integrated hazard assessment of cirenmaco glacial lake in zhangzangbo valley central himalayas abstract glacial lake outburst floods glofs have recently become one of the primary natural hazards in the himalayas there is therefore an urgent need to assess glof hazards in the region cirenmaco a moraine dammed lake located in the upstream portion of zhangzangbo valley central himalayas has received public attention after its damaging 1981 outburst flood here by combining remote sensing methods bathymetric survey and 2d hydraulic modeling we assessed the hazard posed by cirenmaco in its current status inter annual variation of cirenmaco lake area indicates a rapid lake expansion from 0 10 0 08 km2 in 1988 to 0 39 0 04 km2 in 2013 bathymetric survey shows the maximum water depth of the lake in 2012 was 115 2 m and the lake volume was calculated to be 1 8 107 m3 field geomorphic analysis shows that cirenmaco glacial lake is prone to glofs as mass movements and ice and snow avalanches can impact the lake and the melting of the dead ice in the moraine can lower the dam level hec ras 2d model was then used to simulate moraine dam failure of the cirenmaco and assess glof impacts downstream reconstruction of cirenmaco 1981 glof shows that hec ras can produce reasonable flood extent and water depth thus demonstrate its ability to effectively model complex glofs glof modeling results presented can be used as a basis for the implementation of disaster prevention and mitigation measures as a case study this work shows how we can integrate different methods to glof hazard assessment

authigenesis of ferric oolites in superficial sediments from lake malawi central africa abstract lithological examination of sediments from 250 sampling stations in the lake malawi basin revealed the presence of oolitic and pisolitic sequences at four locations all lying at depths of 100 160 m geochemical analyses showed the oolites to be comprised of concentric shells of hydrous fe3 oxide surrounding siliceous nuclei they are also conspicuously enriched with mn zn and pb in adsorbed and reducible oxide phases authigenesis of the oolites and pisolites results from the mobilization of fe2 in the pore waters of deeply buried anoxic strata and subsequent precipitation of fe3 at the sediment water interface this process can operate only at those locations with a two layer oxic anoxic sediment column thus explaining the restriction of oolite beds to relatively shallow water settings in lake malawi where bottom waters are well oxygenated however there is no surficial fe enrichment at shallow sites with predominantly non clastic or pure silt clay sediments suggesting that the availability of both reactive fe and suitable precipitation nuclei constitute additional controls on oolite formation the mode of fe enrichment observed in lake malawi may be of some value as a model for more ancient situations particularly where ironstones have formed in the absence of a definable crustal or volcanogenic fe source

co2 degassing over seismic areas the role of mechanochemical production at the study case of central apennines field observations coupled with experimental results show that co2 can be produced by mechanical energy applied to carbonate rocks becoming an unexpected additional gas source besides that degassed from the mantle or produced by thermometamorphism the evidence that a large amount of carbon dioxide associated with radiogenic type helium r ra as low as 0 01 0 08 is released through continental areas denotes the absence of a contribution from the mantle or from mantle derived fluids data collected during the seismic crisis which struck the central apennines in 1997 98 have shown an enhanced co2 flux not associated with the presence of mantle or thermometamorphic derived fluids on the other hand new experimental results highlight the possibility of producing co2 by mechanical energy that acts on the calcite crystalline lattice while the co2 released over the geothermal areas e g larderello geothermal field is obviously derived by mantlederived activities this is not the case of the huge amount of co2 released over the seismically active areas where the presence mantle derived products is ruled out we propose that mechanical energy e g released during seismic events microseismicity or creeping processes is a possible additional energy source able to produce co2 and thus could explain the presence of co2 degassing over tectonic areas where the influence of the mantle is low

predictive uncertainty of peak outflow relations for landslides dam breach risk assessment development considering the failure of landslide dams often requires the estimation of peak outflow through the breach the empirical equations based on data from case studies tend to be the first direct approach this paper conducted an uncertainty analysis when these empirical relations were utilized to predict the peak outflow of a breached landslide dam the results suggest that the relations derived from manmade dams or embankments typically overestimate the peak outflow about 1 5 to 3 4 of an order of magnitude and the relations derived from the database of landslide dams have much smaller mean prediction errors and also exhibit broad uncertainty bands application of the uncertainly analysis was illustrated by the tangjiashan landslide dammed lake formed during 2008 wenchuan earthquake in addition the predicted results from eq 1 deduced herein were considered to be the reliable estimate of peak outflow through the breach of landslide dam

the 1997 umbria marche italy earthquake sequence a first look at the main shocks and aftershocks a long sequence of earthquakes six with magnitudes between 5 and 6 struck central italy starting on september 26 1997 causing severe damages and loss of human lives the seismogenic structure consists of a nw se elongated fault zone extending for about 40 km the focal mechanisms of the largest shocks reveal normal faulting with ne sw extension perpendicular to the trend of the apennines consistently with the quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions preliminary data on the main shocks and aftershocks show that extension in this region of the apennines is accomplished by normal faults dipping at low angle 40 to the southwest and confined in the upper 8 km of the crust these normal faults might have reactivated thrust planes of the pliocene compressional tectonics the aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km long fault segments adjacent and slightly offset from one another

