the bucobello 322 ka fossil bearing volcaniclastic flow deposit in the eastern vulsini volcanic district central italy mechanism of emplacement and insights on human activity during mis 9 abstract we present a multidisciplinary study of a fossiliferous site located in the vulsini volcanic district on the western side of the tiber river valley north of rome highlighting the peculiar geologic factors that contributed to the origin and preservation of an outstanding archaeological record testifying of the early human frequentation in this region mighty explosive eruptions since at least 500 ka affected the investigated area eventually culminating in the formation of the huge bolsena caldera tectonic deformation accompanying volcanic activity caused large fault displacements shaping the ground surface and contributing to route the path and possibly to trigger the catastrophic emplacement of volcaniclastic flows a sedimentary trap originated by fault scarp cutting through a streambed was likely the cause for the large accumulation of bones and stone artifacts ripped up and carried by a volcaniclastic flow at 322 ka the analysis of the fossil assemblage reveals both gnawing traces by carnivores and cut marks from the percussion tools employed by humans to butch the carcasses however the occurrence of retouched and unretouched blanks within the lithic assemblage also testifies for provenance from a wider area of human activity which included hunting and scavenging probably at a nearby butchering site

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

miocene volcaniclastic sequence within the xiyu formation from source to sink implications for drainage development and tectonic evolution in eastern pamir nw tibetan plateau

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

contrasting zoning profiles in high grade garnets evidence for the allochthonous nature of a grenville province terrane in the central part of the grenville province proterozoic metasediments of the reservoir cabonga terrane arc underlain by gently dipping archean migmatites a major mylonite zone located within the migmatites is the base of a large thrust sheet made up of the reservoir cabonga terrane and a migmatitic sole garnets from meta aluminous assemblages in proterozoic metasediments mylonites and migmatites display contrasting types of ca zoning patterns garnets with ca rich cores are found along the western edge of the reservoir cabonga terrane whereas garnets with flat ca profiles are found in the remaining proterozoic metapelites in the mylonites and in the archean migmatites considering samples in which an infinite reservoir of ca ions is warranted by abundant plagioclase in the matrix pressures well in excess of 1200 mpa at temperatures between 700 and 800 c are indicated for a metamorphic event recorded in the cores of garnets from the western edge of the reservoir cabonga terrane the inner rim of garnet records pressures of around 1000 mpa for the same temperature range in homogeneous garnets a single p t set around 800 mpa and 750 c is recorded in the migmatites some of the mylonites initiate their recrystallization under relatively high pressures which is continued during decompression and record the lowest p t values these metamorphic signatures suggest that the proterozoic metapelites were already metamorphosed under relatively high pressure when emplaced on to archean migmatites and that the entire area was subsequently subjected to metamorphism at a lower pressure

fault kinematics and stress fields in the rwenzori mountains uganda the rwenzori mountains in western uganda form an active rift transfer zone in the western branch of the east african rift system here we quantify local stress fields in high resolution from field observations of fault structures to shed light on the complex polyphase tectonics expected in transfer zones we apply the multiple inverse method which is optimized for heterogeneous fault slip data to the northern and central rwenzori mountains observations from the northern rwenzori mountains show larger heterogeneity than data from the central rwenzori including unexpected compressional features thus the local stress field indicates polyphase transpressional tectonics we suggest that transpression here is linked to rotational and translational movements of the neighboring victoria block relative to the rwenzori block that includes strong overprinting relationships stress inversions of data from the central rwenzori mountains indicate two distinct local stress fields these results suggest that the rwenzori block consists of smaller blocks

erosional furrows formed during the lateral blast at mount st helens may 18 1980 nearly horizontal quasi periodic erosional features of 7 m average transverse wavelength and of order 100 m length occur in scattered locations from 3 5 to 9 km from the crater at mount st helens under deposits of the lateral blast of may 18 1980 we attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography namely by streamline curvature in regions of reattachment downstream of sheltered regions and by the cross flow component of flow subparallel to ridge crests the diameter of the vortices and their transverse spacing inferred from the distance between furrows are taken to be of the order of the boundary layer thickness the inferred boundary layer thickness 14 m at 9 km from the source of the blast is consistent with the running length from the mountain to the furrow locations by using knowledge of ablation patterns on bodies and lofting of dust in high speed flow we are able to infer some features of the flow field within the blast within the furrows the erosion rate was of the order of 9 kg m 2 s 1 about 4 times greater than that expected from laboratory data obtained in flow free of longitudinal vortices the orientation of furrows induced by the cross flow instability can be used to measure the upwash angle and estimate the flow mach number at the central ridge of spirit lake the mach number is inferred to have been about 2 5 and the flow velocity approximately 235 m s the similarities and differences between the furrows reported here and channels observed at other volcanoes are discussed

