empirical prediction of debris flow mobility and deposition on fans a new method to predict the runout of debris flows is presented a data base of documented sediment transporting events in torrent catchments of austria switzerland and northern italy has been compiled using common classification techniques with this data we test an empirical approach between planimetric deposition area and event volume and compare it with results from other studies we introduce a new empirical relation to determine the mobility coefficient as a function of geomorphologic catchment parameters the mobility coefficient is thought to reflect some of the flow properties during the depositional part of the debris flow event the empirical equations are implemented in a geographical information system gis based simulation program and combined with a simple flow routing algorithm to determine the potential runout area covered by debris flow deposits for a given volume and starting point of the deposits a monte carlo technique is used to produce flow paths that simulate the spreading effect of a debris flow the runout zone is delineated by confining the simulated potential spreading area in the down slope direction with the empirically determined planimetric deposition area the debris flow volume is then distributed over the predicted area according to the calculated outflow probability of each cell the simulation uses the arc objects environment of esri and is adapted to run with high resolution 2 5 m 2 5 m digital elevation models generated for example from lidar data the simulation program called toprundf is tested with debris flow events of 1987 and 2005 in switzerland copyright 2009 john wiley sons ltd

a probabilistic model of debris flow delivery to stream channels demonstrated for the coast range of oregon usa debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance identification of channels susceptible to debris flow inputs of sediment and organic debris and quantification of the likelihood and magnitude of those inputs are key tasks for characterizing spatial and temporal patterns found in channel conditions and associated habitats in a river network widely available digital elevation and land cover data 10 m dems and 25 m satellite imagery offer the potential to assess debris flow runout paths over regional extents this paper presents a model for using these data to calculate empirical probabilities for debris flow runout over dem determined flow paths and shows how these probabilities can be combined over all sources to estimate the potential for debris flow delivery to stream reaches throughout entire channel networks the model is calibrated and model predictions are compared to field mapped debris flow travel paths from study sites in the coast range of oregon usa this model predicts debris flow probability over channel reach scales that can be aggregated to basin scale measures of debris flow potential it offers unprecedented ability to characterize debris flow effects over channel networks providing a tool for risk assessment and for generating hypotheses that relate topographic and forest cover controls on debris flow runout to the types and abundance of channel habitats in a river basin

understanding how volume affects the mobility of dry debris flows 1 the prediction of the runout length l of large dry debris flows has long been the subject of a considerable research effort primarily due to the obvious concern caused by their destructive power one seemingly well established feature is the increase of the mobility of a rock avalanche defined as the ratio of the runout distance to the fall height with its volume v the physical nature of this lubrication mechanism remains however controversial in this paper we analyse field data and discrete numerical simulations of granular flows and demonstrate the geometrical origin of the apparent enhancement of the mobility with the volume we evidence the intertwined role of volume and topography and show the existence of two contributions in the runout defining two flow regimes one dominated by sliding in which the runout is independent of v and another dominated by spreading in which the runout is strongly dependent on v in the light of these results the search of a volume dependent lubrication mechanism appears to be an ill posed problem

sedimentology and clast orientations of the 18 may 1980 southwest flank lahars mount st helens washington abstract three lahars that resulted from the flow transformation of an milled pyroclastic surge caused by ejected lithic debris and hydrothermal water during the cataclysmic mount st helena eruption of 18 may 1980 deposited about 1 106 m3 of massive poorly sorted poorly graded volcaniclastic sediment on the southwest flank swf mean peak flow velocities over a 5 km radius ranged from more than 30 m s in the proximal area mean slope angle of 13 to about 5 m s in the distal area mean slope angle of 4 9 the lahars rapidly decelerated as deposition occurred on forested slopes average yield strength of the swf lahars ranged from 9 000 to 12 000 dn cm2 bingham viscosity ranged from 2 8 103 to 50 103 poises average flow density of the swf lahars was about 2 0 g cm3 to determine the grain size distribution of the swf lahars spot sampling of deposit matrix from vertical exposures was supplemented with point count sampling of larger particles results from these analyses indicate that downflow changes in mean gram size and sorting occur only in the coarse fraction of the deposits larger than a critical diameter of about 4 mm and occur only in the basal portion of the deposits both mean grain size and sorting coefficient increase slightly with distance the deposits show weak inverse grading with respect to mean grain size and exhibit a weak trend of upwardly poorer sorting fabric analyses of clast long axes indicate strong planar orientations parallel to flow surfaces an eigenvalue analysis demonstrates the occurrence of both flow parallel long axis orientations with upstream dips and flow transverse orientations similar clast fabric results were obtained for deposits of the north fork toutle river lahar however the mean clast long axis dip in the swf lahars is significantly shallower than the mean clast long axis dip in the north fork toutle lahar and is more like clast long axis dips reported for tills and other sediment flows the data from the swf lahars indicate that lahar clast fabric may be more complex and variable than previously suggested

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

flow characteristics of large eruption triggered debris flows at snow clad volcanoes constraints for debris flow models abstract theoretical modelling is not yet adequate to predict the behavior of debris flows which can be an extremely hazardous hydrologic process commonly associated with volcanic eruptions particularly at snow clad stratovolcanoes to provide a realistic basis for modelling the behavior of large 1000 m3 s debris flows this paper summarizes kinematic volumetric and hydraulic characteristics of ten large historic volcanic debris flows from four different volcanoes although debris flows larger than these are known to have occurred in the past the ten summarized here define a practical upper range in magnitude of more typical flows to be considered for future hazard prediction peak flow velocities of the ten debris flows studied were indirectly measured to be between about 5 and 20 m s on gradients of 0 005 to 0 25 m m but locally they were as great as 40 m s hydraulic average depths were as great as 25 m but were more commonly between 5 and 15 m in channels up to 400 m wide computed peak discharges volumetric flow rates were as high as 105 m3 s and total volumes were as much as 108 m3 total flow volumes increased by as much as four times in relatively steep channels as eroded sediment was incorporated into the debris flows flows generally achieved supercritical flow and deposited minimal volumes of sediment on gradients steeper than 0 02 m m subcritical flow and active deposition predominated on gradients less than 0 01 m m although flows travelled tens of kilometers on such low gradients while laying down deposits total distances travelled as debris flows were as far as 120 km