pre seismic slip on the 26 september 1997 umbria marche earthquake fault unexpected clues from the analysis of 1951 1992 elevation changes we studied 1951 1992 elevation changes recorded by a first order leveling line that intercepts the surface projection of the 26 sep 1997 mw 6 0 umbria marche earthquake causative fault the line documents 1951 1992 localized subsidence along a 12 km section above the fault we calculated the expected 1997 coseismic elevation changes along the line using standard dislocation modeling and found that their trend has an amplitude three times larger than the trend of the observed pre 1997 signal but with a similar shape we suggest that this signal is the result of 10 cm of pre 1992 slip along the northernmost 5 km of the 1997 earthquake fault where coseismic slip was found to be less than the average estimated for the entire fault this result implies unusually fast slip along this section of the fault and may suggest slip acceleration in preparation for the impending failure

analysis of seismological and geological observations formoderate size earthquakes the colfiorito fault system central apennines italy to contribute to the understanding of the relationships between moderate earthquakes and the faults that are recognisable in the geological record we analysed seismological and geological data related to the 1997 98 umbria marche central italy earthquake swarm the seismological recordings collected by local networks allowed accurate location of about 1000 events whereas the geological field observations provided a picture of the structural features and the ground surface deformations we also re examined and utilised some already published data and results mostly about the fault plane solutions and the geology on the basis of earthquake locations fault plane solutions and geological mapping we explored the possible correlation between the earthquake causative fault planes and the normal faults exposed in the area our results show that the two mainshocks that occurred on september 26 1997 mw 5 7 and mw 6 0 originated on the same structure reactivating at depth the colfiorito normal faults both ruptures did not propagate up to the ground surface but triggered gravitational sliding that occurred along pre existing fault scarps the earthquake that occurred on october 14 1997 mw 5 6 originated on another fault branch at a much shallower depth in spite of the lower magnitude this earthquake produced tectonic ruptures where the fault plane projects to the surface in an area where no faults were previously mapped by comparing the paleostress reconstruction based on slickenside lineations analysis and the focal mechanism solutions we also suggest a possible correlation between the long term early middle pleistocene cumulative effects of the colfiorito fault system and the short term behaviour of the fault planes observed during this earthquake swarm favouring the idea of a seismogenic source producing clustered moderate size earthquakes rather than large events scattered in time our results suggest that the integration of geological and seismological observations can constrain the seismotectonic interpretations in regions of low level seismicity and that this integration can pose a reliable basis in the seismic hazard assessment

overtopping induced failure of noncohesive homogeneous fluvial dikes accurate predictions of breach characteristics are necessary to reliably estimate the outflow hydrograph and the resulting inundation close to fluvial dikes laboratory experiments on the breaching of fluvial sand dikes were performed considering a flow parallel to the dike axis the breach was triggered by overtopping the dike crest a detailed monitoring of the transient evolution of the breach geometry was conducted providing key insights into the gradual and complex processes involved in fluvial dike failure the breach develops in two phases 1 the breach becomes gradually wider and deeper eroding on the downstream side along the main channel and 2 breach widening controlled by side slope failures continuing in the downstream direction only increasing the inflow discharge in the main channel the breach formation time decreases significantly and the erosion occurs preferentially on the downstream side the downstream boundary condition has a strong influence on the breach geometry and the resulting outflow hydrograph

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

the maximum discharge of outburst floods caused by the breaching of man made and natural dams the sudden release of water impounded in natural and man made reservoirs has been responsible for some major disasters in mountainous regions of the world recent natural damming events and failures of natural dams have illustrated the need to examine the nature and magnitude of outburst floods and the behaviour of debris dams in general an empirical relationship between maximum discharge qmax and volume of water released during the outburst event vmax is established qmax 0 72vmax0 53 for man made dams and the relationship is thought applicable to the breaching of natural debris dams landslides and moraines this relationship allows a first order estimate to be made of qmax in the vicinity of the breach for a given vmax during the failure of a man made dam or a natural debris dam key words outburst floods man made dams natural dams landslide dam failure

coseismic and postseismic displacements related with the 1997 earthquake sequence in umbria marche central italy we study the coseismic and postseismic displacements related with the 1997 umbria marche earthquake sequence by means of leveling lines along a deformed aqueduct located in the epicentral area comparing the 1960 and 10 1997 measurements we obtain 0 49 0 10 m of coseismic displacement distributed along 3 km across the normal fault zone modeling of the coseismic surface dislocation is obtained from a combination of low angle 38 faults at depth and high angle 80 upper fault branches the best fit model indicates that the upper branches stop at 0 4 km below the ground surface and have 60 of slip with respect to the lower faults the postseismic displacement measured during 1998 is 0 18 m and represents 36 of the apparent coseismic deformation moderate earthquakes in the apennines and related surface deformation may thus result from curved faults that reflect the brittle elastic properties of the uppermost crustal structures