sedimentologic and dynamic differences between hot and cold laharic debris flows of mayon volcano philippines numerous hot lahars produced during and immediately after the 1984 eruption of mayon volcano along with frequent cold lahars of the succeeding wet monsoon seasons have left widespread debris flow deposits fresh deposits of hot debris flows have thin crusts that are remarkably resistant to erosion and to vegetal growth these crusts contain clasts with uniform thermoremanent magnetization directions rare soft sediment deformation structures and gas escape tubes deposits of unchannelized hot and cold debris flows both have sheetlike or lobate geometry non erosional bases poor sorting relatively minor silt and only traces of clay sized ash either matrix or clast support and common out sized clasts at their tops it is difficult to distinguish between the deposits after burial but they have subtle significant sedimentologic differences the inversely graded bases of hot debris flow deposits are thick suggesting a lack of cohesion and considerable dispersive pressure they have long clast axes aligned parallel to bedding due to strongly sheared laminar flow and generally they are succeeded by gradual normal grading from waning flow conditions in cold debris flow beds only the basal few centimeters may be inversely graded the bulk being commonly ungraded indicating the active role of cohesive forces in the hot flows vaporization of water by heat from large clasts may have facilitated mobility by decreasing internal friction indirect velocity calculations indicate that they moved faster and traveled farther than did cold flows proximal hot debris flows were all supercritical with froude numbers decreasing enroute the most distal hot debris flows and all of the cold ones were subcritical cold debris flows show no correlation between froude number and distance of transport

determining rheological parameters of debris flow material abstract a 2 0 m diameter steel 30 inverted cone and plate viscometer rheometer was designed constructed and used to test the behaviour of coarse grained debris flow materials a 1 5 scale model machine was also constructed and used to test the internal flow dynamics of the viscometer rheometer and to obtain results for fluids grain fluid mixtures and debris flow fines for fluids and grain fluid mixes our results were similar to those obtained earlier using standard viscometric systems derived rheological parameters for debris flow materials and clay slurries agreed well with those determined from calculation direct measurement and field observation apparent viscosities were shear rate dependent extremely sensitive to water content and as high as 6000 pa s instantaneous stresses within shearing debris flow material varied over a wide range debris flow materials with bimodal grain size distributions had a dilatant plastic rheology those with a low content of coarse material and unimodal grain size distribution or exceptionally high fines content had a plastic or viscoplastic rheology

significance of coarse clasts in viscous debris flows abstract debris flows are flowing mixture of water and sediments from clay to boulder sized particles the sediments control both occurrence and characteristics of debris flows however the relevant literature has concentrated mainly on fine debris considering their large fractions in debris flows the significance of coarse clasts 0 005 mm is investigated by comparing the crude debris cd the fractions of aggregation of data collected in 39 tested debris water mixtures leads us to conclude that the coarse clasts can greatly affect the slurrying susceptibility of debris masses and bulk behavior of slurries the debris flow indices id from the cd to rd slurries with maximum grain sizes of 10 and 5 mm decrease by 29 and 17 respectively the cd slurries possess higher yield strength and viscosity than their rd counterparts with the same solid volumetric concentrations cvs the areas inundated by 10 cd slurries with maximum grain sizes of 10 and 5 mm are approximately 17 39 of those of their rd counterparts the excess pore pressures in the rd slurries dissipate more quickly than those in the cd slurries the shape and surface texture of coarse clasts regulate slurrying of debris masses as well as influence their liquefaction potential which in turn has an impact on the mobility and persistence of subsequent slurries the platy flaky debris producing mountain catchments generally experience lower magnitude higher frequency lower cv debris flows of relatively less destructive power and the debris flows dominated by equidimensional clasts are often more powerful and hazardous despite their potentially lower frequency

improved estimates of glacier change rates at nevado coropuna ice cap peru accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice clad volcanoes especially in arid regions like southern peru in these regions glacier and snow melt are crucial dry season water resources in order to verify previously reported rates of ice area decline at nevado coropuna in peru which are anomalously rapid for tropical glaciers we measured changes in ice cap area using 259 landsat images acquired from 1980 to 2014 we find that coropuna ice cap is presently the most extensive ice mass in the tropics with an area of 44 1 km 2 and has been shrinking at an average area loss rate of 0 409 km 2 a 1 0 71 a 1 since 1980 our estimated rate of change is considerably lower than previous studies 1 4 km 2 a 1 or 2 43 a 1 but is consistent with other tropical regions such as the cordillera blanca located 850 km to the nw 0 68 a 1 thus if glacier recession continues at its present rate our results suggest that coropuna ice cap will likely continue to contribute to water supply for agricultural and domestic uses until 2120 which is nearly 100 years longer than previously predicted

