specific gravity characteristics of recent volcaniclastic sediment implications for sorting and grain size analysis specific gravity of water saturated surface dried individual grains and bulk sieved samples of pumice lapilli ash and slightly vesiculated rock fragments produced by recent eruptions at mount st helens washington as well as the composition of sediment derived from this material indicate two major departures in the character of volcaniclastics from more familiar quartzo feldspathic sediment these are 1 a three to five fold variation in the specific gravity of volumetrically important detrital grains as opposed to a less than 5 variation in 99 of the volume of average quartzo feldspathic sandstone and 2 significant variation in specific gravity that is inversely related to grain size within clast populations of the same composition this latter observation is attributed to the larger volume of vesicles particularly non interconnected vesicles with increasing grain size sorting in volcaniclastic sediment therefore is not only a function of depositional process environment and post de

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

extreme rainfall induced lahars and dike breaching 30 november 2006 mayon volcano philippines on 29 30 november 2006 heavy rains from supertyphoon durian remobilized volcanic debris on the southern and eastern slopes of mount mayon generating major lahars that caused severe loss of life and property in downstream communities the nearby legaspi city weather station recorded 495 8 mm of rainfall over 1 5 days at rates as high as 47 5 mm h far exceeding the initiation threshold for mayon lahars for about 18 h floods and lahars from the intense and prolonged rainfall overtopped river bends breaching six dikes through which they created new paths buried downstream communities in thick widespread deposits and caused most of the 1 266 fatalities in order to mitigate damage from future lahars the deposits were described and analyzed for clues to their generation and impact on structures and people post disaster maps were generated from raw aster and spot images using automated density slicing to characterize lahar deposits flooded areas croplands and urbanized areas fieldwork was undertaken to check the accuracy of the maps especially at the edges of the lahar deposits and to measure the deposit thicknesses the durian event was exceptional in terms of rainfall intensity but the dikes eventually failed because they were designed and built according to flood specifications not to withstand major lahars

depositional features of march 1982 mount st helens sediment flows on 19 march 1982 2 yr after initial eruption mount st helens erupted explosively resulting in the deposition of new sediment flows in the toutle river drainages fig 1 we conducted field observations of these flows during the period 29 march 5 april 1982 by this time the rivers rapidly re establishing pre eruption channel levels had down cut through the new flows allowing us to examine the internal structure of the flows before they could be extensively modified by reconstruction projects the flows were characterized by a distinct three unit sequence a basal massive to graded layer unit 1 consists of large clasts in grain to grain contact it is overlain by a distinctly finer grained stratified unit unit 2 of similar thickness the top unit unit 3 contains very large matrix supported clasts and transported log debris fig 2 this sequence has not previously been documented where its origin could clearly be ascribed to a single catastrophic depositional event the sequence provides a useful model for interpreting similar deposits in the rock record

interpreting flash flood palaeoflow parameters from antidunes and gravel lenses an example from montserrat west indies the wavelength of stationary water surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow in sand bed flume experiments alexander et al 2001 found that lens structures were preserved during antidune growth and change and the dimension of the lenses were empirically related to antidune wavelength and thus could be used to estimate flow velocity and depth this study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting testing the alexander et al 2001 relationship at a field scale trains of stationary and upstream migrating water surface waves were prevalent during the flash flood in october 2012 in the belham valley montserrat west indies wave positions and wavelengths were assessed at 900 s intervals through the daylight hours of the event within a monitored reach the wave data indicate flow depths up to 1 3 m and velocity up to 3 6 m s 1 sedimentary structures formed by antidune growth and change were preserved in the event deposit these structures include lenses of clast supported gravel and massive sand with varying internal architecture the lenses and associated low angle strata are comparable to sand bed structures formed from stationary and upstream migrating waves in flume experiments confirming the diagnostic value of these structures using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow

