seismic activity related to the 1991 eruption of colima volcano mexico ten years after the last effusive eruption and at least 15 years of seismic quiescence volcanic seismic activity started at colima volcano on 14 february 1991 with a seismic crisis which reached counts of more than 100 per day and showed a diversity of earthquake types four other distinct seismic crises followed before a mild effusive eruption in april 1991 the second crisis preceded the extrusion of an andesitic scoriaceous lava lobe first reported on 1 march during this crisis an interesting temporary concentration of seismic foci below the crater was observed shortly before the extrusion was detected the third crisis was constituted by shallow seismicity featuring possible mild degassing explosion induced activity in the form of hiccups episodes of simple wavelets that repeat with diminishing amplitude and accompanied by increased fumarolic activity the growth of the new lava dome was accompanied by changing seismicity on 16 april during the fifth crisis which consisted of some relatively large shallow volcanic earthquakes and numerous avalanches of older dome material part of the newly extruded dome which had grown towards the edge of the old dome collapsed producing the largest avalanches and ash flows afterwards block lava began to flow slowly along the sw flank of the volcano generating frequent small incandescent avalanches the seismicity associated with the stages of this eruptive activity shows some interesting features most earthquake foci were located north of the summit some of them relatively deep 7 11 km below the summit level underneath the saddle between the colima and the older nevado volcanoes an apparently seismic quiet region appears between 4 and 7 km below the summit level in june harmonic tremors were detected for the first time but no changes in the eruptive activity could be correlated with them after june the seismicity decreasing trend was established and the effusive activity stopped on september 1991

exploring the factors that influence the perception of risk the case of volcan de colima mexico abstract volcan de colima has increased its activity considerably since 1998 with four periods of effusion and since 2003 daily vulcanian explosions during 2005 the magnitude of the explosivity increased producing many pyroclastic flows two of which reached over 5 km from the volcano making them the largest events since the last plinian eruption in 1913 a significant risk is also presented by the lahar hazard with various examples of damage to infrastructure during the last few years and 23 people killed in 1955 nearly 5000 people live in small settlements within 15 km of the volcano since 1997 six studies have been carried out in the region in an attempt to define the relationship that exists between the population and its neighbour although the methodologies used were different each study considered the results of the previous and attempted to contribute further data to define geographical variation in the perception of risk the results of the studies highlight the minor role of increasing activity on risk perception and distance from the volcano was shown to not directly influence risk perception in most cases it is the combination of various socio cultural historical and political factors that defines the perception of volcanic risk within these villages by studying the social representation of the risk such complexity could be better understood the 1997 2000 information campaign evidently improved risk perception however it is clear that this type of program needs to be continued to achieve a long lasting impact increased knowledge however does not guarantee willing participation in official risk mitigation strategies

self sustained oscillations at volcan de colima mexico inferred by independent component analysis we have analyzed long period lp seismic events of volcan de colima mexico recorded by four three component broad band seismometers during january 2006 frequency domain analysis shows spectra mainly peaked in the range 0 3 2 hz and characterized by a monotonic decreasing envelope as those produced in a cylindrically symmetric self oscillating cavity interacting with a confined jet independent component analysis a time series decomposition method extracts two or three nonlinear oscillation modes depending on the station with the fundamental one peaked at 0 4 0 5 hz these decomposed waves have a well defined spectral content and are self sustained oscillations with low dimensionality as shown by dynamic system reconstruction methods moreover they show radial polarization in near field and transverse polarization in far field in north west south east direction finally we hypothesize a branched plumbing system with two principal conduits having alignments orthogonal to one another

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

spatio temporal reconstruction of lahars on the southern slopes of colima volcano mexico a dendrogeomorphic approach historical records of lahar occurrence and distribution are typically scarce in volcanic environments even more so if they occur outside of human settlements in the context of hazard assessment and process understanding documenting their temporal frequency and drivers of activity might be crucial on forested volcanoes lahars may significantly damage trees along their flow paths and sometimes even eliminate entire forest stands this study is based on growth disturbances in trees affected by lahars i to assess the potential of dendrogeomorphic techniques in lahar research and ii to analyze the temporal frequency and spatial patterns of lahars at montegrande and arena two of the most active of the ephemeral streams on the southern sector of colima volcano a total of 78 pinus leiophylla live trees were sampled along the ravines yielding evidence for 20 lahar events after the ad 1913 eruption adding seven events to the historic records although the number of lahars reconstructed with tree ring records can only be considered as a minimum frequency the method clearly improves the local lahar chronology despite the scarcity of meteorological records at the study sites the timing of reconstructed lahars points to heavy rainfalls after explosive activity as the main driver of events

generation of pyroclastic flows and surges by hot rock avalanches from the dome of mount st helens volcano usa several hot rock avalanches have occurred during the growth of the composite dome of mount st helens washington between 1980 and 1987 one of these occurred on 9 may 1986 and produced a fan shaped avalanche deposit of juvenile dacite debris together with a more extensive pyroclastic flow deposit laterally thinning deposits and abrasion and baking of wooden and plastic objects show that a hot ash cloud surge swept beyond the limits of the pyroclastic flow plumes that rose 2 3 km above the dome and vitric ash that fell downwind of the volcano were also effects of this event but no explosion occurred all the facies observed originated from a single avalanche erosion and melting of craterfloor snow by the hot debris caused debris flows in the crater and a small flood that carried juvenile and other clasts north of the crater a second broadly similar event occured in october 1986 larger events of this nature could present a significant volcanic hazard

temporal variation of intermittent surges of debris flow debris flows especially those of high density or high viscosity usually appear in the form of surge sequence each debris flow event consists of tens or hundreds of surges a debris flow is thus equal to a surge series which is expected to feature the intrinsic properties statistics of observation data indicates that different events have the similar distributions in parameters such as velocity flow depth discharge runoff and time interval which can be considered as the signs of an underlying dynamics but there are currently difficulties in extracting the dynamics from the surge series this paper is concerned with the temporal variations of surge series based on observation data in the last forty years in jiangjia gully jjg the temporal process of a surge series is characterized by the accumulative curve of the interval time a surge series is found to be dominated by the peak discharge in that the peak discharge determines the exponent of the distribution moreover the average discharge evolves with surge progress and finally decays in a power law form it follows that a surge series behaves as a whole which requires a unified dynamical framework to encompass all the appearances c 2008 elsevier b v all rights reserved