hydraulics and basin morphometry of the largest flash floods in the conterminous united states abstract the maximum rainfall runoff floods measured by indirect methods in small basins 0 39 370 km2 in the conterminous united states are examined this analysis identified twelve floods that were the largest ever measured these floods all occurred in semiarid to arid areas for eleven of the twelve largest rainfall runoff floods measured in small basins by the slope area method values of hydraulic depth hydraulic radius width depth ratio n value mean velocity velocity head coefficient froude number water surface energy and channel slopes shear stress and unit stream power are tabulated estimated composite n values weighted by subsection conveyance range from 0 028 to 0 048 with a mean of 0 038 mean velocities ranged from 3 47 to 9 97 m s 1 froude numbers ranged from 0 81 to 2 49 with 9 of 12 floods having values greater than 1 00 water surface energy and channel slopes vary considerably for each flood energy slope always was less than water surface slope by values of 1 104 channel slope was greater than energy slope in eight floods shear stresses ranged between 61 and 855 n m 2 and unit stream power from 212 to 8131 w m 1 floods in these small basins produced shear stresses and unit stream powers several hundred times greater than floods in large rivers floods on other small streams with smaller unit discharges produced greater shear stresses and stream powers this indicates that the force of a flood is controlled by the depth slope product not absolute discharge in the twelve watersheds studied basin relief ranged from 165 to 1280 m elongation ratios ranged from 0 55 to 0 80 the number of first order streams basin magnitude ranged from 10 to 4297 drainage density ranged from 4 1 to 10 9 km km 2 basin slope ranged from 0 0043 to 0 2486 relief ratio ranged from 0 0097 to 0 34 ruggedness number ranged from 0 69 to 7 17 and first order channel frequency ranged from 5 1 to 38 6 km 2 elongation ratios were larger and drainage density and first order channel frequency lower than other small flash flood prone basins in the united states these twelve basins have neither the most favorable morphometric characteristics which contribute to flash flood peaks nor did the storms causing these flash floods have the greatest short duration intensities maximum flood peaks originate from an optimal combination of basin morphology and physiography and storm intensity

an empirical method for estimating travel times for wet volcanic mass flows travel times for wet volcanic mass flows debris avalanches and lahars can be forecast as a function of distance from source when the approximate flow rate peak discharge near the source can be estimated beforehand the near source flow rate is primarily a function of initial flow volume which should be possible to estimate to an order of magnitude on the basis of geologic geomorphic and hydrologic factors at a particular volcano least squares best fits to plots of flow front travel time as a function of distance from source provide predictive second degree polynomial equations with high coefficients of determination for four broad size classes of flow based on near source flow rate extremely large flows 1 000 000 m3 s very large flows 10 000 1 000 000 m3 s large flows 1000 10 000 m3 s and moderate flows 100 1000 m3 s a strong nonlinear correlation that exists between initial total flow volume and flow rate for instantaneously generated debris flows can be used to estimate near source flow rates in advance differences in geomorphic controlling factors among different flows in the data sets have relatively little effect on the strong nonlinear correlations between travel time and distance from source differences in flow type may be important especially for extremely large flows but this could not be evaluated here at a given distance away from a volcano travel times can vary by approximately an order of magnitude depending on flow rate the method can provide emergency management officials a means for estimating time windows for evacuation of communities located in hazard zones downstream from potentially hazardous volcanoes

sedimentology and event timing of a catastrophic volcaniclastic mass flow volcan hudson southern chile eruption of volcan hudson aisen region southern chile on 12 august 1971 melted up to 80 of ice within the 9 km wide hudson caldera rapid mobilisation of abundant fluvio glacial sediment within the adjacent huemules valley led to the generation of a catastrophic mass flow which swept westwards along the valley eventually entering the fjord some 40 km downstream the mass flow developing from one source and being unaffected by tributary input was characterised by three events within the flood hydrograph 1 a precessional flood possibly linked to breakage of an early formed dammed lake 2 a main mass flow which varied in its rheological behaviour from plug flow to hyperconcentrated flow and 3 a recessional flood at the tail of the main flow which diluted towards a concentrated streamflow the main debris flow displayed characteristics of pulsing internal segregation density stratification significant downstream sediment assimilation cohesive frictional freezing with ensuing fluidisation and development of an advancing runout phase consideration of these sedimentary characteristics and spatial temporal flow transformations are used to propose a schematic model of event timing within this catastrophic volcaniclastic flow

a re examination of the mechanism and human impact of catastrophic mass flows originating on nevado huascaran cordillera blanca peru in 1962 and 1970 abstract the 1962 and 1970 huascaran mass movements originated as rock ice falls from the mountain s north peak transformed into higher volume high velocity mud rich debris flows by incorporation of snow from the surface of a glacier below huascaran and the substantial entrainment of morainic and colluvial material from slopes below the glacier terminus water for fluidization of the entrained material originated in the melting of incorporated snow and the liberation of soil moisture contained within the entrained materials eyewitness reports indicate very high mean velocities for the events 17 35 m s 1962 and 50 85 m s 1970 the runout distances and velocity profiles of both events were simulated using dan w both mass movements continued downstream in the rio santa as debris floods aluviones that in 1970 reached the pacific at a distance of 180 km in strong contrast to publications in the geosciences literature 1961 peru census data indicates that the death toll of the 1970 event is ca 6000 and that total life loss in the two events did not exceed 7000 people

