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

mobility of pyroclastic flows and surges at the soufriere hills volcano montserrat the soufriere hills volcano on montserrat has produced avalanche like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows the largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall h run out distance l area inundated a and volume transported v dome collapse flow mobilities characterised by either l h or a v2 3 resemble those of terrestrial and extraterrestrial cold rockfalls dade and huppert 1998 in contrast fountain fed pumice flows and fine grained secondary pyroclastic flows travel slower but for comparable initial volumes and heights can inundate greater areas

sand waves along the dutch coast sand waves defined as longshore wave like movements of the shoreline measured in a horizontal plane are described along several stretches of the shoreline of the netherlands they have a celerity in the order of 50 200 m yr a period of 50 150 years and an amplitude of 30 500 m they are found along the whole dutch shoreline analysis of sand waves shows that the assumed effect of groins might be very small along this shoreline there are indications that groins did not have any long term effect on coastal regression

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

stratigraphic reconstruction of two debris avalanche deposits at colima volcano mexico insights into pre failure conditions and climate influence abstract throughout its history colima volcano has experienced numerous partial edifice collapses with associated emplacement of debris avalanche deposits of contrasting volume morphology and texture a detailed stratigraphic study in the south eastern sector of the volcano allowed the recognition of two debris avalanche deposits named san marcos 28 000 cal yr bp v 1 3 km 3 and tonila 15 000 16 000 cal yr bp v 1 km 3 this work sheds light on the pre failure conditions of the volcano based primarily on a detailed textural study of debris avalanche deposits and their associated pyroclastic and volcaniclastic successions furthermore we show how the climate at the time of the tonila collapse influenced the failure mechanisms the 28 000 cal yr bp san marcos collapse was promoted by edifice steep flanks and ongoing tectonic and volcanotectonic deformation and was followed by a magmatic eruption that emplaced pyroclastic flow deposits in contrast the tonila failure occurred just after the last glacial maximum 22 000 18 000 cal bp and in addition to the typical debris avalanche textural characteristics angular to sub angular clasts coarse matrix jigsaw fit it shows a hybrid facies characterized by debris avalanche blocks embedded in a finer homogenous and partially cemented matrix a texture more characteristic of debris flow deposits the tonila debris avalanche is directly overlain by a 7 m thick hydromagmatic pyroclastic succession massive debris flow deposits often more than 10 m thick and containing large amounts of tree trunk logs represent the top unit in the succession fluvial deposits also occur throughout all successions these represent periods of highly localized stream reworking all these lines of evidence point to the presence of water in the edifice prior to the tonila failure suggesting it may have been a weakening factor the tonila failure appears to represent an anomalous event related to the particular climatic conditions at the time of the collapse the presence of extensive water at the onset of deglaciation modified the mobility of the debris avalanche and led to the formation of a thick sequence of debris flows the possibility that such a combination of events can occur and that their probability is likely to increase during the rainy season should be taken into consideration when evaluating hazards associated with future collapses at colima volcano

