mechanics of upward propagation of cover collapse sinkholes cover collapse sinkholes occur by failure of the walls of a soil void above cavernous bedrock i examine conditions for failure in compression by crack propagation and coalescence and for failure by sloughing in which pore water pressure produces a net tension perpendicular to the wall of the void compressive failure without relaxation of stress does not explain observed long term stability of thick soils nor failures in thin residual soils if stress relaxation occurs with compressive failure soil voids tend to stabilize and sinkholes are not predicted sloughing failure is not predicted for steady state pore pressure fields even for a perched water table at the surface over a drained void transient pore pressure conditions that could produce sloughing may result from 1 rapid drawdown causing soil consolidation and transient high pore pressure gradients 2 approach of a wetting front in unsaturated soil with high permeability behind the front 3 dissolution of air from bubbles in the soil and exsolution near the void producing a low permeability zone near the void

comment on gas hydrate growth methane transport and chloride enrichment at the southern summit of hydrate ridge cascadia margin off oregon by torres et al earth planet sci lett 226 2004 225 241 formation evolution and destruction of natural gas hydrate systems in marine environments have been extensively discussed since the first gas hydrate samples were recovered n30 yr ago 1 the origin and sources of hydrate bound gases 2 and waters 3 the distribution of phases within and below the gas hydrate stability zone ghsz 4 mechanisms of crystal growth 5 and gas hydrate concentration in pore space 6 are among the most debated issues recent field studies facilitated by ocean drilling program odp 7 8 and dedicated government programs 9 10 provided a wealth of geological geophysical and geochemical information from hydrate bearing locations integrated interpretation of various datasets holds a great potential to advance our understanding of gas hydrate systems and to constrain speculations about the role of gas hydrates as a potential energy source 11 and a component of the global carbon cycle 12

prediction of undrained sinkhole collapse sinkholes are surface depressions or shafts resulting from the collapse of a submerged cavity in soil the cavities that lead to sinkholes form as a result of underlying geology in limestone areas or as a result of human activity such as mining or leakage from a sewer the formation of sinkholes is often sudden and can lead to extensive damage and loss of life especially in urban areas much of the literature on the subject of sinkhole formation is empirical in nature often being associated with specific locations this paper presents the results of a study using numerical modeling of the undrained stability of the submerged cavities that lead to sinkhole formation finite element limit analysis techniques using programs developed at the university of newcastle are used to obtain upper and lower bound values of a suitable load parameter which bracket the exact solution the results are compared to analytical solutions both from literature and derived independently

estimating thermal inflow to el chichon crater lake using the energy budget chemical and isotope balance approaches abstract el chichon crater lake appeared immediately after the 1982 catastrophic eruption in a newly formed 1 km wide explosive crater during the first 2 years after the eruption the lake transformed from hot and ultra acidic caused by dissolution of magmatic gases to a warm and less acidic lake due to a rapid magmatic to hydrothermal transition input of hydrothermal fluids and oxidation of h 2 s to sulfate chemical composition of the lake water and other thermal fluids discharging in the crater stable isotope composition d and 18 o of lake water gas condensates and thermal waters collected in 1995 2006 were used for the mass balance calculations cl so 4 and isotopic composition of the thermal flux from the crater floor the calculated fluxes of thermal fluid by different mass balance approaches become of the same order of magnitude as those derived from the energy budget model if values of 1 9 and 2 mmol mol are taken for the catchment coefficient and the average h 2 s concentration in the hydrothermal vapors respectively the total heat power from the crater is estimated to be between 35 and 60 mw and the co 2 flux is not higher than 150 t day or 200 gm 2 day 1

a kinetic model for the methane hydrate precipitated from venting gas at cold seep sites at hydrate ridge cascadia margin oregon we develop a kinetic model for hydrate crystallization from methane gas venting through shallow sediments at hydrate ridge on the cascadia margin of oregon that predicts how pore water chlorinity temperature and crystallized hydrate evolve after the onset of steady venting predictions are compared to observations at ocean drilling program site 1249 in the preferred model calculated gas hydrate saturation and chloride concentrations reach those observed at depths less than 20m below seafloor bsf under the southern summit of hydrate ridge in similar to 650years and the vertical water flux must be less than 50kg m 2 yr hydrate accumulates more slowly between 20m bsf and the base of the hydrate stability zone where there is no free gas accumulating to observed levels of a few volume percent of hydrate in 10 5 to 10 6 years depending on the water flux that is assumed through this zone this dichotomy means that the presently observed gas venting must have been diverted to this area similar to 650years ago or be episodic and infrequent if the gas venting for the last 650years has been as observed today the latent heat of hydrate precipitation in the upper 20m of sediments would have caused the temperature to increase similar to 0 8 degrees c at similar to 20m bsf and similar to 0 2 degrees c at similar to 100m bsf this would have caused a similar to 5m rise in the elevation of the base of hydrate stability zone and decreased the rate of hydrate crystallization from 1 5kg ch4 m 2 yr 650years ago to 0 7kg ch4 m 2 yr today