swift snowmelt and floods lahars caused by great pyroclastic surge at mount st helens volcano washington 18 may 1980 the initial explosions at mount st helens washington on the moring of 18 may 1980 developed into a huge pyroclastic surge that generated catastrophic floods off the east and west flanks of the volcano near source surge deposits on the east and west were lithic sorted lacking in accretionary lapilli and vesiculated ash not plastered against upright obstacles and hot enough to char wood all attributes of dry pyroclastic surge material deposited at the surge base on steep slopes near the volcano transformed into high concentration lithic pyroclastic flows whose deposits contain charred wood and other features indicating that these flows were hot and dry stratigraphy shows that even the tail of the surge had passed the east and west volcano flanks before the geomorphically distinct floods lahars arrived this field evidence undermines hypotheses that the turbulent surge was itself wet and that its heavy components segregated out to transform directly into lahars nor is there evidence that meters thick snow slab avalanches intimately mixed with the surge to form the floods the floods must have instead originated by swift snowmelt at the base of a hot and relatively dry turbulent surge impacting hot pyroclasts probably transferred downslope momentum to the snow surface and churned snow grains into the surge base melting snow and accumulating hot surge debris may have moved initially as thousands of small thin slushflows as these flows removed the surface snow and pyroclasts newly uncovered snow was partly melted by the turbulent surge base this and accumulating hot surge debris in turn began flowing a self sustaining process feeding the initial flows the flows thus grew swiftly over tens of seconds and united downslope into great slushy ejecta laden sheetfloods gravity accelerated the floods to more than 100 km h as they swept down and off the volcano flanks while the snow component melted to form great debris rich floods lahars channeled into valleys

lahars initiated by the 13 november 1985 eruption of nevado del ruiz colombia the eruption of nevado del ruiz in colombia on 13 november 1985 was accompanied by the formation of four lahars mud flows triggered by the melting of glacial ice near the summit of the volcano the lahars began as flows of water sand and gravel but they incorporated clay by eroding the soil along the steep valleys through which they passed the largest flow was a cohesive debris flow more than 45 m deep and moving at 12 ms 1 when it debouched from the canyon of the rio lagunilla 2 5 km from armero where it killed 25 000 people the continuing volcanic activity and abundant remaining glacial ice create an extremely high risk of future destructive flows

the rain triggered atenquique volcaniclastic debris flow of october 16 1955 at nevado de colima volcano mexico abstract on october 16 1955 at 10 45 a m local time after three days of intense rain 140 mm that was twice the monthly average precipitation a devastating flood surge formed a volcaniclastic debris flow on the eastern slopes of nevado de colima volcano nearly simultaneous flood surges formed in the arroyo seco los platanos and dos volcanes ravines that coalesced with the larger flow in the atenquique ravine at each confluence with a tributary the flow was diluted the texture and structure of the preserved 1955 deposits near high water marks indicate that the downstream flow was mainly in the lower range of debris flow concentration 60 sediment concentration by weight downstream the tributaries the flood encountered a 0 06 10 6 m 3 water reservoir that failed significantly increasing the surge volume additional entrained sediment also increased the flow volume downstream the flood wave reached the town of atenquique as an 8 9 m catastrophic wave causing the death of more than 23 people the partial destruction of the town and losses of 13 000 000 pesos 1 million us dollars today to a paper mill and company facilities according to eyewitness accounts the flood wave had a peak discharge that lasted ca 10 to 15 minutes at atenquique deposits at the site and the high water marks observed from photographs of the town s church indicate that sediment concentration was ca 60 wt the flood continued for about 1 km to its junction with the tuxpan river where it was diluted by mixing with normal flood flow the deposits covered an area of 1 2 km 2 and had a minimum volume of 3 2 10 6 m 3 the main deposit consists of a single unit averaging 4 m in thickness with weak textural variations that suggest surging within the flood wave the deposit is heterolithologic and consists of boulders set in a matrix of sand size sediment with polymodal or bimodal distributions and normal grading varying with distance from source the town of atenquique has been reconstructed largely within the area inundated by the 1955 flood wave thus creating the conditions for a future disaster a rainfall intensity warning system and an educational program for inhabitants are strategies to mitigate this risk

sinuous gullies on mars frequency distribution and implications for flow properties recent gullies on mars are suspected to be the result of liquid water bearing flows a formation from wet flows has been challenged by studies invoking granular dry flows our study focuses on the sinuous shapes observed for some of the recent martian gullies sinuous gullies are found in locations and slopes of 10 15 similar to straight gullies and they are therefore related to the same formation processes numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles roughness or slope changes that could possibly generate flow sinuosity none of these simulations was able to reproduce sinuous shapes on a slope lower than 18 with friction angles typical of dry granular material the only way to simulate sinuous shapes is to create small amplitude periodic variations of the topography of the deposit an origin not supported by current martian imagery given the presence of sinuosity in natural terrestrial debris flows we have concluded that sinuous martian gullies are better reproduced by liquid water bearing debris flows sinuous shapes in leveed flows are used to derive mechanical parameters from several martian gullies using photoclinometry values in yield strength of 100 2200 pa velocities of 1 1 3 3 m s 1 and viscosities from 40 to 1040 pa s are found which are all within the range of values for terrestrial debris flows with various proportions of liquid water 20 40

