hydraulic physical and rheological characteristics of rain triggered lahars at semeru volcano indonesia lahars volcanic debris flows have been responsible for 40 of all volcanic fatalities over the past century mount semeru east java indonesia is a persistently active composite volcano that threatens approximately one million people with its lahars and pyroclastic flows despite their regularity the behaviour and the propagation of these rain triggered lahars are poorly understood in situ samples were taken from lahars in motion at two sites in the curah lengkong river on the southeast flank of semeru providing estimates of the particle concentration grain size spectrum grain density and composition this enables us to identify flow sediment from three categories of lahars a hyperconcentrated flow b non cohesive clast and matrix supported debris flow and c muddy flood to understand hyperconcentrated flow sediment transport processes it is more appropriate to sample the active flows than the post event lahar deposits because in situ sampling retains the full spectrum of the grain size distribution rheometrical tests on materials sampled from moving hyperconcentrated flows were carried out using a laboratory vane rheometer despite technical difficulties results obtained on the 63 180 and 400 m fractions of the sampled sediment suggest a purely frictional behaviour importantly and contrary to previous experiments conducted with monodisperse suspensions our results do not show any transition towards a viscous behaviour for high shear rates these data provide important constraints for future physical and numerical modelling of lahar flows copyright 2010 john wiley sons ltd

steepland resources characteristics stability and micromorphology abstract steeplands of central america are a major land resource but due to population pressures they are rapidly being deforested leading to landscape instability microwatersheds of southern honduras were examined to correlate soil type landform slope gradient and slump potential soils most susceptible to slumping were moderately deep 0 5 1 m haplustalfs and haplustepts these soils occupy about 25 of the landscape and have slope gradients of 45 90 soils are developed on plagioclase rich andesitic parent material are loam to clay loam in texture and have high base status however due to weathering of parent material sand and silt fractions are dominated by quartz with smaller amounts of plagioclase vermiculite and kaolinite the a and b horizons have an open porphyric related distribution with plagioclase as the coarse fraction in a fine grained groundmass the andesitic parent rock contains abundant hydrothermally altered plagioclase phenocrysts in a single spaced porphyric related c f5 m ratio of 4 1 distribution some feldspars are partially to completely altered to clay pseudomorphs probably vermiculite microfabric analysis of soil and pararock did not show any striated b fabric indicative of shear failure however microfabrics do confirm translocated clay into the subsoil as typic pore coatings indicating long term landscape stability prior to deforestation

the relationship between pedogenic and geomorphic processes in mountainous tropical forested area in sierra madre del sur mexico abstract both mature and underdeveloped soils are present in tropical mountainous landscapes the spatial arrangement of mountainous soils is ascribed mainly to geomorphologic processes we studied two soil toposequences one on a convex and the other on a concave slope with a gradient 40 60 at the coffee growing farm la cabana situated in the mountains of the sierra madre del sur southern mexico mature alisols as well as moderately developed luvic phaeozems and underdeveloped soils fluvic and skeletic phaeozems were detected in the study area the sequence of sediments and soils is unusual for a classical soil catena buried clayey reddish soils are present on the shoulder of a slope colluvial sediments with weakly developed soils form convex and concave footslopes the peculiarity of the slopes and spatial distribution of soils in the studied toposequences were ascribed to intensive linear erosion due to tectonic uplift seismically induced landslides and k cycles of laminar erosion the diversity of sediments leads to considerable variation in soil texture and mineralogical composition and thus to the diversity of soil properties which is considered to be a positive feature of a landscape

numerical modeling of the emplacement of socompa rock avalanche chile 1 the 7 5 ka socompa sector collapse emplaced 25 km3 of fragmented rock as a thin but widespread 500 km2 avalanche deposit followed by late stage sliding of 11 km3 as toreva blocks most of the avalanche mass was emplaced dry although saturation of a basal shear layer cannot be excluded modeling was carried out using the depth averaged granular flow equations in order to provide information on the flow behavior of this well preserved long run out avalanche results were constrained using structures preserved on the surface of the deposit as well as by deposit outline and run up a proxy for velocity models assuming constant dynamic friction fail to produce realistic results because the low basal friction angles 1 to 3 5 necessary to generate observed run out permit neither adequate deposition on slopes nor preservation of significant morphology on the deposit surface a reasonable fit is obtained however if the avalanche is assumed simply to experience a constant retarding stress of 50 100 kpa during flow this permits long run out as well as deposition on slopes and preservation of realistic depositional morphology in particular the model explains a prominent topographic escarpment on the deposit surface as the frozen front of a huge wave of debris reflected off surrounding hills the result that socompa avalanche experienced a small approximately constant retarding stress during emplacement is consistent with a previously published analysis of avalanche data

record of late holocene debris avalanches and lahars at iliamna volcano alaska abstract iliamna volcano is a 3053 meter high glaciated stratovolcano in the southern cook inlet region of alaska and is one of seven volcanoes in this region that have erupted multiple times during the past 10 000 yr prior to our studies of iliamna volcano little was known about the frequency magnitude and character of holocene volcanic activity here we present geologic evidence of the most recent eruptive activity of the volcano and provide the first outline of late holocene debris avalanche and lahar formation iliamna has had no documented historical eruptions but our recent field investigations indicate that the volcano has erupted at least twice in the last 300 yr clay rich lahar deposits dated by radiocarbon to 1300 and 90 yr bp are present in two major valleys that head on the volcano these deposits indicate that at least two large possibly deep seated flank failures of the volcanic edifice have occurred in the last 1300 yr noncohesive lahar deposits likely associated with explosive pyroclastic eruptions date to 2400 1300 1500 300 and debris avalanche deposits from recent and historical small volume slope failures of the hydrothermally altered volcanic edifice cover most of the major glaciers on the volcano although these deposits consist almost entirely of hydrothermally altered rock debris and snow and ice none of the recently generated debris avalanches evolved to lahars a clay rich lahar deposit that formed