sinkhole formation mechanisms and geostatistical based prediction analysis in a mantled karst terrain abstract efforts to evaluate sinkhole formation and quantify the controlling factors are hindered by the lack of historical observations or coarse resolution datasets in many areas we applied recent advances in gis based sinkhole mapping and spatial statistics to comprehensively investigate the factors controlling sinkhole formation in the mantled karst setting of dougherty county georgia sinkholes form at varying spatial and temporal scales within the test site a three stage methodology was conducted firstly 275 sinkholes that formed or were enlarged between 1999 and 2011 were detected by comparing the results of sinkhole inventories derived from two dems acquired in 1999 and 2011 additionally a lidar dem 1 m resolution was used to gather a spatially detailed sinkhole inventory of 3412 sinkholes the sinkhole inventory data was converted into sinkhole density maps for subsequent analyses ordinary least squares ols and geographically weighted regression gwr spatial statistical models were applied to quantify the impact of controlling factors on sinkhole density controlling factors included geologic hydrologic anthropogenic hydrogeologic and geomorphologic variables for the two sinkhole inventory datasets analyzed overburden thickness aquifer fluctuations and proximity to fractures streams and wetlands were the most influential controlling factors on sinkhole formation gwr p values

halogen and 129i systematics in gas hydrate fields at the northern cascadia margin iodp expedition 311 insights from numerical modeling we measured halogen concentrations and i 129 i ratios in five drilling sites of integrated ocean drilling program expedition 311 offshore vancouver island canada in order to identify potential sources of fluids and methane in gas hydrate fields iodine is dominated by organic decomposition and transports with fluids in reducing environments and the presence of the cosmogenic radioisotope i 129 t 1 2 15 7 ma allows the age determination of organic sources for iodine here we report halogen concentrations in 135 pore water samples i concentrations in 48 sediment samples and i 129 i ratios measured in a subset of 20 pore water samples most i 129 i ratios fall into a range around 500 x 10 15 corresponding to a minimum age of 25 ma and the lowest ratio of 188 x 10 15 t min 47 ma was observed at 208 m below sea floor mbsf in site 1326 these ages are considerably older than that of the local sediments in the gas hydrate fields and that of the subducting sediments on the juan de fuca plate indicating that old accreted sediments in the accretionary wedge contribute a significant amount of iodide and by association of methane to the gas hydrate occurrences a geochemical transport reaction model was applied to simulate the advection of deeply sourced fluids and the release of iodide bromide and ammonia in the host sediments due to organic matter degradation the model was first tested with data from two well studied areas ocean drilling program site 1230 peru margin and site 1245 hydrate ridge the model results for the expedition 311 sites indicate that the in situ release of young iodine is relatively minor in comparison to the contribution of migrating fluids carrying large amounts of old iodine from deep sources the comparison between the sites demonstrates that the total organic content has a strong effect on the rate of in situ iodine release and that lateral flows along fractures can have a significant influence on pore water chemistry especially at the cascadia margin the iodine results indicate that mobilization and transport of methane from sources in the upper plate of active margins is an important process which can also play a substantial role in the formation of gas hydrate fields

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

preferential mode of gas invasion in sediments grain scale mechanistic model of coupled multiphase fluid flow and sediment mechanics 1 we present a discrete element model for simulating at the grain scale gas migration in brine saturated deformable media we rigorously account for the presence of two fluids in the pore space by incorporating forces on grains due to pore fluid pressures and surface tension between fluids this model which couples multiphase fluid flow with sediment mechanics permits investigation of the upward migration of gas through a brine filled sediment column we elucidate the ways in which gas migration may take place 1 by capillary invasion in a rigid like medium and 2 by initiation and propagation of a fracture we find that grain size is the main factor controlling the mode of gas transport in the sediment and we show that coarse grain sediments favor capillary invasion whereas fracturing dominates in fine grain media the results have important implications for understanding vent sites and pockmarks in the ocean floor deep subseabed storage of carbon dioxide and gas hydrate accumulations in ocean sediments and permafrost regions our results predict that in fine sediments hydrate will likely form in veins following a fracture network pattern and the hydrate concentration will likely be quite low in coarse sediments the buoyant methane gas is likely to invade the pore space more uniformly in a process akin to invasion percolation and the overall pore occupancy is likely to be much higher than for a fracture dominated regime these implications are consistent with laboratory experiments and field observations of methane hydrates in natural systems

distribution and height of methane bubble plumes on the cascadia margin characterized by acoustic imaging submersible investigations of the cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence acoustic profiles of these bubble plumes in the water column in the vicinity of hydrate ridge offshore oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column the gas vent sites remained active over the span of two years but varied dramatically on time scales of a few hours all plumes emanated from local topographic highs near the summit of ridge structures the acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m independent of the seafloor depth this coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution the upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

a new non archie model for pore structure numerical experiments using digital rock models summary tortuosity is a key parameter for investigating the pore structure of sedimentary rock the conventional model for calculating the tortuosity is derived from archie s law which is only valid for one conductive phase contained in a porous rock however there have been increasingly cases to show the non archie phenomenon in instances where the rock matrix has extra conductive phases such as surface conductivity caused by the electrical double layer therefore such model may be inapplicable in these cases and in calculations involving partial melting we investigated the relation between formation factor and porosity f o ver aw ide range of porosities by the lattice gas automata method lga with the electrical double layer the digital rock samples were constructed by packing up solid grains with different shapes and size distribution as previously measured in the laboratory on real rock specimens our purpose was to identify the origin of non archie behaviour of the f relation sometimes observed the simulations show that archie s law may only be an approximation of the f relation in a high porosity range based on our lga simulations and additional laboratory experimental data we developed new equations for non archie f relation and tortuosity potentially useful for improving the evaluation of pore structure

