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

multistage damming of the rhine river by tephra fallout during the 12 900 bp plinian laacher see eruption germany syn eruptive rhine damming i abstract the rhine the largest river in western europe was dammed during the plinian laacher see eruption lse 12 900 bp damming during the climactic plinian episode of lse occurred both upstream and downstream of the broad tectonic lower neuwied basin lnb that interrupts the narrow rhine canyon we here document details of the upstream damming at the bottleneck entrance to the lnb near the present city of koblenz our reconstruction is based on a high resolution analysis and correlation of the complex intercalation of primary fallout tephra relics with fluvially reworked laacher see tephra in the lnb tephra units representing complete eruptive cycles repeatedly fell on drained ground in between one minor and 4 major flooding events even at the base of side channels that had been active prior to the lse and that had been flooded by a preceding flooding event this demonstrates that flooding occurred generally during breaks and not during fallout events the repeated formation and breach of a dam at the upstream entrance of the lnb koblenz dam consisting of fallout components and driftwood washed together convincingly explains the multiple repetition of the drainage of the channels in the lnb followed by large magnitude flooding in rapid succession the strongly pulsating nature of the lse reflected in multiple interruptions of eruptive activity fundamentally controlled the damming and flooding dynamics the rhine became completely blocked during distinct fallout phases due to overloading with pumice that had fallen into the river and its major tributaries the temporary dam collapsed during eruptive breaks this is the first recorded example of tephra fallout damming a major watercourse the extremely low gradient of the rhine river allowed the repeated accumulation of large volumes of water in a long multi phase dammed up lake lake koblenz that extended along the upstream course of the river for up to c 30 km despite the low height damming of a major river while a large plinian eruption is in full progress represents an extraordinary challenge for hazard mitigation this is especially pertinent for an area close to and downwind from the vent and therefore simultaneously affected by massive plinian fall such as in the lnb

the 25 september 2007 eruption of mount ruapehu new zealand directed ballistics surtseyan jets and ice slurry lahars abstract at 20 26 nzdt on 25 september 2007 a moderate gas driven eruption beneath the summit crater lake of mt ruapehu new zealand generated a directed ballistic fallout apron and surtseyan jet that impacted an area of c 2 5 km2 to the north of the vent two climbers were caught in the blast at a hut 600 m from the vent primary ice slurry lahars were generated in two catchments draining the summit region including a flow that entered a commercial ski field the ejecta consists of blocks of andesitic lava and scoria erupted during previous volcanic episodes a variety of mineral cemented lake floor sediments vent fill debris and rare glassy material interpreted to be derived from a fresh batch of magma a minority of clasts contain formerly molten elemental sulphur indicating that vent temperatures at the base of the lake were in excess of 119 c the ballistic deposit is confined to a c 40 wide swath directed northwards that extends up to 2 km from the inferred vent location beneath crater lake the strong directionality of the jetted deposits and ballistic free shadow zones sheltered by intervening topography all point to a relatively low angle directed blast previous similar eruptions at ruapehu also show preferred deposit orientations that are here correlated with an inclined and off centre vent beneath crater lake the 25 september 2007 eruption appears to have resulted from failure of a relatively shallow hydrothermal seal composed of elemental sulphur and other mineral precipitates developed in the vent breccia which breached following overpressurization by a pulse of magmatic gases released from deeper in the conduit this event highlights the potential hazard from relatively minor gas driven eruptions at ruapehu that can occur with little or no warning improved understanding of the eruption mechanism for this style of eruption will inform future risk assessments for ruapehu and other similar volcanoes worldwide

a constitutive model for water flow in unsaturated fractured rocks a conceptual model for describing effective saturation in fractured hard rock is presented the fracture network and the rock matrix are considered as an equivalent continuum medium where each fracture is conceptualized as a porous medium of granular structure and the rock matrix is assumed to be impermeable the proposed model is based on the representation of a rough walled fracture by an equivalent porous medium which is described using classical constitutive models a simple closed form equation for the effective saturation is obtained when the van genuchten model is used to describe saturation inside fractures and fractal laws are assumed for both aperture and number of fractures the relative hydraulic conductivity for the fractured rock is predicted from a simple relation derived by liu and bodvarsson the proposed constitutive model contains three independent parameters which may be obtained by fitting the proposed effective saturation curve to experimental data two of the model parameters have physical meaning and can be identified with the reciprocal of the air entry pressure values in the fractures of minimum and maximum apertures effective saturation and relative hydraulic conductivity curves match fairly well the simulated constitutive relations obtained by liu and bodvarsson copyright 2008 john wiley sons ltd

a facies model for a quaternary andesitic composite volcano ruapehu new zealand ruapehu composite volcano is a dynamic volcanic sedimentary system characterised by high accumulation rates and by rapid lateral and vertical change in facies four major cone building episodes have occurred over 250 ka from a variety of summit flank and satellite vents eruptive styles include subplinian strombolian phreatomagmatic vulcanian and dome related explosive eruptions and extrusion of lava flows and domes the volcano can be divided into two parts a composite cone of volume 110 km3 surrounded by an equally voluminous ring plain complementary portions of ruapehu s history are preserved in cone forming and ring plain environments cone forming sequences are dominated by sheet and autobrecciated lava flows which seldom reach the ring plain the ring plain is built predominantly from the products of explosive volcanism both the distal primary pyroclastic deposits and the reworked material eroded from the cone much of the material entering the ring plain is transported by lahars either generated directly by eruptions or triggered by the high intensity rain storms which characterise the region ring plain detritus is reworked rapidly by concentrated and hyperconcentrated streams in pulses of rapid aggradation immediately following eruptions and more gradually in the longer intervals between eruptions

fracture network analysis of the st eustache quarry quebec canada for groundwater resources management a detailed structural survey has been conducted on a fractured sedimentary rock formation in the st eustache quarry quebec canada to supplement a hydrogeological study the two main types of dis

a geochemical transport model for redox controlled movement of mineral fronts in groundwater flow systems a case of nitrate removal by oxidation of pyrite a one dimensional prototype geochemical transport model was developed in order to handle simultaneous precipitation dissolution and oxidation reduction reactions governed by chemical equilibria total aqueous component concentrations are the primary dependent variables and a sequential iterative approach is used for the calculation the model was verified by analytical and numerical comparisons and is able to simulate sharp mineral fronts at a site in denmark denitrification has been observed by oxidation of pyrite simulation of nitrate movement at this site showed a redox front movement rate of 0 58 m yr 1 which agreed with calculations of others it appears that the sequential iterative approach is the most practical for extension to multidimensional simulation and for handling large numbers of components and reactions however slow convergence may limit the size of redox systems that can be handled

cryptic eruption of mount ruapehu revealed by deposits of sediment laden streamflow in a steep mountain valley the 4 ka kiwikiwi formation whangaehu valley nz abstract a distinctive deposit of unaltered reworked volcaniclastic sediment here designated the kiwikiwi formation is described from the upper whangaehu valley at mount ruapehu new zealand the grain size distribution and sedimentary features of the unit suggest deposition from a sheetflow dominated alluvial system but simple sediment entrainment calculations show that the unit s granulometry is inconsistent with normal streamflow deposition at the observed steep depositional slope streams have produced deposits at mount st helens and mount pinatubo under similarly anomalous conditions following debris avalanche and or volcanic eruptions when highly charged with sediment and subject to common lahars debris flows and hyperconcentrated flows reported sediment transport rates from mount st helens toutle river and pinatubo s pasig potrero river show that a virtually unlimited supply of relatively fine grained sand range tephra renders some established sediment transport formulae inapplicable because the volume of available material effectively exceeds the transport capacity of the system we use simple equilibrium flow calculations to demonstrate that this sedimentary unit which has open porosity framework grain support and bedding characteristics compatible with alluvial sheet flows would not have been deposited under normal streamflow conditions this approach provides a means to confirm the role of capacity limitations on stream behaviour during the post eruptive sedimentary response phase in catchments overwhelmed by pyroclastic material and is particularly useful given the lack of clear depositional fingerprints for hyperconcentrated flow we further infer that because the material in the kiwikiwi formation is uniform unaltered and minimally abraded differs from older sediment in the valley overlies a 4 6 ka debris avalanche deposit and was emplaced from an over capacity stream by hyperconcentrated flows or extremely thinned ones and without evidence of interruption it represents the previously unidentified proximal products of an unstudied holocene eruption of ruapehu