rutile solubility in albite h2o and na2si3o7 h2o at high temperatures and pressures by in situ synchrotron radiation micro xrf abstract rutile is an important mineral host for high field strength elements so its solubility in geologic fluids at high pressure and temperature plays an important role in the crustal and mantle processes that control the terrestrial cycling of these elements however experimental measurements of rutile solubility are in conflict by a factor of more than 100 at most studied conditions we performed new measurements of rutile solubility in h 2 o albite and h 2 o na 2 si 3 o 7 ns3 fluids by in situ synchrotron radiation x ray fluorescence spectroscopy using modified bassett type hydrothermal diamond anvil cells minimum detection limits were 1 9 and 2 3 ppm ti by weight for the two cells three albite h 2 o experiments at starting bulk compositions of 2 7 6 7 and 10 3 wt albite involved spectral acquisition at rutile saturation in the presence of albite crystals melt or a single homogeneous fluid phase after accounting for the additional phases corrected fluid compositions were 0 6 to 7 5 wt dissolved silicate over the run conditions at 2 7 wt albite rutile dissolution rate was slow and steady state was not achieved at 600 800 c however at higher dissolved albite contents constant solubility with time was observed rutile solubilities in the presence of a single fluid phase at 700 c 0 79 gpa 5 4 wt albite and at 800 c 1 10 gpa 6 7 wt albite were 37 2 and 156 6 ppm respectively these data agree with results acquired using hydrothermal piston cylinder methods with long run times and suppression of new crystal growth but not with data derived from visual observation in hydrothermal diamond anvil cells this discrepancy is likely due to lack of equilibrium in the latter approach two experiments in 10 and 30 wt ns3 at 660 800 c 0 5 0 1 gpa show extreme concentration dependent enhancement of rutile solubility to 4500 ppm the data indicate a strong positive correlation between rutile solubility and na al because na k al is likely to be greater than unity in aqueous fluids at high pressure and temperature due to incongruent dissolution of albite and micas the increase in rutile solubility along the albite ns3 join points to the possibility of significant ti transport by silicate bearing aqueous fluids in the lower crust and upper mantle

paleomagnetism magnetic fabric and 40ar 39ar dating of pliocene and quaternary ignimbrites in the arequipa area southern peru 40ar 39ar ages and paleomagnetic correlations using characteristic remanent magnetizations chrm show that two main ignimbrite sheets were deposited at 4 86 0 07 ma la joya ignimbrite lji and at 1 63 0 07 ma arequipa airport ignimbrite aai in the arequipa area southern peru the aai is a 20 100 m thick ignimbrite that fills in the arequipa depression to the west of the city of arequipa the aai is made up of two cooling units an underlying white unit and an overlying weakly consolidated pink unit radiometric data provide the same age for the two units as both units record exactly the same well defined paleomagnetic direction 16 sites in the white unit of aai dec 173 7 inc 31 2 95 0 7 k 2749 and 10 sites in the pink unit of aai dec 173 6 inc 30 3 95 1 2 k 1634 showing no evidence of secular variation the time gap between emplacement of the two units is unlikely to exceed a few years the 50 m thick well consolidated white underlying unit of the arequipa airport ignimbrite provides a very specific magnetic zonation with low magnetic susceptibilities high coercivities and unblocking temperatures of nrm above 580 c indicating a ti poor titanohematite signature the anisotropy of magnetic susceptibility ams is strongly enhanced in this layer with anisotropy values up to 1 25 the fabric delineated by ams was not recognized neither in the field nor in thin sections because most of the aai consists in a massive and isotrope deposit with no visible textural fabric pumices deformation due to welding is only observed at the base of the thickest sections ams within the aai ignimbrite show a very well defined pattern of apparent imbrications correlated to the paleotopography with planes of foliation and lineation dipping often at more than 20 toward the expected vent buried beneath the nevado chachani volcanic complex in contrast with the relatively small extent of the thick aai the la joya ignimbrite covers large areas from the altipano down the piedmont ti poor titanomagnetites are the dominant magnetic carriers and ams values are generally lower than 1 05 magnetic foliations are sub horizontal and lineations directions are scattered in the lji the ams fabrics are probably controlled by post depositional compaction and welding of the deposit rather than transport dynamics

topographic reflection of the socompa debris avalanche chile one of the most remarkable features of the exceptionally well preserved 26 km3 socompa debris avalanche deposit is the evidence for topographically driven secondary flow the avalanche formed by sector collapse of socompa stratovolcano and spread 40 km across a pre existing basin forming a sheet of 50 m average thickness as the avalanche impinged on the western and northern margins of the basin it was reflected back forming a secondary flow that continued to travel 15 km down a gentle slope at an oblique angle to the primary flow the front of the return wave being preserved frozen on the surface of the deposit as a prominent escarpment satellite images aerial photos digital elevation models and field observations were used to reconstruct the sequence of events during avalanche emplacement and in particular during secondary flow the avalanche sheet was divided into distinct terrane groups each believed to have experienced a particular strain history during emplacement evidence for avalanche reflection includes clearly recognizable secondary slide masses sub parallel sets of curvilinear shear zones headwall scarps separating the primary levee from the secondary terranes extensional jigsaw breakup of surface lithologies during return flow and cross cutting or deflection of primary flow fabrics by secondary terranes reflection off the basin margin took place in an essentially continuous manner most major return motions being simultaneous with or shortly following primary flow the secondary flow occurred as a wave that swept obliquely across the primary avalanche direction remobilizing the primary material which was first compressed then stretched as it passed over and rearward of the wave front as return flow occurred surface lithologies were rifted in a brittle manner and the slabs were sheared pervasively as they glided and rotated back into the basin some sank into the more fluidal interior of the avalanche which drained out into a prominent distal lobe extension by factors of up to 1 8 took place during return flow secondary flow took place on slopes of only a few degrees and the distal lobe flowed 8 km on a slope of 1 overall the avalanche is inferred to have slid into place as a fast moving sheet of fragmental rock debris with a leading edge and crust with near normal friction and an almost frictionless fluidal interior and base the avalanche emplacement history deduced from field evidence is consistent with the results of a previously published numerical model of the socompa avalanche