helium and carbon isotopes in the dissolved gases of friuli region ne italy geochemical evidence of co2 production and degassing over a seismically active area abstract the first geochemical data showing the existence of an active degassing activity over a large seismically active sector of the southern alps friuli region ne italy are presented the dissolved gases helium and carbon isotopic systematics of 46 water samples taken from 13 sites running along e w and ne sw faults besides the natural degassing of a 5000 km 2 wide area are investigated the chemical composition of the dissolved gases revealed that a co 2 rich gas phase feeds the local groundwaters 3 he 4 he ratios r normalized to the atmospheric 3 he 4 he ratio ra 1 39 10 6 and corrected for the atmospheric contamination r ra c range from 0 29 to 1 as a result of a two component radiogenic and atmospheric mixing the 13 c values of total dissolved inorganic carbon tdic ranging from 15 28 to 0 75 vs pdb show the occurrence of multiple gas water interactions the mixing between the atmospheric air and a crustal source and the gas water interactions occurring at various extents appears to be the main control on the observed he c systematics the natural co 2 degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that generated destructive seismic sequences e g the gemona sequence of 1976 main shocks m6 4 of 6th may and m6 1 of 11th and 15th september the results obtained show that a significant amount of crustal originated gases are released over the continental area of eastern southern alps the evidence that carbon dioxide is associated with radiogenic type helium denotes the lack of the mantle as primary energy and degassing source highlighting the possibility that co 2 is produced by thermo mechanical processes occurring at seismogenic depth the information provided here may be used to start up a long term geochemical monitoring of this seismically active area and could be able to detect the modifications occurring to the circulating fluids to gain a better insight on the relationships between the fluids geochemistry and the activity of the local seismogenic faults

breaching parameters for earth and rockfill dams dam risk analysis is at the heart of dam failure prevention and mitigation in order to assess dam risk it is essential to conduct a quantitative analysis of the process of a dam breach which can be described by such parameters as breach geometry breaching duration and peak outflow rate the main objective of this paper is to develop robust empirical formulas with physical meaning for predicting dam breaching parameters based on past dam failure data a database of 182 earth and rockfill dam failure cases has been compiled among these cases nearly one half are for large dams higher than 15 m a multiparameter nonlinear regression model is recommended to develop empirical relationships between five breaching parameters breach depth breach top width average breach width peak outflow rate and failure time and five selected dam and reservoir control variables dam height reservoir shape coefficient dam type failure mode and dam erodibility the relative importance of each control variable is evaluated the dam erodibility is found to be the most important factor influencing all five breaching parameters the reservoir shape coefficient and the failure mode also play an important role in the prediction models two case studies are presented to show the application of the empirical models developed in this paper

geochemical evidence of seismogenic induced anomalies in the dissolved gases of thermal waters a case study of umbria central apennines italy both during and after the 1997 1998 seismic swarm 1 in this paper we present the first geochemical data set regarding long term monitoring of dissolved gases in thermal waters from a seismic area three sites in umbria central apennines italy were studied both for the chemical and for the helium isotopic composition of the dissolved gases data were collected during and after the seismic crisis that struck the region in 1997 1998 the chemical composition of the dissolved gases revealed that a co2 rich gas phase was always mixed with an atmospheric derived component dominated by n2 a normal faulting marked the beginning of the seismic activity enhancing the release of co2 on a regional scale variations in both the chemical and isotopic compositions of the dissolved gases were also observed as preseismic synseismic and postseismic phenomena related to the seismic shock of march 1998 those geochemical modifications were interpreted as being the consequence of a drop in the co2 degassing rate in good agreement with the compressive focal mechanism of that seismic event furthermore this interpretation was also consistent with the geologic and tectonic setting of the study area and induced us to postulate that changes in the local rock permeability due to crustal deformations i e coseismic deformation and postseismic release were responsible for the geochemical modifications observed on the basis of the foregoing we have concluded that the geochemistry of dissolved gases in groundwaters represents a useful tool for the investigation of the relationships between circulating fluids and seismic activity

the september 26 1997 colfiorito italy earthquakes modeled coseismic surface displacement from sar interferometry and gps the largest events of the 1997 umbria marche seismic sequence were the two september 26 earthquakes of mw 5 7 00 33 gmt and mw 6 0 09 40 gmt which caused severe damage and ground cracks in a wide area around the epicenters we created an ers sar differential interferogram where nine fringes are visible in and around the colfiorito basin corresponding to 25 cm of coseismic surface displacement gps data show a maximum horizontal displacement of 14 1 8 cm and a maximum subsidence of 24 3 cm we used these geodetic data and the seismological parameters to estimate geometry and slip distribution on the fault planes modeled fault depths and maximum slip amplitudes are 6 5 km and 47 cm for the first event and 7 km and 72 cm for the second one in good agreement with those derived from the seismological data

modelling outburst floods from moraine dammed glacial lakes in response to climatic change the size and number of moraine dammed supraglacial and proglacial lake systems have increased dramatically in recent decades given an appropriate trigger the natural moraine dams that impound these proglacial lakes are breached producing catastrophic glacial lake outburst floods glofs these floods are highly complex phenomena with flood characteristics controlled in the first instance by the style of breach formation downstream glofs typically exhibit transient often non newtonian fluid dynamics as a result of high rates of sediment entrainment from the dam structure and channel boundaries combined these characteristics introduce numerous modelling challenges in this review the historical contemporary and emerging approaches available to model the individual stages or components of a glof event are introduced and discussed a number of methods exist to model the stages of a glof event dam breach models can be categorised as being empirical analytical or numerical in nature with each method having significant advantages and shortcomings empirical relationships that produce estimates of peak discharge and time to peak are straightforward to implement but the applicability of these models is often limited by the nature of the case study data from which they are derived furthermore empirical models neglect the inclusion of basic hydraulic principles that describe the mechanics of breach formation analytical or parametric models simulate breach development using simplified versions of the physically based equations that describe breach enlargement whilst complex physically based codes represent the state of the art in numerical dam breach modelling to date few of the latter have been applied to investigate the moraine dam failure problem despite significant advances in the physical complexity and availability of higher order hydrodynamic solvers the majority of published accounts that have attempted to reconstruct or predict glof characteristics have been limited often by necessity to the use of relatively simplistic models this is in part attributable to the unavailability of terrain models of many high mountain catchments at the fine spatial resolutions required for the effective application of numerically sophisticated codes and their proprietary and often cost prohibitive nature however advanced models are experiencing increasing use in the glacial hazards literature in particular the suitability of emerging mesh free particle based methods for simulating dam breach and glof routing may represent a solution to many of the challenges associated with modelling this complex phenomenon sources of uncertainty in the glof modelling chain have been identified by various workers however to date their significance for the robustness of reconstructive and predictive modelling efforts have been largely unexplored and quantified in detail these sources include the geometric and material characterisation of moraine dam complexes including lake bathymetry and the presence and extent of buried ice initial conditions freeboard precise spillway dimensions spatial discretisation of the down valley domain hydrodynamic model dimensionality and the dynamic coupling of successive components in the glof model cascade