analysis and simulation of reactive transport of metal contaminants in ground water in pinal creek basin arizona abstract large scale mining activities have generated a plume of acidic ground water more than 15 km long in the regional aquifer of the pinal creek basin a one dimensional reactive transport model was developed using phreeqc to aid in the analysis of transport and chemical processes in the plume and to determine the uses and limitations of this type of modeling approach in 1984 the acidic part of the plume had a ph as low as 3 4 and contained milligram per liter concentrations of iron copper aluminum and other metals from 1984 to 1994 concentrations of contaminants in the alluvial aquifer in pinal creek basin arizona decreased as a result of mixing recharge remedial pumping and chemical reactions for reactions involving gypsum and rhodochrosite the equilibrium modeling assumption of a local geochemical equilibrium was generally valid from 1984 to 1990 water along the simulated flow path was at equilibrium or slightly supersaturated with gypsum and gypsum equilibria controlled dissolved concentrations of calcium and sulfate beginning in 1991 water in the acidic part of the plume became increasingly undersaturated with respect to gypsum indicating that the gypsum available for dissolution in the aquifer may have been completely consumed by about 1991 rhodochrosite precipitation was thought responsible for the measured attenuation in dissolved manganese in the neutralized zone for reactions involving calcite the assumption of a local geochemical equilibrium was generally not valid dissolution of calcite in the transition zone was not sufficient to establish equilibrium although following neutralization the calcite saturation index decreased to 1 2 in 1986 calcite undersaturation decreased along the flow path in the neutralized zone and equilibrium was attained about 7 km downgradient of the transition zone the assumption of a local geochemical equilibrium was not valid for oxidation reduction reactions that involved iron oxides and manganese oxides kinetically controlled oxidation reduction reactions continued in the acidic part of the flow path for years following the passage of the transition zone although the equilibrium approach helped to provide an increased understanding of contaminant transport at pinal creek future work will require a kinetic modeling approach to more accurately simulate selected reactions between the plume and aquifer materials

from sink to volcanic source unravelling missing terrestrial eruption records by characterization and high resolution chronology of lacustrine volcanic density flow deposits lake inawashiro ko fukushima japan

the impact of present lahars on the geomorphologic evolution of proglacial gorges popocatepetl mexico abstract popocatepetl 19 03 n 98 35 w 5450 m is located 70 km southeast of mexico city the volcano resumed its eruptive activity in 1994 with emissions of pyroclasts that partially melted the glacier located on the north face the sudden release of water generated large lahars that flowed downslope though proglacial gorges this paper examines the geomorphologic evolution of these gorges since 1992 and focuses particularly on the landforms created by the most recent lahars of july 1997 the research suggests that the transport capacity of the lahars has increased despite the fact that the sediments they carry originate in deposits formed by earlier processes the presence of continuous permafrost in the area is a key factor in the formation of lahars

numerical simulation and evaluation of groundwater resources in a fractured chalk aquifer a case study in zinder well field niger groundwater is often a unique water source for agriculture industry and domestic use for local inhabitants in semi arid african continent owing to shortage of surface water and rainfall it is of significance to quantify and assess the groundwater resources for local sustainable development in order to correctly evaluate groundwater resources of zinder well field with fractured media in zinder niger a conceptual model of hydrogeology was set up by a geological and hydrogeological survey for simulating the real conditions a large multi well pumping test with designed pumping rate was conducted in addition a two dimensional finite element transient flow model was developed to simulate groundwater flow at the site results show that generally good agreements have been found between the simulated and observed hydrogeology heads for the test the hydraulic parameters were obtained from the pumping test a 11 year prediction of groundwater resources has been made under three exploitation schemes respectively and it indicates that the well field can offer 7 000 m3 day when the aquifer remains confined an optimal scheme of exploitation is provided

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

evaluation of titan2d modelling forecasts for the 2007 crater lake break out lahar mt ruapehu new zealand abstract following the 1995 1996 eruptions of mt ruapehu the hazard of a dam breakout lahar was immediately recognised because an unstable 7 9 m pile of volcaniclastic ejecta had accumulated over the former stable outlet of the normally 10 106 m3 crater lake prior to the dam breakout lahar of 18 march 2007 a range of flow scenarios down the eastern flanks of mt ruapehu were simulated using the titan2d mass flow numerical code to forecast flow travel times and inundation areas titan2d is a depth averaged code that solves the movement of a granular or two phase mass over digital representations of natural terrains we compared modelled scenarios run before the 18 march 2007 break out lahar of ruapehu to details from the actual event the titan2d models were accurate in predicting both the inundation areas and travel times of the lahar at various key points down the volcano s flanks to 9 km beyond 9 km and a major break in slope the initial model parameters did not cope with the fundamental change that occurred in flow rheology velocity and discharge predicted at a lahar deflection structure the bund at 9 km from the lake were up to 20 less than those of the actual 2007 flow but matched closely those of the largest 1995 lahar at this location predicted paths of flow including sites of avulsion correlated well with those in the march 2007 event in addition the simulations predicted dynamic behaviour such as super elevation of flow in corners and hydraulic ponding that corresponds to real event measurements this application shows that the titan2d model can be used to reliably forecast certain parameters of lahar flow however care must be taken when choosing parameters and flow length scales over which the comparison should be made

fine grained debris flows and extraordinary vertebrate burials in the late cretaceous of madagascar vertebrate fossils are remarkably abundant and exceptionally well preserved within the upper cretaceous maevarano formation of northwestern madagascar the vast majority of these fossils including all of the currently known bone beds are entombed within deposits of fine grained cohesive debris flows these deposits are typically massive and are characterized by very poor sorting and a significant montmorillonite dominated silt clay mud fraction ranging from 17 to 46 by weight deposition is attributed to recurrent exceptional rainfall events that prompted erosion and flooded ancient channel belts with sediment laden flows these extraordinary burial events shielded vertebrate remains from destructive surface processes and also afforded protection for soft tissues taphonomic attributes of associated bone concentrations suggest that debris flows had limited transport potential and generally entombed subaerially exposed bone assemblages the remarkable and recurrent association of bone beds and debris flow deposits likely reflects marked seasonality in this late cretaceous terrestrial ecosystem with prolonged dry spells prompting mortality and subsequent rains setting debris flows in motion

localized and distributed erosion triggered by the 2015 hurricane patricia investigated by repeated drone surveys and time lapse cameras at volcan de colima mexico abstract in october 2015 patricia a major category 5 hurricane made landfall in western mexico resulting in 500 mm cumulated rainfall and lahar generation along the southerly directed montegrande valley of volcan de colima we monitored lahar deposition and erosion using time lapse trail cameras and conducted repeated camera drone overflights two days before and after the hurricane using photogrammetric processing we derive a unique dataset of high resolution digital terrain models and study the geomorphologic impacts of a single lahar event results reveal different types of erosion at 8 km distance from the volcano with overland flow and rill networks developing into major erosion gullies exceeding a depth of 4 m as well as bank collapse oversteepening and marginal erosion we find alternating deposition and erosion zones that depend on general slope and valley width and find that the overland flow related erosion is an important contributor to the bulking process of lahars moreover this study shows that camera monitoring is very useful for studying the relationship between volcano landscape evolution and hydrometeorological extremes and for rapid assessment associated with single lahar events