pedogenetic investigation of soil degradation on a deforested loess hillslope of golestan province northern iran abstract genesis mineralogy and micromorphology of soils formed on a forest and adjacent cultivated loess hillslope were investigated to assess the effects of deforestation and hillslope position on soil properties and the intensity of soil degradation the study revealed that deforestation caused a loss of soil organic carbon a reduction of cation exchange capacity and an increase in carbonates in the surface soil the soils of the different slope positions of the forest land were alfisols and mollisols with well developed argillic horizons speckled b fabric of the argillic horizons and the crystallitic b fabric of the underlying calcic horizon are evidence for a more stable landscape under forest ecosystem downward leaching caused decalcification of the upper horizons and clay movement in the profile formation of the mollic epipedon in the forest land confirms the accumulation of organic carbon and lower erosion in the surface soil soils of the adjacent cultivated area however are less developed and classified as inceptisols and mollisols absence of the mollic epipedon in the shoulder backslope and footslope positions presence of the near surface calcic horizon and absence of argillic horizon in all slope positions are due to severe erosion absence of speckled b fabric in all the slope positions of the deforested land is evidence that downward and surface movements of water have resulted in soil erosion and flooding higher smectite concentrations and occurrence of vermiculite in the forest area indicate favorable moisture availability pedology is an effective way of documenting the adverse effects of land use change especially in the hilly regions

soil erosion processes and sediment sorting associated with transport mechanisms on steep slopes summary sediment size distribution greatly affects sediment transport and deposition a better understanding of sediment sorting will improve understanding of erosion and sedimentation processes which in turn will improve erosion modeling to address this issue a total of 12 rainfall simulation experiments were conducted in a 1 m by 5 m box with varying steep slopes 10 15 20 and 25 and the simulated rainfall lasted for 1 h at a rate of 90 mm h 1 for each simulated event runoff and sediment were sampled at 3 min intervals which were performed to study in detail the temporal change in size distribution of the eroded materials these data were used to interpret the real time sequence of transport mechanisms acting in response to the simulated rainfall total soil loss is the sum of suspended saltating and contact loads the proportion of sediment r 2 0 452 p n 120 suspension saltation transports the finer than 0 054 mm size sediment was the most important erosion mechanism during interrill erosion processes however after rill development on hillslopes bed load transport by rolling of medium to large sized sediment particles coarser than 0 152 mm became an increasingly important transport mechanism and it were also enhanced by increased slope overall the study supports a strong relationship between the sediment transport of contact rolling load and stream power the partition of soil loss into these more meaningful components appears to be essential both for initial data interpretation and for subsequent use of such data for soil loss prediction

volcanic avalanche fault zone with pseudotachylite and gouge in french massif central abstract structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non depositional to depositional conditions during volcanic avalanche emplacement in the well exposed impact sheared contact along volcanic avalanche fault zone in the french massif central we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress sequential events of basal aggradation along avalanche fault zone have been established related to fractal d values temperature pressure regime and oscillatory stress during slow wave velocity a typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge a cataclastic gradient is characterised by the fractal d values from 2 7 in jigsaw breccias with pseudotachylite partial melt to 2 6 in the polymodal gouge shock brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris avalanche deposit gouge microstructures show granular segregation cataclasis with antithetic rotational riedel shear and an arching effect between the riedel shear bands x ray microtomography provided 3d microfabrics along the clastic vein in the sandy gouge from the available statistical dataset a few equations have been developed implicating the same cataclastic origin with a co genetic evolution of lithofacies an impact wave during primary shear propagation may contribute to produce hydroclastic matrix pseudotachylite partial melt and proximal gouge thixotropy with v 50m s and a t

rainfall kinetic energy controlling erosion processes and sediment sorting on steep hillslopes a case study of clay loam soil from the loess plateau china summary rainfall kinetic energy ke can break down aggregates in the soil surface a better understanding of sediment sorting associated with various kes is essential for the development and verification of soil erosion models a clay loam soil was used in the experiments six kes were obtained 76 90 105 160 270 and 518 j m 2 h 1 by covering wire screens located above the soil surface with different apertures to change the size of raindrops falling on the soil surface while maintaining the same rainfall intensity 90 3 5 mm h 1 for each rainfall simulation runoff and sediment were collected at 3 min intervals to investigate the temporal variation of the sediment particle size distribution psd comparison of the sediment effective psd undispersed and ultimate psd dispersed was used to investigate the detachment and transport mechanisms involved in sediment mobilization the effective ultimate ratios of clay sized particles were less than 1 whereas that of sand sized particles were greater than 1 suggesting that these particles were transported as aggregates under higher ke the effective ultimate ratios were much closer to 1 indicating that sediments were more likely transported as primary particles at higher ke owing to an increased severity of aggregate disaggregation for the clay loam soil the percentage of clay sized particles and the relative importance of suspension saltation increased with increasing ke when ke was greater than 105 j m 2 h 1 while decreased with increasing ke when ke was less than 105 j m 2 h 1 a ke of 105 j m 2 h 1 appeared to be a threshold level beyond which the disintegration of aggregates was severe and the influence of ke on erosion processes and sediment sorting may change results of this study demonstrate the need for considering ke influenced sediment transport when predicting erosion

structural environment of iron in hydrous aluminosilicate glass and melt evidence from x ray absorption spectroscopy abstract the iron speciation in hydrous haplotonalitic and haplogranitic silicate glasses was studied using xafs spectroscopy and transmission electron microscopy tem spectral features occurring at the main crest of the xanes at the iron k edge of hydrous glasses indicate contributions to the spectra by iron moieties present in a more ordered structural environment than found in the dry glass these differences are also suggested by analysis of the exafs these effects are not completely suppressed even for those samples that were quenched with a higher cooling rate strongest differences to the dry glass are observed for a sample that was quenched slowly through the temperature of glass transformation crystals 60 to 1500 nm in size of magnetite maghemite and another unidentified phase were observed in this sample by tem whereas no crystals were found in samples quenched with regular or high cooling rates in situ xanes measurements up to 700 c and 500 mpa were performed to reveal the origin i e during synthesis or quench of the structural differences for those hydrous glasses that do not display any detectable crystallization the comparison of xanes spectra collected on fe 2 in water saturated haplogranitic melt at 700 c and 500 mpa and on fe 2 in dry melt at 1150 c shows that the local structural environment of fe 2 in both systems is similar this indicates that there is no detectable and direct influence of water on the local structure around iron in this type of melt hence the differences observed between hydrous and dry glasses can only be related to artefacts formed during the quench process