prediction of debris flow inundation areas using empirical mobility relationships abstract a method proposed for delineating lahar hazard zones in volcanic valleys is adapted to debris flows the original method is based on two predictive equations that relate the lahar volume to the cross sectional inundated area and to the planimetric inundated area these predictive equations were derived by combining a scaling analysis of lahar kinematics with the statistical analysis of data for 27 historical lahars this paper tests the applicability of this approach to debris flow fans forty debris flow basins in the italian alps were surveyed and data on 27 historical debris flow events were collected in the field or by means of aerial photo analysis collected data reveal that the flow area a and the planimetric area b of a debris flow are linearly correlated to the debris flow volume v on a logarithmic scale with high statistical significance moreover the computed regression equations are very similar to those obtained from other published datasets on debris flows leading to the global fitting equations a 0 08 v 2 3 and b 17 v 2 3 these predictive equations are then implemented in an automated code dflowz that delineates the inundated area on a debris flow fan on the basis of a user specified debris flow volume taking the statistical uncertainty in the prediction into account dflowz is simple reproducible and it can handle both confined and unconfined flow the model is tested against 10 historical debris flow events providing a satisfactory agreement between observed and computed inundated areas in spite of the limitations due to dem accuracy and statistical uncertainty of the regression parameters test results show that the method can be useful for practical applications

evidence for catastrophic volcanic debris flows in pemberton valley british columbia the mount meager volcanic complex in southern british columbia is snow and ice covered and has steep glaciated and unstable slopes of hydrothermally altered volcanic deposits three large volume 108 m3 volcanic debris flow deposits derived from the mount meager volcanic complex have been identified the volcanic debris flows travelled at least 30 km downstream from the volcanic complex and inundated now populated areas of pemberton valley clay content and mineralogy of the deposits indicate that the volcanic debris flows were clay rich 5 7 clay in the matrix and derived from hydrothermally altered volcanic material the youngest volcanic debris flow deposit is interpreted to be associated with the last known volcanic eruption 2360 calendar cal years bp the other two debris flows may not have been directly associated with eruptions volcanic debris flow hazard inundation maps have been produced using the geographic information system gis based modelling program laharz the maps provide esti

magnetization carriers and remagnetization of bedded chert abstract article history received 22 october 2010received in revised form 11 january 2011accepted 25 february 2011editor p demenocalkeywords bedded chertremanencebiogenic magnetitehematite bedded chert is the only sediment type representative of the paleozoic to early mesozoic pelagic marineenvironment becauseoftheirassociationwithophiolitesandislandarcrocks presenceofdatablemicrofossilsandpaleohorizontalreferenceprovidedbywell developedbeddingsurfaces beddedchertsequencesareoftentargeted for paleomagnetic tectonic studies however processes of magnetization acquisition in biosiliceoussediments and consequently the signi cance of their magnetic record are not well understood our rockmagnetic study of a triassic jurassic radiolarian chert sequence the mino terrane central japan shows thatthe ferrimagnetic assemblage of the gray chert units is of detrital origin while the red chert s assemblage isdominated by authigenic phases pigmentary hematite and biogenic magnetite which contribute to thenatural remanent magnetization the presence of magnetofossils places red oxic chert in the category ofprospective environmental archives magnetite producing magnetotactic bacteria were apparently able totolerate elevated concentrations of dissolved silica as well as a steep redox gradient in sedimentary pore waters during the deposition of red chert layers a strong uniaxial anisotropy due to chain alignment of thebiogenic magnetite grains likely contributes to the acquisition of anomalously stable partial thermoviscousmagnetization by chert even at low metamorphic temperatures 2011 elsevier b v all rights reserved

a comparison of pyroclastic flow and debris avalanche mobility many pyroclastic flows have runout distances longer than expected from basic frictional arguments in these cases the ratio of the height descended h and the runout l are as small as 0 2 a feature which has been attributed to fluidization however significant fluidization by gases is now considered unlikely during emplacement of debris avalanches where h l and volume are inversely related we determine whether pyroclastic flows are more mobile than debris avalanches of the same volume and if different emplacement mechanisms are needed to describe their runout h l and volume data were compiled for 34 nonvolcanic and 40 volcanic debris avalanche deposits as well as 15 pyroclastic flow deposits systematic differences in the volume versus h l plots were explored by statistical analysis results show an inverse relationship between h l and volume for both nonvolcanic and volcanic debris avalanche deposits as expected and also for pyroclastic flow deposits regression lines for plots of pyroclastic flow and volcanic debris avalanche data are statistically indistinguishable and the non volcanic debris avalanche line is parallel to the other two we argue that the nonvolcanic and volcanic debris avalanche differences are due to material properties rather than emplacement mechanisms therefore since pyroclastic flows and volcanic debris avalanches have indistinguishable h l versus volume it is unlikely that pyroclastic flows have a significantly different primary emplacement mechanism based on the data in hand we conclude that it is unnecessary to invoke gas fluidization to explain the mobility of the types of pyroclastic flows examined or the excess runout of large volume debris avalanches

probabilistic modeling of tephra dispersal hazard assessment of a multiphase rhyolitic eruption at tarawera new zealand 1 the tarawera volcanic complex comprises 11 rhyolite domes formed during five major eruptions between 17 000 b c and a d 1886 the first four of which were predominantly rhyolitic the only historical event erupted about 2 km3 of basaltic tephra fall a d 1886 the youngest rhyolitic event erupted a tephra fall volume more than 2 times larger and covered a wider area northwest and southeast of the volcano a d 1315 kaharoa eruption we have used the kaharoa scenario to assess the tephra fall hazard from a future rhyolitic eruption at tarawera of a similar scale the plinian phase of this eruption consisted of 11 discrete episodes of vei 4 we have developed an advection diffusion model tephra that allows for grain size dependent diffusion and particle density a stratified atmosphere particle diffusion time within the rising plume and settling velocities that include reynolds number variations along the particle fall simulations are run in parallel on multiple processors to allow a significant implementation of the physical model and a fully probabilistic analysis of inputs and outputs tephra is an example of a class of numerical models that take advantage of new computational tools to forecast hazards as conditional probabilities far in advance of future eruptions three different scenarios were investigated for a comprehensive tephra fall hazard assessment upper limit scenario eruption range scenario and multiple eruption scenario hazard curves and probability maps show that the area east and northeast of tarawera would be the most affected by a kaharoa type eruption

physical models of rock avalanche spreading behaviour with dynamic fragmentation the dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or sturzstrome this paper investigates whether test