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

40ar 39ar geochronology of magmatic activity magma flux and hazards at ruapehu volcano taupo volcanic zone new zealand we have determined precise eruption ages for andesites from ruapehu volcano in the tongariro volcanic centre of the taupo volcanic zone tvz using 40ar 39ar furnace step heating of separated groundmass concentrates the plateau ages indicate several eruptive pulses near 200 134 45 22 and 300 m section of lavas in whangaehu gorge as well as some lavas in ohinepango and waihianoa catchments on eastern ruapehu and this suite of lavas belongs to the waihianoa formation this pulse of activity is not represented on nearby tongariro volcano indicating that the two volcanoes have independent magmatic systems a younger group of lavas yields dates between 50 and 20 ka and includes lava flows from the turoa skifield and in the ohinepango and mangatoetoenui catchments and is consistent with two pulses of magmatism around the time of the last glacial maximum relating it broadly to the mangawhero formation syn and post last glacial activity lavas with ages 15 ka are assigned to the whakapapa formation and include the voluminous flows of the rangataua member on southern ruapehu magma flux integrated over 1000 yr periods averages 0 6 km3 ka 1 assuming a volcano lifespan of 250 ka fluxes for the te herenga waihianoa and mangawhero formations are consistent at 0 93 0 9 and 0 88 km3 ka 1 respectively these fluxes are broadly comparable with those measured at other modern andesite arc volcanoes e g ngauruhoe 0 88 merapi 1 2 and karymsky 1 2 km3 ka 1 the relatively low flux 0 17 km3 ka 1 calculated for the whakapapa formation may derive from underestimates of erupted volume arising from an increase in phreatomagmatic explosive eruptions in postglacial times however using volume estimates for the 1995 1996 eruptions and a recurrence interval of 25 yr has yielded an integrated 1000 yr flux of 0 8 km3 ka 1 in remarkable agreement to estimates for the prehistoric eruptions overall ruapehu shows consistency in magma flux but at time scales of the order of one hundred to some thousands of years field evidence suggests that short bursts of activity may produce fluxes up to twenty times greater this is significant from the perspective of future activity and hazard prediction

environmental hazards of fluoride in volcanic ash a case study from ruapehu volcano new zealand abstract the vent hosted hydrothermal system of ruapehu volcano is normally covered by a c 10 million m3 acidic crater lake where volcanic gases accumulate through analysis of eruption observations granulometry mineralogy and chemistry of volcanic ash from the 1995 1996 ruapehu eruptions we report on the varying influences on environmental hazards associated with the deposits all measured parameters are more dependent on the eruptive style than on distance from the vent early phreatic and phreatomagmatic eruption phases from crater lakes similar to that on ruapehu are likely to contain the greatest concentrations of environmentally significant elements especially sulphur and fluoride these elements are contained within altered xenolithic material extracted from the hydrothermal system by steam explosions as well as in residue hydrothermal fluids adsorbed on to particle surfaces in particular total f in the ash may be enriched by a factor of 6 relative to original magmatic contents although immediately soluble f does not show such dramatic increases highly soluble naf and casif6 phases demonstrated to be the carriers of available f in purely magmatic eruptive systems are probably not dominant in the products of phreatomagmatic eruptions through hydrothermal systems instead slowly soluble compounds such as caf2 alf3 and ca5 po4 3f dominate fluoride in these phases is released over longer periods where only one third is leached in a single 24 h water extraction this implies that estimation of soluble f in such ashes based on a single leach leads to underestimation of the f impact especially of a potential longer term environmental hazard in addition a large proportion of the total f in the ash is apparently soluble in the digestive system of grazing animals in the ruapehu case this led to several thousand sheep deaths from fluorosis

timescales of magmatic processes at ruapehu volcano from diffusion chronometry and their comparison to monitoring data abstract recent eruptions from mt ruapehu have been difficult to predict despite the presence of a multi parametric monitoring network as a result it is necessary to assess precursory signals prior to an eruption and align those to magmatic processes at depth fortuitously scoria from all historical ruapehu eruptions contains pyroxene crystals that are strongly reversely zoned in the form of a thin 2 to 3 m outermost rim these crystals therefore preserved changes in the magmatic system soon before their eruption we used experimentally determined diffusion coefficients to assess the timescales of magma magma interaction and compared those to the monitoring record four of the five eruptions analysed 1969 1971 1977 1995 gave diffusion timescales 3 to 5 months before their eruption with an increased number of crystals recording timescales within 1 month of eruption pyroxene crystals from the 1996 eruption record events that occurred prior to and during the 1995 eruption suggesting that the bulk of the 1996 crystals was derived from the 1995 magma these diffusion timescales do not compare well to a change in any monitoring signal before historical eruptions however an examination of recent seismicity 2005 2013 since a significant upgrade both in number of stations and type of seismometers showed that two phreatic eruptions in 2006 and 2007 were preceded by a seismic swarm from 5 to 15 km depth 3 to 5 months before each eruption consistent with the diffusion timescales based on this correlation deep seismic swarms likely indicate a period of pressurisation in the magmatic system which may lead to gas rich phreatic eruptions

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

sediment transportation and deposition by rain triggered lahars at merapi volcano central java indonesia abstract a lahar is a general term for a rapidly flowing mixture of rock debris and water other than normal streamflow from a volcano and refers to the moving flow located in the populated area of central java the stratovolcano merapi 2965 m is prone to lahar generation due to three main factors 1 millions of cubic meters of pyroclastic deposits are the product of frequent pyroclastic flows which have occurred on 2 to 4 year intervals 2 rainfall intensity is high often 40 mm in 2 h on average during the rainy season from november to april and 3 drainage pattern is very dense following the 22 november 1994 eruption of merapi 31 rain triggered lahar events were recorded in the boyong river between december 1994 and may 1996 on merapi s slopes instantaneous sediment concentration at any given time of the lahars varies widely over time and space lahars are transient sediment water flows whose properties are unsteady so that the sediment load fluctuates during the flow the boundary between the flow types debris flow with sediment concentration 60 volume or hyperconcentrated flow with sediment concentration ranges from 20 to 60 volume may fluctuate within the flow itself grain size distribution physical composition of sediments shear stress yield stress and water temperature play each a role on this boundary natural self damming and rapid breakout are partly responsible for the sediment variations of the flows debris flow phases at merapi typically last a few minutes to 10 min and are often restricted to the lahar front debris flow surges are sometimes preceded and always followed by longer hyperconcentrated flow phases as a result mean sediment concentration of the lahars is low commonly from 20 to 50 volume besides transient normal streamflow phases sediment concentration low sediment load and frequent transient flows in the merapi channels may result from at least three factors 1 several breaks in slope along the channel increase the deposition rate of sediment and hinder the bulking capacity of the lahars 2 source material is mainly coarse debris of merapi type block and ash flows consequently the remobilization of coarse debris is more difficult and the clast deposition is accelerated 3 variations of rainfall intensity over time and space common in tropical monsoon rainfall also influence the sediment load variations of the lahars sedimentologic analyses of the lahar deposits in the boyong river at merapi encompass clast supported and matrix supported debris flow deposits hyperconcentrated flow deposits and streamflow deposits the stratigraphic succession of massive and stratified beds observed immediately after any given lahar event in the boyong river indicates that the sediment concentration varies widely over time and space during a single lahar event sedimentation rate varies from 3 to 4 5 cm min during relatively long lived surges to as much as 20 cm min during short lived surges these results indicate that the sediment load fluctuates during lahar flow further demonstrating that lahars are transient sediment water flows with unsteady flow properties

