involvement of magmatic fluids at the laloki and federal flag massive sulfide cu zn au ag deposits astrolabe mineral district papua new guinea sulfur isotope evidence we present the first sulfur s isotope data of sulfides sulfates pyrite in host mudstone and bulk sulfur of gabbroic rocks from the laloki and federal flag massive cu zn au ag deposits in the astrolabe mineral district papua new guinea early stage pyrite marcasite chalcopyrite and sphalerite from laloki display wide range of 34s values from 4 5 to 7 0 n 16 late stage pyrite chalcopyrite and sphalerite have restricted 34s values of 1 9 to 4 7 n 16 the mineralizing stage these correspond to had moderately saline 5 9 8 4 nacl eq wt mineralizing fluids of possible magmatic origin a single analysis of late stage barite has a value of 34s 17 9 which is likely similar to coexisting seawater sulfate pyrite from the foot wall mudstone at laloki has very light 34s values of 36 1 to 33 8 n 2 which suggest an organic source for s pyrite marcasite and chalcopyrite from federal flag show 34s values of 2 4 to 1 9 n 2 consistent with a magmatic origin either leached from intrusive magmatic rocks or derived from magmatic hydrothermal fluids the very narrow range and near zero 34s values 1 0 to 0 6 of bulk gabbroic samples is consistent with mantle derived magmatic s sulfur isotope characteristics of sulfides and sulfates are however very similar to base metal sulfide accumulations associated with modern volcanic arcs and sedimented mid ocean ridges the most reasonable interpretation is that the range of the sulfide and sulfate 34s values from both laloki and federal flag massive sulfide deposits is indicative of the complex interaction of magmatic fluids seawater gabbroic rocks and mudstone

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

lahar infrasound associated with volcan villarrica s 3 march 2015 eruption the paroxysmal 2015 eruption of volcan villarrica chile produced a 2 5 h long lahar which descended more than 20 km within the rio correntoso turbio drainage and destroyed two small bridges a three element infrasound array 10 km from the summit and 4 km from the lahar s closest approach was used to study the flow s progression array processing using cross correlation lag times and semblance places constraints on the lahar s dynamics including detection of an initial flow pulse that traveled from 2 to 12 km at an average speed of 38 m s subsequently the lahar signal evolved to a relatively stationary infrasonic tremor located 10 to 12 km from the vent and adjacent to a topographic notch through which sound may have preferentially diffracted toward the recording site this study demonstrates the powerful capabilities of infrasound arrays for lahar study and suggests their potential application for future hazard monitoring

estimation of lahar flow velocity on popocatepetl volcano mexico during 1997 and 2001 two lahars took place in the tenenepanco and huiloac gorges on the northeastern sector of the popocatepetl volcano in mexico these lahars were the result of volcanic activity characterized by a pyroclastic fall and flow the lahars were triggered by the mass failures produced hours after the eruption the well known superelevation technique commonly used in this kind of study was applied to infer the lahar s mean velocity estimations show a broad flow velocity range of 1 3 13 8 m s depending on the following geomorphological parameters channel depth and slope peak discharge and distance from the initial source these results were compared with lahar velocities from mount st helens 1980 and nevado del ruiz 1985 which were obtained by the same superelevation technique according to the data the lahars from nevado del ruiz and popocatepetl were triggered by similar conditions while at mount st helens they were the result of the conversion of a pyroclastic surge cloud actually the mount st helens lahars were almost twice as fast as the ones at nevado del ruiz and popocatepetl this observation shows the importance of the lahars genesis in that the pyroclastic surge clouds produce faster lahars than do pyroclastic falls such results should be taken into account in lahar risk assessment studies for communities located near active volcanoes 2007 elsevier b v all rights reserved

