trachyandesite magma average sio2 55 3 wt which subsequently underwent crystal growth and gas exsolution ultimately overpressurizing the zoned magmatic system to erupt explosively on the basis of el chichon s known eruptive history the intrusion mixing event occurred sometime after the 900 year b p eruption the hybrid magma had a preeruption temperature of 820 830 c and was water undersaturated 5 6 wt h2o at pressures of 2 2 5 kbar

strike slip faults and k alkaline volcanism at el chichon volcano southeastern mexico abstract el chichon volcano is located in the northern part of the state of chiapas in southeastern mexico the volcano is situated within the transcurrent fault province characterized by a series of rising and sinking blocks bounded by sinistral strike slip faults the basement around el chichon is a sequence of jurassic evaporates cretaceous limestones and tertiary terrigenous rocks folded into open and an echelon structures the main structures in the area are the la union and caimba anticlines and the buena vista syncline the region is cross cut by two conjugate fault systems a dextral strike slip n s trending set and a sinistral strike slip e w set the most significant fault of the latter system is the san juan fault which controlled the emplacement of a basaltic dike near the village of chapultenango some 1 1 ma ago and the activity of el chichon during the last 0 2 ma additionally a series of n45 e trending faults chapultengo fault system have produced a half graben geometry of blocks on top of which el chichon has been emplaced microstructures such as slickensides tension fractures layer parallel slip stylolites and macro and meso folds of the sedimentary rocks indicate that during the late miocene the el chichon area was affected by a maximum principal stress 1 oriented n70 e a minimum principal stress 3 oriented n20 w and a vertical intermediate principal stress this stress pattern indicates that the area underwent a strike slip motion that produced widespread deformation the occurrence of crustal earthquakes

calculation of lahar transit times using digital elevation data abstract volcanic debris flows or lahars represent a significant hazard because of their rapid emplacement long runout distances and tremendous destructive potential accurate knowledge of advance rates and flow depths is therefore critical to hazard mitigation in lahar prone areas with the increasing availability of digital topographic data models of lahar transit can now be applied to better representative descriptions of natural topography with the expectation of improved hazard predictions using an elementary model of lahar transport dynamics we have developed a mathematical treatment of lahar propagation over digital topography our results show that flow depths and transit times depend on the cumulative effects of changes in local slope along the flow path these cumulative effects can be significant in predicting lahar advance rates and transit times in adapting the continuum model to digital topography we treat the changes in elevation between each adjacent pair of elevations as contiguous inclined planes and establish new boundary conditions sequentially for all downstream intervals to satisfy both local and total volume conservation requirements thus we are able to derive transit times and the evolution of flow velocity and depth profile as a function of distance x and time t to illustrate the usefulness of this approach we have applied the model using parameters typical of large volume 10 6 to 10 7 m 3 long runout 25 50 km lahars at mt ruapehu new zealand by discretizing an analog topography model into n equal sized intervals we demonstrate that as n increases the predicted transit time over the digital topography decreases asymptotically several hundred intervals are required to achieve convergence thus yielding estimates of the minimum resolution of the digital topography 10 m vertical 250 m horizontal required to give accurate transit time assessments we also show that one cannot simply model irregular topography as a drop in elevation over a runout distance without risking significant errors in transit time predications the result that transit time predictions decrease with increasing topographic resolution has significant implications for both hazard assessment and the ability to provide timely warnings to communities in the flow paths of lahars

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

the sensitivity of a volcanic flow model to digital elevation model accuracy experiments with digitised map contours and interferometric sar at ruapehu and taranaki volcanoes new zealand abstract a growing trend in the field of volcanic hazard assessment is the use of computer models of a variety of flows to predict potential areas of devastation these can be compared against historic and geologic evidence of past events for model calibration or used to construct hazard zone maps for mitigation and planning purposes the accuracy of these computer models depends on two factors the nature and veracity of the flow model itself and the accuracy of the topographic data set over which it is run all digital elevation models dems contain innate errors the nature of these depends on the accuracy of the original measurements of the terrain and on the method used to build the dem in this paper we investigate the effect that these errors have on the performance of a volcanic flow model designed to delineate areas at risk from lahar inundation the model was run over two dems of southern ruapehu volcano derived from 1 digitised 1 50 000 topographic maps and 2 airborne c band synthetic aperture radar sar interferometry obtained using the nasa airsar system on steep slopes of 4 or more drainage channels are more likely to be incised deeply and flow paths predicted by the model are generally in agreement for both dems despite the differing nature of the source data over shallow slopes

reappraisal of the 1982 eruptions of el chichon volcano chiapas mexico new data from proximal deposits additional data from proximal areas enable a reconstruction of the stratigraphy and the eruptive chronology of phases iii and iv of the 1982 eruption of el chichon volcano phase iii began on 4 april at 0135 gmt with a powerful hydromagmatic explosion that generated radially fast moving 100 ms 1 pyroclastic clouds that produced a surge deposit s1 due to the sudden reduction in the confining pressure the process continued by tapping of magma from a deeper source causing a new explosion the ejected juvenile material mixed with large amounts of fragmented dome and wall rock which were dispersed laterally in several pulses as lithic rich block and ash flow f1 partial evacuation of juvenile material from the magmatic system prompted the entrance of external water to generate a series of hydromagmatic explosions that dispersed moisture rich surge clouds and small volume block and ash flows iu up to distances of 3 km from the crater the eruption continued by further decompression of the magmatic system with the ensuing emission of smaller amounts of gas rich magma which with the strong erosion of the volcanic conduit formed a lithic rich plinian column that deposited fallout layer b associated with the widening of the vent an increase in the effective density of the uprising column took place causing its collapse block and ash flows arising from the column collapse traveled along valleys as a dense laminar flow f2 in some places flow regime changes due to topographic obstacles promoted transformation into a turbulent surge s2 which attained minimum velocities of approximately 77 ms 1 near the volcano the process continued with the formation of a new column on 4 april at 1135 gmt phase iv that emplaced fall deposit c and was followed by hydromagmatic explosions which produced pyroclastic surges s3