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

caldera formation at volcan colima mexico by a large large holocene volcanic debris avalanche abstract about 4 300 years ago 10 km 3 of the upper cone of ancestral volcan colima collapsed to the southwest leaving a horseshoe shaped caldera 4 km in diameter the collapse produced a massive volcanic debris avalanche deposit covering over 1550 km 2 on the southern flanks of the volcano and extending at least 70 km from the former summit the avalanche followed a steep topographic gradient unobstructed by barriers resulting in an unusually high area volume ratio for the colima deposit the apparent coefficient of friction fall height distance traveled for the colima avalanche is 0 06 a low value similar to those of other large volume deposits the debris avalanche deposit contains 40 75 angular volcanic clasts from the ancestral cone a small proportion of vesicular blocks that may be juvenile and in distal exposures rare carbonate clasts plucked from the underlying surface by the moving avalanche clasts range in size to over 20 m in diameter and are brecciated to different degrees pulverized and surrounded by a rock flour matrix the upper surface of the deposit shows prominent hummocky topography with closed depressions and surface boulders a thick coarse grained compositionally zoned scoria fall layer on the upper northeastern slope of the volcano may have erupted at the time of collapse a fine grained surge layer is present beneath the avalanche deposit at one locality apparently representing an initial blast event most of the missing volume of the ancestral volcano has since been restored at an average rate of 0 002 km 3 yr through repeated eruptions from the post caldera cone as a result the southern slope of volcan colima may again be susceptible to collapse over 200 000 people are now living on primary or secondary deposits of the debris avalanche and a repetition of this event would constitute a volcanic disaster of great magnitude ancestral volcan colima grew on the southern trenchward flank of the earlier and larger volcano nevado de colima trenchward collapse was favored by the buttressing effect of nevado the rapid elevation drop to the south and the intrusion of magma into the southern flank of the ancestral volcano other such trenchward younging paired volcanoes are known from mexico guatemala el salvador chile and japan the trenchward slopes of the younger cones are common sites for cone collapse to form avalanche deposits as occurred at colima and popocatepetl in mexico and at san pedro volcano in chile

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

stratigraphy sedimentology and inferred flow dynamics from the july 2015 block and ash flow deposits at volcan de colima mexico abstract the july 2015 block and ash flow baf events represent the first documented series of large volume and long runout bafs generated from sustained dome collapses at volcan de colima this eruption is particularly exceptional at this volcano due to 1 the large volume of baf material emplaced 0 0077 0 001 km3 2 the long runout reached by the associated bafs max 10 km and 3 the short period 18 h over which two main long sustained dome collapse events occurred on 10 and 11 july respectively stratigraphy and sedimentology of the 2015 baf deposits exposed in the southern flank of the volcano based on lithofacies description grain size measurements and clast componentry allowed the recognition of three main deposit facies i e valley confined overbank and ash cloud surge deposits correlations and lithofacies variations inside three main flow units from both the valley confined and overbank deposits left from the emplacement of the second series of bafs on 11 july provide detailed information about 1 the distribution volumes and sedimentological characteristics of the different units 2 flow parameters i e velocity and dynamic pressure and mobility metrics as inferred from associated deposits and 3 changes in the dynamics of the different flows and their material during emplacement these data were coupled with geomorphic analyses to assess the role of the topography in controlling the behaviour and impacts of the successive baf pulses on the volcano flanks finally these findings are used to propose a conceptual model for transport and deposition mechanisms of the july 2015 bafs at volcan de colima in this model deposition occurs by rapid stepwise aggradation of successive baf pulses flow confinement in a narrow and sinuous channel enhance the mobility and runout of individual channelized baf pulses when these conditions occur the progressive valley infilling from successive sustained dome collapse events promote the overspill and lateral spreading of the upper and marginal regions of the main flow body generating highly mobile overbank flows that travel outside of the main valley volume and distance dependent critical channel capacities for the generation of overbank flows are used to better estimate the inundation area of these hazardous unconfined pyroclastic flows these results highlight the importance of including and correctly assessing the hazards posed by large volume and long runout bafs associated with frequent small vei sustained dome collapse eruptions

aeromechanic analysis of pyroclastic density currents past a building an aeromechanic analysis of pyroclastic density currents pdcs past a building is carried out on the results of a computer simulation the analysis shows that pdcs strongly interact with buildings resulting in turbulent boundary layer separation and recirculation these results could be used to better assess the hazard of pdcs impacting urban areas and be of service to civil protection authorities and urban planners who work in active volcanic areas