geology of el misti volcano near the city of arequipa peru approximately 750 000 people live at risk in the city of arequipa whose center lies 17 km from the summit 5820 masl meters above sea level of the active el misti volcano the composite edifice comprises a stratovolcano designated misti 1 ca 833 112 ka partially overlapped by two stratocones designated misti 2 and misti 3 112 ka and younger and a summit cone misti 4 11 ka and younger eight groups of lava flows and pyroclastic deposits indicate the following volcanic history 1 three cones have been built up since ca 112 ka at an average eruptive rate of 0 63 km3 k y 2 several episodes of growth and destruction of andesitic and dacitic domes triggered dome collapse avalanches and block and ash flows deposition of these flows alternated with explosive events which produced pyroclastic flow deposits and tephra fall and surge deposits 3 nonwelded dacitic ignimbrites may reflect the formation of a 6 5 km incremental caldera collapse on misti 2 ca 50 000 and 40 000 yr b p and a 2 1 5 km summit caldera on misti 3 ca 13 700 to 11 300 yr b p 4 tens of pyroclastic flows and at least 20 tephra falls were produced by vulcanian and sub plinian eruptions since ca 50 ka on average ash falls have occurred every 500 to 1500 yr and pumice falls every 2000 to 4000 yr 5 misti erupted relatively homogeneous andesites and dacites with a few rhyolites but misti 4 reveals a distinct mineral suite less evolved andesites prevail in scoriaceous products of group 4 1 including historical ash falls scoriae of misti 4 and the ca 2300 2050 yr b p banded pumice commonly show heterogeneous textures of andesite and rhyolite composition this heterogeneity may reflect changes in physical conditions and magma mixing in the reservoir 6 deposits emplaced during the vulcanian a d 1440 1470 event and the sub plinian eruption s at ca 2050 yr b p are portrayed on one map the extent and volume of these deposits indicate that future eruptions of el misti even if moderate in magnitude will entail considerable hazards to the densely populated area of arequipa

neogene and quaternary ignimbrites in the area of arequipa southern peru stratigraphical and petrological correlations abstract this study focuses on the correlation of four newly identified rhyolitic ignimbrites located around arequipa which were previously described as a single ignimbrite sheet 1 the rio chili ignimbrite ca 13 33 ma crops out in the rio chili canyon and consists of a cooling unit of non welded to partially welded massive crystal rich lapilli tuff this ignimbrite represents the base of the neogene ignimbrite succession in the arequipa area and may be stratigraphically equivalent to the 14 13 ma huaylillas ignimbrites in southern peru 2 the second voluminous 20 km3 and widespread la joya ignimbrite sheet ca 4 87 ma filled the arequipa depression its probable source is now buried underneath the chachani volcanic complex the la joya ignimbrite covers both the arequipa batholith toward the rio vitor piedmont and also part of the altiplano to the east and north of the chachani complex 3 the arequipa airport ignimbrite aai sheet ca 1 6 ma 18 km3 the third and latest infill of the arequipa basin consists of a lower white columnar jointed massive lapilli tuff indurated by vapor phase recrystallization and is overlain by an upper pink lithic rich non welded massive lapilli tuff the source of this ignimbrite is also buried underneath the chachani complex as indicated by anisotropy of magnetic susceptibility measurements and component lithology 4 the yura non welded pumice flow deposits ca 1 02 ma 1 5 km3 are restricted to the northern and western flanks of the chachani complex and may correlate with tuffs of the capillune formation on the altiplano all ignimbrites are high k calc alkaline to alkaline rhyolites which contain variable amounts of plagioclase biotite quartz sanidine and fe ti oxides the modal composition of mineral phases and chemistry of amphiboles and biotites are useful for distinguishing the ignimbrites specific geochemical fingerprints such as sr y rb ba cs ree and sr isotopes were effective discriminator elements magmatic differentiation crustal residence time and contamination and source melting processes are discussed in order to explain compositional variations the older la joya ignimbrite and rio chili ignimbrite reflect initial wetter crustal melts closer to granite composition whereas with time the younger arequipa airport ignimbrite and yura tuffs initial melts are slightly less evolved and dryer due to more extensive crustal melting the voluminous 40 km3 neogene ignimbrites of the arequipa area were produced by three major explosive volcanic pulses in the central volcanic zone of southern peru whose genetic relation with tectonic uplift and crustal thickening of the andean cordillera are still a matter of debate

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

grain size distribution and sedimentology in volcanic mass wasting flows implications for propagation and mobility the sedimentological characteristics of mass wasting flow deposits are important for assessing the differences between phenomena and their propagation and emplacement mechanisms in the present study nine volcanic debris avalanche deposits and eight lahar deposits are considered from the literature their sedimentology is expressed in the descriptive statistics median grain size sand gravel and finer particle fractions skewness and sorting analysis of the data confirms that lahars and debris avalanches diverge in their grain size distribution and in their evolution during propagation water saturation in lahars is the main factor enabling debulking a mechanism that is not recorded in the data derived from debris avalanches deposits on the contrary evidence of comminution of particles due to particle particle interactions is observed in debris avalanches and not in lahars these findings support previous studies suggesting that although water content in debris avalanches plays a role in propagation the effects of inertial collision of solid fragments are more important than fluid effects confirming that particle particle interactions are the main factor influencing the mobility of non saturated mass wasting flows

sedimentary signatures of cyclic growth and destruction of stratovolcanoes a case study from mt taranaki new zealand abstract the long term behaviour of andesite stratovolcanoes is characterised by a repetition of edifice growth phases followed by collapse this cyclic pattern represents a natural frequency at varying timescales in the growth dynamics of stratovolcanoes worldwide around the 130 ka mt taranaki egmont volcano new zealand coastal cliff successions at 20 40 km distance comprise repeating packages of lithologically and sedimentologically distinctive mass flow deposits varying depositional mechanisms and source properties of these units record growth and collapse cycles of the central edifice these are used to construct a model for cyclic volcaniclastic sedimentation in the surrounds of stratovolcanoes during edifice construction phases thick packages of tabular predominantly monolithologic hyperconcentrated flow and debris flow deposits accumulate with intercalated tephra beds the mass flow units commonly contain large proportions of fresh pumice or juvenile lithic andesite intervals of quiescence separating eruptive periods are characterised by landscape re adjustment accompanied by deposition of fluvial and aeolian sediments along with steady accretion of medial ash in contrast brief episodes of destruction are marked by wide spread distinctively clay rich polylithologic debris avalanche deposits and related marginal debris flow units the growth stages can be terminated by an eruption triggered sector collapse or by external forces once the edifice exceeds a critical stable height or profile dependent on eruptive style and local geo tectonic conditions once the edifice becomes metastable regional tectonic earthquakes or shallow level intrusion events are likely triggers for collapse although the resulting debris avalanches represent the greatest individual hazard from such andesite stratovolcanoes their frequency is relatively low compared with other types of mass flows generated during edifice growth phases accurate forecasts of future hazard from mass flow events are therefore dependent on recognition of both the frequency of a stratovolcano s growth cycle and its current position in that cycle