s sr and pb isotopic systematics of hydrothermal chimney precipitates from the eastern manus basin western pacific evaluation of magmatic contribution to hydrothermal system 1 sulfur strontium and lead isotopic analyses were performed on chimneys from the hydrothermal vent fields the pacmanus and susu knolls in the eastern manus back arc basin lead isotope composition varies in a narrow range 206pb 204pb 18 75 18 78 207pb 204pb 15 51 15 54 and 208pb 204pb 38 31 38 40 strontium isotopic ratios 87sr 86sr of sulfate minerals vary from 0 7051 to 0 7077 falling between those of seawater 0 7090 and the hydrothermal fluid end member 0 7050 the 34s values of the chimneys are 8 0 to 3 9 for the susu knolls sulfide 1 0 to 4 3 for the pacmanus sulfides and 7 4 to 20 6 for sulfate the susu knolls sulfides have the lowest values so far reported for volcanic hosted massive sulfides from modern seafloor the low 34s values of sulfates and sulfides cannot be explained by a simple seawater circulation model without an additional source of light sulfur this is also supported by the presence of sulfate in hydrothermal end member fluid indicated by sulfur and strontium isotopic ratios in chimney sulfates biogenic sulfur and or oxidation of h2s after boiling are excluded from the possible sources of light sulfur because of the lack of sediment cover and nonequilibrium in isotopic fractionation by boiling at seafloor disproportionation of magmatic so2 introduced into hydrothermal system through preeruptive degassing is the most plausible mechanism for the observed low 34s values the lighter 34s values and more radiogenic lead isotope compositions of the susu knolls samples indicate that magmatic degassing was more vigorous at the susu knolls than pacmanus

sulfur mineralogy and geochemistry of serpentinites and gabbros of the atlantis massif iodp site u1309 abstract in situ uplifted portions of oceanic crust at the central dome of the atlantis massif mid atlantic ridge 30 n were drilled during expeditions 304 and 305 of the integrated ocean drilling program iodp and a 1 4 km section of predominantly gabbroic rocks with minor intercalated ultramafic rocks were recovered here we characterize variations in sulfur mineralogy and geochemistry of selected samples of serpentinized peridotites olivine rich troctolites and diverse gabbroic rocks recovered from hole 1309d these data are used to constrain alteration processes and redox conditions and are compared with the basement rocks of the southern wall of the atlantis massif which hosts the lost city hydrothermal field 5 km to the south the oceanic crust at the central dome is characterized by ni rich sulfides reflecting reducing conditions and limited seawater circulation during uplift and exhumation seawater interaction in gabbroic dominated domains was limited as indicated by homogeneous mantle like sulfur contents and isotope compositions of gabbroic rocks and olivine rich troctolites local variations from mantle compositions are related to magmatic variability or to interaction with seawater derived fluids channeled along fault zones the concomitant occurrence of mackinawite in olivine rich troctolites and an anhydrite vein in a gabbro provide temperature constraints of 150 200 c for late circulating fluids along local brittle faults below 700 m depth in contrast the ultramafic lithologies at the central dome represent domains with higher seawater fluxes and higher degrees of alteration and show distinct changes in sulfur geochemistry the serpentinites in the upper part of the hole are characterized by high total sulfide contents high 34ssulfide values and low 34ssulfate values which reflect a multistage history primarily controlled by seawater gabbro interaction and subsequent serpentinization the basement rocks at the central dome record lower oxygen fugacities and more limited fluid fluxes compared with the serpentinites and gabbros of the lost city hydrothermal system our studies are consistent with previous results and indicate that sulfur speciation and sulfur isotope compositions of altered oceanic mantle sequences commonly evolve over time heterogeneities in sulfur geochemistry reflect the fact that serpentinites are highly sensitive to local variations in fluid fluxes temperature oxygen and sulfur fugacities and microbial activity