acid alteration in the fumarolic environment of usu volcano hokkaido japan abstract the last eruptive activity of usu volcano in 1977 78 involved the development of high temperature 550 710 c fumaroles the gases emitted were h2o rich 95 99 mol with cl s 0 05 0 9 f cl 0 3 0 2 and with rh 2 5 close to the rock buffer feo feo1 5 cooling and oxidation of the high temperature gases resulted in the formation of acidic condensates ph 1 6 that interacted with the wall rock complete leaching of the cations ca na mg al and fe from the primary minerals and matrix glass occurred leaving in place only silica these mobilized cations precipitated as secondary minerals from acidic fluids that circulated in microcracks sem study shows mineral associations reflecting increasing fluid oxidation a al fluorides such as ralstonite namgalf6 h2o pyrite and anhydrite gypsum b an al hydroxide hematite gypsum and amorphous silica or cristobalite c al sulfates such as hydronium alunite h3o al3 so4 2 oh 6 alunite kal3 so4 2 oh 6 amorphous silica cristobalite hematite and anhydrite gypsum d al sulfates al fluorides amorphous silica cristobalite pyrite and anhydrite gypsum a ti oxide a fe mg sulfate and barite are present in minor amounts clay minerals are absent from the observed assemblages primary phenocrysts and matrix glass undergo a complete transformation to silica enriched in fluorine 1 7 wt this fluorine enrichment in the silicified parts of silicates and in silica incrustations suggests that f may play a role in silica mobilization modeling of the cooling of the high temperature gases was performed with the program gasworks the calculations suggest that 66 of the total sulfur from the gases may be lost by deposition as native sulfur at temperatures below 160 c thermochemical modeling of condensate rock interaction using chiller indicates that the cooling of gases was the source of the altering solutions oxidation by atmospheric o2 of the sulfur reduced species in the volcanic gas condensates resulted in their extreme acidification condensate rock interactions produce supersaturation with respect to the following mineral assemblages at 95 c 1 pyrite native sulfur cristobalite barite anhydrite diaspore log m h 2 s aq 2 32 2 cristobalite anhydrite hematite alunite diaspore log m h 2 s aq gypsum replaces anhydrite at t 25 c the calculated mineral assemblages are in agreement with those observed in the field

first study of the heat and gas budget for sirung volcano indonesia with at least four eruptions over the last 20 years sirung is currently one of the more active volcanoes in indonesia however due to its remoteness very little is known about the volcano and its hyperacid crater lake we report here on the first measurements of gas and heat emissions from the volcano notable is the substantial heat loss from the crater lake surface amounting to 220 mw in addition 17 gg of so2 representing 0 8 of indonesian volcanic so2 contribution into the atmosphere 11 gg of h2s 17 gg of co2 and 550 gg of h2o are discharged into the atmosphere from the volcano annually the volatiles degassed from sirung magmas are subjected to hydrothermal fluid rock interactions and sulfide depositions initiated by the disproportionation of so2 these processes lead to distinct gas compositions and changing lake water chemistry in the sub craters and the main crater lake however the occurrence of so2 rich fluids and strong gas flux appear to highlight a rapid fluid transfer to surface avoiding re equilibration with lower temperature rocks fluids in the conduits

the influence of urbanization of sinkhole development in central pennsylvania the karsted limestone valleys of central pennsylvania contain two populations of sinkholes solution sinkholes occur in the champlainian limestone units along the margins of the valleys solution sinkholes are permanent parts of the landscape and although a nuisance to construction do not present other problems the second population is the suffosional or soil piping sinkholes these occur on all carbonate rock units including the beekmantown and gatesburg dolomites that comprise the two principal carbonate aquifers in the valley suffosional sinkholes are the principal land use hazard suffosional sinkholes are transient phonomena they occur naturally but are exacerbated by runoff modifications that accompany urbanization suffosional sinkholes are typically 1 5 2 5 m in diameter depending on soil thickness and soil type the vertical transport of soil to form the void space and soil arch that are the precursors to sinkhole collapse is through solutionally widened fractures and cross joints and less often through large vertical openings in the bedrock the limited solution development on the dolomite bedrock combined with soil thickness seldom greater than 2 m limits the size of the sinkholes all aspects of suffosional sinkhole development are shallow processes transport piping void and arch formation and subsequent collapse take place usually less than 10 m below the land surface factors exacerbating sinkhole development include pavement street and roof runoff which accelerates soil transport such seemingly minor activities as replacing high grass and brush with mowed grass is observed to accelerate sinkhole development dewatering of the aquifer is not a major factor in this region

sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids implications for the δ 34 s variations of dissolved bisulfate and elemental sulfur from active crater lakes sulfur isotope effects during the so 2 disproportionation reaction to form elemental sulfur 3so 2 3h 2 o 2hso 4 s 2h at 200 330 c and saturated water vapor pressures were experimentally determined initially a large kinetic isotopic fractionation takes place between hso 4 and s followed by a slow approach to equilibrium the equilibrium fractionation factors estimated from the longest run results are expressed by 1000 in hso 4 s 6 21 10 6 t 2 3 62 the rates at which the initial kinetic fractionation factors approach the equilibrium ones were evaluated at the experimental conditions 34 s values of hso 4 and elemental sulfur were examined for active crater lakes including noboribetsu and niseko hokkaido japan khloridnoe bannoe and maly semiachik kamchatka poas costa rica ruapehu new zealand and kawah ijen and keli mutu indonesia hso4 s values are 28 for keli mutu 26 o for kawah ijen 24 c for ruapehu 23 for poas 22 for maly semiachik 21 for yugama 13 for bannoe 9 for niseko 4 o for khloridonoe and 0 for noboribetsu in the decreasing order the so 2 disproportionation reaction in the magmatic hydrothermal system below crater lakes where magmatic gases condense is responsible for high hso4 s values whereas contribution of hso 4 produced through bacterial oxidation of reduced sulfur becomes progressively dominant for lakes with lower hso4 s values currently noboribetsu crater lake contains no hso 4 of magmatic origin a 40 year period observation of 34 s hso4 and 34 s s values at yugama indicated that the isotopic variations reflect changes in the supply rate of so 2 to the magmatic hydrothermal system this implies a possibility of volcano monitoring by continuous observation of 34 s hso4 values the 18 o values of hso 4 and lake water from the studied lakes covary indicating oxygen isotopic equilibration between them the covariance gives strong evidence that lake water circulates through the sublimnic zone at temperatures of 140 30 c