the 15 september 1991 pyroclastic flows at unzen volcano japan a flow model for associated ash cloud surges large scale collapse of a dacite dome in the late afternoon of 15 september 1991 generated a series of pyroclastic flow events at unzen volcano pyroclastic flows with a volume of 1 106 m3 as dre descended the northeastern slope of the volcano changing their courses to the southeast due to topographic control after they exited a narrow gorge an ash cloud surge rushed straight ahead detaching the main body of the flow that turned and followed the topographic lows to the east the surge swept the kita kamikoba area which had been devastated by the previous pyroclastic flow events and transported a car as far as 120 m following detachment the surge lost its force after it moved several hundred meters but maintained a high temperature the deposits consist of a bottom layer of better sorted ash unit 1 a thick layer of block and ash unit 2 and a thin top layer of fall out ash unit 3 unit 2 overlies unit 1 with an erosional contact the upper part of unit 2 grades into better sorted ash at distal block and ash flow deposits the bottom part of unit 2 also consists of better sorted ash and the contact with the unit 1 deposits becomes ambiguous video footage of cascading pyroclastic flows during the 1991 1995 eruption traveling over surfaces without any topographic barriers revealed that lobes of ash cloud protruded intermittently from the moving head and sides and that these lobes surged ahead on the ground surface this fact together with the inspection by helicopter shortly after the events suggests that the protruded lobes consisted of better sorted ash and resulted in the deposits of unit 1 the highest ash cloud plume at the oshigadani valley exit and the thickest deposition of fall out ash over kita kamikoba and ohnokoba indicate that abundant ash was also produced when the flow passed through a narrow gorge in the model presented here the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration main body an overriding and intermediate fluidization zone and an overlying dilute cloud release of pressurized gas in lava block pores due to collisions among blocks and the resulting upward current caused a zone of fluidization just above the main body the mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current where the ash was deposited as surge deposits the main body which had high internal friction and shear near its base then overran the surge deposits partially eroding them when the upward current of gas fluidization waned better sorted ash suspended in the fluidization zone was deposited on block and ash deposits in the distal places of block and ash deposits unit 2 probably was deposited in non turbulent fashion without any erosion of the underlying layer unit 1

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

preliminary report on the july 10 11 2015 eruption at volcan de colima pyroclastic density currents with exceptional runouts and volume abstract on july 10 11 2015 an eruption occurred at colima volcano produced 10 5 km long pyroclastic density currents pdcs along the montegrande and 6 5 km long along the san antonio ravines the summit dome was destroyed and a new crater excavated and breached to the south this new breach connects to a narrow channel that descends along colima s southern flank and was used by a subsequent lava flow the montegrande pdcs represent the longest and hottest flow of this type recorded during the past 30 years but are still smaller in comparison to the 15 km long pdcs produced during the 1913 plinian eruption data obtained from field reconnaissance lahar monitoring stations and satellite imagery suggest that at least six pdcs occurred the two largest pdcs h l 0 2 were able to surmount topographic barriers or bends based on field reconnaissance and digital elevation models extracted from spot satellite imageries we estimate a minimum volume for the valley pond and distal fan deposits of 4 5 106 m3 after one week the deposits were still hot with burning trees on the surface and millimeter sized holes from which fumes were emanating the juvenile components of the deposits consist of gray dense blocks and vesicular dark gray blocks and bombs with bread crust textures and cooling joints the mineral association of these rocks consists of plagioclase clinopyroxene orthopyroxene feti oxides olivine and resorbed hornblende in a dark glassy matrix that corresponds to an andesitic composition

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

testing the suitability of frictional behaviour for pyroclastic flow simulation by comparison with a well constrained eruption at tungurahua volcano ecuador we use a well monitored eruption of tungurahua volcano to test the validity of the frictional behaviour also called mohr coulomb which is generally used in geophysical flow modelling we show that the frictional law is not appropriate for the simulation of pyroclastic flows at tungurahua with this law the longitudinal shape of the simulated flows is a thin wedge of material progressively passing over several hundreds of metres from an unrealistic thickness at the front 1 mm to some tens of centimetres simulated deposits form piles which accumulate at the foot of the volcano and are more similar to sand piles than natural pyroclastic deposits finally flows simulated with a frictional rheology are not channelised by the drainage system but affect all the flanks of the volcano in addition their velocity can exceed 150 m s 1 allowing pyroclastic flows to cross interfluves at bends in the valley affecting areas that would not have been affected in reality and leaving clear downstream areas that would be covered in reality instead a simple empirical law a constant retarding stress i e a yield strength involving only one free parameter appears to be much better adapted for modelling pyroclastic flows a similar conclusion was drawn for the socompa debris avalanche simulation kelfoun and druitt j geophys res 110 b12202 2005

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

a mechanical model for merapi type pyroclastic flow abstract a numerical simulation model of merapi type pyroclastic flow for predicting a potential hazardous area is given and its applicability is examined by numerically reproducing actual phenomena that occurred in 1991 at unzen volcano kyushu japan merapi type pyroclastic flow arises from collapse of the lava dome whereby large lava blocks are crushed into smaller particles during movement down the steep slope the early stage of flow it may be called the debris avalanche stage in which the dominant particles are coarser than about 1 mm in diameter is considered as a grain granular flow in an inertial grain flow particle collision stress plays an important role in the mechanism of flow and the effect of gas emitted from the lava blocks is minimal most of the particles composing the inertial grain flow deposit over a comparatively short range on steep slope due to marked resistance within the flow the remainder which is composed of mainly fine particles smaller than 1 mm continues to run down by a support of the upward flow of gas ejected from the material itself thereby the resistance to flow becomes small thus the pyroclastic flow stage in a narrow sense appears the main body of the pyroclastic flow is composed of lower insufficiently fluidized layer bottom layer and upper fluidized layer in which the entire weight of the particles is supported by the upward gas flow sometimes the fluidized layer cannot exist if gas emission is insufficient as the slope down which the pyroclastic flow moves becomes milder downstream the bottom layer deposits some solids because the driving force due to gravity within this layer becomes smaller than the resistance due to inter particle contact then a part of the fluidized layer if exists changes to a part of the bottom layer because of the shortage of the upward gas flow that is caused by deposition of the gas emitting particles upstream thus the entire main body stops when it arrives at a gently sloping area smaller particles and gas escape from the main body generating a hot ash cloud layer above the main body the hot ash cloud layer can travel independent of the main body but its development or attenuation depend on the conditions of the supply of particles and gas from the main body when the hot ash cloud lacks the supply of particles and gas due to the stopping of the main body upstream or by its swerving from the course of the main body it becomes soon weakened and stops the entrainment of ambient air the escape of air and ash from the upper boundary as a buoyant plume and the particle settling also affect the behaviors of the hot ash cloud fundamental mechanics of the grain granular flow stage the pyroclastic flow stage and the transition from the former to the latter stages are discussed theoretically and experimentally and mathematical formulae describing the phenomena are obtained these one dimensional equations are extended to fit the planar two dimensional system behaviors of the main body as well as the hot ash cloud are simulated using the obtained system of equations the results of simulation are very satisfactory in comparison to the actual phenomena