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

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

quantifying the geomorphic impacts of a lake breakout lahar mount ruapehu new zealand at 11 18 h new zealand time gmt 12 on 18 march 2007 an impoundment of 0 01 10 6 m 3 of tephra collapsed releasing 1 3 10 6 m 3 of water from crater lake at 2536 m elevation on mount ruapehu the lahar traveled 200 km along the whangaehu river aerial lidar surveys of the upper 62 km of flow path were made before and after the lahar we present here the first large scale quantification of the geomorphic impact of the dam break flood along with the rates and controls on its sediment entrainment and deposition the flood mobilized a net value of 2 5 3 1 10 6 m 3 of boulders gravel and sand over the first 5 km of travel to form a lahar of at least 4 4 10 6 m 3 passing instruments at 6 9 km lidar volume transfer calculations match dynamic measurements made after a logarithmic increase in cumulative net sediment entrainment the lahar appeared to reach its maximum sediment carrying capacity at 22 km patterns of alternating sediment erosion and deposition occurred that dominantly reflect a combination of channel morphology and confinement on the local sediment carrying capacity of the flow

impacts of the 1945 and 1995 1996 ruapehu eruptions new zealand an example of increasing societal vulnerability over the past 50 yr the risk to society from volcanic eruptions has increased sharply due to an increased population more developed and diversified economies and a more technologically advanced infrastructure this fact is demonstrated vividly by the impacts from the two largest eruptions of the twentieth century from the cone volcano of ruapehu which suggest that the vulnerability of key sectors in new zealand society has increased by one to two orders of magnitude over this period both the 1945 and 1995 1996 eruptions included explosive phases that dispersed ash over a wide area of the north island for a period of several months individual ash falls were only a few millimeters thick in communities within 150 km of the volcano and only trace amounts were found in communities farther away the 1995 1996 eruption caused similar physical effects to the 1945 eruption but had considerably greater social and economic impacts the greatest contribution to the cost of the 1995 1996 eruption estimated in excess of 130 million new zealand dollars was the impact on the alpine tourist industry in the central north island essentially nonexistent in 1945 other significant impacts were felt by the rapidly growing aviation and electricity generation sectors the cost of any future eruption of the same magnitude is likely to grow as the vulnerability of our society increases at a rapid rate

fluid flow modeling of a coastal fractured karstic aquifer by means of a lumped parameter approach fluid flow and solute transport phenomena in fractured and karstic aquifers remain an open issue that calls the attention of numerous researchers belonging to different disciplinary fields as far as the aspects linked both to shallow and to deep phenomena are concerned the hydrogeologic knowledge of these phenomena proves to be of high importance especially if considered in relationship with water resource exploitation with the problems linked to contamination and the ones linked to urban and industrial development of the territory in the examined area characterized by a dismissed contaminated site the realization of the landfill has required the development of a 3d flow model supported by a detailed local scale geologic model in order to evaluate the effects on groundwater flow and subsequently on contaminant propagation the results of the flow model prove to be coherent with the fractured and karstic nature of the site in that they show at higher depths the presence of a subterranean stream channel that would speed up pollutant propagation the obtained results represent the fundamental basis to implement a transport model that will permit to achieve a more in depth knowledge of the subsoil transport phenomena and therefore to optimize any anthropic intervention that can involve the site

moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits boulders moving in flash floods cause considerable damage and casualties more and bigger boulders move in flash floods than predicted from published theory the interpretation of flow conditions from the size of large particles within flash flood deposits has until now generally assumed that the velocity or discharge is unchanging in time i e flow is steady or changes instantaneously between periods of constant conditions standard practice is to apply theories developed for steady flow conditions to flash floods which are however inherently very unsteady flows this is likely to lead to overestimates of peak flow velocity or discharge flash floods are characterised by extremely rapid variations in flow that generate significant transient forces in addition to the mean flow drag these transient forces generated by rapid velocity changes are generally ignored in published theories but they are briefly so large that they could initiate the motion of boulders this paper develops a theory for the initiation of boulder movement due to the additional impulsive force generated by unsteady flow and discusses the implications keywords

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

extracting palaeoflood data from coarse grained pleistocene river terrace archives an example from se spain field based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of long term landscape evolution however the reconstruction of past flow event histories magnitude and frequency over long term quaternary timescales is fraught with difficulties here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective we utilize manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach which is applied to coarse grained strath terrace deposits we evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012 the findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross section and in longitudinal section and calibrated against the sedimentology for palaeo flow depth problems can arise where constrictive channel geometries allow boulder jams to develop acting as sediment traps for the coarsest material and leading to downstream boulder starvation useful sites to target for palaeoflood reconstruction therefore would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped sites to avoid would be downflow where the deposited material would poorly represent palaeoflood competence underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events in this environmental setting copyright 2016 john wiley sons ltd

depositional record of historic lahars in the upper whangaehu valley mt ruapehu new zealand implications for trigger mechanisms flow dynamics and lahar hazards mt ruapehu in the central north island of new zealand is one of the most lahar prone volcanoes in the world since historic observations began in 1861 ad more than 50 individual lahars have been recorded in the whangaehu valley alone the natural outlet to the summit crater lake these lahars have been triggered by a variety of mechanisms including explosive eruptions that displaced crater lake water over the outlet or ejected it onto the snow clad summit area of the volcano rain remobilisation of tephra deposits on steep slopes displacement over the outlet as a result of syn eruptive changes in lake bathymetry and lake break outs from crater lake following impoundment of excess water behind temporary barriers of tephra and or ice emplaced over the outlet however only 9 lahar deposits can be distinguished in the upper whangaehu valley on sedimentological stratigraphic geomorphic and petrological grounds and these are skewed towards either the largest or the most recent flows in some cases magnitude can be reconstructed from deposit geometry with the largest lahars producing the highest level terraces the coarsest deposits and crossing drainage divides into normally inactive channels this under representation of historic events reflects the low preservation potential of unconsolidated deposits in a steep alpine environment and the overprinting and recycling effect of large magnitude lahars that rework material down to bedrock and effectively reset the stratigraphic record development of magnitude frequency relationships for ruapehu lahars therefore requires the identification of lahar deposits in proximal medial and distal settings in order to ensure that the full range of events is represented

modelling hydrostratigraphy and groundwater flow of a fractured and karst aquifer in a mediterranean basin salento peninsula southeastern italy the control exerted by the hydrostratigraphic structure on aquifer recharge groundwater flow and discharge along the coastal areas of a mediterranean basin salento peninsula about 5 000 km2 wide southern italy is assessed through the development and application of a groundwater flow model based on the reconstruction of the hydrostratigraphic architecture at the regional scale the hydrostratigraphic model obtained by processing surface and subsurface data is applied to map the top of the main aquifer which is hosted in the deep hydrostratigraphic unit corresponding to cretaceous and oligocene limestones with complex geometrical relationships with the sea it is also used to estimate the aquifer recharge which occurs by percolation through overlying younger sediments with low permeability these data are completed with information about the soil use to estimate water abstraction for irrigation and with literature data to estimate the water abstraction for drinking and industrial purposes the above sketched conceptual model is the basis for a finite difference groundwater 2d pseudo stationary flow model which assumes the following fundamental approximations the fractured and karst limestone hydrostratigraphic unit can be approximated at the model scale as a continuous medium for which the discrete darcy s law is valid the transition zone between salt and fresh water is so small with respect to the grid spacing that the ghyben herzberg s approximation for a sharp interface can be applied along the coastline different boundary conditions are assigned if the top of the limestone hydrostratigraphic unit lies either above the sea level the aquifer has a free surface and fresh water is drained or below the sea level the aquifer is under pressure and the contact with sea occurs off shore the groundwater flow model correctly predicts the areas where the aquifer is fully saturated with salt water

stability assessment of the crater lake te wai ā moe overflow channel at mt ruapehu new zealand and implications for volcanic lake break out triggers abstract the presence of lakes on active volcanoes gives rise to several unique volcano hydrologic hazards including those directly related to volcanic activity e g phreatic explosions and non volcanic phenomena e g lake outbursts mt ruapehu volcano hosts the 107 m3 crater lake te wai moe in the active summit crater making it prone to lahars due to the abundance of water stored at high elevation apart from eruptive periods when water is commonly ejected from the lake large lahar events can occur when portions of the crater rim fail during quiescent periods leading to partial lake drainage the latter occurred recently in 1953 and 2007 here we investigate the potential of future lahars due to rim failure at the current overflow channel considering several triggering scenarios during non eruptive periods the geomechanical properties of a matrix dominated breccia unit composing part of the overflow channel were analyzed using physical and mechanical laboratory methods these properties combined with previous geomechanical studies of lava units in the overflow channel were used in finite element and limit equilibrium method based groundwater and stability models groundwater models indicate that a low permeability barrier inside the crater rim is preventing water from seeping through the unconsolidated and potentially permeable breccia unit of the overflow channel the removal of this barrier or weathering of a resistive lava cap could cause water to seep through the overflow channel elevating the potential of collapse slope stability models indicate that under certain conditions the overflow channel is below a conservative threshold of stability and can be destabilized with continued mechanical or chemical weathering that reduces strength properties this is also true during high magnitude tectonic or volcanic earthquakes where large ground accelerations could result in several centimeters of displacement at the overflow channel corresponding to high hazard categories of stability in the worst case scenario modeled here full collapse of the overflow channel could result in the release of c 2 4 million m3 of lake water this could drive a lahar substantially larger than well documented historic events including the more common lahars produced during eruptions the identification of key factors affecting stability can be used to inform future monitoring and the risk of these high impact events