morphometrical and geochronological constraints on the youngest eruptive activity in east central europe at the ciomadul csomad lava dome complex east carpathians abstract the timing of late pleistocene volcanic activity of the ciomadul csomad dacitic lava dome complex site of the youngest eruptions in the carpathians has been constrained by morphometric analysis and radiometric chronology pelean domes and asymmetric domes coulees built up the volcano including the central edifice that hosts the youngest twin craters of mohos mohos peat bog and lake st ana szent anna a comparative digital elevation model dem based morphometric analysis of lava domes 29 worldwide examples including 5 domes from ciomadul shows that it is the mean slope of the upper dome flank that correlates best with age although the logarithmic relationship is only moderately strong r 0 80 slope characteristics of the ciomadul domes fit to those of 10 100 ka old domes these young ages contradict the previous k ar dates giving as old as 1 ma ages on a number of domes but are supported by ongoing u pb and u th he zircon dating the latter methods constrain the whole volcanic activity to the past 250 ka and the emplacement of most lava domes within the period of 150 100 ka the volcanism at ciomadul produced alternating effusive and explosive eruptions including lava dome collapses and successive crater formations the latest possibly subplinian explosive event formed the well preserved st ana crater radiocarbon dating of organic remains from a sediment core that reached 11 m into the lacustrine infill of st ana suggests that the crater was formed prior to 26 000 years bp

morphology of ash aggregates from wet pyroclastic surges of the 1982 eruption of el chichon volcano mexico the detailed stratigraphic study of the pyroclastic surge units s1 iu and s3 produced during the most violent phases of the 1982 eruption of el chichon volcano contains a complex succession of hydromagmatic events triggered by the interaction of different proportions of magma and external water component analyses of the horizons within single units reveal that almost all wet and cohesive horizons contain ash aggregates based on their morphology and internal structure four different types of aggregates were distinguished a accretionary lapilli b armored lapilli c irregular aggregates and d cylindrical aggregates the first three types have been described in the volcanological literature field and experimental studies cylindrical forms are reported here for the first time these hollow cylindrical aggregates consist of concentric layers of crystals and glass fragments set in a finer grained matrix they formed around millimeter size foliage fragments that are locally preserved in the interior of the aggregates as scorched or completely carbonized vestiges sem analyses suggest different mechanisms of formation for the four types of aggregates irregular aggregates and armored lapilli formed nearly instantaneously whereas accretionary lapilli and cylindrical aggregates resulted from progressive aggregation of ash in different regions of the eruptive cloud

the latest explosive eruptions of ciomadul csomad volcano east carpathians a tephrostratigraphic approach for the 51 29 ka bp time interval abstract the most recent mainly explosive eruptions of ciomadul the youngest volcano in the carpatho pannonian region have been constrained by detailed field volcanological studies major element pumice glass geochemistry luminescence and radiocarbon dating and a critical evaluation of available geochronological data these investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of ciomadul s twin craters st ana and mohos that received tephra deposition during the last eruptions of the volcano our analysis shows that significant explosive activity collectively called eppa early phreatomagmatic and plinian activity started at ciomadul in or around the present day mohos the older crater at 51 ka bp these eruptions resulted in a thick succession of pyroclastic fall deposits found in both proximal and medial distal localities around the volcano characterized by highly silicic rhyolitic glass chemical compositions ca 75 2 79 8 wt sio 2 the eppa stage was terminated by a subplinian plinian eruption at 43 ka bp producing pumiceous pyroclastic fall and flow deposits of similar glass composition probably from a proto st ana vent located at or around the younger crater hosting the present day lake st ana after a quiescent period with a proposed lava dome growth in the st ana crater a new explosive stage began defined as mpa middle plinian activity in particular a significant two phase eruption occurred at 31 5 ka bp producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of sf ana and followed by pumiceous fallout from a plinian eruption column related pyroclastic deposits show a characteristic less evolved rhyolitic glass composition ca 70 2 74 5 wt sio 2 and occur both in proximal and medial distal localities up to 21 km from source the mpa eruptions that may have pre shaped a crater similar to but possibly smaller than the present day st ana crater was followed by a so far unknown but likewise violent last eruptive stage from the same vent creating the final morphology of the crater this stage referred to as lspa latest st ana phreatomagmatic activity produced pyroclastic fall deposits of more evolved rhyolitic glass composition ca 72 8 78 8 wt sio 2 compared to that of the previous mpa stage according to radiocarbon age constraints on bulk sediment charcoal and organic matter from lacustrine sediments recovered from both craters the last of these phreatomagmatic eruptions that draped the landscape toward the east and southeast of the volcano occurred at 29 6 ka bp some 2000 years later than the previously suggested last eruption of ciomadul