long term 1997 2007 geochemical monitoring of gases from the umbria marche region abstract the paper presents the results of ten year long geochemical monitoring carried out in the area hit by the 1997 98 umbria marche seismic sequence northern apennines italy showing the advancement in our understanding of the reciprocal relationships between fluids and tectonic structures in this area long term geochemical monitoring has allowed us to define the geochemical features of the gas phase and to model its origins and interactions all the released gases including dissolved and venting gases have predominantly crustal origin and have suffered from substantial modifications in their geochemical features the whole seismogenic process is considered to be responsible for the modifications recorded over a wide time interval including the production of co 2 from mechanical stress on carbonate rocks we interpret the modifications occurred to the gas phase during the 1997 98 period as related to faulting activity while those recorded after the end of the seismic crisis are interpreted as being a consequence of the crustal relaxation the data show that it is almost impossible to interpret the temporal variation without coupling long term geochemical monitoring and knowledge of the genetic features of the fluids therefore the information coming from the circulating fluids is a powerful tool to better understand the physical processes governing the faulting activity

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

earthquake induced chemical changes in the thermal waters of the umbria region during the 1997 1998 seismic swarm the compositional data collected at three thermal springs in the umbria region over a sampling period lasting two and a half hydrological years included the entire seismic sequence striking the central apennines italy in 1997 1998 wide temporal variations in the chemical composition and temperature of thermal waters were observed at all the sampling sites the widest were recorded at the triponzo sampling site where a temperature drop of 2 c and 20 c preceded by 4 days and 2 days respectively the occurrence of the event characterized by the deepest hypocentre of the entire seismic sequence despite such a macroscopic preseismic anomaly the recorded variations were not related to single seismic events or to the release rate of the seismic energy they actually seem to have been induced by permeability variations related to crustal deformation in the absence of elastic energy release and were thus linked to the whole seismogenic process

anomalies of mantle derived helium during the 1997 1998 seismic swarm of umbria marche italy more than 100 he 4he isotope ratios were measured in co2 dominated gas samples collected during the 1997 1998 seismic crisis that shook the umbria marche central apennines italy although the gas emissions were located in a typical crustal environment the measured values delineate variable mixing proportions between mantle derived and crustal helium during the monitoring period anomalous he 4he ratios were observed together with a significant increase of fluid outflows the observed he 4he anomalies appear to be driven by stress induced crustal deformations affecting micro fracturing and bulk permeability and in turn by a seismogenic induced modification of the crustal permeability of rocks since crustal deformations can also occur aseismically the geochemical anomalies must be considered indicators of processes occurring below the surface which could eventually help to estimate the probability increase of an impending earthquake instead of pure empirical precursors

spatiotemporal patterns of high mountain lakes and related hazards in western austria abstract climate induced environmental changes are triggering the dynamic evolution of high mountain lakes worldwide a phenomenon that has to be monitored in terms of lake outburst hazards we analyzed the spatial distribution and recent temporal development of high mountain lakes in a study area of 6139 km 2 covering the central european alps over most of the province of tyrol and part of the province of salzburg in western austria we identified 1024 natural lakes while eight lakes are ice dammed one third of all lakes are located in the immediate vicinity of recent glacier tongues half of them impounded by moraines half by bedrock two thirds of all lakes are apparently related to lia or earlier glaciations one landslide dammed lake was identified in the study area the evolution of nine selected pro glacial lakes was analyzed in detail using multitemporal remotely sensed images and field reconnaissance considerable glacier retreat led to significant lake growth at four localities two lakes experienced stagnant or slightly negative areal trends one lake experienced a more significant negative areal trend and two lakes drained completely during the investigation period we further i analyzed the susceptibility of selected lakes to glacial lake outburst floods glofs using two different methods ii identified potential triggers and mechanisms of glofs iii calculated possible flood magnitudes for predefined flood scenarios for a subset of the lakes and iv delineated potentially impacted areas we distinguished three phases of development of bedrock dammed lakes a a proglacial b a glacier detached and c a nonglacial phase the dynamics and also the susceptibility of a lake to glofs decrease substantially from a to c lakes in the stages a and b are less prominent in our study area compared to other glacierized high mountain regions leading us to the conclusion that i the current threat to the population by glofs is lower but ii the future development of emerging lakes has to be monitored carefully