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

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

the emplacement of a large chemically zoned rheomorphic lava like ignimbrite the sgurr of eigg pitchstone nw scotland the sgurr of eigg pitchstone on the isle of eigg nw scotland is a crystal rich trachydacitic partially vitrophyric rock which has previously been interpreted both as a lava and as a sill we interpret this rock as a chemically zoned rheomorphic lava like ignimbrite that formed during a sustained pyroclastic eruption the sgurr of eigg pitchstone can be subdivided into discrete emplacement units distinguished by the following features 1 their present day weathering characteristics 2 the orientation spacing and morphology of the columnar joints 3 sharp undulating boundaries with marked topographic breaks the absence of weathered surfaces palaeosols pyroclastic fall deposits or sedimentary rocks at emplacement unit boundaries suggests deposition from a single eruption the emplacement units some of which display upper and basal vitrophyres represent distinct depositional packages that record several rapidly emplaced ignimbrites which welded cooled and devitrified as a simple essentially single cooling unit during eruption from a sustained low pyroclastic column the sgurr of eigg pitchstone displays a pervasive base parallel flow banding which is folded into intrafolial recumbent isoclinal folds the flow banding and folds indicate that rheomorphism occurred throughout deposition the sgurr of eigg pitchstone is interpreted as an erosional remnant of an extensive ignimbrite sheet the first such unit recorded within the north atlantic igneous province

short term evolution of an active basin fan system aspromonte south italy abstract alluvial fans are widespread throughout calabria southern italy but only a minority of them show evidence of current activity by means of interpretation of aerial photographs orthophotos and satellite images comparison of topographic maps reconstruction of major rainfall events and geomorphologic and sedimentologic field observations we reconstructed the recent history of the geomorphic and sedimentation events and the consequent morphological changes of an active basin fan system merging with the bed of an ephemeral stream locally named fiumara the case study is located along the ionian side of the aspromonte massif a sector of calabria where mass movement intensive erosion and channel mass transport are the predominant morphodynamic processes evidence is available of large volumes of debris produced by mass movements and erosion processes affecting the upper sector of the feeder basin the aggressive climate with intense winter storms is the principal cause of erosion and mass movements largest rainfall events occurred in clusters of 4 6 events between the 1930s and the early 1970s at roughly 20 year time intervals the development of the fan appeared as incipient in 1955 air photos activity continues today with events of sediment output from the feeder basin large rainfall events are reflected with a delay of ca eight years by aggradation dissection and progradation retrogradation cycles in the feeder channel and the fan respectively mutual interference between fan development and human activity exists as well as does the interaction between the fan progradation and the floods of the receiving fiumara stream based on the aforementioned survey tools two almost 10 year cycles were recognised feeder channel aggradation owing to the debris input of the feeder subbasin and to the presence of check dams built along the feeder channel continues until the channel slope reaches a threshold value this can also be caused by the trimming of the fan toe by the fiumara the stored alluvium is therefore released resulting in progradation at the fan site until the feeder channel slope decreases subsequently a renewed cycle starts again in response to sediment input from the source area the morphological and sedimentological evolution of the active basin fan system indicates how short term trends and cyclic modifications of such systems can be important especially where tributary basins join larger stream beds of a fiumara type torrent

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

acute sedimentation response to rainfall following the explosive phase of the 2008 2009 eruption of chaiten volcano chile the 10 day explosive phase at the start of the 2008 2009 eruption of chaiten volcano in southern chile 42 83 s 72 65 w blanketed the steep rain forest cloaked 77 km2 chaiten river drainage basin with 3 to 100 cm of tephra predominantly fine to extremely fine rhyolitic ash fell during the latter half of the explosive phase rain falling on this ash blanket within days of cessation of major explosive activity generated a hyperconcentrated flow lahar followed closely by a complex multi day muddy flood streamflow bordering on dilute hyperconcentrated flow sediment mobilized in this lahar flood event filled the chaiten river channel with up to 7 m of sediment buried the town of chaiten 10 km downstream of the volcano in up to 3 m of sediment and caused the lower 3 km of the channel to avulse through the town although neither the nature nor rate of the sedimentation response is unprecedented they are unusual in several ways 1 nearly 70 percent of the aggradation almost 5 m in the 50 70 m wide chaiten river channel was caused by a lahar triggered by an estimated 20 mm of rainfall over a span of about 24 h an additional 2 m of aggradation occurred in the next 24 36 h 2 direct damage to the town was accomplished by the sediment laden water flood phase of the lahar flood event not the lahar phase 3 the volume of sediment eroded from hillslopes and delivered to the chaiten river channel was at least 3 8 106 m3 roughly 15 40 of the minimum tephra volume that mantled the chaiten river drainage basin 4 the acute sedimentation response to rainfall appears to have been due to the thickness and fineness of the ash blanket inhibiting infiltration of rain and the steepness of the basin s hillslopes other possible factors such as the prior formation of an ash crust development of a hydrophobic surface layer or large scale destruction of rain intercepting vegetation did not play a role