subsidence rates and urban damages in alluvial dolines of the central ebro basin ne spain in the central ebro basin alluvial dolines develop on quaternary materials overlying neogene evaporites this process is very active analysing aerial photographs of different years important differences can be observed since the 1970s when the urbanisation of the area took place karst processes have damaged many buildings and infrastructures from the dates of construction and the repair of a number of buildings and pavements we calculate subsidence rates 12 120 mm year moreover we decided to monitor for around 4 years three dolines developed on urban areas to determine their subsidence behaviour a water level device with an error of 2 3 mm was utilised for this purpose the subsidence rates so obtained are 64 5 39 and 21 mm year which fit with the previous data from repaired zones

volcano hydrothermal system and activity of sirung volcano pantar island indonesia abstract sirung is a frequently active volcano located in the remote parts of western timor indonesia sirung has a crater with several hydrothermal features including a crater lake we present a timeseries of satellite images of the lake and chemical and isotope data from the hyperacid hydrothermal system the fluids sampled in the crater present the typical features of hyperacidic systems with high tds low ph and 34s h s o 4 34s s 0 among the highest for such lakes the cations concentrations are predominantly controlled by the precipitation of alunite jarosite silica phases native sulfur and pyrite which dominate the shallow portions of the hydrothermal system these minerals may control shallow sealing processes thought to trigger phreatic eruptions elsewhere sparse mg cl and so4 cl ratios and lake parameters derived from satellite images suggest gradual increase in heat and gas flux most likely so2 rich prior to the 2012 phreatic eruption an acidic river was sampled 8 km far from the crater and is genetically linked with the fluids rising toward the active crater this river would therefore be a relevant target for future remote monitoring purposes finally several wells and springs largely exceeded the world health organization toxicity limits in total arsenic and fluoride

gas hydrate systems at hydrate ridge offshore oregon inferred from molecular and isotopic properties of hydrate bound and void gases abstract we report and discuss molecular and isotopic properties of hydrate bound gases from 55 samples and void gases from 494 samples collected during ocean drilling program odp leg 204 at hydrate ridge offshore oregon gas hydrates appear to crystallize in sediments from two end member gas sources deep allochthonous and in situ as mixtures of different proportions in an area of high gas flux at the southern summit of the ridge sites 1248 1250 shallow 0 40 m below the seafloor mbsf gas hydrates are composed of mainly allochthonous mixed microbial and thermogenic methane and a small portion of thermogenic c2 gases which migrated vertically and laterally from as deep as 2 to 2 5 km depths in contrast deep 50 105 mbsf gas hydrates at the southern summit sites 1248 and 1250 and on the flanks of the ridge sites 1244 1247 crystallize mainly from microbial methane and ethane generated dominantly in situ a small contribution of allochthonous gas may also be present at sites where geologic and tectonic settings favor focused vertical gas migration from greater depth e g sites 1244 and 1245 non hydrocarbon gases such as co2 and h2s are not abundant in sampled hydrates the new gas geochemical data are inconsistent with earlier models suggesting that seafloor gas hydrates at hydrate ridge formed from gas derived from decomposition of deeper and older gas hydrates gas hydrate formation at the southern summit is explained by a model in which gas migrated from deep sediments and perhaps was trapped by a gas hydrate seal at the base of the gas hydrate stability zone ghsz free gas migrated into the ghsz when the overpressure in gas column exceeded sealing capacity of overlaying sediments and precipitated as gas hydrate mainly within shallow sediments the mushroom like 3d shape of gas hydrate accumulation at the summit is possibly defined by the gas diffusion aureole surrounding the main migration conduit the decrease of gas solubility in shallow sediment and refocusing of gas by carbonate and gas hydrate seals near the seafloor to the crest of the local anticline structure

naturally acid waters from copahue volcano argentina volcanic acid sulfate chloride brines form through absorption of volcanic vapors in shallow reservoirs of meteoric water reaction with surrounding volcanic rocks leads to partial neutralization of the fluids and precipitation of secondary minerals chemical data of such acid waters from copahue volcano argentina covering 8 years of observations show evidence for changes in composition related to water rock interaction at depth prior to emergence of the fluids at the surface the chemical composition changed dramatically during the 2000 eruption of copahue with enhanced concentrations and fluxes of mg na fe and al followed in 2001 by rapidly declining concentrations and element fluxes the subsequent 5 years saw more variable element ratios and strong depletions in k and al most incompatible elements are released from the rock matrix stochiometrically whereas some elements are enriched through vapor input from the magma as pb zn most fluids have lree enrichments relative to the rock matrix but during periods of new magma intrusion the lree enrichment decreases as does the magnitude of the negative eu anomaly in the fluids these observations are interpreted assuming early dissolution of plagioclase olivine and volcanic glass that occurs during intrusion of new magma into the hydrothermal system the high field strength elements are virtually immobile even in these hot acid fluids with nb and ta more so than hf and zr the mobility of u and th in these fluids is comparable at variance with th behavior in neutral fluids the local rivers and lakes of copahue are fertilized by volcanic dissolved p and most surface waters with ph 3 have high levels of as the acid fluids from copahue may be surficial analogs for deep subduction fluids that evolve below zones of arc magma generation as well as for early mars environments that are thought to have had large acid lakes