the effect of water and fo2 on the ferric ferrous ratio of silicic melts new experiments on the effect of dissolved water on the ferric ferrous ratio of silicic melts have been performed at 200 mpa between 800 c and 1000 c and for fo2 between nno 1 35 and nno 6 6 water saturated conditions were investigated compositions studied include six metaluminous synthetic melts with feotot progressively increasing from 0 47 to 4 25 wt two natural obsidian glasses one peraluminous and the other peralkaline and a synthetic rhyolitic glass having the composition of the matrix glass of the june 15 1991 pinatubo dacite ferrous iron was analyzed by titration and feotot by electron microprobe variation of quench rate was found to have no detectable effect on the ferric ferrous ratio of the hydrous silicic melts investigated at nno no dependence of the ferric ferrous ratio with temperature is observed at fo2 nno 1 the experimental ferric ferrous ratios are equal or lower than calculated the peralkaline samples show the same type of behaviour a non linear relationship between xfe2o3 xfeo and fo2 implies that a term for dissolved water must be added to the kc equation if it is to be applied to the calculation of ferric ferrous ratios of hydrous silicic melts above nno 1 the ferric ferrous ratio is essentially controlled by the anhydrous melt composition and fo2 however differences exist between measured and calculated ferric ferrous ratios of silicic melts that are not all attributable to the effect of dissolved water additional work is needed to describe more precisely the dependence of the ferric ferrous ratio on anhydrous melt composition the oxidizing effect of water is restricted to relatively reduced magmatic liquids in oxidized calk alkaline magma series the presence of dissolved water will not largely influence melt ferric ferrous ratios

north american microtektites are more oxidized than tektites iron oxidation states and coordination numbers have been determined by micro x ray absorption near edge spectroscopy xanes on the cores of a large group of microtektites from the australasian ivory coast and north american na tektite strewn field the north american microtektites used in this study have been collected from five sites at different distances from the source crater most have sio2 content between 70 and 80 wt accurate analysis of the pre edge peak energy position and integrated area allowed determination of fe3 fe2 fe3 ratios on all samples with an estimated error of 0 05 microtektites from the australasian and ivory coast strewn fields show low values of the fe3 fe2 fe3 ratios in fair agreement with tektites from the same strewn field in contrast microtektites from the north american strewn fields show a wide range of fe3 fe2 fe3 ratios from 0 02 to ca 0 61 comparison of fe oxidation state data with chemical composition do not show any relation between fe3 fe2 fe3 ratios and na ca or k contents thus suggesting that the high fe oxidation states are not the consequence of sea water alteration the difference between the fe oxidation state of tektites and microtektites from the north american strewn fields suggests that some factors in the formation of the north american microtektites were different than for the north american tektites and for microtektites in the other strewn fields previous fe oxidation state data on na tektites strongly suggest that the wide range in fe oxidation state we found on na microtektites is not related to lateral heterogeneity of the target rocks despite a correlation between microtektite oxidation state and distance from the source crater we maintain that fe oxidation state is not related only to the microtektite droplet flight distance this is in keeping with the fact that no significant variations in the fe oxidation state have been found in microtektites from the australasian strewn field even for australasian microtektites recovered in antarctica the fe oxidation state in north american microtektites could be explained by interaction of melt droplets with a h2o rich vapor plumes generated during the impact these data point out that some difference must exist between the thermal histories of microtektites and tektites from the na strewn field moreover microtektites from the na strewn field show also distinctively higher oxidation states than those from ivory coast or the australasian strewn fields

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

micro raman determination of iron redox state in dry natural glasses application to peralkaline rhyolites and basalts abstract the position scaled intensity and topology of the raman stretching envelope at 1000 cm 1 hf have been established in complex anhydrous glasses having variable fe 3 fe ratios and contrasting compositions of peralkaline rhyolite pantellerite feo t 7 8 wt iron poor and iron rich basalts feo t 7 6 and 10 1 wt sensitivity of glass structure to iron redox decreases with increasing glass basicity raman spectra of pantellerite glasses fe 3 fe 0 04 0 97 evidence the sharp increase of a band at 970 cm 1 with the progressive entry of 4 fold fe 3 in alkali bonded q 3 units the spectral evolution of basalts with increasing iron oxidation fe 3 fe 0 05 0 87 is more subtle and is likely determined by formation of less polymerized units the moderate to low influence of redox state changes on the structure of natural basalt glass compared with the high sensitivity of their synthetic analogues can be attributed to strong competition between network forming cations al fe in the absence of an excess of alkalis we demonstrate that raman calibration against reference glasses allows precise determination of fe 2 fe 3 ratio but is highly composition dependent as a consequence of the variable link existing between fe 2 fe 3 and glass polymerization specific calibration procedures based on deconvolution shift or intensity of hf band are required for compositions with high acid glasses moderate or poor basic glasses sensitivity to iron redox changes respectively