geology of the northern colima and zacoalco grabens southwest mexico late cenozoic rifting in the mexican volcanic belt the south trending northern colima graben intersects two other grabens the northwest trending zacoalco graben and the east trending chapala graben to form a rift rift rift triple junction 50 km south southwest of guadalajara in southwest mexico the northern colima graben represents the northernmost extension of the 190 km long 20 to 65 km wide colima rift which overlies the projection of the subducting boundary of the rivera and cocos plates and represents a rift of probable pliocene pleistocene age of the east trending mexican volcanic belt mvb associated with the northernmost 90 km of the rift there are 4 6 m y old to holocene alkaline volcanic rocks rarely found in continental volcanic arc environments and which are more typically associated with either continental intraplate rifting or oceanic islands these alkaline lavas have erupted side by side with 10 m y old to holocene calc alkaline lavas that represent typical arc volcanism it is proposed that the grabens are associated with the initiation of a rifting of a portion of southwest mexico away from the mexican mainland similar to the rifting of baja california away from the mexican mainland the calc alkaline k ar dates are consistent with post mid miocene development of east trending mvb volcanism

first evidence of hydromagmatism at colima volcano mexico abstract here we report for the first time evidences of hydromagmatism at colima volcano western sector of trans mexican volcanic belt the studied location exposes 9 m of fine ash deposits dated at around 15 cal kyr bp by 14 c measurement on organic matter collected at the very base of the stratigraphic succession the ash deposits rest directly on the top of a debris avalanche deposit the morphology and grain size distribution of ash samples from the basal part of the stratigraphic succession testify for an explosive magma water interaction which produced finely bedded layers with blocky fragments characterized by adhering particles quenching cracks and chemical pitting the availability of ground water was hypothesized to be in close relationship with the amelioration of climate conditions at the end of the last glacial period with rising temperatures that induced melting of glaciers and snow previously accumulated on the volcano summit slopes this recognition demonstrates how even a dry volcano like colima can experience hydromagmatism under adequate climatic conditions

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

structural architecture of the colima volcanic complex 1 the colima volcanic complex cvc is currently the most active mexican volcano and is located in the western sector of the trans mexican volcanic belt inside the active colima rift a regional n s striking extensional structure the colima rift is filled by a 1 km thick sequence of quaternary lacustrine sediments alluvium and colluvium mostly underling the about 3000 m thick volcanic pile of the cvc in this work we present the results of a detailed morphostructural and field study of quaternary faults and fractures in the cvc and the surrounding area including the regional structures of the colima rift we also present a geometrical modeling of the faults inside the volcano and a numerical model of the gravity induced stress and strain fields of the cvc the study attempts to characterize the geometry kinematics and dynamics of the deformation features of the cvc and relate it with the volcano structure the geology of the substratum and the geodynamic setting of the region our model considers that the observed deformation of the cvc and the surroundings results from the interplay between the active n s trending regional extensional tectonics and the southward spreading of the volcano over its basement forming an e w oriented volcanotectonic graben the interaction between regional tectonics and previously unrecognized volcanic spreading can control magma migration and flank instability in an area where eruptions and sector failures represent a potential high risk for more than 500 000 people

active rifting in southwestern mexico manifestations of an incipient eastward spreading ridge jump a major ongoing episode of continental rifting has formed a system of three intersecting grabens in the western mexican volcanic belt these structures may mark the initial stage of an eastward spreading ridge jump beneath continental crust eastward ridge segment jumps have been propagating northward along this part of the east pacific rise for the past 12 m y but this is the first plate boundary reorganization event to involve continental crust since the separation of baja california in the miocene since pliocene time small volumes of unusual alkaline magmas have erupted in the graben areas in close association with the more abundant subduction related calc alkaline magmas erupted from andesitic stratovolcanoes the alkaline magmas are varieties found in zones of active rifting elsewhere in the world

mt pelee martinique may 8 and 20 1902 pyroclastic flows and surges abstract the distribution stratigraphic relationships and fragmental components of the may 8 and 20 1902 pyroclastic flows from mt pelee martinique together with eyewitness accounts suggest the following explanation for those eruptions the eruptions were vertically directed magmatic perhaps initiated phreatically and contained abundant juvenile lithics from congealed magma of the dome and neck this resulted in a two part eruption column having 1 a dense lithic charged part which collapsed into the crater and flowed out of a pre existing notch in its side giving rise to pyrochlastic flows and 2 a magmatically derived column containing gases juvenile vitric material and crystals which largely by passed the neck and dome and escaped into the atmosphere all of the energy of the flows was apparently focused through the notch they emerged fully turbulent and flowed down riviere blanche gravity segregation of large and abundant fragments soon resulted in a dense high concentration poorly fluidized block and ash flow confined to the valley leaving above a fully turbulent high energy ash cloud surge as the ash cloud surge moved down the mountain it continued to expand outward the process of gravity segregation continued as the ash cloud surge expanded resulting in secondary block and ash underflows toward st pierre the secondary block and ash flows developed on a gently sloping upland surface 100 m or more above the valley of riviere blanche the turbulent fragment depleted surges above the secondary block and ash flows maintained sufficient energy to devastate the landscape outward to about 3000 m including st pierre the surges refracted around obstacles and in one place moved up a small valley in a direction opposite to the main flows