a rational method for estimating maximum discharge of a landslide induced debris flow a case study from southwestern china this paper presents a rational method for estimating the maximum discharge of a landslide induced debris flow the method has five basic principles or steps a to identify and measure representative bends and straight zones along a channel through which a debris flow went down b to evaluate peak debris flow velocity in the bends c to assess peak debris flow velocity in the straight channel zones d to use the peak velocities to estimate the distribution of peak discharge along the entire channel and e to find the maximum velocity and discharge of the debris flow the method is illustrated with a case study of a landslide induced debris flow at a mountainous region near chengdu southwestern china the results show that the peak debris velocity was between 2 4 and 4 7 m s 1 and the peak debris discharge was between 6 7 and 35 7 m 3 s 1 the peak discharge initially increased at the upper portion of the channel then decreased at the lower portion indicating that the upper channel experienced erosion but the lower channel experienced deposition the location with the maximum debris flow discharge corresponds to the point where the volume of the debris flow started to decrease the method presented in this paper can help to prevent or mitigate debris flow hazards c 2006 elsevier b v all rights reserved

sedimentary and volcano tectonic processes in the british paleocene igneous province a review research on the british paleocene igneous province bpip has historically focused on the emplacement chemistry and chronology of its elaborate central intrusive complexes and lava fields however the bpip has also been dramatically shaped by numerous erosion sedimentation and volcano tectonic events the significance of which becomes ever clearer as localities in the bpip are re investigated and our understanding of volcano sedimentary processes advances the resultant deposits provide important palaeo environmental palaeo geographical and stratigraphical information and highlight the wide range of processes and events that occur in ancient volcanic settings such as the bpip in this paper we review the sedimentary and volcano tectonic processes that can be distinguished in the bpip and conceptualize them within a generalized framework model we identify and describe the sedimentary responses to four broadly chronological stages in the history of the bpip volcanoes 1 the development of the lava fields 2 early intrusion induced uplift 3 caldera collapse and 4 post volcano denudation and exhumation of central complexes we highlight and illustrate the range of sedimentary processes that were active in the bpip these operated on and helped shape a dynamic landscape of uplands and lowlands of alluvial fans braided rivers lakes and swamps and of volcanoes torn apart by catastrophic mass wasting events and or caldera collapse

subglacial conditions in a branching saalian esker in north central poland abstract the results of a sedimentological study of a branching esker system near uniszki north central poland provide a deeper insight into the depositional processes that took place within a subglacial tunnel formed during the wartanian late saalian glaciation the internal structure of the esker deposits is complex and coarse grained debris intercalates with silt and clay layers ten main lithofacies types are recognized including one formed in a tunnel mouth environment and three other lithofacies which must have been deposited in a truly subglacial environment a subglacial tunnel association is defined fluctuations in meltwater discharge through the tunnels resulted in cyclicity in the sedimentary succession deposition of fine grained facies took place during low discharge whereas boulder and gravel lithofacies formed in the tunnel mouth during high discharge changes in the hydrostatic conditions finally resulted in the collapse of the tunnel roof so that the succession became covered with supraglacial deposits the uniszki deposits record deposition under highly variable sedimentary hydrostatic conditions which is typical of environments in the polish lowlands the results of the present study provide some criteria for the interpretation of subglacial meltwater debris and thus may contribute to the current discussion on subglacial tunnel sedimentation