tracing mineralization history from the compositional textures of sulfide association a case study of the zhenzigou stratiform zn pb deposit ne china abstract the qingchengzi orefield located in northeastern china hosts more than ten pb zn deposits and several au ag deposits among those the zhenzigou zn pb deposit displays a typical stratiform morphology comprising ore bodies in layers and lenses the ore minerals are simply composed of sphalerite galena pyrite and pyrrhotite together with minor arsenopyrite marcasite and argentite a sulfide association of sphalerite galena pyrite arsenopyrite was selected for this study the interior compositional texture of the sulfide association was investigated by means of la icpms spot and mapping analysis with the aim of constraining the ore genesis fluid evolution history and element partitioning behavior the results show that three distinct fluids were involved in the mineralization namely an episode of sedimentary fluids at 2052 ma which is responsible for the precipitation of pyrite core py0 an episode of metamorphic fluids at 1800 ma which formed an overgrowth of pyrite py 1 and new crystallization of sphalerite sph1 and arsenopyrite aspy1 and a final episode of hydrothermal fluids related to the triassic magmatism forming another overgrowth of pyrite py2 sphalerite sph2 and arsenopyrite aspy2 together with minor precipitation of galena ga the sedimentary fluids are relatively low in temperature 300 c and have remobilized as co and ni but only at mineral grain scale the late metamorphic and magmatic fluids are enriched in in cd au as ag cu pb sb sn co and ni and depleted in bi w mo te and se the partitioning of most of the metals from the fluids into the sulfide minerals was controlled by the metals availability in the fluids and by the compatibility with crystal structure through direct or coupled substitutions pyrite acts as the main host of co ni pb and as arsenopyrite hosts a major amount of sb and pb and a minor amount of au sphalerite is the primary host of cd in cu and the secondary host of ag and sn galena is the primary host of ag sb sn and subordinately hosts cd in and as in particular a remarkable amount of in and cd was carried by the hydrothermal fluids associated with the triassic magmatism indicating that the contribution of magmatic hydrothermal fluids to the mineralization is significant in conclusion our in situ geochemical evidence of sulfide minerals reinforces a sedimentation metamorphism magmatic hydrothermal reworking model for the zhenzigou stratiform zn pb mineralization this case study underlines the significance of compositional textures of coexisting sulfide minerals when assessing the ore genesis overall our study demonstrates that by integrating trace element mapping and spot analysis on coexisting sulfide minerals it is possible to re construct the fluid evolution history resolve the metal behaviors associated with fluids evolution and review the contribution of individual fluids to mineralization

the 1982 eruptions of el chichon volcano mexico stratigraphy of pyroclastic deposits abstract following a repose period of 500 to 600 years el chichon volcano in se mexico erupted explosively during the months of march and april 1982 three major eruptions involving trachyandesite magma injected ash into the stratosphere on 29 march at 0515 gmt and on 4 april at 0139 and 1110 gmt the first major eruption generated only tephra fall which was dispersed ene in the troposphere over the yucatan peninsula and wsw in the stratosphere towards the pacific ocean the second eruption produced tephra fall and pyroelastic surges and pyroclastic flows by repeated collapse of a lithicrich eruption column the surge and flow activity devastated a roughly circular area 153 km 2 around el chichon to a distance of about 6 km from the vent nine villages within the zone were either partially or completely destroyed and loss of human life was perhaps as high as 2000 pyroclastic flows and surges were also generated during the third eruption although ash fall was the primary activity as a result of both the second and third eruptions tephra was transported ene in the troposphere and wsw in the stratosphere the total volume of material ejected during the three major eruptions 0 50 km 3 d r e is represented by tephra fall 0 37 km 3 pyroclastic surges 0 09 km 3 and pyroclastic flows and debris flows 0 04 km 3 as a result of the eruptions a new 1 km wide and 300 m deep crater was formed by the disruption and excavation of a pre existing summit dome

evaluation of geophysical mass flow models using the 2006 block and ash flows of merapi volcano java indonesia towards a short term hazard assessment tool abstract the dynamics and depositional processes associated with block and ash flows bafs are most commonly inferred to be a function of granular or inertial grain flow similar to debris flows and cold rock avalanches existing geophysical mass flow models are either based on frictional mohr coulomb behavior the titan2d model developed at the state university of new york at buffalo usa or another rheological law i e a constant retarding stress eventually adding some viscous and turbulent components the volcflow model developed at the laboratoire magmas et volcans clermont ferrand france the 2006 bafs of merapi present a rare opportunity to test these two well established models against a well constrained field example integration of high resolution field based data into numerical simulations allows the validity of these models to be tested and rapid quantification of best fit input parameters we first show that with the incorporation of spatially varying bed friction angles titan2d is capable of reproducing the paths runout distances areas covered and deposited volumes of the 2006 merapi flows over highly complex topography however some discrepancies with field data are noted and the velocity and travel time of the flows do not match entirely using a single free parameter a constant retarding stress simulations obtained with the volcflow model also reproduce the morphology and distribution of the natural deposits as well as the time of emplacement and velocities of the flows the results suggest that the performance of these models in simulating actual events is critically dependent on 1 the calibration of the model by using extensive field based data such as deposit distribution and processes of flow generation transport and deposition 2 the incorporation of a suitable numerical topographic dataset i e high resolution digital elevation model and 3 the choice of input parameters such as location and volume of the initial pile of material and source characteristics single or multiple dome collapse dome collapse duration and total volume of collapsed material sensitivity analyses and inundation maps based on the probability of impact were used to produce a suite of potentially inundated areas from future gravitational dome collapse events affecting the gendol valley and adjacent areas on the southern flank of the volcano our results provide the basis for defining hazard zonations of key areas at risk from bafs which will be generated during future comparable eruptions at merapi

numerical simulation of block and ash flows for different eruptive scenarios of the tacana volcanic complex mexico guatemala abstract the tacana volcanic complex tvc shared by mexico and guatemala is considered an active volcano that resumed phreatic explosions in 1949 and 1986 the tvc has recorded at least eight eruptions emplacing block and ash flows bafs around the volcanic edifice during the past 42 000 years the largest event generated the mixcun deposit some 1950 yr b p from san antonio volcano the youngest structure of the complex based on the eight mapped baf deposits of the complex we perform numerical simulations with the titan2d code to recreate the distribution and extent of these deposits the results were used to prepare the zonation of the tvc based on the surface bed friction angles which are related to the different morphologies of the volcano from this zonation and the features of the past baf deposits we define three new eruptive impact scenarios low medium and high to perform a hazard assessment of this phenomenon but considering the present morphology of the complex of the four eruptive centers next we ranged the input parameters for each case scenario to analyze the dispersal thickness and maximum runout of simulated flows from the numerical simulations we found that the most influential parameter in the model outputs is the basal friction angle which varied from 23 to 12 then we merged the eruptive scenarios simulated to construct new hazard maps for the different mass volumes simulated for each scenario these maps clearly evidenced that the mexican territory would be seriously affected in case of a renewed explosive activity of the tvc in fact even the partial collapse of any of the tvc domes would produce bafs capable to flow over 70 communities affecting ca 20 000 inhabitants as well as promote the generation of syn and post eruptive lahars if they flow into the main rivers that drain the volcano therefore these maps are a great advance to evaluate the destructive potential of the tvc and must serve as the basis for the construction of a new risk map by the local authorities to update the operative and evacuation plans of the region these actions would help to the 350 000 inhabitants living in a 35 km radius from the volcano s summit to be aware of the perils posed by the volcano and how to act and evacuate in case of a volcanic crisis