hazardous processes and events from glacier and permafrost areas lessons from the chilean and argentinean andes glacier and permafrost hazards such as glacial lake outburst floods and rock ice avalanches cause significant socio economic damages worldwide and these processes may increase in frequency and magnitude if the atmospheric temperature rises in the extratropical andes nearly 200 human deaths were linked to these processes during the twentieth century we analysed bibliographical sources and satellite images to document the glacier and permafrost dynamics that have caused socio economic damages in this region in historic time including glacial lake outburst floods ice and rock ice avalanches and lahars to unravel their causes and geomorphological impacts in the extratropical andes at least 15 ice dammed lakes and 16 moraine dammed lakes have failed since the eighteenth century causing dozens of floods some floods rank amongst the largest events ever recorded 5000 106 m3 and 229 106 m3 respectively outburst flood frequency has increased in the last three decades partially as a consequence of long term decades to centuries climatic changes glaciers shrinkage and lake growth short term days to weeks meteorological conditions i e intense and or prolonged rainfall and high temperature that increased meltwater production have also triggered outburst floods and mass movements enormous mass failures of glaciers and permafrost 10 106 m3 have impacted lakes glaciers and snow covered valleys initiating chain reactions that have ultimately resulted in lake tsunamis and far reaching 50 km flows the eruption of ice covered volcanoes has also caused dozens of damaging lahars with volumes up to 45 106 m3 despite the importance of these events basic information about their occurrence e g date causes and geomorphological impact which is well established in other mountain ranges is absent in the extratropical andes a better knowledge of the processes involved can help to forecast and mitigate these events copyright 2014 john wiley sons ltd

presenting regional shallow landslide movement on three dimensional digital terrain abstract a storm can trigger numerous shallow landslides on hilly terrains this paper presents a distributed cell model for presenting regional shallow landslide movement on a three dimensional digital terrain the model consists of five components namely a digital terrain module a spatial rainfall distribution module an infiltration analysis module a slope stability evaluation module and a movement prediction module the locations and volumes of landslides are analyzed first through rainfall infiltration and slope stability analyses the detached material is assumed to move along the steepest path from one cell to a lower cell empirical equations that are developed based on local landslide inventories are adopted as a landslide movement cessation criterion the effect of landslide size on travel distance is considered by grouping unstable cells that are bounded at least at one side or corner the uncertainties in soil shear strength parameters and the landslide movement process are considered in determining the possible bounds of travel distance the movement analysis method is applied to a 164 5 km 2 hilly terrain in the wenchuan earthquake zone to test its performance in presenting regional shallow landslide movement the method predicts the volume of landslides reasonably well the observed and computed movement traces and deposition locations of the detached material also agree reasonably well the volume of individual landslide and travel distance may be substantially underestimated if the size effect is not considered

rain triggered lahar susceptibility using a shallow landslide and surface erosion model abstract lahars are mass flows containing variable concentrations of water and volcanic debris that can cause catastrophic impacts to life livelihoods and infrastructure downstream from their volcanic origin accurate and quantitative information on lahar hazards are essential for reducing the impact of these events lahar hazard assessments often focus on the use of numeric or empirical models to describe flow behaviour and inundation areas which rely on historic lahar events and expert elicitation to define model inputs this results in qualitative or semi quantitative estimates of hazard that do not account for the mechanics of lahar initiation or in the case of rain triggered lahars the dependence of rainfall intensity and duration on initiation here we develop a method for calculating rain triggered lahar susceptibility defined as the occurrence probability of a particular lahar initial volume at a specific location the model relies on terrain and deposit characteristics and a probabilistic measure of rainfall in the form of rainfall intensity frequency duration relationships results for a case study of the october 28 1995 lahar at mangatoetoenui stream ruapehu volcano new zealand indicate lahar volume is controlled by a characteristic timescale relating the deposit depth h to the hydraulic diffusivity d 0 in the ratio h 2 d 0 the timescale describes the transmission of positive pore pressures within the deposit leading to shallow failure as a consequence of this timescale rainfall duration is the most important factor determining initial lahar sediment volume rainfall intensity plays a minor role controlling the volume of water in the lahar mixture this observation is consistent with power law relationships used to determine lahar triggering rainfall thresholds the rain triggered lahar susceptibility approach developed here is anticipated to improve probabilistic lahar hazard assessments by providing quantitative reproducible estimates of initial lahar volumes

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

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

analyzing debris flows with the statistically calibrated empirical model laharz in southeastern arizona usa abstract hazard zone delineation for extreme events is essential for floodplain management near mountain fronts in arid and semiarid regions on 31 july 2006 unprecedented debris flows occurred in the santa catalina mountains of southeastern arizona following extreme multiday precipitation recurrence interval 1000 years for 4 day precipitation most mobilized sediment contributing to debris flows was derived from shallow seated failures of colluvium on steep slopes a total of 435 slope failures in the southern santa catalina mountains released 1 34 million mg of sediment into the channels of 10 drainage basins five drainages produced debris flows that moved to the apices of alluvial fans on the southern edge of the mountain front damaging infrastructure and aggrading channels to reduce future flood conveyance using the statistically calibrated empirical debris flow model laharz and modified model coefficients developed to better match conditions in southeastern arizona we predicted the approximate area of deposition and travel distance in comparison to observed depositional areas and travel distance for seven debris flows two of the modeled debris flows represented single slope failures that terminated downslope with no additive influence of other debris flows or streamflow flooding five of the simulated debris flows represented the aggregation of multiple slope failures and streamflow flooding into multiple debris flow pulses because laharz is a debris flow hazard zone delineation tool the complexity of alternating transport and deposition zones in channels with abrupt expansions and contractions reduces the applicability of the model in some drainage basins