geochemistry of the magmatic hydrothermal system of kawah ijen volcano east java indonesia samples from kawah ijen crater lake spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis an extremely low ph 0 3 lake contains so 4 cl waters produced during absorption of magmatic volatiles into shallow ground water the acidic waters dissolve the rock isochemically to produce immature solutions the strong d and 18 o enrichment of the lake is mainly due to enhanced evaporation at elevated temperature but involvement of a magmatic component with heavy isotopic ratios also modifies the lake d and 18 o content the large so4 s d 23 8 26 4 measured in the lake suggest that dissolved so 4 forms during disproportionation of magmatic so 2 in the hydrothermal conduit at temperatures of 250 280 c the lake 18 o so4 and 18 o h2o values may reflect equilibration during subsurface circulation of the water at temperatures near 150 c significant variations in the lake s bulk composition from 1990 to 1996 were not detected however we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased so 2 rich gas input to the lake system thermal springs at kawah ijen consist of acidic so 4 cl waters on the lakeshore and neutral ph hco 3 so 4 cl na waters in blawan village 17 km from the crater the cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock the so 4 cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic so 4 cl water and ground water the lakeshore fumarole discharges t 170 245 c have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur the apparent equilibrium temperature of the gas is 260 c the proportions of the oxidized so 2 dominated magmatic vapor anti of the reduced h 2 s dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996 this may be the result of interaction of so 2 bearing magmatic vapors with the summit acidic hydrothermal reservoir this idea is supported by the lower h 2 s so 2 ratio deduced for the gas producing the so 4 cl reservoir feeding the lake compared with that observed in the subaerial gas discharges the condensing gas may have equilibrated in a liquid vapor zone at about 350 c elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor the sediments were precipitated in the past during inorganic oxidation of h 2 s in the lake water this process was not continuous but was interrupted by periods of massive silica poorly crystallized precipitation similar to the present day lake conditions we suggest that the factor controlling the type of deposition is related to whether h 2 s or silica rich volcanic discharges enter the lake this could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater quenched liquid sulfur products show 34 s values similar to those found in the banded deposits suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom

estimation of the global amount of submarine gas hydrates formed via microbial methane formation based on numerical reaction transport modeling and a novel parameterization of holocene sedimentation this study provides new estimates for the global offshore methane hydrate inventory formed due to microbial ch4 production under quaternary and holocene boundary conditions a multi 1d model for particular organic carbon poc degradation gas hydrate formation and dissolution is presented the novel reaction transport model contains an open three phase system of two solid compounds organic carbon gas hydrates three dissolved species methane sulfates inorganic carbon and one gaseous phase free methane the model computes time resolved concentration profiles for all compounds by accounting for chemical reactions as well as diffusive and advective transport processes the reaction module builds upon a new kinetic model of poc degradation which considers a down core decrease in reactivity of organic matter various chemical reactions such as organic carbon decay anaerobic oxidation of methane methanogenesis and sulfate reduction are resolved using appropriate kinetic rate laws and constants gas hydrates and free gas form if the concentration of dissolved methane exceeds the pressure temperature and salinity dependent solubility limits of hydrates and or free gas with a rate given by kinetic parameters global input grids have been compiled from a variety of oceanographic geological and geophysical data sets including a new parameterization of sedimentation rates in terms of water depth we find prominent gas hydrate provinces offshore central america where sediments are rich in organic carbon and in the arctic ocean where low bottom water temperatures stabilize methane hydrates the world s total gas hydrate inventory is estimated at 0 82 x 10sup13 m3 2 10 x 10sup15 m3 ch4 at stp conditions or equivalently 4 18 995 gt of methane carbon the first value refers to present day conditions estimated using the relatively low holocene sedimentation rates the second value corresponds to a scenario of higher quaternary sedimentation rates along continental margins our results clearly show that in situ poc degradation is at present not an efficient hydrate forming process significant hydrate deposits in marine settings are more likely to have formed at times of higher sedimentation during the quaternary or as a consequence of upward fluid transport at continental margins

investigating crater lake warming using aster thermal imagery case studies at ruapehu poas kawah ijen and copahue volcanoes abstract a two channel or split window algorithm designed to correct for atmospheric conditions was applied to thermal images taken by the advanced spaceborne thermal emission and reflection radiometer aster of lake yugama on kusatsu shirane volcano in japan in order to measure the temperature of its crater lake these temperature calculations were validated using lake water temperatures that were collected on the ground overall the agreement between the temperatures calculated using the split window method and ground truth is quite good typically 1 5 c for cloud free images data from fieldwork undertaken in the summer of 2004 at kusatsu shirane allow a comparison of ground truth data with the radiant temperatures measured using aster imagery further images were analyzed of ruapehu poas kawah ijen and copahue volcanoes to acquire time series of lake temperatures a total of 64 images of these 4 volcanoes covering a wide range of geographical locations and climates were analyzed results of the split window algorithm applied to aster images are reliable for monitoring thermal changes in active volcanic lakes these temperature data when considered in conjunction with traditional volcano monitoring techniques lead to a better understanding of whether and how thermal changes in crater lakes aid in eruption forecasting