the 1982 eruptions of el chichon volcano mexico 2 observations and numerical modelling of tephra fall distribution tephra fallout from the a 1 march 29 0532 ut b april 4 0135 ut and c april 4 1122 ut 1982 explosive eruptions of el chichon produced three tephra fall deposits over southeastern mexico bidirectional spreading of eruption plumes as documented by satellite images was due to a combination of tropospheric and stratospheric transport with heaviest deposition of tephra from the ene tropospheric lobes maximum column heights for the eruptions of 27 32 and 29 km respectively have been determined by comparing maximum lithic clast dispersal in the deposits with predicted lithic isopleths based on a theoretical model of pyroclast fallout from eruption columns these column heights suggest peak mass eruption rates of 1 1 108 1 9 108 and 1 3 108 kg s maximum column heights and mass eruption rates occured early in each event based on the normal size grading of the fall deposits sequential satellite images of plume transport and the production of a large stratospheric aerosol plume indicate that the eruption columns were sustained at stratospheric altitudes for a significant portion of their duration new estimates of tephra fall volume based on integration of isopach area and thickness yield a total volume of 2 19 km3 1 09 km3 dre dense rock equivalent or roughly twice the amount of the deposit mapped on the ground up to one half of the erupted mass was therefore deposited elsewhere as highly dispersed tephra

volcan el chichon mexico pre 1982 s rich eruptive activity abstract mapping and sampling of the interior of el chichon volcano was made possible by the exposures of the 1982 explosion crater the 1 km diameter 200 m deep crater exposes rocks produced during several eruptive episodes volcanic domes talus breccias plinian airfall deposits and pyroclastic flow deposits of compositionally similar alkalic hornblende trachyandesites with phenocrysts of anhydrite all of the rocks except those leached of anhydrite have extremely high s contents el chichon consists of a volcanic dome complex airfall debris and pyroclastic outflow sheets prior to 1982 its last major activity was about 650 100 yr b p

holocene eruptive activity of el chichon volcano chiapas mexico geologic and radiometric age data indicate that el chichon was frequently and violently active during the holocene including eruptive episodes about 600 1250 and 1700 years ago and several undated older eruptions these episodes involving explosive eruptions of sulfur rich magma and associated dome growth processes were apparently separated by intervals of approximately 350 to 650 years some of el chichon s eruptions may correlate with unusual atmospheric phenomena around a d 1300 and possibly a d 623

the 1982 eruptions of el chichon volcano mexico 3 physical properties of pyroclastic surges two major pyroclastic surges generated during the 4 april 1982 eruption of el chichon devastated an area of 153 km2 with a quasi radial distribution around the volcano the hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation field evidence indicates voidage fraction of 0 99 in the surge cloud with extensive entrainment of air thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud the dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10 20 characterized by stoss side erosion and lee side deposition of 1 10 cm reversely graded laminae a systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals resulting in loss of at least 10 25 of the cloud mass due to winnowing out of fines during surge emplacement greatest fractionation from the 1 0 0 0 grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud extensive pumice rounding indicates abrasion during bed load transport flow of pyroclastic debris in the turbulent surge cloud was by combination of bed load and suspended load transport the surges are viewed as expanding pyroclastic gravity flows which entrain and mix with air during transport the balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence which persisted to the distal edge of the surge zone

parallel adaptive numerical simulation of dry avalanches over natural terrain high fidelity computational simulation can be an invaluable tool in planning strategies for hazard risk mitigation the accuracy and reliability of the predictions are crucial elements of these tools being successful we present here a new simulation tool for dry granular avalanches using several new techniques to create a highly accurate tool with a combination of good models and numerical methodologies highlights of our methodology are the use of a depth averaged model of the conservation laws and an adaptive grid godunov solver to solve the resulting equations the software is designed to run on distributed memory supercomputers and make use of digital elevation data dynamically i e refine the grid and input data to finer resolutions to better capture flow features as the flow evolves our simulations are validated using quantitative and qualitative comparisons to tabletop experiments and data from field observations our software is freely available and can be used on a range of hardware from inexpensive desktop computers to the largest supercomputers

modeling of pyroclastic flows of colima volcano mexico implications for hazard assessment the 18 24 january 1913 eruption of colima volcano consisted of three eruptive phases that produced a complex sequence of tephra fall pyroclastic surges and pyroclastic flows with a total volume of 1 1 km 3 0 31 km 3 dre among these events the pyroclastic flows are most interesting because their generation mechanisms changed with time they started with gravitanional dome collapse block and ash flow deposits merapi type changed to dome collapse triggered by a vulcanian explosion block and ash flow deposits soufriere type then ended with the partial collapse of a plinian column ash flow deposits rich in pumice or scoria the best exposures of these deposits occur in the southern gullies of the volcano where heim coefficients h l were obtained for the various types of flows average h l values of these deposits varied from 0 40 for the merapi type similar to the block and ash flow deposits produced during the 1991 and 1994 eruptions 0 26 for the soufriere type events and 0 17 0 26 for the column collapse ash flows additionally the information of 1991 1994 and 1998 1999 pyroclastic flow events was used to delimit hazard zones in order to reconstruct the paths velocities and extents of the 20th century pyroclastic flows a series of computer simulations were conducted using the program flow3d with appropriate heim coefficients and apparent viscosities the model results provide a basis for estimating the areas and levels of hazard that could be associated with the next probable worst case scenario eruption of the volcano three areas were traced according to the degree of hazard and pyroclastic flow type recurrence through time zone 1 has the largest probability to be reached by short runout b5 km merapi and soufriere pyroclastic flows that have occurred every 3 years during the last decade zone 2 might be affected by soufriere type pyroclastic flows 9 km long similar to those produced during phase ii of the 1913 eruption zone 3 will only be affected by pyroclastic flows 15 km long formed by the collapse of a plinian eruptive column like that of the 1913 climactic eruption today an eruption of the same magnitude as that of 1913 would affect about 15 000 inhabitants of small villages ranches and towns located within 15 km south of the volcano such towns