origin and early evolution of lahar channel at mabinit mayon volcano philippines mabinit channel 5 km long 15 to 70 m wide and 2 to 22 m deep was formed by lahars on the southeastern slope of mayon volcano during its 1984 eruption in 1985 the channel was drastically modified by a lahar triggered by a typhoon sediment budget calculations from surveys conducted in 1985 and 1986 corroborate inferences from other volcanoes that lahars can grow significantly in volume by eroding their channels the 1984 eruption produced a deep summit ravine and at its base a fan of avalanche and pyroclastic flow deposits 2 km2 in area and 40 x 106 m3 in volume lahars initiated in the ravine by heavy rains from eruption updrafts carved out 5 km long mabinit channel along the west margin of the pyroclastic avalanche field a position that could not have been predicted from pre eruption topography by eroding the channel the lahars generated more than half of their own solid contents below 240 m where the volcano slope decreases from 5 to 3 the first eruption debris flows were unconfined and spread out over a 512 000 m2 area depositing a layer locally more than 4 m thick with a volume of 1 25 x 106 m3 the thin margins of these unconfined flows were non erosional however as they stopped their thick central portions continued flowing extending the new channel downslope through the depositional field subsequent eruption lahars modified the channel and overflowed at its bends a moderately intense typhoon in october 1985 triggered a single 9 hr lahar event that widened the channel by an average of 25 m and caused as much as 66 m of lateral bank erosion debris flows overtopping the channel at four sites coalesced to cover a 2 km long 200 000 m2 area with bouldery sediment in wider channel stretches debris flow margins left prominent paired levees while their central portions continued moving down channel as rigid plugs the lahar plugged the lower 0 5 km stretch of the channel and replaced it by eroding a new channel of comparable size this demonstrated how easily lahars can change the courses of channels on the upwardly convex debris apron of a stratovolcano with serious consequences for farmland and communities

relevance of erosion processes when modelling in channel gravel debris flows for efficient hazard assessment abstract a storm composed of two delayed cells hit the monte antelao slopes dolomites north eastern italy in the early morning of july 18th 2009 the resulting runoff triggered two consecutive debris flows along the rovina di cancia channel the detailed topographic data collected before and just after this event allowed an accurate reconstruction of the morphological changes experienced by the channel bed these data are here used as benchmark to test the ability of numerical models to reproduce the dynamics of a real event taking into account the morphology changes of the channel bed the aim is to provide an efficient model for engineering applications on large scales such as those required by debris flow hazard assessment a rainfall runoff transformation is applied to reconstruct the solid liquid hydrograph needed for computing the debris flow propagation two routing models are used a gis based movable bed model and a widely used fixed bed model flo 2d although similar results are obtained in terms of areas subjected to deposition significant differences emerge in terms of mobilized volumes only the simulation of both the deposition and entrainment processes allows to reliably reproduce the sediment volumes estimated from the pre and post event topographic data this information is fundamental in any hazard assessment because the volume of sediment mobilized by debris flow events exerts a fundamental control on the extension of areas subjected to inundation and on the thickness of sediment deposits the capability to reproduce correctly the mobilized volumes also entails a more reliable simulation of the evolution of the peak and volume of the solid liquid hydrograph as the debris flow propagates downstream allowing the identification of the channel reach where banks could be overflowed conversely adopting a fixed bed model leads mainly to an underestimation of the both the transported sediments volumes and the area subjected to deposition as a consequence the maximum debris flow depth in the portion of the channel subjected to erosion is underestimated and that in the portion of the channel subjected to deposition is overestimated all these types of information are of great importance for an effective hazard assessment

the role of multiple glacier outburst floods in proglacial landscape evolution the 2010 eyjafjallajokull eruption iceland the 2010 eyjafjallajokull eruption in iceland provided a unique opportunity to quantify the evolution of proglacial geomorphology during a series of volcanogenic jokulhlaups glacial outburst floods 140 events time lapse imagery and repeat terrestrial laser scans before and directly after the eruption show that the jokulhlaup of 14 april 2010 composed 61 of the 57 106 m3 total discharge of the combined events and had the highest peak discharge for the two main flood events but only deposited 18 of the total volume of sediment in front of gigjokull glacier the majority of sediments 67 of a total volume of 17 12 106 m3 were deposited by the 15 april 2010 jokulhlaup and this was followed by extensive reworking by a series of smaller jokulhlaups over the following 29 days that deposited 15 of the total sediment the geomorphological and sedimentary signatures of the two largest jokulhlaups associated with the onset of the eruption have either been reworked by later floods or are buried by later flood deposits consequently the ice proximal posteruption landscape cannot be used to reconstruct the characteristics or magnitudes of either of the two largest jokulhlaups the findings support a complex response model in which peak discharge and the bulk of the sediment transported is decoupled by changing routing mechanisms and water sediment ratios during the eruption

linking rainfall induced landslides with debris flows runout patterns towards catchment scale hazard assessment abstract debris flows and landslides induced by heavy rainfall represent an ubiquitous and destructive natural hazard in steep mountainous regions for debris flows initiated by shallow landslides the prediction of the resulting pathways and associated hazard is often hindered by uncertainty in determining initiation locations volumes and mechanical state of the mobilized debris and by model parameterization we propose a framework for linking a simplified physically based debris flow runout model with a novel landslide hydro mechanical triggering lht model to obtain a coupled landslide debris flow susceptibility and hazard assessment we first compared the simplified debris flow model of perla 1980 with a state of the art continuum based model ramms and with an empirical model of rickenmann 1999 at the catchment scale the results indicate that predicted runout distances by the perla model are in reasonable agreement with inventory measurements and with the other models predictions of localized shallow landslides by lht model provides information on water content of released mass to incorporate effects of water content and flow viscosity as provided by lht on debris flow runout we adapted the perla model the proposed integral link between landslide triggering susceptibility quantified by lht and subsequent debris flow runout hazard calculation using the adapted perla model provides a spatially and temporally resolved framework for real time hazard assessment at the catchment scale or along critical infrastructure roads railroad lines

the cohesive naranjo debris flow deposit 10 km3 a dam breakout flow derived from the pleistocene debris avalanche deposit of nevado de colima volcano mexico abstract mass movement processes on volcanic terrains such as landslides and debris avalanches can cause the obstruction of main drainages producing the formation of temporary dams a good example of this occurred 18 5 ka ago when the eastern flank of the nevado de colima volcano collapsed producing a debris avalanche deposit that was previously described as one of the largest in the world the deposit extended from the volcanic summit as far as the pacific coast 120 km away new stratigraphic sedimentological and componentry data suggest that the volcanic collapse of nevado de colima resulted in a debris avalanche that traveled 20 km southeast to the naranjo river there it crashed against a topographic barrier consisting of cretaceous limestones cerro la carbonera and the flow direction was diverted to the south down the naranjo river channel for another 25 km before the avalanche came to a halt the obstruction of the drainage produced a temporary dam that stored ca 1 km3 of water and deposited fluvial and slack water sediments some time after the damming the accumulated water sediment load was able to overtop the obstructing material and to release a breakout flow with a calculated initial flow discharge of 3 5 million m3 s the resulting flood cohesive debris flow followed the channel of the naranjo river and due to the high erodibility of the channel and introduction of substrate material the debris flow progressively increased its volume up to 10 km3 six times its initial volume this study highlights the relevance of evaluating the potential remobilization of debris avalanche deposits to initiate large magnitude cohesive debris flows therefore the hazard and risk analysis of future potential events of this nature must consider the pre eruption conditions and the topography surrounding a volcano