volcanic mixed avalanches a distinct eruption triggered mass flow process at snow clad volcanoes a generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at mount st helens nevado del ruiz and redoubt volcano between 1982 and 1989 these mixed avalanches traveled as far as 14 km at velocities up to 27 m s involved as much as 10 7 m 3 of rock and ice and left unmelted deposits of single flow units as thick as 5 m during flow downslope heat transfer from hot rocks to snow produced meltwater that partially saturated the mixtures apparently giving these mixed avalanches mobilities equal to or greater than those of dry debris avalanches of similar volume the avalanches studied for this report began as snow avalanches triggered during explosive phases of the eruptions by ballistic bombardment of snow slopes by hot pyroclastic debris erosion by the avalanches incorporated additional snow fragments of glacier ice and other rock debris mixed avalanche deposits were massive very poorly sorted and ungraded to inversely graded prior to melting although rock debris composed as much as 70 wt of the frozen samples the bulk volumetric content of rock debris was only 9 to 36 snow and ice composed between 36 and 72 of the frozen samples with void space making up the remainder of the volume deformation and consolidation after melting of the ice content reduced the deposits to loose porous layers that were only a fraction of their original thickness and that later gave little hint of their origin after melting and desiccation the deposits are highly susceptible to erosion and unlikely to be well preserved in the stratigraphic record

the 55 to 60 ka te whaiau formation a catastrophic avalanche induced cohesive debris flow deposit from proto tongariro volcano new zealand te whaiau formation is a massive volcaniclastic deposit interbedded within gravelly and sandy volcanogenic sediments of the northwestern tongariro ring plain the ca 0 5 km3 deposit comprises a clay rich matrix supported diamicton with lithological and physical properties that are typical of a cohesive debris flow deposit clays identified in the matrix are derived from hydrothermally altered andesite lava and pyroclastic rocks the distribution pattern of the deposit and the nature of the clay matrix point to a source area that was located in the vicinity of mt tongariro s current summit 1967 m most of the proximal zone is buried under late pleistocene lavas forming the northwestern flank of the massif in contrast the medial and distal zones are well exposed to the northwest in the whanganui river catchment lithofacies exposed in these latter zones contain isolated volcaniclastic megaclasts and well preserved jointed blocks of andesite small hummocks up to 5 m high are present only in the distal margins of the deposit based on these observations possible source areas and analogy with similar deposits elsewhere we infer that te whaiau formation was initiated as a fluid saturated debris avalanche that transformed downstream into a single cohesive debris flow it is interpreted that the mass flow was initially confined to the northwestern flank of tongariro before spreading laterally onto the lowlands to the northwest the resulting heterolithological diamicton filled stream channels in the western sector of the tongariro ring plain at 15 km from source the debris flow encountered an elevated terrain which acted as a barrier to further spreading to the north the stratigraphy of the cover beds and k ar data on an underlying lava indicate that te whaiau formation was emplaced between 55 and 60 ka a cool period characterized by intense volcaniclastic sedimentation around the tongariro massif jigsaw fit fractured volcanic bombs suggest that an explosive eruption through hydrothermally altered rock and pyroclastic deposits probably triggered the mass flow the characteristics of the deposit indicate that a large portion of the proto tongariro edifice collapsed en masse to form the initial avalanche hence we infer that the current morphology of tongariro volcano is derived not only from glacial erosion but also from gravitational failure prehistoric eruptions and current geothermal activity on the upper northern and western slopes of the tongariro massif suggest that avalanche induced debris flows must be considered a potential future volcanic hazard for the region

transport and emplacement mechanisms of channelised long runout debris avalanches ruapehu volcano new zealand the steep flanks of composite volcanoes are prone to collapse producing debris avalanches that completely reshape the landscape this study describes new insights into the runout of large debris avalanches enhanced by topography using the example of six debris avalanche deposits from mount ruapehu new zealand individual large flank collapses 1 km3 produced all of these units with four not previously recognised five major valleys within the highly dissected landscape surrounding mount ruapehu channelled the debris avalanches into deep gorges 15 m and resulted in extremely long debris avalanche runouts of up to 80 km from source classical sedimentary features of debris avalanche deposits preserved in these units include the following very poor sorting with a clay sand matrix hosting large subrounded boulders up to 5 m in diameter jigsaw fractured clasts deformed clasts and numerous rip up clasts of late pliocene marine sediments the unusually long runouts led to unique features in distal deposits including a pervasive and consolidated interclast matrix and common rip up clasts of tertiary mudstone as well as fluvial gravels and boulders the great travel distances can be explained by the debris avalanches entering deep confined channels 15 m where friction was minimised by a reduced basal contact area along with loading of water saturated substrates which formed a basal lubrication zone for the overlying flowing mass extremely long runout debris avalanches are most likely to occur in settings where initially partly saturated collapsing masses move down deep valleys and become thoroughly liquified at their base this happens when pore water is available within the base of the flowing mass or in the sediments immediately below it based on their h l ratio confined volcanic debris avalanches are two to three times longer than unconfined spreading flows of similar volume the hybrid qualities of the deposits which have some similarities to those of debris flows are important to recognise when evaluating mass flow hazards at stratovolcanoes

evolution of a vent hosted hydrothermal system beneath ruapehu crater lake new zealand a two year chemical monitoring program of ruapehu crater lake shows that it has evolved considerably since the volcano s more active eruptive periods in the early 1970s the present ph 20 c of 0 6 is about one half unit more acid than the baseline values in the 1970s whereas s cl ratios have increased markedly owing in part to declining hcl inputs into the lake but also to absolute increases in so4 levels which now stand at the highest values ever recorded increases in k mg and na mg ratios over the 20 year period are attributed to hydrothermal reaction processes in the vent which are presently causing dissolution of previously formed alteration phases such as natroalunite these observations combined with results of a recent heat budget analysis of the lake have led to the development of hydrothermal convection model for the upper portion of the vent possible vent lake chemical reaction processes between end member reactants have been modelled with the computer code chiller the results are consistent with the view that variations in lake chemistry which are initiated by the introduction of fresh magmatic material into the vent reflect the extent of dissolution reaction progress on the magmatic material and or its alteration products the results also provide insights into the role of such vent processes in the formation of high sulfidation type ore deposits

geomorphological evolution of a fluvial channel after primary lahar deposition huiloac gorge popocatepetl volcano mexico abstract popocatepetl volcano 19 02 n 98 62 w 5424 m began its most recent period of volcanic activity in december 1994 the interaction of volcanic and glacier activity triggered the formation of lahars through the huiloac gorge located on the northern flank of the volcano causing significant morphological changes in the channel the most powerful lahars occurred in april 1995 july 1997 and january 2001 and were followed by secondary lahars that formed during the post eruptive period this study interprets the geomorphological evolution of the huiloac gorge after the january 2001 lahar variations in channel morphology at a 520 m long research site located mid way down the gorge were recorded over a 4 year period from february 2002 to march 2005 and depicted in five geomorphological maps scale 1 200 for 14 february and 15 october 2002 27 september 2003 9 february 2004 and 16 march 2006 a gis was used to calculate the surface area for the landforms identified for each map and detected changes and erosion deposition processes of the landforms using the overlay function for different dates findings reveal that secondary lahars and others types of flows like sediment laden or muddy streamflows caused by precipitation rapidly modified the gorge channel following the january 2001 non eruptive lahar a period associated with volcanic inactivity and the disappearance of the glacier once located at the headwall of the gorge field observations also confirmed that secondary flows altered the dynamics and geomorphological development of the channel these flows incised and destroyed the formations generated by the primary lahars 1997 and 2001 causing a widening of the channel that continues today after february 2004 a rain triggered lahar and other flows infilled the channel with materials transported by these flows the deposits on the lateral edges of the channel form terraces a recent lull in lahar activity contrasts with the increasing instability of the edges of the channel and the continuous edification and destruction of recent lahar terraces