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

computer simulations of tsunamis due to sector collapse at stromboli italy abstract stromboli is an island volcano of the aeolian volcanic arc characterised by persistent activity the cone rises about 2500 3000 m from its submarine base with very steep slopes its summit at 924 m above the sea level the subaerial growth of stromboli occurred in the last 100 ka has been marked by repeated episodes of large gravitational collapses especially affecting the nw flank of the island in the last 13 ka the last one occurred less than 5000 years ago forming the deep depression on the nw seaward flank named sciara del fuoco sdf and it produced very likely large water waves this paper envisages a scenario where a huge mass of volcanic material collapses into the sea in the same sector in which the sdf collapse took place in holocenic times and it computes possible tsunami evolutions assuming the present day bathymetry numerical simulations are performed by means of two distinct models one for the mass collapse and one for the tsunami slope failure dynamics are calculated with the aid of a lagrangian model the landslide is subdivided into blocks and the motion of each constituent block is calculated by applying the basic principle of mechanical momentum conservation with block block and block ambient interactions being taken into account water waves are computed by solving a system of shallow water equations including a forcing term dependent on the sliding mass motion the finite element fe technique is employed since it permits the use of non uniform grids which are adequate to account for marine basins with irregular coastlines in addition to the sensitivity analysis concerning the main parameters governing the slide motion two main cases are explored differing in the slide path followed by the mass the resulting tsunami is very large with giant waves as high as several meters tens of meters in the worst cases impinging the coast due to the strong wave refraction induced by bathymetry waves travel around the island affecting even the island coast opposite the source

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

general solutions for viscoplastic debris flow theoretical velocity profile and theoretical pressure and concentration distributions for steady uniform debris flow in wide channels are derived from a generalized viscoplastic fluid gvf model without imposing bagnold s assumption of constant grain concentration good agreement between the theoretical velocity profile and the experimental data of japanese scientists strongly supports the validity of both the gvf model and the proposed method of solution from the model it is shown that both bingham and bagnold versions or submodels of the gvf model can be used to simulate debris flow at the dynamic state although bagnold s dilitant submodel appears to fit the japanese data better than the bingham submodel for flow of noncohesive grains the choice between them is by no means clear cut no matter which submodel is used a full understanding of the major factors that affect the behavior of debris flows is essential prior to its application this paper thus lays theoretical ground for extensive further studies of such factors

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

toward a model for the bulking and debulking of lahars 1 the incorporation and loss of material sediments or water during the advance of a lahar can significantly influence the advance rate mobility rheology and inundation limits of the flow and therefore these processes have consequences for destructive potential we have developed a theoretical treatment based on the conservation of flow volume and mass to describe the influence of such processes on the depth discharge and density during transit we apply our model to a common scenario of lahar generation and evolution the formation of an initially dilute flow by catastrophic breaching or ejection of a volcanic summit crater lake followed by bulking due to incorporation of substrate materials and later debulking due to sediment deposition the key features of our model are time dependence and the inclusion of two terms describing the influx or efflux of sediments to or from the flow for lahars triggered by crater lake water we derive the time evolution of flow behavior for comparison with the well documented 1953 lahar of mount ruapehu new zealand our model demonstrates the importance of these processes on observable quantities such as flow depth density and deposit profiles hydrograph evolution and transformations between rheologic density regimes

coupled fluid dynamics sediment transport modelling of a crater lake break out lahar mt ruapehu new zealand summary lahars and other sudden onset floods are highly dynamic with temporally and spatially evolving sediment loads numerical models of sudden onset flood behaviour particularly those applied to real world events have tended to neglect sediment transport processes this is a serious though perhaps understandable shortcoming given a lack of field measurements on flow bed interactions the extra computational complexity required and the problem of iteratively updating plastic channel boundaries this paper applies a fluid dynamics model with suspended sediment and bedload transport to calculate flow conditions and rapid landscape change due to an initially dilute lahar from mt ruapehu new zealand we take advantage of an unprecedented dataset of net topographic changes determined from pre and post lahar airborne lidar surveys and time series of hydrological measurements to run and validate the model a sensitivity analysis of key controls on water surface elevation and final sediment thickness illustrates how the flow was supply limited in the upper reaches it was capable of transporting a greater volume and calibre of material than that available modelled patterns of net erosion and deposition can replicate those observed r 2 0 79 and are dominantly controlled by channel gradient and topographic