transport and emplacement mechanisms of large volcanic debris avalanches evidence from the northwest sector of cantal volcano france abstract large volcanic debris avalanche vda deposits of miocene age occur within the stratigraphic sequence of cantal stratovolcano central france the vda of cantal volcano were initiated by sector collapse of a cone of high elevation up to 4500 m a s l two distinct superimposed vda deposit units breccias i and ii resulted from at least two successive large scale collapse events during the evolution of the volcanic complex breccia i the oldest one is very thick up to 200 m and heterolithologic it is overlain by breccia ii which is thinner up to 50 m and contains more heterometric clasts ranging from hectometer to millimeter size the vda deposits are poorly sorted clasts are angular and highly fractured at different scales often with jigsaw fit in breccia ii jigsaw megaclasts have usually subspheric shapes with size decreasing distally basal deposits commonly display thin inversely graded layers reorientated clasts along ramp structures and cataclasis of the substratum some units have a distal fabric in the form of a poorly developed clast imbrication the clasts are commonly sub rounded thereby indicating abrasion during viscous flow anisotropy of magnetic susceptibility a m s measurements indicate absence of a preferentially oriented matrix fabric magnetic foliation parallel to the bedding suggests that the depositional process is dominated by particle settling the magnetic fabric is better organized in distal deposits where magnetic carriers are imbricated moreover the fragmented clasts and megaclasts are not abraded rather inflation led to isotropic spherical dispersion of clastic material isotropic dispersive inflation which fed the interclast matrix this is also confirmed by the lack of rotation at the individual crystal level all these data strongly suggest transport of vda by liquified non turbulent granular flows distally imbricated deposits suggest more turbulent flow emplacement of the vda results from progressive upward aggradation of the particles by volume reduction and deflation loss the non turbulent liquified stage of the vda disappears the vda behaves as a sliding rigid mass plug flow that exerts strong friction on the basement leading to gouge formation

h2o diffusion in peralkaline to peraluminous rhyolitic melts the diffusion of water in a peralkaline and a peraluminous rhyolitic melt was investigated at temperatures of 714 1 493 k and pressures of 100 and 500 mpa at temperatures below 923 k dehydration experiments were performed on glasses containing about 2 wt h2ot in cold seal pressure vessels at high temperatures diffusion couples of water poor 0 5 wt h2ot and water rich 2 wt h2ot melts were run in an internally heated gas pressure vessel argon was the pressure medium in both cases concentration profiles of hydrous species oh groups and h2o molecules were measured along the diffusion direction using near infrared nir microspectroscopy the bulk water diffusivity d text h 2 text o t was derived from profiles of total water c text h 2 text o t using a modified boltzmann matano method as well as using fittings assuming a functional relationship between d text h 2 text o t and c text h 2 text o t both methods consistently indicate that d text h 2 text o t is proportional to c text h 2 text o t in this range of water contents for both bulk compositions in agreement with previous work on metaluminous rhyolite the water diffusivity in the peraluminous melts agrees very well with data for metaluminous rhyolites implying that an excess of al2o3 with respect to alkalis does not affect water diffusion on the other hand water diffusion is faster by roughly a factor of two in the peralkaline melt compared to the metaluminous melt the following expression for the water diffusivity in the peralkaline rhyolite as a function of temperature and pressure was obtained by least squares fitting log d text h 2 text o t 1 text wt 7 09 pm 0 15 frac 4 788 pm 166 0 56 pm 0 21 times p t where d text h 2 text o t 1 text wt is the water diffusivity at 1 wt h2ot in m2 s t is the temperature in k and p is the pressure in mpa the above equation reproduces the experimental data 14 runs in total with a standard fit error of 0 15 log units it can be employed to model degassing of peralkaline melts at water contents up to 2 wt

sequential fragmentation transport theory pyroclast size density relationships and the emplacement dynamics of pyroclastic density currents a case study on the mt st helens usa 1980 eruption abstract pyroclastic density currents pdcs are the most dangerous hazard associated with explosive volcanic eruptions despite recent advancements in the general understanding of pdc dynamics limited direct observation and or outcrop scarcity often hinder the interpretation of specific transport and depositional processes at many volcanoes this study explores the potential of sequential fragmentation transport theory sft cf wohletz et al 1989 a modeling method capable of predicting particle mass distributions based on the physical principles of fragmentation and transport to retrieve the transport and depositional dynamics of well characterized pdcs from the size and density distributions of individual components within the deposits the extensive vertical and lateral exposures through the may 18th 1980 pdc deposits at mt st helens msh provide constraints on pdc regimes and flow boundary conditions at specific locations across the depositional area application to msh deposits suggests that sft parameter distributions can be effectively used to characterize flow boundary conditions and emplacement processes for a variety of pdc lithofacies and deposit locations results demonstrate that 1 the sft approach reflects particle fragmentation and transport mechanisms regardless of variations in initial component distributions consistent with results from previous studies 2 sft analysis reveals changes in particle characteristics that are not directly observable in grain size and fabric data and 3 sft parameters are more sensitive to regional transport conditions than local outcrop scale depositional processes the particle processing trends produced using sft analysis are consistent with the degree of particle processing inferred from lithofacies architectures for all lithofacies examined in this study suspension sedimentation products exhibit much better processing than concentrated current deposits integrated field observations and sft results provide evidence for increasing density segregation within the depositional region of the currents away from source as well as for comparable density segregation processes acting on lithic concentrations and pumice lenses within the current these findings further define and reinforce the capability of sft analysis to complement more conventional pdc study methods significantly expanding the information gained regarding flow dynamics finally this case study demonstrates that the sft methodology has the potential to constrain regional flow conditions at volcanoes where outcrop exposures are limited

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

the experimental calibration of the iron isotope fractionation factor between pyrrhotite and peralkaline rhyolitic melt abstract a first experimental study was conducted to determine the equilibrium iron isotope fractionation between pyrrhotite and silicate melt at magmatic conditions experiments were performed in an internally heated gas pressure vessel at 500 mpa and temperatures between 840 and 1000 c for 120 168 h three different types of experiments were conducted and after phase separation the iron isotope composition of the run products was measured by mc icp ms i kinetic experiments using 57 fe enriched glass and natural pyrrhotite revealed that a close approach to equilibrium is attained already after 48 h ii isotope exchange experiments using mixtures of hydrous peralkaline rhyolitic glass powder 4 wt h 2 o and natural pyrrhotites fe 1 x s as starting materials and iii crystallisation experiments in which pyrrhotite was formed by reaction between elemental sulphur and rhyolitic melt consistently showed that pyrrhotite preferentially incorporates light iron no temperature dependence of the fractionation factor was found between 840 and 1000 c within experimental and analytical precision an average fractionation factor of 56 fe 54 fe pyrrhotite melt 0 35 0 04 2se n 13 was determined for this temperature range predictions of fe isotope fractionation between fes and ferric iron dominated silicate minerals are consistent with our experimental results indicating that the marked contrast in both ligand and redox state of iron control the isotope fractionation between pyrrhotite and silicate melt consequently the fractionation factor determined in this study is representative for the specific fe 2 fe ratio of our peralkaline rhyolitic melt of 0 38 0 02 at higher fe 2 fe ratios a smaller fractionation factor is expected further investigation on fe isotope fractionation between other mineral phases and silicate melts is needed but the presented experimental results already suggest that even at high temperatures resolvable variations in the fe isotope composition can be generated by equilibrium isotope fractionation in natural magmatic systems