embankment dam breach parameters and their uncertainties potential flood hazards that would be created by breached embankment dams need to be evaluated to select spillway design floods and to prepare emergency action plans the breaches are often modeled simply usually in the shape of a trapezoid that is defined by its final height base width or average width and side slopes along with the time needed for the opening to form completely data collected from 74 embankment dam failures were used to develop mathematical expressions for the expected values of the final width and side slope of a trapezoidal breach along with its formation time information is provided that allows variances of the predicted quantities to be calculated as well the findings of the statistical analysis were then applied in a monte carlo simulation to estimate the degree of uncertainty of predicted peak flows and water levels downstream from breached embankment dams

middle miocene to pleistocene sedimentary record of rift evolution in the southern albert rift uganda this study presents an almost complete middle miocene to pleistocene sequence of synrift sediments in the western branch of the east african rift the studied succession is exposed in several patches on an eastward tilted block between the northern tip of the rwenzori block and the eastern shoulder of the albert rift in this position it reaches a maximum thickness of 600 m of which 350 m have been logged systematically by analysing lithofacies and sediment architecture stratigraphic subdivision of the succession relies on published biostratigraphic data of endemic mollusc associations and their correlation across east africa the synrift sediments encountered are siliciclastics ranging from clay to coarse gravel with gypsum and ferrugineous interlayers or impregnations lithofacies and architectural analysis indicate alluvial plain delta plain nearshore delta front or lacustrine depositional environments based on the vertical stacking pattern prograding and retrograding trends of the depositional environments and climatic indicators e g conservation of feldspar gypsum and or iron hydroxide precipitation four evolutionary phases can be distinguished i a first phase between ca 14 5 and 10 0 ma is characterised by bedload dominated fluvial environment with massive sandy to gravelly bedforms feldspar rich sands rare iron impregnations and relatively low accommodation space this phase is interpreted as pre and early synrift sedimentation under a semiarid climate ii from ca 10 0 to 4 5 ma predominantly fine grained siliciclastics were deposited in a distal fluvial plain to lacustrine setting characterised by limited accommodation space fluctuation of thin beds dominance of clay and frequent iron impregnations point to a more humid climate with seasonality and weak tectonic activity iii during the third phase between 4 5 and 2 0 ma delta plain and nearshore deposits with frequent ferrugineous impregnations and rich mollusc associations occurred indicating a humid period with lake level highstands and accelerated subsidence iv during the final sedimentary interval between 2 0 and 1 5 ma gravel units reoccurred with less iron but more carbonate and gypsum impregnations and arkosic sandstones this phase recorded a general aridisation trend most probably caused by the upcoming rain barrier of the rwenzori mountains together with accelerated rift flank uplift and strong subsidence of the rift floor the results of this study are of particular importance for delineating key controls on sedimentation in the albert rift

east african rift system offset age and tectonic significance of the tanganyika rukwa malawi intracontinental transcurrent fault zone abstract the 1000 200 km tanganyika rukwa malawi fractures area is shown to be a right lateral intracontinental transform zone belonging to the east african rift system using the results carried out from complementary techniques remote sensing field structural analysis and k ar isotopic dating it appears that tectonics in this area have acted at different times the oldest being at 2000 1400 m y the youngest being still active today and are mainly due to the reactivation of nw se structures the area consists mainly of large nw se en echelon dextral transcurrent faults along which the southern tanganyika rukwa and northern malawi troughs are opening ne sw transverse faults showing a curved horizontal shape end these troughs axially eocene to recent volcanic activity is associated with the intersection of the northeastern main nw se transcurrent fracture the livingstone fault

uncertainty of predictions of embankment dam breach parameters risk assessment studies considering the failure of embankment dams often require the prediction of basic geometric and temporal parameters of a breach or the estimation of peak breach outflows many of the relations most commonly used to make these predictions were developed from statistical analyses of data collected from historic dam failures the prediction uncertainties of these methods are widely recognized to be very large but have never been specifically quantified this paper presents an analysis of the uncertainty of many of these breach parameter and peak flow prediction methods application of the methods and the uncertainty analysis are illustrated through a case study of a risk assessment recently performed by the bureau of reclamation for a large embankment dam in north dakota

springwater continuous monitoring in the l aquila area in concomitance with the april 2009 seismic swarm in central italy constraining factors to possible deep seated fluid emissions abstract a m l 5 8 earthquake rocked the l aquila area on april 6 2009 several aftershocks characterized by 5 l

rift nucleation rift propagation and the creation of basement micro plates within active rifts abstract in this contribution we study the dynamics of rift nucleation and the interaction of propagating rift segments we use the east african rift system ears as a case study with special emphasis on the albertine rift system situated within the western branch of the ears with the 5000 m high rwenzori horst a basement block that was captured by two rift segments fieldwork in the rwenzori mountains shows that the range is not only affected by range parallel faults but that major fault sets cut across the rwenzoris in order to understand these complex fault patterns and the dynamics of the process that leads to the capturing of basement blocks within the extending rift system we developed a two dimensional visco elasto plastic spring model the model shows that propagating rift faults commonly capture micro plates with shapes similar to the rwenzori mountains these micro plates rotate during successive rift opening in a clockwise or anti clockwise sense depending on the direction of the rift segment overstep a left lateral overstep as is the case for the albertine rift system produces a clockwise rotation of the associated micro plate indicating that the rwenzori mountains rotate clockwise during the rotation of the micro plate the local stress field at the rift segment tips is perturbed so that the rifts turn 70 to 90 and propagate towards each other to capture the plates completely this perturbed stress field produces an extensional fault set that is oriented almost parallel to the far field extension direction and explains the range cutting faults that we find in the rwenzori mountains the large scale geometry of the rift system seems to be strongly controlled by rigid cratons in the lithosphere leading to a curvature of the western branch of the ears and a sinistral wrench component in the lake albert rift north of the rwenzori mountains capturing of micro plates of various sizes within the rift system is a common phenomenon and leads to strong perturbations of the local stress field during micro plate rotation the resulting structures are normal and strike slip faults that cut through the micro plates and local reverse faults