interpreting luminescence data from a portable osl reader three case studies in fluvial settings optically stimulated luminescence osl is a technique that has been applied from the mid 1980s mainly for sediment dating the osl technique is based on sample stimulation by light to determine the luminescence signal that is stored in the crystal lattices of sediment grains after deposition burial by later sediment and subsequent exposure to ionizing radiation from radioactive elements in the surrounding sediment in such sediment dating two parameters are required the equivalent dose i e the luminescence signal stored in the grains and the dose rate i e the ionizing energy from and radiation emitted by naturally occurring radioisotopes in the deposit plus the effects of cosmic radiation in this research the osl technique is not used for dating the study goal is to analyse only the luminescence signals the total photon counts in polymineral samples obtained after light stimulation in the blue blsl and infrared irsl wavelengths using a portable osl reader designed and built at the scottish universities environmental research centre suerc three fluvial case studies from cambodia australia and mexico are used to illustrate the geomorphological interpretations possible with the portable osl reader data from sediments resulting from a range of different depositional processes the case studies show that aspects of sediment s transport and depositional processes can be inferred from the portable osl reader data providing valuable insights into geomorphological history copyright 2010 john wiley sons ltd

rheological properties of mudflows associated with the spring 1980 eruptions of mount st helens volcano washington rheological properties of three recent mudflows at mount st helens were estimated using techniques developed for determining the properties of debris flows based on the geometry of their deposits calculated yield strengths of 1100 1000 and 400 pa maximum flow velocities of 10 to 31 m s volumetric flow rates of 300 to 3400 m s and plastic viscosities of 20 to 320 pa s all compare favorably with measured and estimated values cited in the literature a method for determining likely sites of future mudflow initiation based on these data is outlined

feasibility study of spectral pattern recognition reveals distinct classes of volcanic tremor abstract systematic investigations of the similarities and differences among volcanic tremor at a range of volcano types may hold crucial information about the plausibility of inferred source mechanisms which in turn may be important for eruption forecasting however such studies are rare in part because of an intrinsic difficulty with identifying tremor signals within very long time series of volcano seismic data accordingly we develop an efficient tremor detection algorithm and identify over 12 000h of volcanic tremor on 24 stations at k lauea okmok pavlof and redoubt volcanoes we estimate spectral content over 5 minute tremor windows and apply a novel combination of principal component analysis pca and hierarchical clustering to identify patterns in the tremor spectra analyzing several stations from a given volcano together reveals different styles of tremor within individual volcanic settings in addition to identifying tremor properties common to all stations in a given network we find localized tremor signals including those related to processes such as lahars or dike intrusions that are only observed on some of the stations within a network subsequent application of our analysis to a combination of stations from the different volcanoes reveals that at least three main tremor classes can be detected across all settings whereas a regime with a ridge of high power distributed over 1 2hz and a gradual decay of spectral power towards higher frequencies is observed dominantly at three volcanoes k lauea okmok redoubt with magma reservoirs centered at less than 5km below sea level b s l a spectrum with a steeper slope and a narrower peak at 1 2hz is observed only in association with open vents k lauea and pavlof a third regime with a peak at approximately 3hz is confined to two stratovolcanoes pavlof and redoubt these observations suggest generic relationships between the spectral character of the observed signals and volcano characteristics such as magma viscosity storage depths and the physical properties of volcanic edifices similarities among the spectral patterns detected at stations 4km and 8 10km distance from the centers of volcanic activity respectively indicate that path effects do not strongly influence spectral shapes at distances of a few kilometers from the inferred source of the signals our preliminary work shows that a global comparison of tremor is feasible our results suggest that further work on data from a larger sample and diverse range of volcano types will reveal additional classes of tremor signals and plausibly identify fingerprints of source processes that are specific to volcano type but independent of volcano location