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

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

numerical study of flow anisotropy within a single natural rock joint the paper investigates the flow anisotropy within a natural joint subjected to mechanical shear the cubic law is the simplest way to describe fluid flow through rock joints but because of rock wall roughness deviations from this model have been observed the reynolds equation usually gives better results in this study micro scale roughness is taken into account to define a reduced coefficient of permeability numerical simulations have been carried out by applying darcy s law to the rock joint described as an equivalent porous medium the numerical simulations are based on experimental data obtained by hans phd grenoble 2002 from a series of hydromechanical shear tests on a rock joint replica the numerical results have been compared to the experimental ones and to the results obtained by applying the reynolds equation to assess the relevance of the simulations for the fracture studied the approach proposed herein can reproduce relatively well the experimental flow anisotropy and provides consistent values of flow rates whereas the reynolds equation tends to give higher flow rates

geochemical fluxes and weathering of volcanic terrains on high standing islands taranaki and manawatu wanganui regions of new zealand abstract sediment fluxes from high standing oceanic islands hsis such as new zealand are some of the highest known milliman j d and syvitski j p m 1992 geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers j geol 100 525 544 recent geochemical work has suggested that along with their extremely high physical weathering yields many new zealand watersheds also have very high chemical weathering yields in new zealand the magnitude of both the physical and chemical weathering yields is related to the lithology of the watershed most of the previous work on this topic has been undertaken in southern alps watersheds of schist and greywacke and in east cape watersheds of semi consolidated marine sediments and greywacke we recently sampled north island watersheds in the taranaki and manawatu wanganui regions which have been subjected to volcanism since the miocene we sampled watersheds that contain both volcanic and sedimentary rocks a series of water and sediment samples was collected and analyzed for major minor and trace elements this was done to quantify the weathering intensities in the watersheds and to establish the relationship between physical and chemical weathering yields in volcanic lithologies our results reveal distinct chemical signatures for the different regions waters draining the taranaki region volcanics are significantly enriched in k and depleted in ca2 and sr2 compared to waters draining the manawatu wanganui region volcanics which also traverse expanses of sedimentary siltstones and mudstones the ca2 and sr2 depletions may reflect the relative absence of caco3 in the taranaki region watersheds in addition sediment samples from the taranaki region show significant enrichment in ti al ca fe mn mg ca and p and depletion in si and rb compared to those of the manawatu wanganui region from total dissolved solids concentrations and mean annual water discharge we calculate chemical weathering yields of 60 240 tons km 2 a 1 these weathering yields fall within the middle to upper range of those previously documented for the southern alps 93 480 tons km 2 a 1 and east cape 62 400 tons km 2 a 1 calculated silicate weathering yields of 12 33 6 tons km 2 a 1 and co2 consumption of 852 2390 103 mol km 2 a 1 for the rivers draining the taranaki volcanic region are higher than those previously reported for watersheds hosted in sedimentary and metamorphosed rock terrains on hsis co2 consumption is found to be within the range previously measured for the basaltic terrains of the deccan traps 580 2450 103 mol km 2 a 1 and reunion island 1300 4400 103 mol km 2 a 1 our calculated chemical weathering yields demonstrate the importance of hsis particularly those with volcanic terrains when considering global geochemical fluxes

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

rain triggered lahars following the 2010 eruption of merapi volcano indonesia a major risk abstract the 2010 vei 4 eruption of merapi volcano deposited roughly ten times the volume of pyroclastic materials of the 1994 and 2006 eruptions and is recognized as one of the most intense eruption since 1872 however as the eruptive phase is now over another threat endangers local communities rain triggered lahars previous papers on lahars at merapi presented lahar related risk following small scale dome collapse pdcs thus the aim of this study is to provide new insights on lahar related risk following a large scale vei 4 eruption the paper highlights the high number of events 240 during the 2010 2011 rainy season october 2010 may 2011 the frequency of the 2010 2011 lahars is also the most important ever recorded at merapi lahars occurred in almost all drainages located under the active cone with runout distances exceeding 15 km the geomorphic impacts of lahars on the distal slope of the volcano are then explained as they directly threaten houses and infrastructures creation of large corridors avulsions riverbank erosion and riverbed downcutting are detailed through local scale examples related damage is also studied 860 houses damaged 14 sabo dams and 21 bridges destroyed sedimentological characteristics of volcaniclastic sediments in lahar corridors are presented with emphasis on the resource in building material that they represent for local communities risk studies should not forget that thousands of people are exposing themselves to lahar hazard when they quarry volcaniclastic sediment on lahar corridors finally the efficient community based crisis management is explained and shows how local people organize themselves to manage the risk 3 fatalities were reported although lahars reached densely populated areas to summarize this study provides an update of lahar risk issues at merapi with emphasis on the distal slope of the volcano where lahars had not occurred for 40 years and where lahar corridors were rapidly formed

variety and sustainability of volcanic lakes response to subaqueous thermal activity predicted by a numerical model we use a numerical model to investigate the factors that control the presence or absence of a hot crater lake at an active volcano we find that given a suitable pair of parameters e g the enthalpy of subaqueous fumaroles and the ratio of mass flux of the fluid input at the lake bottom to lake surface area hot crater lakes can be sustained on relatively long timescales neither a high rate of precipitation nor an impermeable layer beneath the lake bottom are always necessary for long term sustainability the two controlling parameters affect various hydrological properties of crater lakes including temperature chemical concentrations and temporal variations in water levels in the case of low temperature crater lakes increases in flux and enthalpy which are a common precursor to phreatic or phreatomagmatic eruptions result in an increase in both temperature and water level in contrast a decrease in water level accompanied by a rise in temperature occurs at high temperature lakes furthermore our model suggests that crater geometry is a key control on water temperature for lakes with a conical topography a perturbation in the water level due to trivial non volcanic activity such as low levels of precipitation can cause persistent increases in water temperature and chemical concentrations and a decrease in the water level even though subaqueous fumarolic activity does not change such changes in hot crater lakes which are not caused by changes in volcanic activity resemble the volcanic unrest that precedes eruptions

the coalescence and organization of lahars at semeru volcano indonesia we present multi parameter geophysical measurements of rainfall induced lahars at semeru volcano east java using two observation sites 510 m apart 11 5 km from the summit our study site in the curah lengkong channel is composed of a 30 m wide box valley with a base of gravel and lava bedrock representing an ideal geometry for high density measurements of active lahars instrumentation included pore pressure sensors stage a broad band seismograph arrival times vibrational energy and turbulence video footage and direct bucket sampling a total of 8 rainfall induced lahars were recorded with durations of 1 3 h heights 0 5 2 m and peak velocities 3 6 m s flow types ranged from dilute to dense hyperconcentrated flows these recorded flows were commonly composed of partly coalesced discrete and unsteady gravity current packets represented by multiple peaks within each lahar these packets most likely originate from multiple lahar sources and can be traced between instrument sites those with the highest concentrations and greatest wetted areas were often located mid lahar at our measured reach accelerating towards the flow front as these lahars travel downstream the individual packets thus coalesce and the flow develops a more organised structure observations of different degrees of coalescence between these discrete flow packets illustrate that a single mature debris flow may have formed from multiple dynamically independent lahars each with different origins