stability charts for the collapse of residual soil in karst collapse of the residual soil over bedrock cavities often occurs during construction in karst terrain particularly when the thickness of the residuum is reduced during excavation even if an estimate of the strength of the residual soil is known uncertainty with respect to the size geometry of the subterranean voids makes a detailed analysis difficult and straightforward methods to check the stability are needed in this study numerical analyses were performed to develop a stability chart expressed in terms of a dimensionless stability number and the geometry of a potential void in the residual soil the stability charts include the effect of friction angle and are also developed to allow the investigation of the effect of the inverted strength profile typically observed in karst terrain such stability numbers may be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters

the role of hydrogeology in solution subsidence development and its environmental impacts a case study for sazlica nigde turkey solution subsidence and other types of collapse failures developed in the vicinity of sazlica have been a major source of environmental problems such as groundwater pollution soil erosion and foundation failures extensive pumping of water from the lake dipsiz during irrigation seasons creates landslide developments at the shores of the lake five stages of landslide development were observed in the unconsolidated soils around lake dipsiz bowl shaped solution subsidence features with depths from 1 to 3 m and diameters between 1 and 60 m were formed due to excess pumping and recharge and discharge features of unconfined aquifer the pumping activities must be controlled to prevent further environmental problems lake dipsiz and other subsidence developments are the groundwater exposure areas highly vulnerable to contamination the proposed remedies for overcoming the environmental problems are the establishment of conservation areas around such natural features ceasing the removal of top soil controlling the urbanization and keeping the livestock farming away from the areas susceptible to pollution

the sirung volcanic boiling spring an extreme chloride rich acid brine on pantar lesser sunda islands indonesia abstract the sirung volcano with a history of phreatomagmatic outbreaks has its present active center within a 1000 m wide subsidence crater the sirung crater lake scl has 15 g l 1 cl and 19 g l 1 so4 ph 0 75 temperature 40 c a highly saline brine sirung boiling spring sbs boils to the surface beside the lake it contains 116 g l 1 cl ph 1 4 chemical geothermometers indicate a reservoir temperature of 240 c the maximum depth of this reservoir is estimated to be 400 m the stable isotope composition is d 12 and 18o 5 0 to 6 0 tritium in the sbs is 0 0 tu in the scl 4 6 tu evidence against invading seawater as a source is the negative d value in addition to the six times higher cl concentration of the sbs evaporites are rejected as a source of the cl because of the geologic setting the average cl h 2 o ratio in sirung volcanic glasses as estimated by microprobe is very close to the cl h 2 o ratio of 0 047 for the sbs the zero tritium level in the sbs its high cl concentration and the acid character are other evidences for magmatic water as source for the sbs the acid sbs is poor in sulphur which may have been precipitated at depth as sulphides theories on porphyry cu formation in volcanic arc environments invoke highly saline brines as the transporting agent the acid saline brines from the sirung and white island new zealand craters and cl rich crater lakes associated with andesitic volcanism in subduction zones indicate that such fluids occur more frequently at the surface than has been possibly realized hitherto

source processes of the thermal waters from the phlegraean fields naples italy by means of the study of selected minor and trace elements distribution abstract the geochemical characteristics of hydrothermal waters from the phlegraean fields p f naples italy were analysed for minor and trace elements selectively mobilised in hydrothermal systems such as b f hg as pb and tl the water samples collected from a shallow aquifer likely to be fed by deeper fluids showed various geochemical features resulting from the mixing of three components 1 surface waters of meteoric origin 2 hot deep waters deriving from water rock interaction and including deep waters of marine origin 3 magmatic fluids rising from the local magma chamber lying a few kilometres below the town of pozzuoli this setting although very complex provides a reliable means of studying the distribution of the investigated trace elements in particular within the phlegraean area high contents of b 0 1 48 mg l f 0 5 8 mg l as 16 6050 g l and hg 0 7 232 g l were observed the levels of thallium in the springs close to solfatara about 7 g l were in line with those normally recorded in hydrothermal areas whereas high levels of this element up to 23 3 g l were identified in other wells of the study area lead 1 3 to 29 1 g l appears to be anomalous with respect to its normal content in groundwater about 1 g l owing to the presence of high density brines at depth which enhance the solubility of pb in volcanic rocks under hydrothermal conditions the distribution of the investigated trace elements in the phlegraean fields thermal area is probably related to the different ascent pathways of the fluids clearly apart from the influence exerted by anomalous thermal conditions each element shows a different behaviour depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values which determine ion partitioning in gaseous phases based on geochemical evidences and on the distribution of minor and trace elements the source processes of the investigated hydrothermal waters were defined five main groups were identified 1 acid sulphate waters resulting from mixing of meteoric water with magmatic gases mainly h 2 s 2 high sulphate chloride waters from a deep reservoir located in the major upflow zone 3 waters associated with significant degassing of magmatic co 2 4 waters from a deep geothermal neutral chloride reservoir resulting from heating of marine water modified by water rock interaction processes 5 cold waters from the inner area influenced by low temperature water rock interaction processes