interplay of structural climatic and volcanic controls on late quaternary lacustrine deltaic sedimentation patterns in the western branch of the east african rift system rukwa rift basin tanzania abstract this paper presents the first detailed outcrop based sedimentologic investigation of the pleistocene holocene upper lake beds succession in the rukwa rift basin located in the western branch of the east african rift system southwestern tanzania the goal of this investigation is to examine the sedimentary facies and reconstruct the depositional environments of this important archive of quaternary climate and environmental change eleven diagnostic facies associations comprising 24 facies were identified and provide the basis for recognition of three key deposystems 1 alluvial to fluvial channel system 2 lake delta system and 3 profundal lacustrine system analysis of paleocurrent indicators and sandstone provenance indicate widely dispersed source regions and drainage patterns that were strongly influenced by major border fault systems and episodic volcanism six stratigraphic sequences a f ranging from 2 to 17 m thick were identified based on stratal stacking patterns and the development of sequence bounding unconformities and lacustrine flooding surfaces sedimentation processes facies architecture and stratigraphic packaging record a complex interplay between quaternary climate fluctuations and intense episodic volcanism in the nearby rungwe volcanic province set against large scale tectonic controls associated with synchronous development of the east african rift system sequence stratigraphic analysis reveals that the rukwa rift basin episodically shifted between a balanced fill lake basin and an overfilled lake basin deep water basin wide lake expansion occurred at different times during the late quaternary the final depositional sequence preserved in the basin a fluvial underfilled lake basin initiated 7 9 ka and has persisted to the present day high frequency climate change played the key role in sequence development in the upper lake beds however voluminous rift related volcanism and erosion of abundant labile volcanic materials from the rungwe volcanic province as well as syntectonic evolution of the rift led to high sedimentation rates and transformation of flash floods and debris flows in the hinterlands rift margin to hyperpycnal flows towards the basin depocenter

dynamic interactions between lahars and stream flow a case study from ruapehu volcano new zealand discussion and reply reply the discussion of manville et al highlights several interesting points about interpreting observations of the 1995 whangaehu lahars at ruapehu we would like to add to some of these points and to clarify some of the issues raised by the discussion whereas the three lahars we described were part

gpr derived architecture of a lahar generated fan at cotopaxi volcano ecuador the internal geometry of volcaniclastic fans produced by aggradation during lahar events is difficult to examine in modern settings because of the frequent lack of three dimensional exposures this makes it challenging to i reconstruct the spatial and temporal evolution of such fans and ii interpret observed facies stratigraphy in the context of lahar flow dynamics from proximal to distal fan reaches this research therefore presents the results of a ground penetrating radar gpr survey of the rumipamba fan at the mouth of the burrohuaycu quebrada on the southwestern flank of cotopaxi volcano a survey grid consisting of 50 individual gpr profiles representing a total length of 19 4 km was constructed covering most of the 4 km2 large fan surface all gpr profiles were collected using a pulseekko 100 with a 400 v transmitter fan sediments consist of sandy and gravelly lahar deposits alternating with volcanic fallout including ash and pumice lapilli at times reworked by fluvial processes deposits could be ground truthed to a depth of 3 m whereas gpr penetration depth reaches 15 m data interpretation was based on classification into 15 distinct radar facies characterized by the nature of their bounding surfaces and or internal features cross referenced where possible with shallow exposures three main facies were identified parallel irregular and clinoform erosional contacts were distinguished from aggradational ones vertical channel fill and lateral accretion flow parallel versus flow transverse and proximal distal variations in deposit architecture were featured the results of this study confirm the existence of two major channel systems in the northern and southern extremities of the fan and the more recent formation of a smaller central fan channel system deposit architecture is complex and facies chronologies illustrate that lahars have affected the entire survey area