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

geomorphic and sedimentary evidence of a gigantic outburst flood from towada caldera after the 15 ka towada hachinohe ignimbrite eruption northeast japan abstract this study reports on geomorphic and sedimentary evidence for a gigantic breakout flood from towada caldera honshu island northeast japan as observed along the oirase river downstream from the outlet of the caldera lake a number of features of the oirase river are inconsistent with its present discharge including the occurrence of 1 hanging valleys and a horseshoe shaped waterfall in the upstream gorge area 2 boulder bars and scattered flood boulders 3 a dry valley at a high elevation in the gorge and 4 a large fan the sanbongi fan in the downstream area of the river the sanbongi fan is composed of thick lithic rich hyperconcentrated flow deposits that include pumice clasts derived from the 15 ka towada hachinohe ignimbrite and well rounded meter sized and outsized boulders derived from bedrock of welded ignimbrite the deposits are entirely aggradational with no major channels indicating the absence of a major hiatus during sedimentation the depositional facies also indicate that a single sheet like flood event deposited the sediment within the sanbongi fan area based on the age of the sanbongi fan the flood occurred between 15 and 12 ka after eruption of the towada hachinohe ignimbrite the most probable water source for the flood is towada caldera lake as suggested by landforms and sediments along the lake outlet a paleohydrological analysis indicates that at least 6 km 3 of water was released from the caldera at a peak discharge of 2 10 4 to 3 10 5 m 3 s 1 during the breakout flood although the sanbongi fan was previously considered to be a normal alluvial fan that formed during a stage of low stand sea level the present results show that the formation of the fan was closely related to a catastrophic flood from towada caldera rather than perennial fluvial activity climate change or a change in relative sea level

defining conditions for bulking and debulking in lahars through measurements at semeru volcano east java we define the conditions under which bulking entrainment of sediment and pore water and debulking dilution and sedimentation occur in rain triggered volcanic floods lahars two observation sites were installed 510 m apart along the curah lengkong river 11 5 km southeast of semeru s summit this 30 m wide box valley with a gravel and lava base represents a real world flume analogy pore pressure sensors provided stage measurements a broad band seismograph gave insight into sediment content and frictional collisional behavior video cameras were used to measure surface velocities and direct bucket samples were taken eight rainfall induced lahars were recorded lasting 1 3 h with heights of 0 5 2 m peak velocities of 3 7 m s and discharges of 25 250 m3 s flows ranged from typical 40 wt sediment to coarse and dense hyperconcentrated flows 50 60 wt sediment multiple distinct flow packets occurred within the complex lahars and were used to determine internal changes between sites from the multiparameter data set at each site volumetric bulking and wave shortening due to portions of the lahar accelerating toward the flow front are identified initial debulking of lahars between sites may reflect drainage into the dry substrate estimates of discharge and volume at each site lead to the quantification of bulking and debulking by these actively flowing lahars along the channel reach from this we observe that bulking can be localized to certain parts of lahars resulting in intraevent increases in peak discharge that are greater than what would occur if bulking was evenly distributed throughout the flow such data are essential for the development of numerical descriptions and hazard models for mass flows

volcaniclastic debris flows in the clanio valley campania italy insights for the assessment of hazard potential abstract the rugged and steep slopes of the clanio valley campania southern italy mantled by volcaniclastic deposits from explosive eruptions of somma vesuvius and phlegraean fields volcanoes have a great potential for generating volcaniclastic debris flows during the well known meteorological event of may 5 6 1998 which triggered tens of debris flows causing enormous damage and casualties in the area of sarno quindici siano bracigliano sqsb the clanio valley was also affected by these hazardous phenomena debris flows were triggered by the failure of the volcaniclastic cover of the carbonate relief in the form of soil slips mainly on the sides of steep valleys slope between 26 and 45 a map of the hazard potential was created on the basis of both field and computer assisted morphometric data three classes characterised by a high medium and low hazard potential were distinguished within the higher class a better and more detailed zonation was obtained by studying the shape of the disrupted and undisrupted basins during the may 5 6 1998 event in the nearby sarno quindici siano bracigliano area this type of morphometric analysis can be applied rapidly by using a digital elevation model dem which allows a rapid investigation of large scale areas such an approach can be useful in areas characterised by similar geological and geomorphological settings