hazard map of el chichon volcano chiapas mexico constraints posed by eruptive history and computer simulations abstract el chichon volcano consists of a 2 km wide somma crater compound cone 0 2 ma old with peripheral domes with a central crater reactivated several times during the holocene the most recent eruption at el chichon occurred from march 28 to april 4 1982 resulting in the worst volcanic disaster during historical times in mexico killing more than 2000 people and destroying nine towns and small communities the volcanic hazard map of el chichon is based on detailed field work that documented twelve eruptions during the last 8000 years and computer simulations to validate the results computer simulations were first performed over pre 1982 topography mimicking the extent of the actual deposits produced and afterwards run over post 1982 topography these eruptions have produced pyroclastic fall surge flow and lahar deposits pyroclastic flows have different volumes and heim coefficients varying from 0 2 pumice flows to 0 15 block and ash flows and 0 10 ash flows simulations using flow3d and titan2d indicate that pumice flows and block and ash flows can fill the moat area and follow main ravines up to distances of ca 3 km from the crater with no effect on populations around the volcano on the other hand more mobile ash flows related to column collapse events can reach up to 4 km from the vent but will always follow the same paths and still not affect surrounding populations the energy cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event h l 0 1 and 0 2 and shows that surges may reach some towns around the volcano explosive activity also produced plinian columns higher than 27 km that were dispersed towards the ne by prevailing winds future fallout will seriously disturb the lives of more than 70 000 inhabitants of cities and towns located in a radius of 35 km from the volcano lahar events in the past originated from unconsolidated pyroclastic deposits with volumes varying from 1 to 4 10 6 m 3 for single pulses to a large one from dam breakout with a volume of 40 10 6 m 3 we used the laharz code to model future events with volumes of 1 2 and 3 10 6 m 3 that will reach as far as 10 14 and 16 km from the crater posing some danger to the communities of nicapa volcan and ostuacan even some time after the climax of the eruption

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

numerical simulations of block and ash flows using the titan2d flow model examples from the 2006 eruption of merapi volcano java indonesia we present titan2d simulations of two well characterized block and ash flow baf events of the 2006 eruption of merapi java indonesia that affected the gendol valley on the volcano s southern flank and adjacent densely populated interfluve non valley areas 1 a single dome collapse event to the south that generated one of the smaller post june 14 flows and 2 a sustained multiple dome collapse event also directed to the south that produced the largest flows of the 2006 eruption emplaced in the afternoon of june 14 using spatially varying bed friction angles titan2d is capable of reproducing the paths velocities runout distance areas covered and deposited volumes of these flows over highly complex topography the model results provide the basis for estimating the areas and levels of hazards associated with bafs generated during relatively short as well as prolonged dome collapse periods and guidance during future eruptive crises at merapi

numerical simulation of some lahars from mount st helens abstract an unsteady open channel model is used to simulate lahars discharge flow depth peak arrival time etc under the restriction of negligible volume and solid fraction variations and of channelled flow the model is able to deal with the propagation of steep fronts and transitions from a supercritical to a subcritical flow regime and vice versa conditions frequently occurring on account of the rapidity of lahar triggering mechanisms large water debris volumes are often mobilized in a very short time and of topographical characteristics the model is based on equations governing balance of mass and momentum while the energy dissipation term is expressed as a power function of the flow depth and discharge two past lahars at mount st helens the pine creek and muddy river lahars of may 18 1980 are simulated and the results obtained are discussed for these lahars the triggering mechanism was the melting of snow and ice due to pyroclastic flows and surges many millions of cubic meters of water mostly from the melting of ice and snow and sediments eroded material and pyroclastic products were mobilized in only a few minutes the simulation begins at some kilometers from the vent where lahar volumes reach an almost constant value and the flow is channelled the triggering mechanism plays a fundamental role in the downvalley destructive power of a lahar initial hydrographs characterized by steep slopes such as those occurring as a consequence of pyroclastic flows and surges rapidly flatten downvalley as predicted by the model conversely hydrographs with a prolonged peak discharge even if the peak value is smaller undergo little changes over distances of lens of kilometers with disastrous consequences as in the case of the 1980 north fork lahar at mount st helens triggered by the seismic shaking of an avalanche debris

estimation of risk probability for gravity driven pyroclastic flows at volcan colima mexico abstract mapped pyroclastic flow terminations at colima volcano were used to determine energy lines we assumed straight energy lines initial flow velocities of zero and flow movement starting from the volcano summit heim coefficients h l of the flows plotted on a histogram cluster in two distinct modes one corresponds to large pyroclastic flows pumice flows and block and ash flows for which heim coefficients range from 0 22 to 0 28 this group has a mean value of 0 24 and a standard deviation of 0 021 the other mode corresponds to small block and ash avalanches which have heim coefficients that range from 0 33 to 0 38 a mean value of 0 35 and a standard deviation of 0 025 no flow terminations yield heim coefficients in the range from 0 28 to 0 33 this break probably separates fluidized pyroclastic flows from less mobile hot rock avalanches plots of heim coefficients on arithmetic probability paper are approximate probability functions for the two types of flows heim coefficients calculated for straight lines that connect population centers with the volcano summit can be used with this type of graph to estimate the probability that either type of pyroclastic flow would reach the site we used this technique to determine risk probabilities for various localities around colima volcano these calculations indicate that laguna verde yerbabuena cofradia el fresnal el naranjal atenguillo la becerrera montitlan and san antonio have a probability ranging from 99 to 6 of being covered by large pyroclastic flows laguna verde and yerbabuena are the sites with the highest probability of being reached by small block and ash avalanches the depression situated south southwest of colima volcano is an area with a very high probability of being affected by the pyroclastic phenomena considered above the small avalanche produced by dome collapse of colima on april 16 1991 traveled along the barranca el cordoban toward the area of the highest probability on our map