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

appearance and preservation of natural gas hydrate from hydrate ridge sampled during odp leg 204 drilling abstract the state of preservation of natural gas hydrate samples recovered from 6 sites drilled during odp leg 204 at southern summit of hydrate ridge oregon margin has been investigated by x ray diffraction xrd and cryo scanning electron microscopy cryo sem techniques a detailed characterization of the state of decomposition of gas hydrates is necessary since no pressurized autoclave tools were used for sampling and partial dissociation must have occurred during recovery prior to the quench and storage in liquid nitrogen samples from 16 distinct horizons have been investigated by synchrotron x ray diffraction measurements at hasylab hamburg a full profile fitting analysis rietveld method of synchrotron xrd data provides quantitative phase determinations of the major sample constituents such as gas hydrate structure i si hexagonal ice ih and quartz the ice content ih in each sample is related to frozen water composed of both original existing pore water and the water from decomposed hydrates hydrate contents as measured by diffraction vary between 0 and 68 wt in the samples we measured samples with low hydrate content usually show micro structural features in cryo sem ascribed to extensive decomposition comparing the appearance of hydrates at different scales the grade of preservation seems to be primarily correlated with the contiguous volume of the original existing hydrate the dissociation front appears to be indicated by micrometer sized pores in a dense ice matrix

remarkable geochemical changes and degassing at voui crater lake ambae volcano vanuatu abstract ambae also known as aoba is a 38 16 km 2 lozenge shaped island volcano with a coastal population of around 10 000 at the summit of the volcano is lake voui one of the largest active crater lakes worldwide with 40 10 6 m 3 of acidic water perched 1400 m a s l after more than 300 years of dormancy ambae volcano reawakened with phreatic eruptions through voui in 1995 and culminating in a series of surtseyan eruptions in 2005 followed by a rapid and spectacular colour change of the lake from light blue to red in 2006 integrating lake water chemistry with new measurements of so 2 emissions from the volcano during the 2005 2006 eruptive period helps to explain the unusual and spectacular volcanic activity of ambae initially a degassed magma approached the lake bed and triggered the surtseyan eruption depressurization of the conduit facilitated ascent of volatile rich magma from the deeper plumbing system the construction of a cone during eruption and the high degassing destabilised the equilibrium of lake stratification leading to a limnic event and subsequently the spectacular colour change

the stable isotope geochemistry of volcanic lakes with examples from indonesia abstract stable isotope compositions d 18o and 34s of volcanic lake waters gas condensates and spring waters from indonesia italy japan and russia were measured the spring fluids and gas samples plot in a broad array between meteoric waters and local high temperature volcanic gas compositions the d and 18o data from volcanic lakes in east indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high temperature volcanic gases we investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases an elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors providing relatively flat isotope evolution curves in 18o d diagrams a numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters lake water temperature and fluxes of meteoric water volcanic gas input evaporation and seepage losses the same model is used to derive the flux magnitude of the keli mutu lakes in indonesia the calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters several 100 m3 volcanic water day and indicate a water residence time of 1 2 decades the 34s data from the keli mutu lakes show a much wider range than those from gases and springs which is probably related to the precipitation of sulfur in these acid brine lakes the isotopic mass balance and s cl values suggest that about half of the sulfur input in the hottest keli mutu lake is converted into native sulfur

applying a weighted random forests method to extract karst sinkholes from lidar data summary detailed mapping of sinkholes provides critical information for mitigating sinkhole hazards and understanding groundwater and surface water interactions in karst terrains lidar light detection and ranging measures the earth s surface in high resolution and high density and has shown great potentials to drastically improve locating and delineating sinkholes however processing lidar data to extract sinkholes requires separating sinkholes from other depressions which can be laborious because of the sheer number of the depressions commonly generated from lidar data in this study we applied the random forests a machine learning method to automatically separate sinkholes from other depressions in a karst region in central kentucky the sinkhole extraction random forest was grown on a training dataset built from an area where lidar derived depressions were manually classified through a visual inspection and field verification process based on the geometry of depressions as well as natural and human factors related to sinkholes 11 parameters were selected as predictive variables to form the dataset because the training dataset was imbalanced with the majority of depressions being non sinkholes a weighted random forests method was used to improve the accuracy of predicting sinkholes the weighted random forest achieved an average accuracy of 89 95 for the training dataset demonstrating that the random forest can be an effective sinkhole classifier testing of the random forest in another area however resulted in moderate success with an average accuracy rate of 73 96 this study suggests that an automatic sinkhole extraction procedure like the random forest classifier can significantly reduce time and labor costs and makes its more tractable to map sinkholes using lidar data for large areas however the random forests method cannot totally replace manual procedures such as visual inspection and field verification

molecular and stable isotope compositions of natural gas hydrates a revised global dataset and basic interpretations in the context of geological settings abstract a global dataset of molecular and stable isotope compositions of gases released from 209 different specimens of natural gas hydrate is presented and discussed the 26 hydrate bearing areas from 21 geographic regions are grouped into high gas flux hgf settings low gas flux lgf settings and hydrated gas accumulations hga methane ch4 is the most abundant hydrate bound gas while co2 and c2 hydrocarbon gases are frequently present in small amounts non hydrocarbon gases such as h2s are uncommon the stable isotope composition of hydrate bound gases varies significantly e g 13c of ch4 from 74 7 to 39 6 suggesting that gases of both microbial and thermogenic origin form gas hydrates hydrate bound gases are derived from autochthonous located predominantly within the gas hydrate stability zone ghsz and allochthonous located in deep sediments sources the occurrence and concentration of gas hydrates in sediments are controlled not by the origin of gases but rather by their sources which in turn strongly depend on geological setting allochthonous gases microbial and or thermogenic dominate in hgf and hga settings where they are focused in the shallow ghsz along faults within mud volcanoes in permeable carrier beds and other geological features from underlying petroleum systems relatively high concentrations of gas hydrate average 5 15 of pores and locally up to 100 of volume occurring over small areas are typical of hgf and hga settings in contrast autochthonous and diffuse allochthonous gases mostly microbial occur in stratigraphically and structurally simple lgf settings and result in relatively low concentrations of gas hydrate average 2 of pores in the ghsz spread over large areas the major implication of this finding is that successful prediction of resource and geohazard potential of gas hydrates is possible only if regional petroleum systems extending well below the ghsz are properly evaluated in addition to the diagnosis of origins and sources of hydrate bound gases molecular and isotopic data help to better identify hydrate bearing intervals and provide valuable insights into the dynamics of hydrate bearing sites