long period seismicity during magma movement at volcan de colima during the period from february to september 2005 volcan de colima produced 30 vulcanian explosions of sufficient magnitude to produce pyroclastic flows of variable size with a total volume of at least 2 5 106 m3 swarms of long period events were associated with each event their duration ranging from about 6 h to 3 days and each swarm containing up to 886 events the characteristics of the swarms have been studied to understand the source mechanism and their relationship with the vulcanian explosions in total 12 548 long period events were analysed using various comparative and statistical methods patterns were not apparent in the data with no correlation between different properties of the swarms duration magnitude or frequency of occurrence of lp events and the magnitude of the associated vulcanian explosion whether recorded by seismicity volume of pyroclastics or altitude of the eruption column this along with other characteristics of the swarms such as the continuation of the swarm after the explosion with an increase in long period event amplitude in some cases suggests that the mechanism is not merely associated with the pressurization under an impermeable cap and resulting pressure differentials between adjacent volumes within the system it is more likely that the production of long period events is dominated by brittle fracturing on the margins of an ascending magma body a model is proposed whereby the unloading above the ascending magma column produced by a vulcanian explosion resulted in an increase in ascent rate reflected in the increasing amplitude of long period events the results reflect the complexity of non linear processes involved during magma ascent degassing crystallization and rupture of the impermeable plug during the vulcanian process at volcan de colima as at many volcanoes long period events represent a useful precursor for eruptive activity for monitoring this paper highlights some useful analyses that can be carried out which could illustrate certain characteristics of an eruptive episode a preliminary model is presented of the conduit processes at work during the cyclic extrusive and explosive activity during 2005

emplacement of pyroclastic flows during the 1998 1999 eruption of volcan de colima mexico after three years of quiescence volcan de colima reawakened with increasing seismic and rock fall activity that reached its peak on november 20 1998 when a new lava dome forced its way to the volcano s summit the new lava rapidly reached the s sw edge of the summit area beginning the generation of merapi type pyroclastic flows that traveled down la lumbre and the el cordoban western and eastern ravines reaching distances of 3 4 5 and 3 km respectively on december 1 1998 the lava flow split into three fronts that in early 1999 had reached 2 8 3 1 and 2 5 km in length advancing down the el cordoban ravines the lava flow fronts disaggregated into blocks forming pyroclastic flows one of the best examples occurred on december 10 1998 as the lava flow ceased moving in early 1999 activity became more explosive strong blasts were recorded on february 10 may 10 and july 17 1999 the last event developed a 10 km high eruptive column from which a pyroclastic flow developed from the base traveling 3 3 km sw from the summit into the san antonio montegrande ravines regardless of the mechanism of pyroclastic flow generation each flow immediately segregated into a basal avalanche that moved as a granular flow and an upper ash cloud in which particles were sustained in turbulent suspension when the basal avalanche lost velocity and eventually stopped the upper ash cloud continued to move independently as a dilute pyroclastic flow that produced a massive pyroclastic flow deposit and an upper dune bedded surge deposit the dilute pyroclastic flow scorched and toppled maguey plants and trees and sandblasted vegetation in the direction of the flow at the end of the dilute pyroclastic flow path the suspended particles lifted off in a cloud from which a terminal ash fall was deposited the basal avalanche emplaced block and ash flow deposits up to 8 m thick that filled the main ravines and consisted of several flow units each flow unit was massive monolithologic matrix supported and had a clast supported steep front ca 1 5 to 2 m thick composed of boulders up to 1 7 m in diameter the juvenile lithic clasts had an average density of 1800 kg m3 the dilute pyroclastic flow emplaced overbank deposits found on valley margins or beyond the tip of block and ash flow deposits they consist from bottom to top of a massive medium to coarse sand size flow layer 2 4 cm thick a dune bedded surge layer 2 10 cm thick and a massive silt size layer 0 5 cm thick the total estimated volume of the pyroclastic flow deposits produced during the 1998 1999 eruption is 24 105 m3

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

the characteristics of seismic signals produced by lahars and pyroclastic flows volcan de colima mexico abstract the general characteristics of seismic signals produced by pyroclastic flows generated by either the collapse of a lava dome or an eruptive column and lahars at volcan de colima mexico are discussed the paper concentrates on the 2004 2006 activity associated with and following the extrusion of andesitic block lava in october november 2004 it is shown that the duration of the broad band seismic records of pyroclastic flows lasts a few minutes while the duration of seismic records of lahars continues for tens of minutes or hours the spectra of seismic records produced by pyroclastic flows are characterized by lower peak frequencies around 3 4 hz than for lahars around 6 8 hz this difference in the frequency content together with the difference in the duration of seismic signals allows early diagnostic of the events in real time

rainfall triggered lahars at volcan de colima mexico surface hydro repellency as initiation process article volcan de colima is currently the most active volcano in mexico since 1998 intermittent activity has been observed with vulcanian eruptions lava flows and growing domes that have collapsed producing several block and ash flow deposits during the period of heightened activity since 1998 at volcan de colima pyroclastic flows from dome or column collapse have not reached long distances most of the time less than 6k m from the crater in contrast rain induced laharswere more frequent and have reached relatively long distances upto 15 km causing damage to infrastructureand affecting small villages in 2007 tworain gauge stationswereinstalledonthesouthern flankofthevolcanoregisteringeventsfromjunethroughtooctober the period when rains are intense and lahars frequent by comparing lahar frequency with rainfall intensity and the rainfall accumulated during the previous 3 days lahars more frequently occur at the beginning of the rainfall season with low rain accumulation 10 mm and triggered by low rain intensities 20 mm h during the months with more rainfall july and august lahars are less frequent and higher peak intensities up to 70 mm h are needed to trigger an event in both cases lahars were initiated as dilute sediment laden streamflows which transformed with entrainment of additional sediment into hypercon centratedanddebris flows withalternationsbetweenthesetwo flowtypes ahydro repellencymechanism in highly vegetated areas i e evergreen tree types with considerable amount of resins and waxes such as pines with sandy soils can probably explain the high frequency of lahars at the beginning of the rain season during low rainfall events under hydrophobic conditions infiltration is inhibited and runoff is facilitated at more highly peaked discharges that are more likely to initiate lahars