model for predicting floods due to earthen dam breaching ii comparison with other methods and predictive use a sensitivity analysis of the model presented in the companion paper is made and on the basis of the results a criterion is proposed for the choice of values to assign to the side slopes of the breach in order to use the model for prediction moreover the sensitivity analysis shows that the outflow hydrograph and its peak value depend not only on the dam height and the stored volume but also on the vertical distribution of the water mass in the reservoir the model is compared with some previously published methods and the disadvantages limitations and errors that can be made using parametric models and predictive equations are pointed out finally easy to use equations interpolating the numerical results of the model are provided that predict not only the peak discharge but the whole outflow hydrograph for overtopping failures

isotopic constraints of vein carbonates on fluid sources and processes associated with the ongoing brittle deformation within the accretionary wedge of taiwan terra nova 22 251 256 2010 abstract the continuously distributed well preserved fracture filling carbonates were collected from the cores retrieved from the taiwan chelungpu fault drilling program between 400 and 2000 m depth for carbon and oxygen isotope analyses to constrain the fluid compositions and processes associated with brittle deformation within the accretionary wedge the isotope analyses of fracture filling carbonates yielded 18o values steadily increasing with depth the 13c values exhibited a pattern similar to that of 18o values at shallower depths but an opposite trend at greater depths such variations in the isotopic compositions could be best explained by a mixing of shallow meteoric water and deeply rooted fluid carrying isotopic signatures of various microbial processes the notable excursion of 18o values might infer a conduit for the lateral fluid transport along the high vein density zone overall the isotopic patterns preclude the substantial influence of early diagenesis and suggest pervasive fluid percolation through the fracture network

model for predicting floods due to earthen dam breaching i formulation and evaluation this paper proposes a dam breach model which predicts in a simple but physically based manner not only the peak discharge but the whole outflow hydrograph and breach development the following aspects are taken into account the geometry of the embankment the shape of the reservoir the hydraulic characteristics of the flow through the breach and its erosive capacity and the shape of the breach the model needs only one calibration parameter and can be easily applied to real cases the application of the model with a single value of the calibration parameter produced excellent results in the simulation of 12 historic earthfill dam failures with a discharge range covering three orders of magnitude

rate of diffuse carbon dioxide earth degassing estimated from carbon balance of regional aquifers the case of central apennine italy central italy is characterized by an anomalous flux of deeply derived co2 in the western tyrrhenian sector of central italy co2 degassing occurs mainly from focused emissions vents and strong diffuse degassing and thermal springs whereas in the eastern apennine area deep co2 is dissolved in cold groundwaters of regional aquifers hosted by mesozoic carbonate evaporite formations influx of deep co2 into 12 carbonate aquifers 12 500 km2 of the central apennine is computed through a carbon mass balance that couples aquifer geochemistry with isotopic and hydrogeological data mass balance calculations estimate that 6 5 1010 mol yr 1 of inorganic carbon are dissolved in the studied aquifers approximately 23 of this amount derives from biological sources active during the infiltration of the recharge waters 36 comes from carbonate dissolution while 41 is representative of deep carbon sources characterized by a common isotopic signature 13c 3 the calculated deep co2 influx rate ranges from 105 to 107 mol yr 1 km 2 increasing regionally from east to west in the study area

regional and temporal variations in co2 3he 3he 4he and δ13c along the north anatolian fault zone turkey abstract new he and c relative abundance isotope and concentration results from nine geothermal locations situated along an 800 km transect of the north anatolian fault zone nafz turkey that were monitored during the period november 2001 november 2004 are reported the geothermal waters were collected every 3 6 months to study possible links between temporal geochemical variations and seismic activity along the nafz at the nine sample locations the he isotope ratios range from 0 24 to 2 3 r a 13 c values range from 4 5 to 5 8 and co 2 3 he ratios range from 5 10 9 to 5 10 14 the following geochemical observations are noted 1 the highest 3 he 4 he ratios are found near the galatean volcanic region in the central section of the nafz 2 at each of the nine sample locations the 3 he 4 he ratios are generally constant however co 2 3 he ratios and he contents both show one order of magnitude variability and 13 c values show up to 4 variability and 3 at all locations except resadiye 13 c values show positive correlations with co 2 contents the results indicate that at least three processes are necessary to account for the geochemical variations 1 binary mixing between crustal and mantle derived volatiles can explain the general characteristics of 3 he 4 he ratios 13 c values and co 2 3 he ratios at the nine sample locations 2 preferential degassing of he from the geothermal waters is responsible for variations in co 2 3 he values and he contents at each sample location and 3 co 2 dissolution followed by calcite precipitation is responsible for variations in co 2 contents and 13 c values at most locations for each of the geochemical parameters anomalies are defined in the temporal record by values that fall outside two standard deviations of average values at each specific location geochemical anomalies that may be related to seismic activity are recorded on june 28 2004 at yalova where a m 4 2 earthquake occurred 43 days earlier at 15 km distance from the sample location and on april 7 2003 at efteni where a m 4 0 earthquake occurred 44 days later at a distance of 12 km at both locations the sampling periods containing geochemical anomalies were preceded by an increase in m 3 earthquakes occurring within 60 days and less than 40 km distance