volcanic hazard maps of the nevado del ruiz volcano colombia abstract although the potential hazards associated with an eruption of nevado del ruiz volcano were known to civil authorities before the catastrophic eruption there in november 1985 their low perception of risk and the long quiescent period since the last eruption 140 years caused them to wait for stronger activity before developing an eruption alert system unfortunately the eruption occurred suddenly after a period of relative quiet and as a result more than 25 000 people were killed although it was accurate and reasonably comprehensive the hazard map that existed before the eruption was poorly understood by the authorities and even less so by the general population because the scientific terminology and probabilistic approach to natural hazards were unfamiliar to many of them this confusion was shared by the communication media which at critical times placed undue emphasis on the possibility of lava flows rather than on the more imminent threat from mudflows in keeping with the popular but often inaccurate perception of volcanic eruptions this work presents an updated hazard map of nevado del ruiz that combines information on various hazardous phenomena with their relative probability of occurrence in order to depict numerical hazard levels that are easily comprehensible to nonspecialists and therefore less susceptible to misinterpretation the scale of relative risk is arbitrary ranging from five to one and is intended to provide an intuitive indication of danger to people property and crops the map is meant to facilitate emergency preparedness and management by political and civil authorities to educate the public concerning volcanic hazards and to assist in land use planning decisions

hazard estimation of the possible pyroclastic flow disasters using numerical simulation related to the 1994 activity at merapi volcano abstract a pyroclastic flow generated at merapi volcano on 22 november 1994 flowed down the boyong and krasak rivers which are located on the south slope of the volcano the flow greatly damaged the kaliurang and turgo areas following this event it was feared that another pyroclastic flow might cause additional damage to these areas because the lava dome continued to grow increasingly unstable there was also fear that other pyroclastic flows would affect other areas on the flanks of merapi volcano using a 2 dimensional numerical simulation the authors estimated the areas potentially affected by further pyroclastic flow activity numerical simulation has proved useful in determining potential areas of inundation on the south flank of merapi volcano although the simulations are sensitive to many input parameters we have determined that the strongest influence comes from initial flow direction and topography

quaternary eruptive history and hazard zone model at nevado del tolima and cerro machin volcanoes colombia the ice clad and fumarolic nevado del tourna volcano 4 39 n 75 20 w south of nevado del ruiz is offset toward the southeast from the axis of the volcanic ruiz tolima massif with respect to the major ne trending strike slip palestina fault it is composed of four units 1 a pre tolima plateau like basement of basaltic andesite lava flows of early quaternary age 2 a dissected ancestral tourna stratovolcano cut by a presumed collapse caldera of middle pleistocene age 3 an older tolima stratovolcano of late pleistocene age partly destroyed by a summit caldera and 4 composite domes of the cone shaped young and present tolima young tolima volcano is an andesitic and dacitic composite cone formed over the past 40 000 years within a 3 km wide caldera that opened around 0 14 ma deposits of welded and nonwelded pumice and scoria flows were emplaced toward the southeast rio combeima and northeast rio totare repeated growth of lava domes over the past 16 000 years is witnessed by thick block lava flows on the southern and eastern flanks and by block and ash or scoria rich pyroclastic flow deposits this activity occurred during at least six eruptives stages as follows el placer ca 16 200 14 000 yr b p romerales ca 13 000 12 300 yr b p canalones ca 11 500 9750 yr b p mesetas ca 7200 4600 yr b p encanto ca 3600 1700 yr b p and nieves historical interactions with the ice cap probably triggered debris flows that partly filled the combeima and totare valleys and formed the holocene terraces on the upper pleistocene volcaniclastic fans of ibagueand venadillo as much as 60 km from the source the latest major activity was a plinian eruption which deposited a pumice fall layer ca 3600 yr b p 0 5 km3 actual volume mainly toward the west and northwest minor tephra falls and debris flows occurred during the historical period before the reported 1918 and 1943 small phreatic events a general hazard zone map shows areas potentially affected by future eruptions both at nevado del tolima and at active cerro machin 12 km southward the extent of areas likely to be affected by tephra falls debris flows pyroclastic flows or surges debris avalanches and lava flows is shown subplinian and plinian eruptions of nevado del tolima were used to represent the moderate and large events to be expected 300 000 people live within a 35 km distance from those volcanoes which have exhibited a behaviour more explosive than nevado del ruiz despite the small sized ice cap debris flows are the most probable hazard for even a minor eruption because of the very steep slope gradient and because of probable interactions of hot eruptive products with ice and snow additionally scoria flows and debris avalanches can be directed toward the southeast and could be transformed into debris flows that would devastate the combeima valley and suburbs of ibaguecity where about 50 000 people live

mapping the volcanic hazards from soufriere hills volcano montserrat west indies using an image processor we have used a digital model of the topography of montserrat a simple mathematical model of gravitational flow and some assumptions of the way in which the next eruption will develop to create a map of the volcanic hazards from soufriere hills volcano this has been done using an image processing computer to simulate the deposits produced by pyroclastic flows this technique has the advantages over more traditional cartographic methods of spatial precision rapid computation of multiple eruption models and the explicit nature of the physical model used soufriere hills volcano is a small andesitic volcano characterized by a cluster of summit domes and an apron of pyroclastic flow deposits and mudflows upon which several thousand people now live most of the flanks were covered by deposits from a series of eruptions from 24000 to 16000 a bp though there is some evidence that dome growth and small pyroclastic flows have occurred since the modelling is constrained by field evidence from the deposits of previous eruptions although the evidence is not good enough to model individual flow units the cumulative deposits can be used from the eruption deposit models we have created a new type of map specifically for emergency planning this sequential hazard zone map attempts to portray the regions that would be at hazard from pyroclastic flows during successive stages from the start of an eruption whose energy release was increasing with time