a gravitational spreading origin for the socompa debris avalanche abstract socompa volcano arguably provides the world s best exposed example of a sector collapse derived debris avalanche deposit new observations lead us to re interpret the origin of the sector collapse we show that it was triggered by failure of active thrust anticlines in sediments and ignimbrites underlying the volcano the thrust anticlines were a result of gravitational spreading of substrata under the volcano load about 80 of the resulting avalanche deposit is composed of substrata formerly residing under the volcano and in the anticlines the collapse scar can be traced up to 5 km from the edifice truncating two spreading related anticlines which collapsed in the event outcrops near the volcano preserve evidence of edifice material being carried along on top of mobilised substrata on the north side of the scar the avalanche motion was initially at right angles to the failure edge structural relations indicate that immediately prior to collapse the substrata disintegrated became effectively liquidised and were ejected from beneath the edifice catastrophic mobilisation of substrata probably resulted from breakdown of ignimbrite clasts and cement it may have occurred through progressive rock fracture by high shear strain during spreading material ejected from under socompa formed a layer on which volcanic edifice debris was transported this interpretation of events explains the puzzling observation that avalanche units with the lowest gravitational potential energy moved the furthest it can also account for avalanche motion normal to the collapse scar walls ignimbrites and other rock types probably capable of similar behaviour underlie many other volcanoes identification of spreading at other sites could therefore be a first step towards assessment of the potential for this style of catastrophic sector collapse

biomarkers in sedimentary sequences indicators to track sediment sources over decadal timescales abstract long term sedimentary sequence research can reveal how human activities and climate interact to affect catchment vegetation flooding soil erosion and sediment sources in this study a biomarker sediment fingerprinting technique based on n alkanes was used to identify long timescale decadal sediment sources in a small agricultural catchment however the highly saline carbonate environment and bacterial and algal activities elevated the levels of even chain n alkanes in the sediments leading to an obvious even over odd predominance of short and middle components c 15 c 26 therefore by analyzing three odd long chain n alkanes c 27 c 29 and c 31 in 27 source samples from cropland gully and steep slope areas and one sediment sequence one cultivated horizon and 47 flood couplets a composite fingerprinting method and genetic algorithm optimization were applied to find the optimal source contributions to sediments the biomarker fingerprinting results demonstrated that the primary sediment source is gullies followed by cropland and steep slope areas the average median source contributions associated with 47 flood couples collected from sediment core samples ranged from 0 0 1 to 91 9 0 4 with an average of 45 0 for gullies 0 0 4 to 95 6 1 6 with an average of 38 2 for cropland and 0 2 1 to 60 7 0 4 with an average of 16 8 for steep slopes however because farmers were highly motivated to manage the cropland after the 1980s over half the sediments were derived from cropland in the 1980s biomarkers have significant advantages in the identification of sediments derived from different landscape units e g gully and steep slope areas and n alkanes have considerable potential in high resolution research of environmental change based on soil erosion in the hilly loess plateau region

fault textures in volcanic debris avalanche deposits and transformations into lahars the pichu pichu thrust lobes in south peru compared to worldwide avalanche deposits abstract structures lithofacies and semi quantitative sedimentological analysis of volcanic debris avalanche deposits are essential to constrain syn emplacement processes along avalanche fault zones in the setting of mass flow runout distances at a distance of 28 km from the extinct pichu pichu compound volcano we show how internal structures of thrust lobes faulted as to form horst and graben like structures have recorded the brecciation with granular segregations cataclastic gradients have been recognized in more than eleven breccia structures with statistical grain size parameters among them fractal d values between 1 96 and 2 53 related to an extensional fracturing in dads with fractal d values between 2 and 2 5 leading to granular disaggregation with fractal d values between 2 13 and 2 22 primary fractures related to transport processes and the secondary cataclasis produced during emplacement are quantified as having 50 matrix the hybrid lithofacies in graben like structures may be the precursory stages of the matrix transformation into lahar deposits volcanic debris avalanche structures of eleven worldwide volcanoes that belong to the central andes and the cascades volcanic arc have been compared using sedimentary and statistical methods 156 sieved samples and shape preferred orientation measured on 30 342 clasts median diameter sorting index skewness and kurtosis values help differentiate four deposits and processes 1 the proximal gravitational collapse deposits 2 the avalanche thrust lobes located in inverted extensional fault zones and 3 the hybrid and mixed deposits with polymodal distributions and 4 the bimodal transformed matrix with clast sorting the fractal d values of avalanche matrix range between 2 3 and 2 7 suggesting that extensional fractures have led to granular disaggregation from the available statistical dataset a few equations have been developed that help pointing to a syn emplacement cataclastic gradient along avalanche fault zone three textural classes of avalanche fault zones have been identified based on the ellipse a b values of 2 14 for the planar collapse in fault zone 1 75 to 2 for the crushing of volcanic avalanche breccias and