case study of the big bay dam failure accuracy and comparison of breach predictions the big bay dam embankment failure occurred on march 12 2004 releasing 17 500 000 m3 14 200 acre ft of water in all 104 structures were documented as being damaged or destroyed as a result of this failure no human lives were lost this paper documents data gathered and analyses performed on the hydraulics of the failure high water levels from the failure were marked and measured a hec ras unsteady flow model was developed using observed breach geometry hec ras provided results that agreed with the measured high water marks from 0 02 to 0 90 m and 0 01 to 0 62 m with associated modeled flow depths ranging from 9 3 to 5 7 m from 30 to 19 ft a peak breach flow of 4 160 m3 s 147 000 ft3 s was predicted at the embankment breach peak flow prediction equations were found to substantially underpredict the peak flow indicated by hec ras for this failure hec ras modeling utilizing predicted breach geometry and formation time also underpredicted the peak flow but by a lesser amount the natio

geochemical monitoring of geothermal waters 2002 2004 along the north anatolian fault zone turkey spatial and temporal variations and relationship to seismic activity a total of nine geothermal fields located along an 800 km long e w transect of the north anatolian fault zone nafz turkey were monitored for three years 2002 2004 inclusive 3 sampling periods per year to investigate any possible relationship between seismic activity and temporal variations in the chemistry and isotope characteristics of waters in the fields the geothermal fields monitored in the study were from west to east yalova efteni bolu mudurnu seben kursunlu cankiri hamamozu gozlek and resadiye the chemical major anion cation contents and isotopic 18o 16o d h 3h compositions of hot and cold waters of the geothermal sites were determined in order to both characterize the chemical nature of the individual fields and identify possible temporal variations associated with localized seismic activity the geothermal waters associated with the nafz are dominantly na hco3 whereas the cold waters are of the ca hco3 type the oxygen and hydrogen isotope compositions reveal that the hot waters are meteoric in origin as are their cold water counterparts however the lower 18o d and 3h contents of the hot waters point to the fact that they are older than the cold waters and that their host aquifers are recharged from higher altitudes with virtually no input from recent post bomb precipitation although no major earthquakes e g with m 5 were recorded along the nafz during the course of the monitoring period variations in the chemical and isotopic compositions of some waters were observed indeed the timing of the chemical isotopic changes seems to correlate with the occurrence of seismic activity of moderate magnitude 3 m 5 close to the sampling sites in this respect cl 3h and ca seem to be the most sensitive tracers of seismically induced crustal perturbations and the yalova and efteni fields appear to be the key localities where the effects of seismic activity on the geothermal fluids are most pronounced over the monitoring period the present study has produced a baseline database for future studies directed at characterizing the effects of moderate major earthquakes on the composition of geothermal waters along the nafz future work involving longer monitoring periods with more frequent sampling intervals should lead to a better understanding of the underlying mechanism s producing the observed chemical and isotopic variations

back analysis of the draining process of the tangjiashan barrier lake abstractthis study attempts to use a dam breach model to reproduce the well monitored outflow hydrograph obtained during the dam breaching process of the tangjiashan barrier lake which was formed by a landslide triggered by the wenchuan earthquake on may 12 2008 in china the key parameters that affect the model results such as soil erosion and breach lateral enlargement are reviewed by using field measurements followed by extensive sensitivity studies the present paper advocates a hyperbolic model for soil erosion rate and a circular slip surface approach for breach lateral enlargement which contribute to more reliable model results the governing equations are solved using a numerical method that allows straightforward calculations coded in an excel 2007 spreadsheet this provides an easy transparent and robust tool that could enable practicing engineers to perform dam breach analyses with a comprehensive understanding of the uncertainties involved this back analysis confirms that the peak outf