development of lithic breccias in the 1982 pyroclastic flow deposits of el chichon volcano mexico abstract pyroclastic flow deposit f1 volume 0 02 km 3 produced during phase iii of the 1982 eruption of el chichon volcano mexico contains basal lithic breccias the breccia layers are well exposed in el platanar gully between 2 and 4 km east of the volcano crater the lithic breccias are inversely graded as defined by lithics dense juvenile blocks and pumice supported in a coarse sandy matrix composed of the same constituents the contact between the main body of the pyroclastic flow deposit and the lithic breccias is generally sharp and planar but not erosive in some outcrops it is gradational and is only shown by an alignment of lithic clasts the origin of these beds is interpreted to be due to a hydraulic jump in the moving pyroclastic flow formed after a pronounced slope break from 11 to 3 at the site where the flow began to be funnelled into the el platanar gully we have investigated the possible modes of formation of the lithic breccias with analog laboratory experiments the experiments show that coarse localized segregations could form through a number of mechanisms the field observations interpreted with the assistance of the laboratory results suggest that pyroclastic flow 1 which produced deposit f1 moved as a kind of density stratified flow with a basal lithic rich zone transporting larger particles and an upper less dense zone transporting smaller particles in suspension at the slope break flow 1 lost competence and dumped the largest particles forming a piled up breccia downstream somewhat smaller lithic particles may have been deposited as ballistics from a low angle jetlike structure comprising a hydraulic jump this deposit thins with distance downstream once the deposit was sufficiently thick on its upstream end particles may have been re entrained into the jet to be deposited further along the flow in a low angle downstream prograding bouldery dune reverse grading in the dune beds may result from kinetic sieving we suggest that planar contacts between the lithic breccias and the associated pyroclastic flow deposit may be the result of strong density and velocity gradients between the two parts of the flow

evaluating titan2d mass flow model using the 1963 little tahoma peak avalanches mount rainier washington the titan2d geophysical mass flow model is evaluated by comparing its simulation results and those obtained from another flow model flow3d with published data on the 1963 little tahoma peak avalanches on mount rainier washington the avalanches totaling approximately 10 10 6 m 3 of broken lava blocks and other debris traveled 6 8 km horizontally and fell 1 8 km vertically h l 0 246 velocities calculated from runup range from 24 to 42 m s and may have been as high as 130 m s while the avalanches passed over emmons glacier titan2d is a code for an incompressible coulomb continuum it is a depth averaged dshallow watert granular flow model the conservation equations for mass and momentum are solved with a coulomb type friction term at the basal interface the governing equations are solved on multiple processors using a parallel adaptive mesh godunov scheme adaptive gridding dynamically concentrates computing power in regions of special interest mesh refinement and coarsening key on the perimeter of the moving avalanche the model flow initiates as a pile defined as an ellipsoid by a height z and an elliptical base defined by radii in the x and y planes flow parameters are the internal friction angle and bed friction angle results from the model are similar in terms of velocity history lateral spreading location of runup areas and final distribution of the little tahoma peak deposit the avalanches passed over the emmons glacier along their upper flow paths but lower in the valley they traversed stream gravels and glacial outwash deposits this presents difficulty in assigning an appropriate bed friction angle for the entire deposit incorporation of variable bed friction angles into the model using gis will help to resolve this issue d 2004 elsevier b v all rights reserved

predicting the block and ash flow inundation areas at volcan de colima colima mexico based on the present day february 2010 status abstract maps of areas potentially affected by block and ash flows and associated ash clouds are here presented for the volcan de colima titan2d 2 0 1 code has been used to simulate block and ash flows using as an input volume that of the actual summit dome assessed at 2 10 6 m 3 while the energy cone model has been used to delimit the possible inundated area from associated ash clouds both merapi and soufriere type block and ash flows were generated using different basal friction angles and maintaining fixed the volume and the internal friction angle the setting of the input parameters takes into account some flow characteristics such as the stepwise aggradation of different pulses that piled up to form the total thickness of the block and ash flow deposits the outputs of the computational routines are reported as two maps describing the total thickness of the final deposits they predict that thick deposits will engulf the ravines descending from the main cone to the west south and southeast with expected maximum runouts between 4 5 and 7 km the associated ash clouds have slightly longer runouts and the model predicts they will inundate some higher grounds that are not affected by the concentrate underflows the presented maps represent useful tools for managing the current block and ash flow hazard at volcan de colima