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

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

pumping test analysis using a layered cylindrical grid numerical model in a complex heterogeneous chalk aquifer a groundwater investigation including several pumping tests has been carried out by thames water utilities limited twul to improve the understanding of the distribution of hydraulic properties of the chalk in the swanscombe area of kent in south eastern england the pumping test behaviour is complicated by the fractured condition of the chalk simultaneous pumping from adjacent boreholes and variable pumping rates during the test in addition the groundwater flow system is complicated by quarrying of the chalk analytical solutions for pumping test analysis fail to represent these complex flow processes and cannot reproduce the observed time drawdown curves a layered cylindrical grid numerical model has been applied to the results of the swanscombe pumping test this model can represent the heterogeneity of the aquifer and the detailed flow processes close to the abstraction borehole such as well storage seepage face and well losses it also includes a numerical representation of the moving water table using a grid that deforms to eliminate numerical instabilities the analyses of the test results demonstrate that they are significantly influenced by fracture flow which needs to be included to improve the simulation of the groundwater system not withstanding this the layered cylindrical grid numerical model reproduced many of the features in observed time drawdown which allowed an assessment of the hydraulic characteristics of the aquifer as well as the investigation of the impact of quarries on the test results this has demonstrated that the numerical model is a powerful tool that can be used to analyse complex pumping tests and aid to improvement of the conceptual understanding of a groundwater system

conceptualization of flow and transport in a limestone aquifer by multiple dedicated hydraulic and tracer tests abstract limestone aquifers are of great interest as a drinking water resource in many countries they often have a complex crushed and fractured geology which makes the analysis and description of flow and transport processes in such aquifers a challenging task in this study the solute transport behavior including fracture matrix interaction in hydrogeological units of a limestone aquifer in eastern denmark was characterized by designing conducting and interpreting six depth specific tracer tests involving natural and forced gradient conditions with multiple tracers representing different diffusion properties to determine flow parameters the tracer tests were complemented by a comprehensive set of depth specific borehole and hydraulic tests based on the tests a new and stronger conceptual understanding was developed for the different aquifer units the investigated limestone aquifer is composed of a glacially crushed unit and two fractured units with calcarenitic and bryozoan limestone of similar hydraulic properties hydraulic tests revealed that the crushed unit has a lower hydraulic conductivity than the fractured limestone units likely due to the crushed conditions with small limestone clusters and small aperture fractures potentially filled with fine material in the fractured limestone units a distinct preferential flow and primary transport along major horizontal fractures was inferred from the tracer tests under forced gradient conditions the dominant horizontal fractures were identified on impeller flow logs and appear connected between wells having an extent of up to several hundred meters connectivity between the aquifer units was investigated with a long term pumping test and tracer tests revealing restricted vertical flow and transport a very pronounced hydraulic conductivity contrast between major fractures and matrix could also be inferred from the borehole and hydraulic tests which is consistent with the findings from the tracer tests the difference in the matrix diffusion behavior of the simultaneously injected tracers and a long tailing in the breakthrough curves revealed that matrix diffusion has a strong influence on the solute transport in the fractured limestone

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

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

sediment charged flash floods on montserrat the influence of synchronous tephra fall and varying extent of vegetation damage on 20th may 2006 the soufriere hills volcano on the caribbean island of montserrat experienced a large dome collapse and intense rainfall generated flash floods the floods had very high loads of volcanic debris derived both from this and previous eruptions and can thus be classified as lahars the floods reached unusually high water levels and caused substantial geomorphic change in the belham valley detailed rainfall and geomorphological data coupled with the precise timing of events and yewitness accounts have facilitated an assessment of the relative importance of rainfall volume and intensity older volcanic debris pre and syn flood tephra fall and the extent of pre flood vegetation damage for the behavior of this and subsequent sediment laden floods in this setting the change in runoff behavior was controlled by preexisting vegetation damage and synchronous tephra fall and this was critically important in controlling the impact of these flash floods although rainfall intensity and volume have some control on flood occurrence they are not the critical control on flash flood impact on the geomorphology in the belham valley a significant conclusion of this study is that the extreme nature of the flash floods was not caused by extreme rainfall as is commonly believed to be the primary cause of flash floods but rather it was the result of changed runoff behaviour caused by the widespread syn flood tephra deposition and importantly the widespread vegetation damage by volcanic associated acid rain in the preceding weeks

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

dynamic interactions between lahars and stream flow a case study from ruapehu volcano new zealand discussion and reply discussion cronin et al 1999 1 presented details of an unusual data set obtained from observations of active lahars made during the 1995 eruptions of ruapehu volcano new zealand this data set includes both visual observations and time series variations in stage height and gauged discharge made on

remote sensing data types and techniques for lahar path detection a case study at mt ruapehu new zealand mt ruapehu is new zealand s most active onshore volcano in 2007 the volcano produced a large lahar following a break out from the summit crater lake here satellite and airborne remote sensing and image processing is used to extract the path of the lahar using aster and spot5 visible and near infra red imagery alos palsar l band synthetic aperture radar data and airborne lidar the results obtained from each of these datasets were compared to the lahar deposit manually digitized from aerial photography spot5 imagery produced the most accurate map of the lahar deposit 77 correct even though these data were acquired a year after the event this is attributed to the spatial resolution of the data the alos palsar coherence mapping calculated from images acquired 2 months before and nine months after the lahar was not as accurate as that obtained using the optical imagery 43 correct but this was still considered an important tool for acquiring data during cloudy periods lidar topographic data collected to constrain geomorphic changes caused by the lahar was the least accurate in terms of mapping the lahar path 28 correct no single technique was deemed to be the most accurate under all circumstances and a combination of data types would produce the best results by combining the satellite and lidar data it was possible to accurately classify 92 of the lahar path

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

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use

changes in whangaehu river lahar characteristics during the 1995 eruption sequence ruapehu volcano new zealand abstract during the 1995 ruapehu eruptive sequence multiple lahars occurred in the whangaehu river which drains ruapehu s crater lake during the earlier phreatic and phreatomagmatic eruptions lahars were generated by expulsion of waters from the lake but once the lake had emptied lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra four types of lahars occurred during the eruptive sequence 1 initial snow slurry lahars composed of granular snow and ice incorporated by eruptively expelled crater lake waters which left behind frozen deposits with 2 5 20 clastic sediment 2 large dilute lahars generated as the volumes of ejected lake water increased and removed much of the readily available snow at least one third of the pre eruption crater lake volume was expelled during one day producing the largest lahars of the series these lahars were hyperconcentrated flows for up to 84 km from source leaving extensive deposits along the channel margins 3 concentrated lahars smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined these lahars were able to maintain high sediment concentrations measured at 46 52 by volume suspended sediment at 42 km from source their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins 4 remobilised tephra lahars generated following the two largest tephra eruptions of the sequence seasonal snowpack was covered by water saturated tephra warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra producing several lahars in catchments draining eastern ruapehu

syn and post eruptive erosion gully formation and morphological evolution of a tephra ring in tropical climate erupted in 1913 in west ambrym vanuatu abstract syn and post eruptive erosion of volcanic cones plays an important role in mass redistribution of tephra over short periods descriptions of the early stages of erosion of tephra from monogenetic volcanic cones are rare particularly those with a well constrained timing of events in spite of this lack of data cone morphologies and erosion features are commonly used for long term erosion rate calculations and relative age determinations in volcanic fields this paper offers new observations which suggest differing constraints on the timing of erosion of a tephra ring may be operating than those conventionally cited in 1913 a tephra ring was formed as part of an eruption in west ambrym island vanuatu and is now exposed along a continuous 2 5 km long coastal section the ring surrounds an oval shaped depression filled by water it is composed of a succession of a phreatomagmatic fall and base surge beds interbedded with thin scoriaceous lapilli units toward the outer edges of the ring base surge beds are gradually replaced in the succession by fine ash dominated debris flows and hyperconcentrated flow deposits the inter fingering of phreatomagmatic deposits with syn volcanic reworked volcaniclastic sediments indicates that an ongoing remobilisation of freshly deposited tephra was already occurring during the eruption gullies cut into the un weathered tephra are up to 4 m deep and commonly have c 1 m of debris flow deposit fill in their bases there is no indication of weathering vegetation fragments or soil development between the gully bases and the basal debris flow fills gully walls are steep and superficial fans of collapsed sediment are common most gullies are heavily vegetated although some active ephemeral channels occur these observations suggest that the majority of the erosion of such tephra rings in tropical climates takes place directly during eruption and possibly for only a period of days to weeks afterward after establishment of the gully network tephra remobilisation is concentrated only within them therefore the shape of the erosion modified volcanic landform is predominantly developed shortly after the eruption ceases this observation indicates that gully erosion morphology may not necessarily relate to age of such a landform different intensities of erosion during eruption related to water supply or rainfall are probably the major influence on gully spacing modal depth and form longer term post eruption processes that could be indicators of relative age may include internal gully deepening below basal debris flow fill sediments and possibly widening and side slope lowering due to undercutting and side collapse