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

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

a model for predicting the volumes of vesicles in submarine basalts the total volume percentage of vesicles in submarine pillow basalt rinds can be modelled by the exsolution of h o and co vapor using available solubility determinations for these components in basalt in accordance with observations on natural samples co is predicted to be the major vapor component in vesicles at eruption depths 1 2 km only small initial contents of co 0 1 0 2 wt are consistent with the vesicle volumes observed in most deep sea pillow lavas h o is important only at shallow depths crystallization of pillow interiors can lead to more extensive vesiculation inside of pillow lavas than in the vesicle poor outer rinds

explosive activity and generation mechanisms of pyroclastic flows at arenal volcano costa rica between 1987 and 2001 explosive activity at arenal and associated tephra fall that has occurred over the 14 year period from 1987 2001 is described explosions have been notably variable in both frequency and size a marked decrease in both frequency and quantity of tephra fallout occurred in early 1998 until the end of 2001 grainsize distributions of cumulative tephra samples collected once a month are typically bimodal aggregation causing premature fallout of fine ash and possibly fallout from ash plumes produced by pyroclastic flows are considered responsible for the bimodality of fallout scanning electron microscopy of the glass component of tephra from single explosions show predominantly blocky and blocky fluidal clast types interpreted as being the product of vulcanian type explosions fragmentation of a mainly rigid degassed magma body and a minor molten component is inferred for these explosions pyroclastic flows were produced either associated with the larger explosions by a mechanism of column collapse 1987 1990 or unrelated to explosions by partial collapse of the crater wall 1993 1998 2000 2001 pyroclastic flow activity has migrated from west to north during the period reported pyroclastic flow deposits are variable in the quantity of juvenile material and any associated surge component large juvenile blocks were partially molten on emplacement and many have a typical cauliform texture blocks with both juvenile and lithic textures indicate that at the summit magma was in intimate contact with the pre existing edifice rather than as a simple open crater or lava pool crater wall collapse may have been promoted by the reduction in explosive activity which has increased the lava accumulation at the summit and in turn increased instability of the summit region thus although explosive activity has waned if the lava output is maintained the hazard of pyroclastic flows is likely to continue

giant debris avalanches from the colima volcanic complex mexico implications for long runout landslides 100 km and hazard assessment at least two giant volcanic debris avalanche deposits are associated with the colima volcanic complex located in the western part of the trans mexican volcanic belt one avalanche originated from volcan de colima 3820 m probably 4300 yr ago a much larger avalanche originated from nevado de colima 4240 m 18500 yr ago it traveled more than 120 km from its source and covered an area of at least 2200 km 2 almost twice the area of any previously described avalanche deposit this older debris avalanche is the second largest by volume known has the longest travel distance yet reported and has one of the lowest height length ratios 0 04 the avalanche material was probably hot during emplacement and after initial slope failure may have behaved similarly to a pyroclastic flow such large long runout landslides from volcanic or nonvolcanic constructs present a serious geologic hazard that must be considered in risk assessment

dynamics and deposits generated by the kos plateau tuff eruption controls of basal particle loss on pyroclastic flow transport the explosive eruption of voluminous silicic magmas often produces widespread and massive deposits formed from pyroclastic density currents while these punctuated events dramatically alter the landscape and have potential climate altering impact our understanding of the internal structure and transport dynamics of these eruptions is hampered by a lack of direct observations we utilize the natural boundary conditions encountered by the eruption of the kos plateau tuff to probe its internal structure as well as constrain the neotectonic activity in the region and eruption duration of this moderate to large 60 km3 event at the time of the eruption 161 ka the lower sea level in the mediterranean may have resulted in flows that traversed mostly land to the north of the eruptive vent while flows to the south may have encountered an expanse of water steep topography and overwater transport can impede the transport of the dense basal portions of the flow where particles make multiple or sustained contact with the bed we use an eulerian eulerian lagrangian computational approach coupled with overwater and overland boundary conditions including topography to determine the role of bed load versus suspended load in the transport of these flows we find that a ring vent structure and eruptive fluxes greater than 2 106 m3 s are required for the spatial distribution of the kpt the maximum grain size and deposit locations of the first voluminous ignimbrite unit d can be explained by suspended flow to the south consistent with overwater transport and bed load and suspended load transport to the north consistent with overland transport however the maximum lithic size for the largest and last ignimbrite unit e requires some bed load transport in all directions we propose that the boundary conditions were significantly altered during the course of the eruption through either the in filling of a shallow sea to the south or the development of a thick pumice raft to aid saltation on the basis of the inferred eruptive flux we estimate that the duration of the eruption climax in which most of the material was erupted likely only lasted from a few hours to a day