understanding eruptive style variations at calc alkaline volcanoes the 1913 eruption of fuego de colima volcano mexico the 1913 sub plinian eruption of fuego de colima volcano mexico occurred after almost 100 years of effusive and minor vulcanian explosive activity which modulated dome growth and destruction dome extrusion persisted from 1869 to 1913 the transition to explosive eruption started on 17 january 1913 and it progressed in three phases 1 opening with the generation of block and ash flows 2 vent clearing with strong explosions that destroyed the summit dome and decompressed the magmatic system and 3 sustained column sub plinian fallout with final collapse producing pyroclastic density currents because of this succession of events the 1913 activity represents an excellent case study for investigating the eruptive style changes at calc alkaline volcanoes we investigated the conditions that led to eruptive style transition from effusive dome growth to explosive the final sub plinian fallout through steady state numerical simulations using subsurface data and independently inferred from volcanological data mass discharge rates as constraints results show good matches for hybrid geometrical settings of the shallow conduit feeding system i e dyke developing into a shallower cylindrical conduit and the magma chamber top at 6 km of depth the fragmentation level was shallower than 2 km as inferred from the lithics contained in the sub plinian fall deposits of phase 3 the most likely solution is represented by a dyke having major axis between 200 and 2000 m and the minor axis of 40 m the dyke cylinder transition was set at a depth of 500 m with a cylinder diameter of 40 m it emerges that at least two main mechanisms may be responsible for the effusive to explosive transition that led to the phase 3 of the 1913 eruption i an increase in magma chamber overpressure magmatic triggering or ii decrease of lithostatic stress acting on the volcano non magmatic triggering the former implies arrival into the magma chamber of a batch of fresh magma which can have volume between 10 and 200 106 m3 depending on the values of magma and host rock compressibility the latter requires decompression induced emptying of at least the equivalent of 1000 m of the magma column to produce the necessary unloading of the conduit feeding system a sudden jerk in the lateral spreading of the fuego de colima cone would be a reliable mechanism for decompressing the upper conduit and driving fragmentation processes over a time period of few hours the results are not conclusive on an internal magma chamber overpressure external lowering of lithostatic load or mixed internal and external trigger of the observed eruptive style transition this work highlights how different processes can have non linear cascade effects on close to equilibrium volcanic systems like fuego de colima volcano

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

a model for generation of ash clouds by pyroclastic flows with application to the 1980 eruptions at mount st helens washington pyroclastic flows are defined as consisting of a dense basal avalanche underlying a turbulent ash cloud the generation of ash clouds by the basal avalanche is commonly assumed to be closely related either to fluidization mechanisms within the avalanche or to airflow flow front interactions these mechanisms carry ash upward from the basal avalanche into the ash cloud in currents of gas or air but so far no mechanisms have been proposed to keep the ash in turbulent suspension in the ash cloud here i consider the ash cloud turbulence that is generated in two ways by temperature differences between the basal avalanche and overriding air and by the motions of the blocks lapilli and ash on the outer surface of the basal avalanche this turbulence would carry ash from saltation into turbulent suspension at the base of the ash cloud and this transition would simultaneously occur from the upper surface and front of the basal avalanche this approach quantifies one type of airflow flow front interaction the analysis incorporates studies of heat and mass transfer from rough surfaces during high reynolds number flow equations for conservation of mass momentum heat energy and ash particle concentration are formulated and presented in integral form model results show that for typical avalanche velocities and temperatues temperature differences between the basal avalanche and the surrounding air are insignificant in generating the initial turbulence within the ash cloud instead the initial distribution of particle sizes in the ash cloud is controlled by the turbulence generated by the saltating cascading particles in the basal avalanche study of the morphology of observed ash clouds suggests that thermally driven convection often becomes significant hundreds of meters or more behind the flow front and this may result from deposition of significant quantities of ash from the ash cloud onto the basal avalanche the variations in ash cloud heights morphologies and particle sizes that are predicted by this model are consistent with published observations of small pyroclastic flows at mount st helens in 1980

effects of pore pressure in pyroclastic flows numerical simulation and experimental validation pyroclastic flows are mixtures of volcanic gases and particles that can be very hazardous owing to their fluid like behavior one possible mechanism to explain this behavior is the reduction of particles friction due to the internal gas pore pressure to verify this hypothesis we present a numerical model of a granular flow with high initial pore pressure that decreases with time as the gas particle mixture propagates first we validate the model by reproducing laboratory experiments then the numerical code is applied to pyroclastic flows of lascar volcano 1993 eruption chile the simulation reproduces the runout and the morphological features of the deposits with lateral levees a central channel and a lobate front our results support the hypothesis of the role of gas pore pressure in pyroclastic flows and explain both the fluid like behavior of the flows and the formation of lateral levees

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

a two layer depth averaged model for both the dilute and the concentrated parts of pyroclastic currents pyroclastic currents are very destructive and their complex behavior makes the related hazards difficult to predict a new numerical model has been developed to simulate the emplacement of both the concentrated and the dilute parts of pyroclastic currents using two coupled depth averaged approaches interaction laws allow the concentrated current pyroclastic flow to generate a dilute current pyroclastic surge and inversely the dilute current to form a concentrated current or a deposit the density of the concentrated current is assumed to be constant during emplacement whereas the density of the dilute current changes depending on the particle supply from the concentrated current and the mass lost through sedimentation the model is explored theoretically using simplified geometries as a proxies for natural source conditions and topographies it reproduces the relationships observed in the field between the surge genesis and the topography the increase in surge production in constricted valleys the decoupling between the concentrated and the dilute currents and the formation of surge derived concentrated flows the strong non linear link between the surge genesis and the velocity of the concentrated flow beneath it could explain the sudden occurrence of powerful and destructive surges and the difficulty of predicting this occurrence a companion paper compares the results of the model with the field data for the eruption of merapi in 2010 kelfoun et al submitted and demonstrates that the approach is able to reproduce the natural emplacement of the concentrated and the dilute pyroclastic currents studied with good accuracy