hillslopes rivers plows and trucks mass transport on earth s surface by natural and technological processes the surface of the earth is being transformed by a new force in the form of technological systems and processes that move significant quantities of mass large distances because movement of mass is perhaps the most basic geomorphic process and because the continuing rise of technology appears to characterize a new epoch in earth evolution the anthropocene it is of interest to compare technological and natural mass transport mechanisms a purely dynamical mass action metric representing the product of mass displaced distance moved and mean speed of displacement is used to compare the transport effectiveness of selected systems systems with large mass action tend to be advective and systems with small mass action diffusive local environments are conditioned by mass action through the introduction of transport corridors such as roads and rivers which put constraints on mass transport by embedded diffusive systems advection also subjects local environments to externally determined time scales such as the times for delivery of unit mass of water or sediment to a river mouth and supports the emergence of associated dynamical processes there for example those of human activity or delta construction that are too rapid to be sustained by diffusion most of the world s mass action is generated by the motion of fluids of global or continental extent as in atmospheric circulation or river flow technological mass action exceeds that of all land based geomorphic systems except rivers technological systems with large mass action tend to be comprised of discrete self powered units e g trucks discretization of transported mass reflects the different locomotion strategy required for transport of solids on land compared with the transport requirements of spatially extensive fluids in nature the principle of maximum entropy production may provide a framework for understanding the emergence of advective technological mass transport systems copyright 2010 john wiley sons ltd

a general model for mt ruapehu lahars a mathematical model of the motion of lahars is presented lahar flows and travel speeds are calculated using a kinematic wave model which equates gravitational accelerations to frictional losses a chezyor manning type law of friction is assumed in which lahar flow rate is a simple power function of lahar depth multiplied by another simple power of the chanel slope use of the model requires knowledge of essentially only one parameter which appears to be relatively insensitive for flows down a given channel variable channel slope effects are removed by a longitudinal scaling which applies to all flows down a given channel for lahars generated by a single explosive event it is unnecessary to perform numerical calculations to predict lahar flow and travel time but for lahnars produced by multiple sources in which different lahar flows are interacting numerical calculations appear necessary the model is applied to all recorded lahar flows from mt ruapehu and satisfactorily described all lahar flows generated by a single explosive mechanism such flows depend essentially only on total lahar volume the 1968 mt ruapehu lahar generated by a series of smaller eruptive mechanisms was modelled as the interaction of seven point sources of fluid originating from positions mathematically extrapolated up the mountain good agreement was obtained between the predicted times of formation of these 1968 lahars and the times of greatest seismic amplitude

a probabilistic multidimensional approach to quantify large wood recruitment from hillslopes in mountainous forested catchments abstract large wood lw plays a key role in physical chemical environmental and biological processes in most natural and seminatural streams however it is also a source of hydraulic hazard in anthropised territories recruitment from fluvial processes has been the subject of many studies whereas less attention has been given to hillslope recruitment which is linked to episodic and spatially distributed events and requires a reliable and accurate slope stability model and a hillslope channel transfer model the purpose of this study is to develop an innovative lw hillslope recruitment estimation approach that combines forest stand characteristics in a spatially distributed form a probabilistic multidimensional slope stability model able to include the reinforcement exerted by roots and a hillslope channel transfer procedure the approach was tested on a small mountain headwater catchment in the eastern italian alps that is prone to shallow landslide and debris flow phenomena the slope stability model that had not been calibrated provided accurate performances in terms of unstable areas identification according to the landslide inventory auc 0 832 and of lw volume estimation in comparison with lw volume produced by inventoried landslides 7702 m3 corresponding to a recurrence time of about 30 years in the susceptibility curve the results showed that most lw potentially mobilised by landslides does not reach the channel network only about 16 in agreement with the few data reported by other studies as well as the data normalized for unit length of channel and unit length of channel per year 0 116 m3 km and 0 4 m3 km y 1 this study represents an important contribution to lw research a rigorous and site specific estimation of lw hillslope recruitment should in fact be an integral part of more general studies on lw dynamics for forest planning and management and positioning in channel wood retention structures

high resolution dem generation from spaceborne and terrestrial remote sensing data for improved volcano hazard assessment a case study at nevado del ruiz colombia abstract volcanoes with rugged terrain remain a challenging target for generating high resolution digital elevation models dems especially in tropical areas with frequent cloud cover using nevado del ruiz volcano as an example we combined dems from the tandem x tdx satellite mission terrestrial radar interferometry tri and structure from motion sfm to generate a new dem with 10 m spatial resolution this is the first study combining satellite radar ground based radar photography and freely available global dems to generate a high resolution dem without data gaps tdx data from ascending and descending orbits were combined to generate the base dem instead of using a raster format to fuse dems generated from different data sets with different resolutions we developed a methodology based on 3 d point clouds 1 re georeference the 5 m tri and 1 m sfm dems to the 10 m tdx dem using the iterative closest point icp algorithm to minimize the horizontal and vertical discrepancy between dems then 2 merge the multiple point clouds to generate a final dem without data gaps using an adaptive algorithm that uses two search distances to smooth the transition at the edges of different data sets we assess the new 10 m dem by comparing simulated inundation zones obtained with two volcano flow models laharz for lahars and volcflow for pyroclastic flows and find significant differences with respect to the 30 m srtm dem our laharz simulation over the new dem shows a longer lahar run out distance for pyroclastic flows the volcflow simulation over the new dem produces highly channelized flows over the steep portions of a river channel and gives a larger extent of thicker deposits compared to those obtained with the 30 m srtm dem quantitative and qualitative geomorphic analysis suggests that up to date dems with high spatial resolution 10 m or even better need to be generated to improve volcano hazard assessment for active volcanoes