the whangaehu formation debris avalanche and lahar deposits from ancestral ruapehu volcano new zealand abstract in the north island of new zealand the andesitic tongariro volcanic centre encompasses the tongariro complex the mt ngauruhoe cone and the country s largest stratovolcano mt ruapehu this volcano is surrounded by an equally large volume of late quaternary volcaniclastic deposits forming a circular ring plain in the southern portions of the ring plain the whangaehu formation provides a critical record of the early ruapehu activity because such deposits are not preserved on the present mt ruapehu cone we re interpret the previously described whangaehu formation deposits and their emplacement mechanisms providing new data to support this through the analysis of key stratigraphic sections sedimentary structures and features grain size distributions lithologic components and sem studies of volcaniclastic material the formation in the middle course of the whangaehu river valley comprises three principal stratigraphic units representing an estimated volume of c 1 km3 the lower member comprises a coarse clast supported ungraded megaclast rich breccia with oblique to sub horizontal fractures indicating that shearing occurred at its base the lower member also contains rip up clasts from the underlying tertiary siltstones an indurated and sheared clast mixture of angular to subangular cobbles and pebbles supports large boulders at the base of the breccias with fracturing concentrated near the base of this stratum pockets of shattered clasts representing monolithological domains and boulders showing jigsaw fractures indicate collision effects during transportation from source the breccia is interpreted as a debris avalanche deposit resulting from a collapse of the southern flank of ruapehu some time between 180 ka and 45 ka the middle member suggests fluvial reworking of the debris avalanche deposit interspersed with post collapse lahar deposits on the ancestral ruapehu ring plain the upper member reflects an aggradation phase on the southern ring plain with deposition of lahars associated with volcanic activity as shown by reworked tephra the catastrophic debris avalanche represented by the whangaehu fm lower member illustrates a significant hazard to the surrounds of mt ruapehu that has been previously underestimated

particle size density relationships in pyroclastic deposits inferences for emplacement processes in moving pyroclastic systems particles are sorted as a function of their sizes densities and shapes the analysis of the distribution of these characteristics in particle populations of pyroclastic deposits is a major tool in evaluating properties and regimes of parent transport systems this paper reports a study of size density relationships of component subpopulations from selected quaternary pyroclastic deposits of the latera volcanic complex vulsini italy by means of integrated field and laboratory investigations including grain size and component analyses density measurements and sem crystal morphoscopy three kinds of particle size density relationships characterize the studied deposits as follows 1 a significant correlation of decreasing sizes with increasing component densities exists for direct suspension sedimentation products including plinian fall and pyroclastic surge deposits 2 a wide data dispersion with poor correlation normally occurs for the main zones of deposits from high concentration pyroclastic flows and 3 component subpopulations occur in a narrow size range irrespective of density in granular systems dominated by grain collisions such as traction zones beneath low concentration pyroclastic surges and sheared basal layers of pyroclastic flows the regression coefficients of size density relationships appear as a comparative measure of particle concentration in the parent systems consistent with that inferred from the degree of sorting and abrasion of crystal subpopulations from sequential fragmentation transport analysis of grain size data and quantitative morphoscopy the crystal component becomes less sorted and more abraded as the fit to the size density relationship decreases from plinian fall to pyroclastic surge to pyroclastic flow consistent with increasing particle concentration in the transporting current

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

distinguishing volcanic debris avalanche deposits from their reworked products the perrier sequence french massif central debris avalanches associated with volcanic sector collapse are usually high volume high mobility phenomena debris avalanche deposit remobilisation by cohesive debris flows and landslides is common so they can share textural characteristics such as hummocks and jigsaw cracks distinguishing original deposits from reworked products is critical for geological understanding and hazard assessment because of their different origin frequency and environmental impact we present a methodology based on field evidence to differentiate such epiclastic breccias basal contact mapping constrained by accurate altitude and location data allows the reconstruction of deposit stratigraphy and geometry lithological analysis helps to distinguish the different units incorporation structures kinematic indicators and component mingling textures are used to characterise erosion and transport mechanisms we apply this method to the enigmatic sequence at perrier french massif central where four units u1 u4 have been interpreted either as debris flow or debris avalanche deposits the sequence results from activity on the monts dore volcano about 2 ma ago the epiclastic units are matrix supported with an almost flat top u2 and u3 have clear debris flow deposit affinities such as rounded clasts and intact blocks no jigsaw cracks u1 and u4 have jigsaw cracked blocks with matrix injection and stretched sediment blocks u1 lacks large blocks 10 m wide and has a homogenous matrix with an upward increase of trapped air vesicle content and size this unit is interpreted as a cohesive debris flow deposit spawned from a debris avalanche upstream in contrast u4 has large mega blocks up to 40 m wide sharp contacts between mixed facies zones with different colours and numerous jigsaw fit blocks open jigsaw cracks filled by monogenic intra clast matrix mega blocks are concentrated near the deposit base and are spatially associated with major substratum erosion this deposit has a debris avalanche distal facies with local debris flow affinities due to partial water saturation we also identify two landslide deposits l1 and l2 resulting from recent reworking that has produced a similar facies to u1 and u4 these are distinguishable from the original deposits as they contain blocks of mixed u1 u4 facies a distinctly less consolidated and more porous matrix and a fresh hummocky topography this work shows how to differentiate epiclastic deposits with similar characteristics but different origins in doing so we improve understanding of present and past instability of the monts dore and identify present landslide hazards at perrier

particle interaction inside debris flows evidence through experimental data and quantitative clast shape analysis abstract results of analytical experiments related to the dynamic behavior of debris flows are presented particle interaction and the amount and type of fines content present in the matrix aspects that govern debris flow behavior are studied via the morphological evolution of constituent particles four different mixtures of water and sediment with compositions resembling debris flows were prepared and put into a rotating drum known as a los angeles standard abrasion machine and studied at different time intervals for each sampling time quantitative shape analysis was performed using three morphological coefficients mc 2 mc 3 8 and mc 30 34 coefficient mc 2 gives information about particle ellipticity mc 3 8 is related to basic irregularities at a macro scale such as roundness mc 30 34 is related to microscale irregularities like surface texture coefficient mc 3 8 was shown to be very sensitive to silt content in the matrix and coefficient mc 30 34 to the presence of clay all three coefficients point to the fact that changes in shape between granulometric classes are gradual and follow a power law coarse granulometric classes acquire more circular and smooth profiles while small particles maintain their irregular profiles this phenomenon is the result of clast interaction processes within mixtures clast collisions between particles produce comminution of the coarsest fractions while finer particles fracture along their entire surface the rate at which these changes occur is related to the type of fine sediment present in the matrix changes in particle shape are an important tool for revealing internal dynamics because they are related to clast interaction and affect sedimentation processes inside these flows this type of experiment although not on a real scale provides important physical information for understanding the phenomena that occur inside debris flows enabling the study of a variety of textural parameters and their changes at regular time intervals the experimental patterns observed offer new insights into clast clast interaction rounding and comminuting theory with important implications for understanding rheological behavior and kinematics of flows and related hazards