featureless spectra on the moon as evidence of residual lunar primordial crust we report the global distribution of areas exhibiting no absorption features featureless or fl on the lunar surface based on the reflectance spectral data set obtained by the spectral profiler onboard kaguya selene we found that fl sites are located in impact basins and large impact craters in the feldspathic highlands terrane while there are no fl sites in the procellarum regions nor the south pole aitken basin fl sites in each impact basin crater are mainly found at the peak rings or rims where the purest anorthosite pan sites are also found at the local scale most of the fl and pan points are associated with impact craters and peaks most of the fl spectra show a steeper redder continuum than the pan spectra suggesting the occurrence of space weathering effects we propose that most of the material exhibiting a fl spectrum originate from space weathered pan taking into account all the occurrence trends of fl sites on the moon we propose that both the fl and pan materials were excavated from the primordial lunar crust during ancient basin formations below the megaregolith in the highlands since the fl and pan sites are widely distributed over the lunar surface our new data may support the existence of a massive pan layer below the lunar surface

rainfall triggered lahars at volcan de colima mexico surface hydro repellency as initiation process article volcan de colima is currently the most active volcano in mexico since 1998 intermittent activity has been observed with vulcanian eruptions lava flows and growing domes that have collapsed producing several block and ash flow deposits during the period of heightened activity since 1998 at volcan de colima pyroclastic flows from dome or column collapse have not reached long distances most of the time less than 6k m from the crater in contrast rain induced laharswere more frequent and have reached relatively long distances upto 15 km causing damage to infrastructureand affecting small villages in 2007 tworain gauge stationswereinstalledonthesouthern flankofthevolcanoregisteringeventsfromjunethroughtooctober the period when rains are intense and lahars frequent by comparing lahar frequency with rainfall intensity and the rainfall accumulated during the previous 3 days lahars more frequently occur at the beginning of the rainfall season with low rain accumulation 10 mm and triggered by low rain intensities 20 mm h during the months with more rainfall july and august lahars are less frequent and higher peak intensities up to 70 mm h are needed to trigger an event in both cases lahars were initiated as dilute sediment laden streamflows which transformed with entrainment of additional sediment into hypercon centratedanddebris flows withalternationsbetweenthesetwo flowtypes ahydro repellencymechanism in highly vegetated areas i e evergreen tree types with considerable amount of resins and waxes such as pines with sandy soils can probably explain the high frequency of lahars at the beginning of the rain season during low rainfall events under hydrophobic conditions infiltration is inhibited and runoff is facilitated at more highly peaked discharges that are more likely to initiate lahars

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

tree ring reconstruction of past lahar activity at popocatepetl volcano mexico lahars represent a major threat on the slopes of volcanoes all over the world in order to realistically assess hazards knowledge on the occurrence and timing of past lahar activity is of crucial importance however archival data on past events is usually scarce or completely missing tree ring records have repeatedly proved to be a reliable data source for the reconstruction of past geomorphic events however tree rings have seldom been applied for the identification of past lahars therefore it was the aim of this study i to identify and describe disturbances in tree growth induced by well documented lahar events and on this basis and ii to recognise older unknown lahar events with tree ring analyses based on these goals we collected 140 tree ring series from 62 trees abies religiosa pinus hartwegii and pinus ayacahuite standing inside or adjacent to the lahar channel in the huiloac gorge at popocatepetl volcano central mexico most commonly the known lahar events of 1997 and 2001 resulted in abrupt changes in tree ring width as well as injuries the same growth disturbances could be identified in the tree ring series indicating that five previously unknown lahar events would have occurred during the 20th century popocatepetl is one of the best surveyed volcanoes in the world and past eruptions are precisely noted in archives as most of these unknown events occurred during periods with no volcanic activity we believe that they were rainfall induced rather than related to volcanic activity in order to assess rainfall intensity threshold values for the triggering of events the analyses of meteorological data needs to be integrated in general the investigated tree species proved to be highly suitable for the reconstruction of mass movement processes therefore the applied methods can be transferred to other locations where data on past events are missing