the nahal oz reservoir dam break flood geomorphic impact on a small ephemeral loess channel in the semi arid negev desert israel abstract the nahal oz reservoir in the coastal semi arid southwestern israel was designed to enhance local irrigation of crops using reclaimed sewage water during the dry summer months on march 2001 part of the western dike of the reservoir was breached and generated a flow release of 3 5 106 m3 of secondary irrigation water that was channeled down the 1st order ephemeral loess stream nahal yare akh the consequent 12 hour flood surge with an estimated peak discharge of 1000 m3s 1 inflicted severe loess erosion agricultural property and infrastructural damage downstream 6 million post flood mapping documented the geomorphic response to the flood which included channel scour and widening along the initial 2 km downstream of the reservoir where a spillway channel was formed the increase in the cross sectional area was about 60 and had an estimated 170 000 m3 of sediment bed bank and floodplain erosion calculated maximum shear stress and stream power along this section are estimated at 300 nm 2 and 900 wm 2 respectively the peak discharge at the end of this segment was estimated at 800 m3s 1 indicating only minor attenuation along this segment two km downstream of the breach a wide braided fan indicated deposition of the eroded sediments at the end of this segment the floodwater diverged into several watercourses and inundated tilled agricultural fields and neighborhoods downstream 9 km from the reservoir the discharge attenuated to 100 m3s 1 slightly above bankfull further downstream and upon reaching the large shikma stream the flow was already very low this reduction in discharge is attributed to the anthropogenic infrastructure roads neighborhoods and agricultural fields and the large transmission losses typical of sandy ephemeral streams the study shows that channels within erodible materials respond to high peak discharges very locally erosional thresholds that severely incised the channel are only maintained for 2 km below the breached reservoir and as distance from the source area increases available energy is substantially reduced due to high transmission losses gentler valley gradients very wide shallow flow and the ability of the drainage network to accommodate large discharges consequently the geomorphic impact was limited to the first 2 6 km with only minor erosional or depositional evidence downstream the current natural flow regime has only minor impact on the newly formed channel geometry below the breached dam accordingly the channel geometry may be preserved for a relatively long time however channel recovery in this segment was rapid and within a few years all bare loess surfaces exposed during the flood have been covered by dense vegetation the analysis also shows that nahal oz reservoir s dam break flood transmission losses and flood attenuation rates were extreme in comparison to other case studies this artificial flood event in a desert environment offers a rare opportunity to quantify channel and bank erosion evolution processes during an extremely high magnitude flood within highly erodible fine sediment as well as to detect the recovery processes a few years later

direct estimate of the breach hydrograph of an overtopped earth dam abstractthe quantification of the breach hydrograph of an overtopped earth dam remains a challenge even in controlled laboratory conditions in this work the breach hydrograph is calculated as th

formulas for the peak discharge from breached earthfill dams abstractalthough advanced physically based models have been presented in the last years there is still much interest in equations for predicting the peak discharge indeed simple relations are very useful for technical purposes especially when rough calculations are acceptable this paper presents new equations for assessing the peak discharge of the flood hydrograph caused by the gradual erosion of earth dams the equations are obtained by a regression analysis carried out on the peak discharges provided by a physically based numerical model the approach proposed in this paper has the advantage of taking into account some parameters usually neglected by common best fit equations that have strong influence on the peak discharge in particular the equations discussed in this paper take into account the susceptibility to erosion of the dam the shape of the reservoir and the ratio of filling of the reservoir for failures caused by piping the usefulness of the equations is shown through a comparison w

experimental investigation of pressure load exerted on a downstream dam by dam break flow the failure of a natural or an artificial dam often leads to catastrophic flooding downstream studies have been conducted to investigate the mechanisms of single dam failure and the propagation of dam break flood wave however little attention has been paid to the cascade failure of two or more sequential dams in this article consequences of a dam break flood wave down a channel exerting pressure load on a downstream dam with different backwater effects were studied experimentally three typical flood patterns were observed for different downstream reservoir water depths high precision pressure sensors were employed to measure the pressure load at different heights on the dam changes of the maximum pressure load were measured as the bed slope and the upstream and downstream reservoir water depths varied an empirical formula was obtained by linear regression to predict the maximum pressure load additionally a sinusoidal attenuation function was introduced to describe the time evolution of pressure load exerted on the downstream dam and its parameters were determined using the measurement data in different cases

methods for predicting peak discharge of floods caused by failure of natural and constructed earthen dams floods from failures of natural and constructed dams constitute a widespread hazard to people and property expeditious means of assessing flood hazards are necessary particularly in the case of natural dams which may form suddenly and unexpectedly we revise statistical relations derived from data for past constructed and natural dam failures between peak discharge qp and water volume released v0 or drop in lake level d but assert that such relations even when cast into a dimensionless form are of limited utility because they fail to portray the effect of breach formation rate we then analyze a simple physically based model of dam breach formation to show that the hydrograph at the breach depends primarily on a dimensionless parameter kv0 gl 2d7 2 where k is the mean erosion rate of the breach and g is acceleration due to gravity the functional relationship between qp and takes asymptotically distinct forms depending on whether 1 relatively slow breach formation or small lake volume or 1 relatively fast breach formation or large lake volume theoretical predictions agree well with data from dam failures for which k and thus can be estimated the theory thus provides a rapid means of predicting the plausible range of values of peak discharge at the breach in an earthen dam as long as the impounded water volume and the water depth at the dam face can be estimated

controls of sedimentation in the malawi rift valley central africa abstract the malawi rift is the southermost classic rift valley trough in the cenozoic african rift valley system much of its floor is flooded by lake malawi which is approximately 570 km long 60 km across and up to 500 m deep this rift basin is a potentially useful analogue of many economically important ancient sedimentary troughs rift valley structures are extremely important in controlling both the distribution of sediments in the basin as a whole and also details of sedimentation on a local scale on the basin wide scale an important association between the type of rift boundary structure and amount of rift floor subsidence is recognised this association appears to apply to several section of the african rift system pre rift topography is major control on the position of major rivers and their deltas or turbidite fans along the basin margin the area of pre rift drainage network captured in the course of rift movements is a significant factor in the hydrologic budget of the basin climate is however the dominant control on the hydrologic budget and at present the basin is flooded to overflow level prevailing winds are important in beach ridge and back beach aeolian dune development climatic conditions produce thermal stratification of the lake with an oxic epilimnion down to 250 m depth overlying an anoxic hypolimnion the oxic bottom waters in the shallower parts of the lake appear to promote iron precipitation in the sediments