geochemistry of the volcano hydrothermal system of el chichon volcano chiapas mexico the 1982 eruption of el chichon volcano ejected more than 1 km3 of anhydrite bearing trachyandesite pyroclastic material to form a new 1 km wide and 300 m deep crater and uncovered the upper 500 m of an active volcano hydrothermal system instead of the weak boiling point temperature fumaroles of the former lava dome a vigorously boiling crater spring now discharges 20 kg s of cl rich 15 000 mg kg and sulphur poor 200 mg kg of so4 almost neutral ph up to 6 7 water with an isotopic composition close to that of subduction type magmatic water d 15 18o 6 5 this spring as well as numerous cl free boiling springs discharging a mixture of meteoric water with fumarolic condensates feed the crater lake which compared with values in 1983 is now much more diluted 3000 mg kg of cl vs 24 030 mg kg less acidic ph 2 6 vs 0 56 and contains much lower amounts of s 200 mg kg of so4 vs 3550 mg kg with 34s 0 5 4 2 17 in 1983 agua caliente thermal waters on the southeast slope of the volcano have an outflow rate of approximately 100 kg s of 71 c na ca cl water and are five times more concentrated than before the eruption b r molina unpublished data relative n2 ar and he gas concentrations suggest extensional tectonics for the el chichon volcanic centre the 3he 4he and 4he 20ne ratios in gases from the crater fumaroles 7 3ra 2560 and agua caliente hot springs 5 3ra 44 indicate a strong magmatic contribution however relative concentrations of reactive species are typical of equilibrium in a two phase boiling aquifer sulphur and c isotopic data indicate highly reducing conditions within the system probably associated with the presence of buried vegetation resulting from the 1982 eruption all cl rich waters at el chichon have a common source this water has the appearence of a partially matured magmatic fluid condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in s due to anhydrite precipitation shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits red waters are ca so4 rich and have a negative oxygen isotopic shift probably due to ongoing formation of clay at low temperatures

third version of the hazard map of galeras volcano colombia copyright c 1997 elsevier science b v all rights reserved galeras is an andesitic stratovolcano whose activity is generally characterized by vulcanian eruptions based on 14 c dating the active cone is considered to be 5000 years old during that time six major periods of eruptive activity have been identified together with 45 individual events of pyroclastic flows tephra falls lava flows and lahars excluding those reported in historic time 500 years and those which have occurred since the first signs of the current activity 1988 the stratigraphy of the past 5000 years reveals that the most common events are pyroclastic flows constituting the principal volcanic hazard of galeras additionally lava extrusion tephra falls and lahars have also occurred but are lesser hazards the two previous hazard maps of galeras did not account for the studies mentioned above methodology for this revision of the volcanic hazard map of galeras is based on 1 probabilistic zoning of phenomena associated with eruptions that have occurred during the past 5000 years and 2 modeling of other phenomena which did not appear in the geologic record such as shock waves and ballistic projectiles the map consists of three categories of hazard zones high medium and low the zone of high hazard is defined principally by the distribution of pyroclastic flow deposits while the zone of low hazard is defined by tephra fall deposits the medium hazard is a transition zone and ideally if based on the geological record does not include pyroclastic flows however it is possible that a comparatively large pyroclastic flow could extend into this zone additionally this zone defines the possible trajectories of secondary lahars

using tree ring analysis to evaluate intra eruptive lahar activity in the nexpayantla gorge popocatepetl volcano central mexico abstract lahar activity is one of the most important processes capable of mobilizing large volumes of sediment and producing devastating effects on human populations and infrastructure estimating the frequency distribution and climatic controls on lahar activity is necessary for understanding how sediment is mobilized from hillslopes to channels and how the landscape is modified by this type of process in this study we evaluate the intra eruptive lahar activity in the nexpayantla gorge nw of popocatepetl volcano central mexico by using a dendrogeomorphological analysis of growth ring records of abies religiosa trees n 100 based on the identification of 322 growth disturbances gd and field evidences we identify 23 intra eruptive lahars that occurred from 1959 to 2013 by analyzing the lahar chronology and climatic data we observed that 83 of lahar activity coincides with moderate to strong cold and dry phases of el nino southern oscillation based on the seasonal timing of gd we explored the intra annual lahar activity we found that 43 of the lahars occurred in the latewood season from july to october when the mean summer monthly rainfall is 120 mm approximately 37 of lahars occurred during the first heavy rainfalls from march to june which corresponds to the earlywood season the remaining 20 of the lahar activity corresponds to the dormancy period winter season when snowmelt and or occasional strong rainfalls 100 mm day 1 occur the gd indicate that in nexpayantla gorge intra eruptive lahar activity takes place around every two years we also found that the effects of lahars are concentrated around the transitional and depositional zone of nexpayantla gorge

chemical composition of fumarolic gases and spring discharges from el chichon volcano mexico causes and implications of the changes detected over the period 1998 2000 abstract since the march april 1982 eruption of el chichon volcano intense hydrothermal activity has characterised the 1 km wide summit crater this mainly consists of mud and boiling pools fumaroles which are mainly located in the northwestern bank of the crater lake during the period 1998 2000 hot springs and fumaroles discharging inside the crater and from the southeastern outer flank agua caliente were collected for chemical analyses the observed chemical fluctuations suggest that the physico chemical boundary conditions regulating the thermodynamic equilibria of the deep rock fluid interactions have changed with time the chemical composition of the lake water characterised in the period 1983 1997 by high na cl ca 2 and so 4 2 contents experienced a dramatic change in 1998 1999 turning from a na cl to a ca 2 so 4 2 rich composition in june 2000 a relatively sharp increase in na and cl contents was observed at the same time so 2 h 2 s ratios and h 2 and co contents in most gas discharges increased with respect to the previous two years of observations suggesting either a new input of deep seated fluids or local variations of the more surficial hydrothermal system migration of gas manifestations enhanced number of emission spots and variations in both gas discharge flux and outlet temperatures of the main fluid manifestations were also recorded the magmatic hydrothermal system of el chichon is probably related to interaction processes between a deep magmatic source and a surficial cold aquifer an important role may also be played by the interaction of the deep fluids with the volcanic rocks and the sedimentary limestone and evaporites basement the chemical and physical changes recorded in 1998 2000 were possibly due to variations in the permeability of the conduit system feeding the fluid discharges at surface as testified by the migration of gas and water emanations two different scenarios can be put forward for the volcanic evolution of el chichon 1 build up of an infra crater dome that may imply a future eruption in terms of tens to hundreds of years 2 minor phreatic phreatomagmatic events whose prediction and timing is more difficult to constrain this suggests that unlike the diminished volcanic activity at el chichon after the 1982 paroxistic event the volcano hydrothermal fluid discharges need to be more constantly monitored with regular and more frequent geochemical sampling and at the same time a permanent network of seismic stations should be installed