gis assisted modelling for debris flow hazard assessment based on the events of may 1998 in the area of sarno southern italy part i maximum run out based on the debris flow events that occurred in may 1998 in the area of sarno southern italy this paper presents an approach to simulate debris flow maximum run out on the basis of the flow source areas and an average thickness of 1 2 m of the scarps we estimated debris flow volumes of the order of 104 and 105 m3 flow mobility ratios h l derived from the x y z coordinates of the lower most limit of the source areas i e apex of the alluvial fan and the distal limit of the flows ranged between 0 27 and 0 09 we performed regression analyses that showed a good correlation between the estimated flow volumes and mobility ratios this paper presents a methodology for predicting maximum run out of future debris flow events based on the developed empirical relationship we implemented the equation that resulted from the calibration as a set of gis macros written in visual basic for applications vba and running within arcgis we carried out sensitivity analyses and observed that hazard mapping with this methodology should attempt to delineate hazard zones with a minimum horizontal resolution of 0 4 km the developed procedure enables the rapid delineation of debris flow maximum extent within reasonable levels of uncertainty it incorporates sensitivities and it facilitates hazard assessments via graphic user interfaces and with modest computing resources copyright 2007 john wiley sons ltd

stress estimation in rock a brief history and review for this special issue of the journal on rock stress estimation an introduction to the subject of in situ rock stress is presented here concentrating on the history of the subject and the principles of both stress and its measurement following an historical overview of the need for rock stress information and the nature of rock engineering problems stress and stress estimation are discussed this is followed by a review of the stress measurement techniques the importance of stress estimation and associated numerical modelling is highlighted the conclusions emphasize the importance of a well conditioned stress estimation campaign by using more than one technique and supporting the campaign with a numerical model the appendix focuses on the work at the canadian underground research laboratory

latest pleistocene holocene debris flow activity santa catalina mountains arizona implications for modern debris flow hazards under a changing climate abstract hazard mitigation for extreme events such as debris flows requires geologic mapping and chronologic information particularly for alluvial fans near mountain fronts in the southwestern united states in july 2006 five consecutive days of monsoonal storms caused hundreds of debris flows in southeastern arizona particularly in the southern santa catalina mountains north of tucson before 2006 no historical debris flows from the santa catalina mountains reached the populated mountain front although abundant evidence of prehistoric debris flows is present on downslope alluvial fans we used a combination of surficial geologic mapping and 10 be exposure dating to produce a debris flow history for pima and finger rock canyons the largest debris flows of latest pleistocene to early holocene age covered much of the apices of alluvial fans formed at the mouths of these canyons and extended up to 3 km downslope these debris flow deposits were inset against higher and older alluvial surfaces with few debris flow deposits of late pleistocene age the 10 be ages in this study have considerable scatter for surfaces believed to be of uniform age indicating the dual possibilities of inheritance from previous cosmic ray exposure as well as the potential for composite deposits derived from numerous debris flows we then used an empirical inundation model laharz to assess probable magnitudes of the older debris flows to evaluate possible initiation mechanisms in channel and terrace storage within the canyons is not sufficient to generate volumes likely needed to produce the larger late pleistocene to early holocene debris flow deposits the abundance of latest pleistocene and early holocene deposits suggests that large debris flows were generated during the instability associated with climate and vegetation changes at the pleistocene holocene transition under present watershed conditions with limited sediment supplies modern debris flow hazards are generally limited to within mountains and near mountain fronts

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

monitoring and modeling ice rock avalanches from ice capped volcanoes a case study of frequent large avalanches on iliamna volcano alaska abstract iliamna is an andesitic stratovolcano of the aleutian arc with regular gas and steam emissions and mantled by several large glaciers iliamna volcano exhibits an unusual combination of frequent and large ice rock avalanches in the order of 1 10 6 m 3 to 3 10 7 m 3 with recent return periods of 2 4 years we have reconstructed an avalanche event record for the past 45 years that indicates iliamna avalanches occur at higher frequency at a given magnitude than other mass failures in volcanic and alpine environments iliamna volcano is thus an ideal site to study such mass failures and its relation to volcanic activity in this study we present different methods that fit into a concept of 1 long term monitoring 2 early warning and 3 event documentation and analysis of ice rock avalanches on ice capped active volcanoes long term monitoring methods include seismic signal analysis and space and airborne observations landsat and aster satellite data was used to study the extent of hydrothermally altered rocks and surface thermal anomalies at the summit region of iliamna subpixel heat source calculation for the summit regions where avalanches initiate yielded temperatures of 307 to 613 k assuming heat source areas of 1000 to 25 m 2 respectively indicating strong convective heat flux processes such heat flow causes ice melting conditions and is thus likely to reduce the strength at the base of the glacier we furthermore demonstrate typical seismic records of iliamna avalanches with rarely observed precursory signals up to two hours prior to failure and show how such signals could be used for a multi stage avalanche warning system in the future for event analysis and documentation space and airborne observations and seismic records in combination with srtm and aster derived terrain data allowed us to reconstruct avalanche dynamics and to identify remarkably similar failure and propagation mechanisms of iliamna avalanches for the past 45 years simple avalanche flow modeling was able to reasonably replicate iliamna avalanches and can thus be applied for hazard assessments hazards at iliamna volcano are low due to its remote location however we emphasize the transfer potential of the methods presented here to other ice capped volcanoes with much higher hazards such as those in the cascades or the andes

evaluation of approaches to calculate debris flow parameters for hazard assessment abstract many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment the present article reviews the empirical analytical simple flow routing and numerical techniques all these techniques were applied to back calculate a debris flow which occurred in 1982 at la guingueta catchment in the eastern pyrenees a sensitivity analysis of input parameters was carried out while special attention was paid to the influence of rheological parameters we used the voellmy fluid rheology for our analytical and numerical modelling since this flow resistance law coincided best with field observations the simulation results indicated that the basal friction coefficients rather affect the runout distance while the turbulence terms mainly influence flow velocity a comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones the values of our rheological parameters calibrated at la guingueta agree with data back calculated for other debris flows empirical relationships represent another method to estimate total runout distance the results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions which were the basis for their development with regards to the simple flow routing algorithm this methods could satisfactorily simulate the total area affected by the 1982 debris flow but it was not able to directly calculate total runout distance and velocity finally a suggestion on how different runout prediction methods can be applied to generate debris flow hazard maps is presented taking into account the definition of hazard and intensity the best choice would be to divide the resulting hazard maps into two types final hazard maps and preliminary hazard maps only the use of numerical models provided final hazard maps because they could incorporate different event magnitudes and they supplied output values for intensity calculation in contrast empirical relationships and flow routing algorithms or a combination of both could be applied to create preliminary hazard maps the present study only focussed on runout prediction methods other necessary tasks to complete the hazard assessment can be looked up in the guidelines for landslide susceptibility hazard and risk zoning included in this special issue