objective rapid delineation of areas at risk from block and ash pyroclastic flows and surges assessments of pyroclastic flow pf hazards are commonly based on mapping of pf and surge deposits and estimations of inundation limits and or computer models of varying degrees of sophistication in volcanic crises a pf hazard map may be sorely needed but limited time exposures or safety aspects may preclude fieldwork and insufficient time or baseline data may be available for reliable dynamic simulations we have developed a statistically constrained simulation model for block and ash type pfs to estimate potential areas of inundation by adapting methodology from iverson et al geol soc america bull 110 972 984 1998 for lahars the predictive equations for block and ash pfs are calibrated with data from several volcanoes and given by a 0 05 to 0 1 v2 3 b 35 to 40 v2 3 where a is cross sectional area of inundation b is planimetric area and v is deposit volume the proportionality coefficients were obtained from regression analyses and comparison of simulations to mapped deposits the method embeds the predictive equations in a gis program coupled with dem topography using the laharz program of schilling 1998 although the method is objective and reproducible any pf hazard zone so computed should be considered as an approximate guide only due to uncertainties on the coefficients applicable to individual pfs the authenticity of dem details and the volume of future collapses the statistical uncertainty of the predictive equations which imply a factor of two or more in predicting a or b for a specified v is superposed on the uncertainty of forecasting v for the next pf to descend a particular valley multiple inundation zones produced by simulations using a selected range of volumes partly accommodate these uncertainties the resulting maps show graphically that pf inundation potentials are highest nearest volcano sources and along valley thalwegs and diminish with distance from source and lateral distance from thalweg the model does not explicitly consider dynamic behavior which can be important ash cloud surge impact limits must be extended beyond pf hazard zones and we provide several approaches to do this the method has been used to supply pf and surge hazard maps in two crises merapi 2006 and montserrat 2006 2007

evaluating suitability of a tephra dispersal model as part of a risk assessment framework in volcanic risk assessment it is necessary to determine the appropriate level of sophistication for a given predictive model within the contexts of multiple sources of uncertainty and coupling between models a component of volcanic risk assessment for the proposed radioactive waste repository at yucca mountain nevada usa involves prediction of dispersal of contaminated tephra during violent strombolian eruptions and the subsequent transport of that tephra toward a hypothetical individual via surface processes we test the suitability of a simplified model for volcanic plume transport and fallout tephra deposition ashplume coupled to a surface sediment transport model far that calculates the redistribution of tephra and in light of inherent uncertainties in the system the study focuses on two simplifying assumptions in the ashplume model 1 constant eruptive column height and 2 constant wind speed and direction during an eruption variations in tephra dispersal resulting from unsteady column height and wind conditions produced variations up to a factor of two in the concentration of tephra in sediment transported to the control population however the effects of watershed geometry and terrain which control local remobilization of tephra overprint sensitivities to eruption parameters because the combination of models used here shows limited sensitivity to the actual details of ash fall a simple fall model suffices to estimate tephra mass delivered to the hypothetical individual

thermal imaging and analysis of short lived vulcanian explosions at volcan de colima mexico abstract vulcanian explosions present a major hazard at many active volcanoes but they also provide useful insights into the underlying behaviour of the volcanic system and therefore require close monitoring thermal infrared cameras are an effective tool for imaging vulcanian explosion plumes since they capture detailed temperature information and can reveal the internal dynamics of the plume forming explosions high spatial resolution thermal images of 200 small to moderate sized vulcanian explosions from the summit crater of volcan de colima mexico recorded between 2006 and 2011 were analysed to distinguish different event types and develop an explosion classification scheme explosions display a broad spectrum of sizes and characteristics ranging between two typical end members large impulsive events producing rapidly ascending explosion plumes up to heights of 600 1600 m above the crater rim and small diffusive events with plumes restricted to heights 1 to 29 m s 1 a time series of thermal imagery throughout the period 2006 2011 reveals a weak relationship between apparent plume temperatures and lava dome extrusion with the highest explosion temperatures coinciding with the onset of dome growth in early 2007 temporal variations in the source locations of explosions across the summit crater are also identified and appear to show a close relationship to the patterns of lava dome growth and thermal evolution with explosion source locations associated with the highest temperature thermal features

the role of orography in the dynamics of storm tracks abstract this paper investigates the role of the northern hemispheric orography in the maintenance of the winter storm tracks with a dry balance three layer hemispheric model first the zonal winter mean flow in 1982 83 together with the corresponding orographically induced model planetary wave field is shown to have comparable linear instability properties as the total observed winter mean flow then the nonlinear version of this model is shown to be capable of simulating the pacific and atlantic storm tracks with considerable realism the position of the pacific storm track is slightly off and the intensity of the two model storm tracks is about 70 of the observed while the localized baroclinic regions tend to be neutralized by the eddies in the model they are sufficiently reestablished by the interaction between the slowly varying zonal flow and the tibetan plateau and the rockies to maintain the storm tracks moist dynamics is therefore not believed to be essential for the existence of storm tr

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

field observations of pristine block and ash flow deposits emplaced april 16 17 1991 at volcan de colima mexico abstract for the first time since the effusive activity of 1981 1982 volcan de colima extruded scoriaceous andesitic lava on march 1 1991 this followed a period of increasing seismicity summit dome deformation and fumarolic activity that began in february of 1991 growth of the new lava dome proceeded until april 16 at 16 00 hrs local time gmt 6 hours when a series of gravitational failures of the upper edifice and the new lava dome flow triggered the emplacement of successive small volume non glowing block and ash flows to a distance of 4 km within the upper reaches of barranca el cordoban south southwest of the present summit aerial photos taken at the time of the event clearly show the lack of explosions at the summit dome efficient elutriation of the finest silt and clay sized fraction from the main body of the avalanching material produced large reddish yellowish and grayish ash clouds which rose to an altitude of 1 5 2 5 km for several hours and were carried southeast to northeast by predominant winds vegetation in the path of the debris was totally stripped sand blasted and bent in the sense of flowage but was not burnt no fatalities were reported we present a summary of our field observations of the pristine deposits which we studied prior the rainy season on april 20 27 between 2 200 and 2 500 m elevation