eruption triggered avalanche flood and lahar at mount st helens effects of winter snowpack an explosive eruption of mount st helens on 19 march 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack a blast of hot pumice dome rocks and gas dislodged crater wall snow that avalanched through the crater and down the north flank snow in the crater swiftly melted to form a transient lake from which a destructive flood and lahar swept down the north flank and the north fork toutle river

miocene benthic foraminiferal isotope records a synthesis abstract 18 o 16 o and 13 c 12 c ratios of miocene benthic foraminifera from a number of atlantic pacific and indian ocean dsdp sites 71 77b 206 208 238 279 289 296 329 357 and 366a have been compiled these provide a rather detailed history of miocene deep water especially in the pacific ocean bottom water temperatures rose during the early miocene and then declined rapidly during the middle miocene this decline was accompanied by an increase in antarctic glaciation late miocene bottom temperatures and antarctic ice volumes are inferred to be similar to today s but exhibited some fluctuation the early miocene ocean was less thermally stratified at intermediate and abyssal depths while the late miocene deep ocean had a thermal structure generally similar to the modern ocean foraminiferal carbon isotope ratios at most of the sites varied quasi sympathetically throughout the miocene these variations must reflect comparable variations in the mean 13 c 12 c of marine hco 3 however the causes of such variations are not yet clear

contrasting styles of ephemeral river systems and their interaction with dunes of the skeleton coast erg namibia abstract the skeleton coast erg forms a prominent nnw trending dune belt 6 22 km wide comprising dunes up to 50 m high sub parallel to the south atlantic margin of namibia to a variable degree along its strike the dune belt dams west southwestward flowing ephemeral river systems on their route towards the atlantic ocean the southern rivers koigab uniab and hunkab affecting the erg are characterized by short infrequent ephemeral flows from restricted catchments whereas northern rivers hoanib and hoarusib are fed by large catchment areas favouring higher discharge and more frequent flows as the intertropical convergence zone and greater likelihood of monsoonal rainfall influence is approached the potential for river damming increases in the same downwind direction through the erg because of increasing dune belt width and height and the change from low barchanoid dune forms in the south to large composite transverse dunes in the north whereas cross sections of the southern part of the erg show considerable asymmetry with low barchans and sinuous crested dune forms eastwards but a high dune wall at the western edge cross sections over the northern erg are more uniformly symmetrical as a consequence the northern rivers are effectively dammed at the eastern erg margin causing flood reservoir basins there in contrast southern rivers are dammed within the erg as the most pronounced and commonly encountered barrier is provided by the dunewall at its western border

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

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

topography of the northern hemisphere of mercury from messenger laser altimetry laser altimetry by the messenger spacecraft has yielded a topographic model of the northern hemisphere of mercury the dynamic range of elevations is considerably smaller than those of mars or the moon the most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains within this lowland is a broad topographic rise that experienced uplift after plains emplacement the interior of the 1500 km diameter caloris impact basin has been modified so that part of the basin floor now stands higher than the rim the elevated portion of the floor of caloris appears to be part of a quasi linear rise that extends for approximately half the planetary circumference at mid latitudes collectively these features imply that long wavelength changes to mercury s topography occurred after the earliest phases of the planet s geological history

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

proximal pyroclastic deposits from the 1989 1990 eruption of redoubt volcano alaska stratigraphy distribution and physical characteristics abstract more than 20 eruptive events during the 1989 1990 eruption of redoubt volcano emplaced a complex sequence of lithic pyroclastic flow surge fall ice diamict and lahar deposits mainly on the north side of the volcano the deposits record the changing eruption dynamics from initial gas rich vent clearing explosions to episodic gas poor lava dome extrusions and failures the repeated dome failures produced lithic pyroclastic flows that mixed with snow and glacial ice to generate lahars that were channelled off drift glacier into the drift river valley some of the dome failures occurred without precursory seismic warning and appeared to result solely from gravitational instability material from the disrupted lava domes avalanched down a steep partly ice filled canyon incised on the north flank of the volcano and came to rest on the heavily crevassed surface of the piedmont lobe of drift glacier most dome collapse events resulted in single monolithologic massive to reversely graded medium to coarse grained sandy pyroclastic flow deposits containing abundant dense dome clasts these deposits vary in thickness grain size and texture depending on distance from the vent and local topography deposits are finer and better sorted down flow thinner and finer on hummocks and thicker and coarser where ponded in channels cut through the glacial ice the initial vent clearing explosions emplaced unusual deposits of glacial ice snow and rock in a frozen matrix on the north and south flanks of the volcano similar deposits were described at nevado del ruiz columbia and have probably been emplaced at other snow and ice clad volcanoes but poor preservation makes them difficult to recognize in the geologic record in a like fashion most deposits from the 1989 1990 eruption of redoubt volcano may be difficult to recognize and interpret in the future because they were emplaced in an environment where glacio fluvial processes dominate and quickly obscure the primary depositional record