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 comparison of the landsat image and laharz simulated lahar inundation hazard zone by the 2010 merapi eruption located above the java subduction zone merapi volcano is an active stratovolcano with a volcanic activity cycle of 1 5 years most merapi eruptions are relatively small with volcanic explosivity index vei of 1 3 however the most recent eruption which occurred in 2010 was quite violent with a vei of 4 and 386 people were killed in this study lahars and pyroclastic flow zones were detected using optical landsat images and the lahar and pyroclastic flow zone simulated using the laharz program to detect areal extents of lahar and pyroclastic flows using landsat images supervised classification was performed after atmospheric correction by using a cosine of the solar zenith correction cost model as a result the extracted dimensions of pyroclastic flows are nearly identical to the calatrava volcanic province cvp monthly reports then areas of potential lahar and pyroclastic flow inundation based on flow volume using the laharz program were simulated and mapped finally the detected lahars and pyroclastic flow zones were compared with the simulated potential zones using laharz program and verified results showed satisfactory similarity 55 63 between the detected and simulated zone the simulated zones using the laharz program can be used as an essential volcanic hazard map for preventing life and property damages for merapi volcano and other hazardous volcanic areas also the laharz program can be used to map volcano hazards in other hazardous volcanic areas

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

lahar flow simulations using laharz program application for the popocatepetl volcano mexico lahars are a type of catastrophic event that is generated in volcanic environments due to the recent technological advances computer simulated models have become widely used by the scientific community to predict the distribution of catastrophic events such as floods debris avalanches earth landslides or lahars and to mitigate possible damage to populations located in a risk area our study risk area is located in the popocatepetl volcano a large and active stratovolcano in the trans mexican volcanic belt here lahars have been occurring during the last century and some of them have seriously affected nearby towns since one of the main input parameters into a lahar simulation is the digital elevation model dem this paper focuses on studying lahar simulations on popocatepetl using dems obtained from various sources with the aid of a popular package known as laharz the first simulations were performed using a 1 50 000 topographic map with 20 m contours interval the second set of tests used an enhanced dem with profiles measured during fieldwork in the lahar channel in the last set of tests we added lateral artificial barriers to the channel profiles used in the previous enhanced dem our results show that the use of high resolution and detailed dems does not necessarily guarantee a realistic lahar simulation as was previously thought and a detailed explanation as to why the laharz code computation creates ragged edges is offered our results also offer useful information on the level of detail necessary for an input dem into laharz in order to obtain lahar simulations closer to real lahars the minimum resolution for the dem used in simulations must be less than the width of the narrowest cross section of the channel to realistically reproduce the lahars for dems with lower resolution sometimes the modeled lahars are shorter in length and therefore underestimate real hazards to populations also the results show that lateral barriers are sometimes needed to obtain more realistic inundation areas

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

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

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

multiple edifice collapse events in the eastern mexican volcanic belt the role of sloping substrate and implications for hazard assessment abstract the citlaltepetl cofre de perote volcanic chain forms an important physiographic barrier that separates the central altiplano 2500 masl from the gulf coastal plain gcp 1300 masl the abrupt eastward drop in relief between these provinces gives rise to unstable conditions and consequent gravitational collapse of large volcanic edifices built at the edge of the altiplano eastward sloping substrate caused by the irregular configuration of the basement rocks is the dominant factor that controls the direction of collapsing sectors in all major volcanoes in the region to be preferentially towards the gcp these collapses produced voluminous debris avalanches and lahars that inundated the well developed drainages and clastic aprons that characterize the coastal plain large catastrophic collapses from citlaltepetl las cumbres and cofre de perote volcanoes are well documented in the geologic record some of the avalanches and transformed flows have exceptionally long runouts and reach the gulf of mexico traveling more than 120 km from their source so far no direct evidence has been found for magmatic activity associated with the initiation of these catastrophic flank collapses apparently instability of the volcanic edifices has been strongly favored by very intense hydrothermal alteration abrupt topographic change and intense fracturing in addition to the eastward slope of the substrate the reactivation of pre volcanic basement structures during the late tertiary and the e w to ene ssw oriented regional stress regimes may have played an important role in the preferential movement direction of the avalanches and flows in addition to magmatic hydrothermal processes high amounts of rainfall in the area is another factor that enhances alteration and eventually weakens the rocks it is very likely that seismic activity may be the principal triggering mechanism that caused the flank collapse of large volcanic edifices in the eastern mexican volcanic belt however critical pore water pressure from extraordinary amounts of rainfall associated with hurricanes or other meteorological perturbation cannot be ruled out particularly for smaller volume collapses there are examples in the area of small seismogenic debris flows that have occurred in historical times showing that these processes are not uncommon assessing the stability conditions of major volcanic edifices that have experienced catastrophic sector collapses is crucial for forecasting future events this is particularly true for the eastern mexican volcanic belt where in many cases no magmatic activity was associated with the collapse therefore edifice failure could occur again without any precursory warning

geographical information system approaches for hazard mapping of dilute lahars on montserrat west indies many research tools for lahar hazard assessment have proved wholly unsuitable for practical application to an active volcanic system where field measurements are challenging to obtain two simple routing models with minimal data demands and implemented in a geographical information system gis were applied to dilute lahars originating from soufriere hills volcano montserrat single direction flow routing by path of steepest descent commonly used for simulating normal stream flow was tested against laharz an established lahar model calibrated for debris flows for ability to replicate the main flow routes comparing the ways in which these models capture observed changes and how the different modelled paths deviate can also provide an indication of where dilute lahars do not follow behaviour expected from single phase flow models data were collected over two field seasons and provide 1 an overview of gross morphological change after one rainy season 2 details of dominant channels at the time of measurement and 3 order of magnitude estimates of individual flow volumes modelling results suggested both gis based predictive tools had associated benefits dominant flow routes observed in the field were generally well predicted using the hydrological approach with a consideration of elevation error while laharz was comparatively more successful at mapping lahar dispersion and was better suited to long term hazard assessment this research suggests that end member models can have utility for first order dilute lahar hazard mapping