gis assisted modelling for debris flow hazard assessment based on the events of may 1998 in the area of sarno southern italy ii velocity and dynamic pressure the velocity and dynamic pressure of debris flows are critical determinants of the impact of these natural phenomena on infrastructure therefore the prediction of these parameters is critical for hazard assessment and vulnerability analysis we present here an approach to predict the velocity of debris flows on the basis of the energy line concept first we obtained empirically and field based estimates of debris flow peak discharge mean velocity at peak discharge and velocity at channel bends and within the fans of ten of the debris flow events that occurred in may 1998 in the area of sarno southern italy we used this data to calibrate regression models that enable the prediction of velocity as a function of the vertical distance between the energy line and the surface despite the complexity in morphology and behaviour of these flows the statistical fits were good and the debris flow velocities can be predicted with an associated uncertainty of less than 30 and less than 3 m s 1 we wrote code in visual basic for applications vba that runs within arcgis to implement the results of these calibrations and enable the automatic production of velocity and dynamic pressure maps the collected data and resulting empirical models constitute a realistic basis for more complex numerical modelling in addition the gis implementation constitutes a useful decision support tool for real time hazard mitigation copyright 2008 john wiley sons ltd

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

a smoothed particle hydrodynamic automaton of landform degradation by overland flow abstract a novel model for calculating hillslope degradation by overland flow is based on a coupling of the cellular automaton and smoothed particle hydrodynamics theories simulated debris laden floods were initiated on digital elevation models dems the flows were created by solving equations for diffusion routing and erosion and deposition we separated advection and diffusion terms using operator splitting then solved the advection term via automaton and the diffusion term via smoothed particle hydrodynamics the technique was tested on geometrically simple synthetic slopes against data for erosion and deposition by debris laden flows in a gully developing on a scoria cone arizona and against data on a recent moderate sized debris laden flood generated by possible partial glacier melting at popocatepetl volcano mexico the flow and erosion deposition patterns on the simple synthetic slopes appear intuitively reasonable on the synthetic scoria cone slope the model reproduced some of the observed spatial patterns of event scale erosion and deposition reasonable flow speeds runup heights and runout lengths were produced for the debris laden flood at popocatepetl the coupled cellular automaton smoothed particle hydrodynamics technique represents some advance in the modeling of landform degradation and channel development by cellular automata ca use of the technique may aid our understanding of the link between hillslope scale and landform scale degradation patterns

characterization of fluvial deposits interbedded with flood basalts neoproterozoic catoctin formation central appalachians usa abstract the catoctin formation infills a neoproterozoic age rift basin associated with the development of the laurentian continental margin one of several similar basins that are distributed along the length of the southern to central appalachian basin the catoctin formation consists of a flood basalt sequence with intercalated sedimentary deposits two types of architectural elements channel element ce and sheet element se are recognized within these sedimentary deposits massive structureless sandstones and conglomerates are the dominant facies within the ce and se and are interpreted to record deposition from hyperconcentrated flows lack of vegetative binding of sediment coupled with a relatively high stream gradient and possibly a high water table enhanced the probability of developing hyperconcentrated flows by the process of bulking addition of sediment to a flow additional facies present are the products of normal stream flow that developed from waning hyperconcentrated flows basaltic effusive rate sediment supply and extension subsidence controlled the generation of ce and se all ce reflect deposition in isolated fluvial channels incised into lava flows and are present within the lower member of the catoctin formation the presence of ce most likely indicates a high rate of lava extrusion low sediment supply and possible high subsidence rates the se composing the sedimentary member of the catoctin formation reflects a decrease in effusive and subsidence rates and a increase in sediment supply from the hinterland overlying the se is the last phase of basin infill characterized by basalts with minor interbedded clastic rocks the final phase of infilling was effected by an increase of effusive and subsidence rates and a potential cutoff of sediment supply the catoctin formation basin displays a more complex infill history than generally associated with the rift deposits of the laurentian margin

tomomorphometry of the somma vesuvius volcano italy 1 a tomomorphometric analysis of the somma vesuvius topography is presented this consists in extracting horizontal cross sections at different altitudes and in determining some morphometric parameters radius of the circle with a surface area equal to the cross section circularity ratio between the major and minor axis of the best fitting ellipse orientation of the ellipse major axis and the x y centroid the somma includes three portions the apron zone the flanks and the summit caldera boundary between 225 m and 525 m is 50 60 between 600 m and 775 m is 130 135 these are the preferred strike of the eruptive fissures affecting the northwestern somma flanks the faults affecting the whole edifice the nodal planes from local earthquakes the somma activity developed along a ne sw structural discontinuity whereas the post caldera activity concentrated along a nw se striking structure somma activity migrates from se to nw

particle fabric and sedimentation of structureless sand southern iceland abstract the interpretation of structureless sand units in terms of flow character and associated depositional mechanism is notoriously difficult to deduce from localized outcrop because such units offer no macroscopic features with which to make distinctions of flow parameters this investigation assesses the significance of directional properties of particle fabric samples taken both vertically and horizontally within structureless sand units deposited by jokulhlaups glacier outburst floods in southwest iceland known to be macroturbulent phenomena based on eyewitness accounts and inferences made from the large scale sedimentary architectures of the deposits given this framework we use particle fabric to verify flow character and depositional mechanism highlighting its potential application to deposits where prior knowledge of conditions is unknown vertical and horizontal trends in particle fabric indicate a causative mechanism that is manifested both spatially and temporally within visually structureless units this data indicates sedimentation onto an aggrading bed beneath a turbulent flow which conforms to the documented turbulent character of the jokulhlaup we demonstrate that cryptic information related to flow parameters can be gleaned from visually structureless sand units through detailed particle fabric analysis and clarify aspects of hyperconcentrated flow behavior and sedimentation