the 17 july 1999 block and ash flow baf at colima volcano new insights on volcanic granular flows from textural analysis abstract on july 17 1999 a strong explosion occurred at colima volcano mexico that produced a 10 km high eruptive column the partial column collapse originated a block and ash flow baf that flowed to the south along the san antonio and montegrande ravines travelling 3 3 km from the volcano summit the flow filled the ravines with a volume estimated at 7 9 105 m3 the erosion of these deposits occurred between 1999 and 2002 time of sampling providing excellent longitudinal outcrops that allowed their detailed textural study the study was carried out by means of quantitative textural analysis 1 rosiwal intersections for carrying out vertical granulometric profiles 2 total grain size analysis from 11 to 9 and 3 fourier and fractal analysis of the particle morphology grain size and morphometric parameters obtained with these methods were used to identify vertical and longitudinal variation patterns in the baf deposit the grain size variations allowed to infer the main particle segregation mechanisms that acted during transport and deposition of the studied bafs the two methods used for studying the particle shape morphologies yielded results with different accuracy and reliability in particular fractal analyses have been found to be the most effective in describing the particle support mechanisms that acted during transport and deposition of the studied bafs the results highlight the importance of the information obtained by means of these techniques and provide new insights in transportation and deposition mechanisms of bafs

insights into the october november 2010 gunung merapi eruption central java indonesia from the stratigraphy volume and characteristics of its pyroclastic deposits abstract the 2010 eruption of merapi was the second most deadly in the historic record of this volcano claiming over 380 lives by relating the observations of this eruption with detailed examination of deposit distribution stratigraphy and sedimentology a reconstruction of the properties of the pyroclastic density currents pdcs is presented including the valley controlled block and ash flows bafs and widespread energetic pyroclastic surges the distribution volume and mobility characteristics of all types of pdc during the eruption sequence show evidence for levels of intensity unseen since the large scale 1872 and 1930 eruption phases especially during the climactic events of october 26 and november 5 many tephra falls interbedded with pdc units show that most dome collapse events occurred along with and between explosive vulcanian eruptions the 2010 eruption produced very long runout bafs reaching 16 1 km in the kali gendol on november 5 this runout could be explained by its large volume 20 million m 3 around 10 times that of previous merapi bafs during the last 130 years major avulsion of these dense bafs to form overbank deposits became more common through the eruptive sequence as the valley was progressively filled with successive pdc deposits spreading avulsed bafs were a particular hazard downstream of 10 km where the landscape is less dissected less clear however is why pyroclastic surges extended up to 10 km from the vent on november 5 and 6 4 km on october 26 these expanded much farther from baf margins 2 km than ever seen before at merapi in one location they were decoupled from valley centered bafs with high momentum traveling initially laterally across steep valley systems before draining downslope at this site on the western side of the upper gendol at around 3 km from source surge decoupling was apparently exacerbated by upstream collision and deflection of high flux hot and gas rich bafs against the cliffs of gunung kendil the 1 4 km long cliff face was impacted directly for the first time in 2010 events and may have been responsible for the formation of larger than normal turbulent ash rich clouds above bafs these results imply that future eruption events under the present summit and upper flow path configuration are also highly likely to generate wide dispersal pyroclastic surges and extreme hazard especially now that dense forest has been destroyed on the upper southern slopes of the volcano

effect of grain size on mobility of dry granular flows of angular rock fragments an experimental determination abstract rapid mass movements of rock fragments are among the most hazardous natural phenomena they are too dangerous to be approached and studied directly and for this reason experiments are necessary to understand their flow mechanisms here we present the results of experiments on granular flow mobility obtained releasing batches of angular rock fragments down a curved chute our experiments demonstrate that the finer the grain size of the flow the larger its mobility this is accompanied by a decrease of fragments agitation when grain size decreases as shown by particle image velocimetry measurements of high speed video camera images the smaller the agitation the smaller is also the energy dissipated by flows per unit of travel distance this explains the effect of finer grain size on flow mobility these results are an important step towards the prediction of runout distances as a function of the features that characterize the different geophysical flows