sedimentological processes in lahars insights from optically stimulated luminescence analysis abstract a lahar is a sediment laden flow capable of major destructive impacts on infrastructure and human life how lahars transport sediment is thus a key issue for understanding lahar sedimentology and behavior especially in terms of the lahar s hydraulic and rheological properties which can be substantially altered as the lahar gains or loses material during its travel in this research we analyze lahar entrainment processes by evaluating luminescence signals total photon counts from lahar sediments using blue luminescence signals blsl a portable osl reader that analyzes several grams of polymineral and polygrain size samples was applied we use data from three lahars in the tenenepanco and huiloac gorges on popocatepetl volcano mexico to elucidate the ways in which lahars may gain lose and transport sediment during flow sediment samples for luminescence analysis were taken through the full thickness of the lahar deposits at eight different sites for two lahars 1997 and 2001 and at one site for a lahar that occurred 500 yrs ago mean luminescence values obtained for the 1997 lahar help to evaluate the relationship between the lahar entrainment processes and the drainage at the different sites for the 2001 lahar this relationship was also established taking into account the channel slope the main conclusion is that luminescence signals total photon counts can be used to detect entrained material in the flow because the bulked materials modify the final osl signals the application of this type of luminescence analysis thus has the potential to provide a better understanding of sediment entrainment in these sediment laden flows

a sph depth integrated model for popocatepetl 2001 lahar mexico sensitivity analysis and runout simulation abstract lahars are debris flows of volcanic origin which can endanger or even destroy communities located near the flanks of volcanoes lahars are not always triggered by eruptions they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse decision makers need lahar hazard maps to devise hazard prevention measures that will prevent casualties so lahar modelling is an important tool for assessing flow behavior and determining inundation areas the depth integrated numerical model used in this study is derived from the velocity pressure of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method to simulate a lahar that occurred at popocatepetl volcano in 2001 in order to investigate the convergence of the model we used a range of different sph mesh resolutions once the optimum mesh resolution was bounded we analyzed the model s sensitivity to the initial lahar volume the density of the geomaterial and the rheological parameter of the bingham fluid the results show that the sph depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 lahar the study also shows the effects of sph mesh resolution and the relevant influence of rheological parameters

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

reconstruction of a destructive debris flow event via numerical modeling the role of valley geometry on flow dynamics debris flows are widespread natural phenomena characterized by high mobility high velocity and long runout distance and impact forces which frequently cause human casualties and significant damage to infrastructure to better understand the dynamics of such events analyzing in particular the effect induced by the valley geometry on flow velocity runout and mobilized volumes in this work we reconstruct a real debris flow event through numerical modeling specifically we used a modified version of the bing model a fluid dynamic depth integrated numerical model for debris flows which has been properly modified to account for width changes along the valley the studied event which occurred in scaletta zanclea messina north eastern sicily italy on october 1 2009 is exceptionally well constrained by field and topographic information in this respect the flow velocity estimated from two specific locations on the basis of field evidence the distribution of erosional and depositional areas along the racinazzo valley based on the comparison of pre and post event digital elevation models dems and the runout distance were used as constraints to calibrate the model furthermore we report a detailed description of the main event characteristics based on hydrological records and witness reports the numerical modeling results are consistent with witness reports and the severe damage recorded in the scaletta marina village and highlight the effect of the valley geometry on both the debris flow velocity and the erosion deposition processes the effect of changing valley width has been also quantified resulting in accelerations of the debris in correspondence of the valley narrowing and stagnations at the plateaus copyright 2015 john wiley sons ltd

debris flow velocities and superelevation in a curved laboratory channel the vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius here we report on laboratory e