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

eruptive and magmatic cycles at fuego de colima volcano mexico the fuego de colima volcano displays a pattern of eruptive cyclicity characterized by lava flows and or slow effusions in an open crater alternating with short explosive events historical accounts field investigations and petrological data allow us to refine our understanding of the relationships between recurrent acidic acidic andesite and mafic andesitic products and this eruptive behaviour the second to last 1818 1913 and present 1913 present day cycles are instructive in this respect the short explosive events in 1818 and 1913 correspond to the initial mixing stage of a differentiated magmatic body with a new mafic input mathematical modeling shows that the pyroclastic products of 1913 result from the mixing between an acidic andesite 61 5 sio2 and an olivine andesite 56 sio2 in various ratios the final andesite mixture is made of 38 basaltic andesite and 62 acidic andesite the long effusive extrusive phases correspond to the ensuing differentiation stage of the new magmatic body for example the 1961 lava flows were derived from the final mixed and homogenized magma after the eruption of 1913 by fractionation of 7 plagioclase 9 pyroxene clinopyroxene orthopyroxene and 0 7 titanomagnetite the fractionation of 11 plagioclase 9 pyroxene and 1 4 titanomagnetite is required to produce the composition of the 1986 summit lava dome from the same parent in conclusion at fuego de colima an eruptive cycle begins with a short violent explosive event related to a mixing process and continues with a long effusive phase characterized by magmatic differentiation this scheme differs from others that have been proposed which consider that the eruptive cycles end with an explosive event

flow connectivity in active volcanic areas use of index of connectivity in the assessment of lateral flow contribution to main streams abstract connectivity analysis is an important geomorphological and hydrologic tool that can be used to identify spaces that are prone to removal of primary sediments which are eventually assimilated into granular flows and related epiclastic processes studies of connectivity have been made in various areas but to date not in active volcanic areas where such studies can be very useful due to the constant presence of loose volcanic material easily removed by epiclastic processes mobilization of loose pyroclastic sediments can trigger phenomena such as lahars which are among the most dangerous in nature in this study the index of connectivity ic borselli et al 2008 was calculated by obtaining a weight coefficient w combining two elements the coefficient c related to the universal soil loss equation and the revised universal soil loss equation usle rusle proposed by borselli et al 2008 for areas with vegetation cover or crops and the roughness index ri developed by cavalli et al 2013 which characterizes bare soil areas combining both methods we propose a new joint index of connectivity icj that does not overestimate the degree of connectivity in bare areas while areas with vegetation cover are characterized based on their well recognized hydrologic impedance properties this methodology may enable better characterization in highly dynamic environments such as active volcanic areas we also propose a new lateral hydrological efficiency index lhei that increases the ability to identify watersheds that supply major amounts of sediment to main streams in ravines the application of this methodology in the active volcanic area of volcan de colima the most active volcano in mexico is of great importance because of the constant supply of new pyroclastic material from the top of the edifice the high dynamicity of geomorphological processes and the widespread presence of bare soil areas consisting of loose materials easily sourced or assimilated into epiclastic processes

deposits associated with the 1990 1995 eruption of unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in japan was characterized by lava dome growth and block and ash flows triggered by dome collapse the repeated dome collapse events produced block and ash flow ash cloud surge and fine grained ash fall deposits block and ash flow deposits which are confined to valleys are massive to reversely graded very poorly sorted and contain non vesiculated to poorly vesiculated blocks up to 10 m across the deposits often display finer grained basal parts coarse clast depleted flow units which have intermediate grain size distribution between main flow and surge deposits occur as marginal part of block and ash flow deposits ash cloud surge deposits which spread more widely are finer grained and better sorted than block and ash flow deposits ash fall deposits which were derived from ash clouds of block and ash flows and were dispersed around the volcano are very fine grained and are as well sorted as the surge deposits lahars resulting from remobilization of pyroclastic debris devastated the base of the volcano and their deposits are moderately fines depleted and occasionally display two different lahar facies debris flow and hyperconcentrated flow units

high k mafic plinian eruptions of volcan de colima mexico the last plinian type eruption of volcan de colima mexico occurred in 1913 this resulted in the removal of the top 100 m of the edifice and the deposition of a tephra layer that blanketed the slopes of the colima volcanic complex cvc road cuts on the flanks of the nearby nevado de colima edifice expose pre 1913 air fall tephra pyroclastic flow and ash rich surge deposits resulting from numerous highly explosive events throughout the holocene the majority of the pumice and scoria fallout deposits are medium k subalkaline basaltic andesite and andesite in composition defining a clear major element differentiation trend in contrast three newly discovered scoria fallout deposits are high k subalkaline transitional to alkaline basaltic andesite in composition and are characterized by the presence of phlogopite these deposits have high mgo up to 7 9 wt k2o up to 2 6 wt and p2o5 up to 0 67 wt contents they are also strongly enriched in fluid and melt mobile large ion lithophile elements lile rb ba k sr and th and light ree lree la ce pr and nd relative to the majority of the colima tephra fallout deposits strontium and nd isotope systematics reveal that the high k mafic scoria have more radiogenic sr 87sr 86sr 0 70365 0 70408 and less radiogenic nd 143nd 144nd 0 51279 0 51294 compared with the majority of the subalkaline tephras 87sr 86sr 0 70338 0 70371 and 143nd 144nd 0 51290 0 51295 two component mixing models using whole rock geochemical data indicate the importance of magma mixing in the petrogenesis of the colima magmas with addition of up to 50 by volume of an alkaline mafic magma component in the most potassic magmas this is supported by mineral chemistry and textural data which reveal multiple episodes of decompression and magma mingling within a shallow crustal magma storage region the presence of these potassic tephra fall deposits among the otherwise prevailing medium k subalkaline stratigraphy indicates that pulses of k rich alkaline mafic magmas periodically enter the cvc plumbing system on timescales of a few thousand years and may trigger plinian explosive eruptions

the origin of salinity and sulphate contamination of groundwater in the colima state mexico constrained by stable isotopes chemical compositions and stable isotope ratios of water and sulphate were used to characterise sources and processes responsible for elevated concentrations of sulphate and other constituents in groundwater from aquifers at colima state along mexico s pacific coast the 18o and 2h values of the groundwater were similar to those of precipitation indicating a meteoric origin and recharge processes are relatively uniform in large parts of the study area with only slight local evaporation effects 34ssulphate and 18osulphate analyses indicated that high sulphate concentrations of up to 1 480 mg l are mainly due to dissolution of evaporites and volcanic exhalations chloride is largely related to sources other than seawater the marabasco sub basin is affected by anthropogenic contamination through manganese and iron ore mining activities the obtained knowledge regarding sources and areas of contamination will be essential for the development and design of a water quality monitoring program in the study area