eruption of the nevado del ruiz volcano colombia on 13 november 1985 tephra fall and lahars a small plinian eruption of the nevado del ruiz volcano in colombia ejected 3 5 x 1010 kilograms of mixed dacite and andesite tephra on 13 november 1985 with a maximum column height of 31 kilometers above sea level small pyroclastic flows and surges generated during the initial stage of the eruption caused surface melting of approximately 10 of the volcano9s ice cap leading to meltwater floods the erosive floods incorporated soils and loose sediments from the volcano9s flanks and developed into lahars which claimed at least 25 000 lives

the enormous chillos valley lahar an ash flow generated debris flow from cotopaxi volcano ecuador the chillos valley lahar cvl the largest holocene debris flow in area and volume as yet recognized in the northern andes formed on cotopaxi volcano s north and northeast slopes and descended river systems that took it 326 km north northwest to the pacific ocean and 130 km east into the amazon basin in the chillos valley 40 km downstream from the volcano depths of 80 160 m and valley cross sections up to 337 000 m2 are observed implying peak flow discharges of 2 6 6 0 million m3 s the overall volume of the cvl is estimated to be 3 8 km3 the cvl was generated approximately 4500 years bp by a rhyolitic ash flow that followed a small sector collapse on the north and northeast sides of cotopaxi which melted part of the volcano s icecap and transformed rapidly into the debris flow the ash flow and resulting cvl have identical components except for foreign fragments picked up along the flow path juvenile materials including vitric ash crystals and pumice comprise 80 90 of the lahar s deposit whereas rhyolitic dacitic and andesitic lithics make up the remainder the sand size fraction and the 2 to 10 mm fraction together dominate the deposit constituting 63 and 15 wt of the matrix respectively whereas the silt size fraction averages less than 10 wt and the clay size fraction less than 0 5 wt along the 326 km runout these particle size fractions vary little as does the sorting coefficient average 2 6 there is no tendency toward grading or improved sorting limited bulking is recognized the cvl was an enormous non cohesive debris flow notable for its ash flow origin and immense volume and peak discharge which gave it characteristics and a behavior akin to large cohesive mudflows significantly then ash flow generated debris flows can also achieve large volumes and cover great areas thus they can conceivably affect large populated regions far from their source especially dangerous therefore are snow clad volcanoes with recent silicic ash flow histories such as those found in the andes and alaska

lahar record during the last 2500 years chokai volcano northeast japan flow behavior sourced volcanic activity and hazard implications abstract volcanic fans and volcaniclastic aprons ring plains developed at the foot of a volcano preserve the products of high discharge sediment laden lahar flows that originate from a volcano geological and geomorphological features of a volcanic fan are important for discussing the flow characteristics and history of far reaching flows such as lahars the present study focuses on volcanic fan deposits at the northern base of chokai volcano in northeast japan the authors conducted geomorphological analysis excavation survey at the distal part of the volcanic fan sedimentary facies analysis radiocarbon dating and historical document analysis to understand the flow characteristics and history of far reaching lahars in relation to changes in the depositional processes and their triggering volcanic activity geological observation by manual trenching and coring revealed that the volcanic fan is composed mainly of a series of lahar deposits formed by at least five large lahar events the 14c ages of the lahar deposits and their correlation with historical documents indicate that the large lahars travelled down the volcanic fan at the 2nd 5th century bce l1 2nd to 4th century bce l2 5th to 7th century ce l3 871 ce l4 and 1801 ce l5 after the kisakata debris avalanche 2 5 ka according to the stratigraphy ratio of magmatic fragments and hydrothermally altered material content in the deposits and correlation with historical documents these lahar events can be classified into three types in terms of their material source 1 a cohesive debris flow sourced by the debris avalanche deposit l1 2 a non cohesive lahar by a magmatic eruption l2 l3 l4 and l5 1 subunit and 3 a cohesive debris flow by a phreatic eruption l5 2 subunit the facies analysis revealed that the different flow behaviors of lahars reflect their sourced volcanic activity the oldest lahar l1 incorporating debris avalanche deposit flowed as hazardous cohesive debris flow lahars after magmatic eruptions l2 l3 l4 and l5 1 subunit tends to be streamflow through the flow transformation of sandy debris flow and a cohesive lahar l5 2 subunit by a phreatic eruption tends to be of small scale these results indicate that the characteristics of a lahar depend largely on causal volcanic activity