catalogue of large alluvial fans in martian impact craters abstract we conducted a systematic global survey using thermal emission imaging system infrared themis ir coverage 100 m pixel to search for large alluvial fans in impact craters on mars our survey has focused on large fans apron areas greater than 40 km 2 usually located in craters greater than 20 km in diameter due to the resolution of the themis images and mars orbiter laser altimeter mola coverage we find that the host craters are found to have a distinctive diameter range from 30 150 km the fans generally cluster in three geographic areas southern margaritifer terra southwestern terra sabaea and southwestern tyrrhena terra however several outliers do exist the alluvial fans do not form in a particular orientation along the crater rim nor are they associated with the location of current high rim topography fan area magnitude and variability increase with crater diameter while fan concavity magnitude and variability increase with decreasing crater diameter smaller fan aprons in general have higher more variable concavity the source of the water forming these fans is uncertain given the challenges of accommodating the global distribution pattern and formation patterns within the craters

matrix granulometry of catastrophic debris flows december 1999 in central coastal venezuela abstract after 2 days of intense precipitation devastating flooding and debris flows affected the central coast of venezuela on december 15 16 1999 these events killed nearly 30 000 people and destroyed or damaged 126 000 homes i visited the disaster area in march 2000 coastal valleys affected by debris flows were extensively covered by an interstitial matrix that included large amounts of often impressive boulders up to 35 40 tons in weight granulometric analyses of four matrix samples from the naiguata valley showed they were all similarly coarse their main constituent was sand and grains data suggest the following events must have taken place in coastal venezuela torrential rains quickly caused flooding along creeks and rivers which must have rapidly attained hyperconcentrated streamflow bulking of stream alluvium in flood surges may also have taken place however the storm triggered widespread landsliding along the steep unstable flanks of the coastal cordillera many slides started in upper basin areas underlain by gneiss bedrock pena de mora such slides released vast amounts of coarse sandy debris which mixed with turbulent floodwaters to produce numerous granular noncohesive debris flows these flows despite their coarse matrix exhibited intense particle collisions and interactions thus were able to effectively mobilize vast masses of large boulders

lahar facies of the latest paleozoic arbasay formation geomorphological characters and paleoenvironment reconstruction of northern tian shan nw china abstract texturally well preserved lahars are exposed in the latest paleozoic arbasay formation northern tian shan the lahars consist primarily of two lithofacies massive poorly lithified diamictites and stratified moderately lithified gravelly sandstones the diamictites can be generally divided into two subfacies i e the matrix supported and the clast supported diamictites most diamictites are structureless and nongraded however some crudely stratified beds with a certain grading have also been found they are thick in beds and contain large clasts up to 3 m in dimension the gravelly sandstones display much finer particle size and have wedge or lenticular geometries large clasts are absent within them and the sorting characters are much better than the diamictites despite the different size grading the matrix and the clasts of the two lithofacies appear to be homogeneous the matrix is generally sandy mudstone the clasts comprise rhyolites dacites andesites andesitic basalts and basalts same to the co existing volcanic rocks suggesting they originate from the cognate volcanics the disorganized diamictites are supposed to deposit from a turbulent flood or pyroclastic surge the gravelly sandstone lithofacies are interpreted as sand rich flood flows or hyperconcentrated flood flows during the waning stage of a mass flow event the overall characteristics of the deposits suggest a mass flow dominated alluvial fan environment they are rapidly accumulated within small normal faults bounded depocenters the characteristics of the arbasay formation lahars together with the geochemistry characters of the co existing volcanic rocks clearly prove that they were deposited in a post collisional extensional regime la icp ms zircon dating of the intercalated fallout tuff sample provided an age of 314 4 3 4 ma mswd 1 6 suggesting they were deposited at late carboniferous therefore the north tian shan ocean must have closed before 314 ma and the initial basin type in northern tian shan should be extensional faulted basins rather foreland basins