high spatial resolution imagery helps map deposits of the large vei 4 2010 merapi volcano eruption and their impact the 26 october 23 november 2010 eruption is merapi s largest event vei 4 over the past 140 years we used high spatial resolution hsr imagery from geoeye pleiades ikonos and spot5 satellites to assess the extent and effects of the pyroclastic density currents pdcs and subsequent lahars we have tracked the geomorphic and structural fracturing changes of merapi s summit crater and dome between 2008 and 2012 the 4 september 2011 geoeye image shows that due to the explosive eruption the summit area lost about 10 106 m3 the eruption enlarged the sse trending gendol breach to be 1 3 0 3 0 2 km the 2010 tephra and pdc deposits covered about 26 km2 in the two catchments of gendol and opak rivers on merapi s south flank i e 60 75 of the total pdc deposit area with a total bulk volume of 45 106 m3 the tephra fall deposit covered an area of about 1300 km2 with a range in volume of 18 21 106 m3 supervised and object oriented classification on hsr imagery enables us to map in detail the pdc deposits across the gendol opak catchment we delineated 16 spectrally and or texturally distinct units of pdc deposits and compared them with previously published results they encompass high energy surge deposits within ca 8 km of the summit valley confined pdc deposits channeled as far as 16 5 km in the gendol river and widespread overbank pdc with ash cloud surge deposits on valley margins

nature and velocity of pyroclastic density currents inferred from models of entrainment of substrate lithic clasts abstract deposits of pyroclastic density currents pdcs often contain accidental lithic clasts of typical size of 0 1 1 m captured from an underlying substrate by the parent flows at distances up to several tens of kilometers from the eruptive vent in order to gain insights into the nature of pdcs this study investigates the conditions required for entrainment of particles from a granular substrate by a gas particle density current with special emphasis to ignimbrite forming currents whose dynamics are controversial the two types of physics of emplacement of pdcs proposed in literature are considered the first model deals with a hydraulically rough dilute turbulent pdc of bulk density of 1 10 kg m 3 and considers that entrainment through both traction and saltation is controlled by a shield criterion at high 10 4 particle reynolds number the second model considers entrainment by a pdc consisting of a dense basal flow of bulk density of the order of 10 3 kg m 3 and with high interstitial gas pore pressure this model involves uplift of substrate particles caused by an upward pressure gradient at the flow substrate interface and then transport and deposition on the aggrading basal deposit of the flow as demonstrated by recent laboratory experiments results show that a dilute pdc can entrain blocks of maximum size of 10 15 cm for a block density of 2000 3000 kg m 3 if maximum current velocities up to 100 m s are taken into account this in turn suggests that larger heavier blocks found in deposits were captured by pdcs if these had a dense basal flow the dense flow model predicts that pdcs have the potential to entrain metric blocks whose maximum size up to 2 5 m decreases with decreasing atmospheric pressure i e increasing altitude application of the model considering published data on the characteristics of accidental blocks in several well studied ignimbrites indicates that the velocity of the parent dense pdcs was up to 25 30 m s

deposits and physical properties of pyroclastic density currents during complex subplinian eruptions the ad 472 pollena eruption of somma vesuvius italy small scale pyroclastic density currents pdcs associated with the ad 472 pollena eruption of somma vesuvius italy were generated by both magmatic and phreatomagmatic explosive fragmentation the resulting deposits were emplaced under flow boundary conditions dominated by varying combinations of grain interaction fluid escape and traction processes stratigraphic and lithofacies analysis of these pdcs offers a new perspective on the en masse versus progressive aggradation debate for pdc deposition in particular the analyses indicate that pdcs were density stratified with a basal underflow dominated by grain interactions the underflows comprised trains of self organized granular pulses of variable thickness and magnitude depending on the overall particle concentration and fluid turbulence a change in gradient between the upper and lower slopes of the volcano promoted deposition and the different pulses aggraded sequentially stepwise in this model each pulse stops en masse and the whole deposit aggrades progressively particle concentration density mean velocity and flow height were assessed for the studied pdcs using differaent methods for massive and stratified deposits the calculated mobility of the flows was 0 2 to 0 3 in the expected range for small scale pdcs