energy growth in laharic mass flows lahars debris flows and sediment rich floods are frequent and deadly hazards at all mountain forming volcanoes their hazard potential is traditionally assessed through mass conserving closed system models where peak conversion rates of potential energy to mechanical energy and hence maximum destruction potential are predicted to occur on the steepest volcano flanks this belies evidence of extremely high energy and deadly catastrophes caused by such flows at large distances from volcanoes here we use the first high resolution record of a moving lahar to develop a new model of the temporally and spatially variable mass flow structure we show that bulk flow energy can grow dramatically in such systems over tens to hundreds of kilometers via momentum transfers from the lahar into water and particles along its path we also demonstrate that dynamic transformations of such flows and their ultimate runout are primarily controlled by the mass flow front

modeling the october 2005 lahars at panabaj guatemala an extreme rainfall event in october of 2005 triggered two deadly lahars on the flanks of toliman volcano guatemala that caused many fatalities in the village of panabaj we mapped the deposits of these lahars then developed computer simulations of the lahars using the geologic data and compared simulated area inundated by the flows to mapped area inundated computer simulation of the two lahars was dramatically improved after calibration with geological data specifically detailed field measurements of flow inundation area flow thickness flow direction and velocity estimates collected after lahar emplacement were used to calibrate the rheological input parameters for the models including deposit volume yield strength sediment and water concentrations and manning roughness coefficients simulations of the two lahars with volumes of 240 200 55 400 and 126 000 29 000 m3 using the flo 2d computer program produced models of lahar runout within 3 of measured runouts and produced reasonable estimates of flow thickness and velocity along the lengths of the simulated flows we compare areas inundated using the jaccard fit model sensitivity and model precision metrics all related to bayes theorem these metrics show that false negatives areas inundated by the observed lahar where not simulated and false positives areas not inundated by the observed lahar where inundation was simulated are reduced using a model calibrated by rheology the metrics offer a procedure for tuning model performance that will enhance model accuracy and make numerical models a more robust tool for natural hazard reduction

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

contrasting origin of two clay rich debris flows at cayambe volcanic complex ecuador we investigate the sedimentological and mineralogical properties of a debris flow deposit west of cayambe volcanic complex an ice clad edifice in ecuador the deposit exhibits a matrix facies containing up to 16 wt of clays however the stratigraphic relationship of the deposit with respect to the canguahua formation a widespread indurated volcaniclastic material in the ecuadorian inter andean valley and the deposit alteration mineralogy differ depending on location thus two different deposits are identified the rio granobles debris flow deposit 1 km3 is characterised by the alteration mineral assemblage smectite jarosite and sulphur isotopic analyses point to a supergene hydrothermal alteration environment this deposit probably derives from a debris avalanche initiated before 14 21 ka by collapse of a hydrothermally altered rock mass from the volcano summit in contrast the alteration mineralogy of the second debris flow deposit which may itself comprise more than one unit is dominated by halloysite smectite and relates to a shallower and more recent 3200 m volcanic soils our study reinforces the significance of hydrothermal alteration in weakening volcano flanks and in favouring rapid transformation of a volcanic debris avalanche into a clay rich debris flow it also demonstrates that mineralogical analysis provides crucial information for resolving the origin of a debris flow deposit in volcanic terrains finally we posit that slope instability promoted by ongoing subglacial hydrothermal alteration remains a significant hazard at cayambe volcanic complex

aster observations of thermal anomalies preceding the april 2003 eruption of chikurachki volcano kurile islands russia abstract chikurachki volcano northern kurile islands chain paramushir island 50 20 n 155 27 e elevation 1816 m stratovolcano has been in a state of unrest for over twenty years its most recent eruption that began in april 2003 was preceded by an eruption between january and may 2002 thermal infrared images from the japanese united states advanced spaceborne thermal emission and reflection radiometer aster 5 tir channels 8 12 m 90 m pixel noise equivalent delta temperature ne t 0 1 0 3 k onboard the u s national aeronautics and space administration s terra polar orbiting spacecraft of a snow covered chikurachki volcano taken in january 2003 show muted evidence of thermal activity aster thermal infrared tir images from february 2003 however indicate warmer areas within the summit crater average whole pixel temperatures of adjacent summit slopes are in the range of 250 252 k while many summit crater whole pixel temperatures are 2 6 k greater a two component planck solution for the warmer pixels yields a solution of 275 277 k for 10 15 of the chikurachki summit crater and 285 295 k for 25 35 of a prominent hotspot on its flank an interpretation of this enhanced pre eruption heat flow is the presence of surface melt water the detection in aster data of such subtle precursory heat flow enhancement even retrospectively raises important issues for remote monitoring of dormant snow capped volcanoes especially those that threaten nearby populations like mt rainier

a fluid dynamics approach to modelling the 18th march 2007 lahar at mt ruapehu new zealand lahars are water sediment mass flows from a volcanic source they can be triggered by a variety of mechanisms and span a continuum of flow rheology and hydraulic properties even within the same event lahars are extremely powerful landscaping agents and represent a considerable hazard potential however this highly dynamic character and a lack of direct measurements has made modelling lahars difficult this study therefore applies a fluid dynamics model delft3d to analyse the 18th march 2007 dam break lahar at mount ruapehu new zealand the modelled lahar routed through the whangaehu gorge in 30 min crossed the whangaehu fan in 60 min and then over a further 3 h travelled an additional 22 km distance along the whangaehu river to the tangiwai bridge the modelled mean frontal velocity was 6 5 m s 1 along the gorge although peak velocity reached up to 19 6 m s 1 the modelled lahar flow front progressively slowed across the fan but along the river it accelerated from 2 1 3 3 m s 1 calculated peak velocity along the river was 4 5 m s 1 these results generally compare well with gauged records with historical records and with other modelling approaches however discrepancies in frontal velocity and time to peak stage arise due to 1 specifying roughness which arises from slope variations between adjacent computational nodes and which is stage dependant and 2 due to rapid topographic changes that produce frequent hydraulic jumps which are inadequately accommodated in the numerical scheme the overall pattern of discharge attenuation and of relationships between topographic and hydraulic variables is similar to that calculated for lahars on other volcanoes this modelling method could be applied at other similar sites where a likely source hydrograph and high resolution topographic data are available these results have important implications for hazard management at ruapehu and for examining geomorphic and sedimentary impacts of this lahar