parametric analysis of lava dome collapse events and pyroclastic deposits at shiveluch volcano kamchatka using visible and infrared satellite data abstract for the years 2001 to 2013 of the ongoing eruption of shiveluch volcano a combination of different satellite remote sensing data are used to investigate the dome collapse events and the resulting pyroclastic deposits shiveluch volcano in kamchatka russia is one of the world s most active dome building volcanoes which has produced some of the largest known historical block and ash flows bafs globally quantitative data for deposits resulting from such large and long lived dome forming eruptions especially like those at shiveluch are scarce we use advanced spaceborne thermal emission and reflection radiometer aster thermal infrared tir shortwave infrared swir and visible near infrared vnir data to analyze the dome collapse scars and baf deposits that were formed during eruptions and collapse events in 2001 2004 2005 2007 2009 2010 and two events in 2013 these events produced flows with runout distances of as far as 19 km from the dome and with aerial extents of as much as 22 3 km2 over the 12 years of this period of investigation there is no trend in deposit area or runout distances of the flows through time however two potentially predictive features are apparent in our data set 1 the largest dome collapse events occurred when the dome exceeded a relative height from dome base to top of 500 m 2 collapses were preceded by thermal anomalies in six of the cases in which aster data were available although the areal extent of these precursory thermal areas did not generally match the size of the collapse events as indicated by scar area volumes are available for three collapse events linking the deposit distribution to the area location and temperature profiles of the dome collapse scars provides a basis for determining similar future hazards at shiveluch and at other dome forming volcanoes because of these factors we suggest that volcanic hazard analysis and mitigation at volcanoes with similar baf emplacement behavior may be improved with detailed synoptic studies especially when it is possible to access and interpret appropriate remote sensing data in near real time

tephrochronology petrology and geochemistry of late holocene pyroclastic deposits from volcan de colima mexico abstract volcan de colima in western mexican volcanic belt is the most active volcano in north america we present a detailed tephrochronological study of its holocene proximal tephra fall pyroclastic surge and pyroclastic flow deposits based on 98 new stratigraphic sections 183 new dendrocalibrated radiocarbon 14 c age determinations 209 new geochemical analyses of pumice and ash 50 texture and mineral point counting mode determinations and 230 grain size analyses these results provide a much clearer understanding of the explosive eruptive behavior of volcan de colima during the past 10 000 years our data reveals that only one of the many eruptions described in historic documents has been large enough to be preserved we discuss the major and trace element geochemistry and petrology of the holocene tephra and compare it with the currently erupting calc alkaline andesites and alkaline minettes and basanites from the adjacent cinder cones it appears that several of the oldest 12 000 6000 yrs bp samples of the holocene tephra may record the last episodes of calc alkaline and alkaline magma mixing as first described in the pioneering work of luhr and carmichael 1981 finally the tephrochronological record from the northern downwind side of the colima volcanic complex is compared with the extensive radiocarbon constrained record of holocene debris avalanche deposits on the south side of the complex to build a more integrated picture of its past volcanic activity

movement and emplacement of lava flows at volcan de colima mexico november 1998 february 1999 abstract the first lava eruption of volcan de colima since 1991 was anticipated beginning in mid 1997 when seismic activity began to exceed background levels on 20 november 1998 growth of a new andesitic lava dome began inside a crater produced by an explosion through the summit dome in july 1994 the 1998 block lava dome grew rapidly at a rate of 4 4 m 3 s attaining a volume of 3 8 10 5 m 3 in 24 h about mid day on 21 november the lava dome began to collapse generating a series of block and ash flows that descended the ssw flank at speeds of 80 90 km h at intervals of 3 5 min these pyroclastic flows were mostly deposited in the three branches of barranca el cordoban reaching a maximum distance of 4 8 km from the summit at an altitude of 2040 m the largest pyroclastic flows were emplaced on 25 26 november and their deposits had an estimated volume of 7 3 10 5 m 3 an andesitic block lava flow 59 wt sio 2 then followed down the three branches of barranca el cordoban reaching a maximum distance of 3 8 km in the central branch the lava fronts of the western and central branches almost touched at 2300 m elevation the eastern lava flow reached 2 8 km at 2560 m elevation the total volume of the three lava flows is estimated as 39 10 6 m 3 assuming an average thickness of 20 m the advance rate of the lava fronts in the early hours reached 36 m h on steep slopes up to 40 these diminished to 0 2 1 0 m h on flatter slopes 14 in early february as the activity waned the viscosity of the block lava flows estimated from field observations was extremely high 10 9 10 10 pa s 6 orders of magnitude greater than viscosities estimated for fluid basaltic magmas the lava flows ceased movement in early february 1999 and the style of eruptive activity entered a more explosive phase with a series of dome explosions that have continued into february 2001

landscape and sedimentary response to catastrophic debris avalanches western taranaki new zealand abstract catastrophic volcanic debris avalanches reshape volcanic edifices with up to half of pre collapse cone volumes being removed deposition from this debris avalanche deposit often fills and inundates the surrounding landscape and may permanently change the distribution of drainage networks on the weakly incised mt taranaki ring plain volcanic debris avalanche deposits typically form a large wedge shape in plan view over all flat lying fans following volcanic debris avalanches a period of intense re sedimentation commonly begins on ring plain areas particularly in wet or temperate climates this is exacerbated by large areas of denuded landscape ongoing instability in the scarp source region damming of river stream systems and in some cases inherent instability of the volcanic debris avalanche deposits in addition on mt taranaki the collapse of a segment of the cone by volcanic debris avalanche often generates long periods of renewed volcanism generating large volumes of juvenile tephra onto unstable and unvegetated slopes or construction of new domes with associated rock falls and block and ash flows the distal ring plain impact from these post debris avalanche conditions and processes is primarily accumulation of long run out debris flow and hyperconcentrated flow deposits with a variety of lithologies and sedimentary character common to these post debris avalanche units is evidence for high water content flows that are typically non cohesive hence sedimentary variations in these units are high in lateral and longitudinal exposure in relation to local topography the post collapse deposits flank large scale fans and hence similar lithological and chronological sequences can form on widely disparate sectors of the ring plain these deposits on mt taranaki provide a record of landscape response and ring plain evolution in three stages that divide the currently identified warea formation 1 the deposition of broad fans of material adjacent to the debris avalanche unit 2 channel formation and erosion of stage 1 deposits primarily at the contact between debris avalanche deposits and the stage 1 deposits and the refilling of these channels and 3 the development of broad tabular sheet flows on top of the debris avalanche leaving sediments between debris avalanche mounds after a volcanic debris avalanche these processes represent an ever changing and evolving hazard scape with hazard maps needing to be regularly updated to take account of which stage the sedimentary system is in