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

sector collapse of the sw flank of volcan de colima mexico the 3600 yr bp la lumbre los ganchos debris avalanche and associated debris flows abstract some 3600 years ago the sw flank of volcan de colima collapsed generating a debris avalanche that travelled 25 km to the armeria river and stopped against the cerro grande limestone escarpment the debris avalanche deposit covers an area of 48 km2 has an average thickness of 35 m and a volume of 1 7 km3 with an h l ratio of 0 13 along the la lumbre ravine the deposit forms a series of flat terraces up to 65 m thick a pyroclastic flow deposit overlies the debris avalanche deposit suggesting that the colima collapse was accompanied by a magmatic component the debris avalanche deposit dammed the armeria river forming a temporary lake that accumulated a water volume of 0 19 km3 the subsequent breaking of the dam formed a debris flow that travelled at least 20 km along the armeria river emplacing 15 70 m thick deposits the debris flow deposits cover a surface of 6 4 km2 and have a volume of 0 2 km3 the avalanche deposit contains fragments of carbonized wood that where dated at 3600 120 yr bp by komorowski et al 1997 this deposit underlies a younger debris avalanche 2505 45 yr bp and a debris flow deposit with pottery shards and charcoal dated at 1940 90 yr bp these pottery shards likely related to the capacha people 820 300 yr bc indicating that the region has been inhabited during the last 3000 years a future collapse of volcan de colima in the same direction may affect several towns for a total population of circa 40 000

field observations and surface characteristics of pristine block and ash flow deposits from the 2006 eruption of merapi volcano java indonesia abstract a series of pristine block and ash flow deposits from the may june 2006 eruption of merapi represent an exceptional record of small volume pyroclastic flows generated by gravitational lava dome collapses over a period of about two months the deposits form nine overlapping lobes reaching 7 km from the summit in the gendol river valley on the volcano s southern flank which were produced by successive flows generated during and after the major dome collapse event on june 14 both single pulse post june 14 events and multiple pulse pyroclastic flows generated by sustained dome collapses on june 14 are recognised and three types of deposits spread over an area of 4 7 km are distinguished totalling 13 3 10 6 m 3 1 valley confined basal avalanche deposits 11 7 10 6 m 3 in the gendol river valley 2 overbank pyroclastic flow and associated surge deposits 1 4 10 6 m 3 where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and 3 dilute ash cloud surge deposits 0 2 10 6 m 3 along valley margins variations in the distribution surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic flow forming events and varying modes of transport and deposition of the different flows inferred flow velocities of the largest block and ash flows generated on june 14 vary from 43 8 13 5 m s for the basal avalanche and from 62 6 24 2 m s for the ash cloud surge the minimum temperatures range from 400 c for the basal avalanche to 165 c for the overlying ash cloud due to the potential of being re channeled into adjacent river valleys and flowing laterally away from the main river channel the overbank pyroclastic flows are considered the most hazardous part of the block and ash flow system the conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at merapi and similar volcanoes elsewhere

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

pyroclastic flows generated by gravitational instability of the 1996 97 lava dome of soufriere hills volcano montserrat numerous pyroclastic flows were produced during 1996 97 by collapse of the growing andesitic lava dome at soufriere hills volcano montserrat measured deposit volumes from these flows range from 0 2 to 9 106 m flows range from discrete single pulse events to sustained large scale dome collapse events flows entered the sea on the eastern and southern coasts depositing large fans of material at the coast small runout distance 1 km flows had average flow front velocities in the order of 3 10 m s while flow fronts of the larger runout distance flows up to 6 5 km advanced in the order of 15 30 m s many flows were locally highly erosive field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates

flow and deposition of pyroclastic granular flows a type example from the 1975 ngauruhoe eruption new zealand small volume pyroclastic density currents pdcs are generated frequently during explosive eruptions with little warning assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and or deposits to this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small volume pdc deposits from the 1975 eruption of ngauruhoe volcano whose emplacement were also witnessed during eruption using high resolution gps surveys a series of lateral excavations across the deposits and bulk sedimentological analysis we constrained the geomorphology internal structure and texture of the deposits with respect to laterally varying modes of deposition deposition from these pdcs began only on slopes at or around the material s angle of repose c 30 in unconfined settings the granular pdcs are interpreted to have been quasi steady forming sheets and lobes around the angle of repose where flows were confined sheet like proximal facies made up around 10 of the deposit volume at the angle of repose but 90 of the material was deposited from apparently unsteady inertial granular pdcs as a distal levee and channel facies on slopes well below the repose angle hence confined pdcs were able to travel up to 50 farther than unconfined flows in the distal facies the deposit width is inversely correlated to the local slope and the height of the levees above the deposit centreline is positively correlated with slope internally the deposits comprise three parts a coarse grained fines free sole layer that laterally connects to levees zone i an ashy matrix supported central body zone ii and an overlying coarse plaster of clasts zone ii trends in grain size data suggests these zones derive from a continuous un mixing of coarse particles from the initial bulk material by granular segregation that preferentially drives large particles to the upper free surface of the flow where they are concentrated at the front of flow before being deposited and overrun by comparison to analogue experiments we suggest a model of flow and deposition where the temporally and spatially varying mode of deposition is determined by the flow velocity the local slope the vertical velocity gradient the velocity gradient at the free surface and the vertical deposition rate using this model estimated vertical deposition rates of c 5 cm s 1 from the ngauruhoe pdcs agree with those determined in laboratory experiments on inertial granular flows

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

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

evaluation of the impact of the 2010 pyroclastic density currents at merapi volcano from high resolution satellite imagery field investigations and numerical simulations the 2010 pyroclastic density currents pdc at merapi have presented a rare opportunity to collect a uniquely detailed dataset of the source extent lateral variations and impact of various pdc deposits on a densely populated area using traditional volcanological field based methods and a multi temporal dataset of high resolution satellite imagery a total of 23 pdc events have been recognized including 5 main channeled flows 15 overbank flows derived from overspill and re channelization of the main pdcs into adjacent tributaries and two main surge events the 2010 pdc deposits covered an area of 22 3 km2 unequally distributed between valley filling 6 9 overbank 22 4 and surge and associated fallout deposits 71 7 their total estimated non dre volume is 36 3 106 m3 with 50 2 of this volume accounting for valley filling deposits 39 3 for overbank deposits and 10 5 for surge and associated fallout deposits more than 70 of the total volume was deposited during the third eruptive phase 4 5 november and only 16 6 11 5 and 0 9 during the first 26 29 october second 30 october 3 november and fourth phase 6 23 november respectively the internal architecture and lithofacies variations of the 2010 pdc deposits were investigated using data collected from 30 stratigraphic sections measured after one rainy season of erosion the results show that complex local scale variations in flow dynamics and deposit architectures are apparent and that the major factors controlling the propagation of the main flows and their potential hazards for overbanking were driven by 1 the rapid emplacement of several voluminous pdcs associated with the steady infilling of the receiving landscape after the two first phases of the eruption 2 longitudinal changes in channel capacity following increased sinuosity in the valley and decreased containment space and 3 the effects of varying source mechanisms gravitational dome collapse vertical or lateral dome explosions and column collapse and source materials involved during individual pdc forming events integration of these data into numerical simulations of the channeled and overbank pdcs of the third eruptive phase 4 5 november using two well established geophysical mass flow models titan2d and volcflow allow us to evaluate the ability of these models to reproduce the main features of the natural deposits and some of the flow overbanking processes observed in the field using such a multi technique approach the dataset obtained in this study not only characterizes the pdcs and related hazards at merapi but will allow comparisons with similar events at other volcanoes around the globe