transverse architecture of lahar terraces inferred from radargrams preliminary results from semeru volcano indonesia semeru volcano is the highest mountain of java indonesia and a vulcanian explosion occurs every 15 minutes on average since 1967 thus a constantly renewed stock of material and the heavy monsoon rainfall 3700 mm yr 1 at 1500 m above sea level a s l provide a perfect setting for the study of lahars and their deposits hence we examined the architecture of lahars terraces 9 5 km from the summit in the curah lengkong valley we first used ground penetrating radar gpr over vertical exposures of the lahars cut bank terraces this allowed us to better understand transversal radargrams across terraces which are not visually accessible in the field preliminary results from a single radargram are very instructive since 1 they prove that the lateral architecture does not correspond to that observed from banks only 2 we could observe the presence of lenses and stratigraphic discontinuities 3 the setting of the various units can also help reconstruct deposition processes and the chronology of different units in order to finalize these preliminary results we however need to perform multiple gpr radargrams and provide a complete set of results copyright 2010 john wiley sons ltd

unusual ice diamicts emplaced during the december 15 1989 eruption of redoubt volcano alaska abstract ice diamict comprising clasts of glacier ice and subordinate rock debris in a matrix of ice snow grains coarse ash and frozen pore water was deposited during the eruption of redoubt volcano on december 15 1989 rounded clasts of glacier ice and snowpack are as large as 2 5 m clasts of redoubt andesite and basement crystalline rocks reach 1 m and tabular clasts of entrained snowpack are as long as 10 m ice diamict was deposited on both the north and south volcano flanks on redoubt s north flank along the east side of drift piedmont glacier and outwash valley ice diamict accumulated as at least 3 units each 1 5 m thick two ice diamict layers underlie a pumice lithic fall tephra that accumulated on december 15 from 10 15 to 11 45 ast a third ice diamict overlies the pumiceous tephra some of the ice diamicts have a basal ice sandstone layer the north side icy flows reached as far as 14 km laterally over an altitude drop of 2 3 km and covered an area of about 5 7 km 2 on crescent glacier on the south volcano flank a composite ice diamict is locally as thick as 20 m it travelled 4 3 km over an altitude drop of 1 7 km covering about 1 km 2 the much higher mobility of the northside flows was influenced by their much higher water contents than the southside flow s erupting hot juvenile andesite triggered and turbulently mixed with snow avalanches at snow covered glacier heads these flows rapidly entrained more snow firn and ice blocks from the crevassed glacier on the north flank a trailing watery phase of each ice diamict flow swept over and terraced the new icy deposits the last and perhaps each flood reworked valley floor snowpack and swept 35 km downvalley to the sea ice diamict did not form during eruptions after december 15 despite intervening snowfalls these later pyroclastic flows swept mainly over glacier ice rather than snowpack and generated laharic floods rather than snowflows similar flows of mixed ice grains and pyroclastic debris resulted from the november 13 1985 eruption of nevado del ruiz volcano and from eruptions of snowclad mount st helens in 1982 1984 such deposits at snowclad volcanoes are initially broad and geomorphically distinct but they soon become extensively reworked and hard to recognize in the geologic record

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

the analysis of pulse interference tests conducted in a fractured rock aquifer bounded by a constant free surface an analytical model is presented for the analysis of pulse interference tests conducted in a double porosity medium the special case of a horizontal fracture zone in a fractured rock environment with vertical connection to a high permeability zone at the water table is considered the high permeability zone is modeled as a hydraulic boundary of constant head and the vertical fractures are modeled using a formulation based on equivalent porous media wellbore storage at the source and observation wells is accounted for using an approximate superposition technique the solution is found using the laplace transform method and numerical inversion into real space the derivation is presented in dimensioned terms and a method for estimating the hydraulic conductivity of the vertical fractures is developed several alternate solutions describing differing system geometry and boundary conditions are presented for comparative purposes a sensitivity analysis shows that the new model predicts unique values for horizontal transmissivity and vertical hydraulic conductivity over a range of realistic storage term values for a given distance to the constant head boundary storage values were not found to be uniquely determined with this method several field examples are presented in order to validate the applicability of the analysis to real data the effects of the connection to the water table through double porosity were found to be significant resulting in an observation well response that cannot be simulated using a single porosity model thus the method is very useful for uniquely estimating the vertical hydraulic properties of fractured rock aquifers parameters that are often difficult to measure in this setting

rainfall induced lahars in the belham valley montserrat west indies rain falling on loose volcanic debris over the soufriere hills volcano montserrat generates hazardous floods in the belham valley these rainfall induced lahars vary greatly in discharge and sediment concentration in space and time they differ from examples documented on other volcanoes in that 1 the eruption has been continuing since july 1995 generating repeated pulses of excess sediment 2 rainfall is the only significant trigger 3 the system is small with short distance to the sea and relatively low altitude at the catchment top repeat mapping and comparison with pre eruption data demonstrate significant geomorphological change with c 120 m shoreline progradation and c 0 4 m a 1 mean aggradation rate in the middle to lower valley the nature of the hazard and area of risk have changed as the valley has aggraded the channel widened and the runoff efficiency increased as a result of rilling and vegetation removal lahars in the belham valley correlate with days when 10 mm rain fell in 24 h with more events triggered in the late rainy season the flows are mainly newtonian but one non newtonian flow event has been demonstrated and is described in detail 20 march 2000 this flow is explained by direct volcanic ash input to the runoff

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

landscape and sedimentary response to catastrophic debris avalanches western taranaki new zealand abstract catastrophic volcanic debris avalanches reshape volcanic edifices with up to half of pre collapse cone volumes being removed deposition from this debris avalanche deposit often fills and inundates the surrounding landscape and may permanently change the distribution of drainage networks on the weakly incised mt taranaki ring plain volcanic debris avalanche deposits typically form a large wedge shape in plan view over all flat lying fans following volcanic debris avalanches a period of intense re sedimentation commonly begins on ring plain areas particularly in wet or temperate climates this is exacerbated by large areas of denuded landscape ongoing instability in the scarp source region damming of river stream systems and in some cases inherent instability of the volcanic debris avalanche deposits in addition on mt taranaki the collapse of a segment of the cone by volcanic debris avalanche often generates long periods of renewed volcanism generating large volumes of juvenile tephra onto unstable and unvegetated slopes or construction of new domes with associated rock falls and block and ash flows the distal ring plain impact from these post debris avalanche conditions and processes is primarily accumulation of long run out debris flow and hyperconcentrated flow deposits with a variety of lithologies and sedimentary character common to these post debris avalanche units is evidence for high water content flows that are typically non cohesive hence sedimentary variations in these units are high in lateral and longitudinal exposure in relation to local topography the post collapse deposits flank large scale fans and hence similar lithological and chronological sequences can form on widely disparate sectors of the ring plain these deposits on mt taranaki provide a record of landscape response and ring plain evolution in three stages that divide the currently identified warea formation 1 the deposition of broad fans of material adjacent to the debris avalanche unit 2 channel formation and erosion of stage 1 deposits primarily at the contact between debris avalanche deposits and the stage 1 deposits and the refilling of these channels and 3 the development of broad tabular sheet flows on top of the debris avalanche leaving sediments between debris avalanche mounds after a volcanic debris avalanche these processes represent an ever changing and evolving hazard scape with hazard maps needing to be regularly updated to take account of which stage the sedimentary system is in