debris avalanche deposits of the milo lahar sequence and the opening of the valle del bove on etna volcano italy previously undescribed debris avalanche deposits occur in two locations downslope from the open end of the valle del bove these outcrops comprise unstratified ungraded deposits of metre scale lava blocks in a matrix of weathered and fractured lava clasts the avalanche deposits are unconformably overlain by matrix to clast supported conglomerates representing debris flow and interbedded fluvial deposits that constitute most of the milo lahar sequence we present evidence that the milo lahar sequence which crops out just at the exit of the valle del bove formed during the opening and enlargement of this depression the presence of the avalanche deposits at the base of the milo lahar sequence indicates that catastrophic landslides were involved in the formation of the valle del bove the composition of lavas in the debris avalanche deposits is similar to that of most of the ellittico volcanic sequence exposed along the northern wall of the valle del bove radiocarbon dates of 8400 and 5300 years bp from the base and top respectively of the debris flow sequence indicate that the milo lahars are correlative with the exposed part of the chiancone deposit the basal lahars of the chiancone which contain lava blocks whose compositions partially overlap that of blocks in the avalanche deposits may have formed by water concentration in the distal end of the avalanche causing transformation to debris or alternatively by reworking of the avalanche deposit

lahar hazard assessment using titan2d for an alluvial fan with rapidly changing geomorphology whangaehu river mt ruapehu abstract rapid changes in small areas at the apex of alluvial fans may have devastating consequences by directing downstream flood or lahar impacts into catchments of widely varying population or infrastructure vulnerability during a series of lahars in 1995 at mt ruapehu new zealand aggradation of the whangaehu fan apex draining the eastern edifice caused the onset of avulsion of flows northward into the highly vulnerable tongariro catchment an earth training dike or bund was constructed to protect this catchment by retaining flows on the southern side and the normal lahar outlet path to the south surveys in 2001 late 2005 and following a major lahar in march 2007 now show net degradation of a channel in the whangaehu fan apex bordered by the bund this indicates a net increase in the channel capacity at this site and shows that the bund remains at its effective design capacity past hydrological modelling used for the bund design provided a large range of discharge estimates but lacked precise constraints on the size and nature of lahars from eruption and lake breakout events new modelling has been carried out using titan2d to examine the impacts of a 6 106 m3 volume granular flow down this catchment this simulates either an eruption or a lake breakout induced lahar with a historically typical volumetric bulking factor of 4 these simulations predict minimum discharges between 1800 and 2100 m3 s at the bund site by comparison the largest 1995 flow at this site was estimated at around 1200 m3 s further any single modelled flow from the normal outlet channel of crater lake could not be induced to overtop the bund because discharge appears to be limited by the narrow upper reaches of the whangaehu gorge theoretical discharge levels required to overtop the bund are estimated to be 6800 m3 s assuming no aggradation of the channel by the decelerating flow maximum potential discharge at the bund site is additionally modified by potential bifurcation of lahars above a certain size threshold at a point 2 5 km upstream of the bund a major side channel the chute effectively diverts part of the flows away to the southern side of the whangaehu fan this potential for splitting of the flow appears to have increased since 1995 from aggradation of lahar deposits and reworked sediment in the area immediately upstream of the divide despite remaining at design capacity for lahar events in the whangaehu erosion of new channels following the 2007 lahar renders the bund vulnerable to undercutting