smoothed particle hydrodynamic modeling of volcanic debris flows application to huiloac gorge lahars popocatepetl volcano mexico abstract lahars are among the most catastrophic volcanic processes and the ability to model them is central to mitigating their effects several lahars recently generated by the popocatepetl volcano mexico moved downstream through the huiloac gorge towards the village of santiago xalitzintla the most dangerous was the 2001 lahar in which the destructive power of the debris flow was maintained throughout the extent of the flow identifying the zone of hazard can be based either on numerical or empirical models but a calibration and validation process is required to ensure hazard map quality the geoflow sph depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity pressure version of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method the results of the calibrated sph model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel moreover the dependency of the results on topographic mesh resolution initial lahar mass shape and dimensions is also investigated the results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution and an initial lahar mass shape that adopted the source area morphology field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths the error being less than 20 for 11 of the 16 cross sections this study demonstrates that the geoflow sph model was able to accurately reproduce the lahar path and the extent of the flow but also reproduced other parameters including flow velocity and deposit depth

using tree ring analysis to evaluate intra eruptive lahar activity in the nexpayantla gorge popocatepetl volcano central mexico abstract lahar activity is one of the most important processes capable of mobilizing large volumes of sediment and producing devastating effects on human populations and infrastructure estimating the frequency distribution and climatic controls on lahar activity is necessary for understanding how sediment is mobilized from hillslopes to channels and how the landscape is modified by this type of process in this study we evaluate the intra eruptive lahar activity in the nexpayantla gorge nw of popocatepetl volcano central mexico by using a dendrogeomorphological analysis of growth ring records of abies religiosa trees n 100 based on the identification of 322 growth disturbances gd and field evidences we identify 23 intra eruptive lahars that occurred from 1959 to 2013 by analyzing the lahar chronology and climatic data we observed that 83 of lahar activity coincides with moderate to strong cold and dry phases of el nino southern oscillation based on the seasonal timing of gd we explored the intra annual lahar activity we found that 43 of the lahars occurred in the latewood season from july to october when the mean summer monthly rainfall is 120 mm approximately 37 of lahars occurred during the first heavy rainfalls from march to june which corresponds to the earlywood season the remaining 20 of the lahar activity corresponds to the dormancy period winter season when snowmelt and or occasional strong rainfalls 100 mm day 1 occur the gd indicate that in nexpayantla gorge intra eruptive lahar activity takes place around every two years we also found that the effects of lahars are concentrated around the transitional and depositional zone of nexpayantla gorge

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

sulfur isotope characteristics of metamorphosed zn cu volcanogenic massive sulfides in the areachap group northern cape province south africa zn and cu rich massive sulfide ores of volcanogenic origin volcanogenic massive sulfide vms deposits occur as stratiform stratabound lenses of variable size hosted by gneisses amphibolites and schists of the areachap group in the northern cape province of south africa the areachap group represents the highly deformed and metamorphosed remnants of a mesoproterozoic volcanic arc that was accreted onto the western margin of the kaapvaal craton during the 1 0 1 2 ga namaquan orogeny sulfur isotope data 34s are presented for 57 sulfide separates and one barite sample from five massive sulfide occurrences in the areachap group although sulfides from each site have distinct sulfur isotope values all 34s values fall within a very limited range 3 0 to 8 5 barite has a 34s value of 18 5 very different from that of associated sulfides at one of the studied sites kantienpan a distinct increase in 34s of sulfides is observed from the massive sulfide lens into the disseminated sulfides associated with a distinct footwall alteration zone sulfide sulfide and sulfide barite mineral pairs which recrystallized together during amphibolite and lower granulite facies metamorphism are not in isotopic equilibrium sulfur isotope characteristics of sulfides and sulfates of the zn cu ores in the areachap group are however very similar to base metal sulfide accumulations associated with modern volcanic arcs and unsedimented mid ocean ridges it is thus concluded that profound recrystallization and textural reconstitution associated with high grade regional metamorphism of the massive sulfide ores of the areachap group did not result in extensive sulfur isotopic homogenization this is similar to observations in other metamorphosed vms deposit districts and confirms that massive sulfide ores remain effectively a closed system for sulfur isotopes for both sulfides and sulfates during metamorphism