deposit architecture and dynamics of the 2006 block and ash flows of merapi volcano java indonesia the internal architecture of the 2006 block and ash flow deposits of merapi volcano java indonesia was investigated using data collected from 27 stratigraphic sections measured immediately after flow emplacement and after one and two rainy seasons of erosion identification of different depositional units and their longitudinal and lateral facies variations provide detailed information about i the distribution volumes and sedimentological characteristics of the different units ii flow types and mobility as inferred from associated deposits and iii changes in the dynamics of the different flows and their material during emplacement two main types of block and ash flows short runout to medium runout block and ash flows and long runout block and ash flows are defined based on flow generation mechanism flow volume travel distance deposit morphology distribution lithology and grain size distribution conceptual models for the transport and depositional mechanisms of these two types of block and ash flows are presented variations in the runout distances observed for short runout to medium runout block and ash flows are linked directly to different initial flow volumes degree of fragmentation and material properties of the moving mass during transport with the largest and finer grained flows having the greatest mobility deposition occurs only over a narrow range of basal inclinations close to the angle of repose for pyroclastic material indicating that such flows behave in a similar way to granular free surface flows on unconfined planes the flow mechanisms of long runout block and ash flows at merapi are interpreted to be similar in many respects to unsteady cohesionless grain flows with an inertial flow regime where collisional forces largely overcome frictional forces flow unsteadiness causes the main body to be segmented into different pulses that run closer to each other as the flow moves downslope deposition occurs stepwise with rapid aggradation of stacked sub units from different parts of the major flow pulses in such a model the arrival of each flow pulse front at selected sites in the main river valley controls the generation and development of highly mobile unconfined pyroclastic flows outside valley regions and their associated overbank deposits

paroxysmal dome explosion during the merapi 2010 eruption processes and facies relationships of associated high energy pyroclastic density currents an 11 minute sequence of laterally directed explosions and retrogressive collapses on 5 november 2010 at merapi indonesia destroyed a rapidly growing dome and generated high energy pyroclastic density currents pdcs spreading over 22 km2 with a runout of 8 4 km while contemporaneous co genetic valley confined pdcs reached 15 5 km this event formed stage 4 of the multi stage 2010 eruption the most intense eruptive episode at merapi since 1872 the deposits and the widespread devastating impact of associated high energy pdcs on trees and buildings show striking similarities with those from historical volcanic blasts montagne pelee martinique bezymianny russia mount st helens usa soufriere hills montserrat we provide data from stratigraphic and sedimentologic analyses of 62 sections of the first unequivocal blast like deposits in merapi s recent history we used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree blowdown the stratigraphy of stage 4 consists of three depositional units u0 u1 u2 that we correlate to the second third and fourth explosions of the seismic record both u1 and u2 show a bi partite layer stratigraphy consisting each of a lower l1 layer and an upper l2 layer the lower l1 layer is typically very coarse grained fines poor poorly sorted and massive and was deposited by the erosive waxing flow head the overlying l2 layer is much finer grained fines rich moderately to well sorted with laminar to wavy stratification l2 was deposited from the waning upper part and wake of the pdc field observations indicate that pdc height reached 330 m with an internal velocity of 100 m s 1 within 3 km from the source the summit s geometry and the terrain morphology formed by a major transversal ridge and a funneling deep canyon strongly focused pdc mass towards a major constriction thereby limiting the loss of kinetic energy this favored elevated pdc velocities and high particle concentration promoted overspilling of pdcs across high ridges into other river valleys and generated significant dynamic pressures to distances of 6 km that caused total destruction of buildings and the forest the merapi 2010 eruption highlights that explosive and gravitational disintegration of a rapidly growing dome can generate devastating high energy high velocity pdcs this constitutes a credible high impact scenario for future multi stage eruptions at merapi and at other volcanoes that pose particular monitoring crisis response and risk reduction challenges

lessons in reducing volcano risk since 1980 volcanologists have confronted more volcanic crises than any time since the mont pelee catastrophe in 1902 good science alone will not do the job of reducing volcano risk