three dimensional characterization of complex mantled karst structures decision making and engineering solutions applied to a road overlying evaporite rocks in the ebro basin spain abstract at mantle cover evaporite karst settings evidences of surficial subsidence are usually strongly dependent on geomechanical properties and spatial inhomogeneities within the cover series in infrastructure assets affected by karst processes the evaluation of mitigation or engineering solutions requires a 3d reconstruction of the underground karst affected materials analysis and surveillance are also required to avoid deterioration of natural conditions and the migration or the increase in rate of karst features in the central ebro basin fluvial deposits cover soluble salts mainly gypsum located below the regional water table variations of geomechanical parameters of the cover mainly related to carbonate crusts and the contemporaneous sedimentation of fluvial deposits during karst activity can complicate the characterization of affected volumes in this work an integrated analysis including the available information 3d characterization by means of gpr and three boreholes in a peri urban road was carried out to finally define the geometry and evolution of karst phenomena an evaluation of metastable situations is also considered in order to define the zoning for hazard mitigation this evaluation shows that the volumetric affection to the cover series is in the range of tens of thousands of cubic meters a proposed list of factors related to social aspects infrastructure relevance and budget is analyzed

designing foundations around sinkholes there is an increasing awareness among developers and owners of the need to conduct subsurface exploration studies before planning a project the use of geophysical methods in subsurface exploration has been established to be valuable in locating sinkhole activity and suggesting pro active measures however the value of geophysical exploration to supplement geotechnical investigation has not yet been stressed primarily out of cost concerns ground penetrating radar and electrical resistivity tests which were used to determine void spaces below proposed buildings are gaining wider acceptance as a result of information obtained from geophysical tests foundation designs were modified to use post tensioned mats or to include grouting an improved grouting technique that controls the volume of grout being pumped is also discussed this paper is an attempt to document some case studies which resulted in making design improvements to mitigate the effects of known sub surface solution activity these case studies illustrate the use of geophysical exploration methods in adding value to the engineered design

cyclic processes and factors leading to phreatic eruption events insights from the 25 september 2007 eruption through ruapehu crater lake new zealand abstract a dangerous block ash eruption occurred without warning from ruapehu crater lake on 25 september 2007 ending a 6 month period of temperature decline in the lake the northerly directed blast sent ballistics of up to 2 m diameter more than 2 km from the source the ejecta comprised a variety of volcano lacustrine lithologies many showing evidence of intense hydrothermal alteration petrographic studies of the ballistics reveal numerous examples of pores vesicles being filled with assemblages of elemental sulphur anhydrite pyrite and natroalunite and many ballistics exuded liquid sulphur from their pores during cooling at atmospheric pressure up to 5 of the ash was comprised of fine grained juvenile glass material confirming the presence of magma in the shallow vent environment a long recognised characteristic of this volcano is the thermal cycling behaviour of the crater lake behaviour which has remained effectively unchanged through two magmatic eruption events in 1945 and in 1995 96 airborne measurements of co2 and so2 flux from the volcano since 2003 show a strong positive correspondence with temperature cycling in the lake pointing to a definitive link between heat and mass discharge through the system low so2 emission rates and c s mole ratios 30 were typical of the period 2003 to early 2007 and appear to reflect vigorous scrubbing of s gases in the hydrothermal system during this time to better understand the chemical and physical processes operating in this very dynamic volcanic hydrothermal system and its propensity to develop potentially dangerous hydrothermal seals we have developed an integrated finite difference tough2 heat mass transport simulation of the hydrothermal environment the model which is constrained by observed heat and mass flux characteristics of the volcano demonstrates the transient nature of the heating cycles on the vent lake system of particular interest is the role of co2 as a relatively inert pressure transmitting medium in the hydrothermal environment seal formation was simulated using the reactive transport code x1t which showed that condensation of magmatic vapour into a highly porous medium of andesitic composition leads to rapid formation of an elemental sulphur anhydrite natroalunite mineral assemblage and a drastic reduction in permeability we suggest that since the 1995 96 vent clearing eruptions a shroud of elemental sulphur and other alteration phases formed along the margins of the 2 phase liquid vapour region enclosing the conduit this effectively seals the upper portion of the vent from the adjacent hydrostatically controlled environment and allows for development of pressurised vapour static gas columns beneath the northern and central vents

acid sulfate chloride volcanic waters formation and potential for monitoring of volcanic activity abstract this paper deals mainly with acidic sulphate chloride asc waters that are discharged at volcanic edifices generally not associated with crater lakes geographically the largest number of such manifestations were found on japanese and kuril islands these waters are formed by 1 condensation of magmatic vapor under shallow conditions and or 2 dissolution of magmatic gases in underground waters 3 near surface mixing of steam heated sulphate waters with sodium chloride waters of deeper formation 4 interaction of sodium chloride waters with the rocks undergone by argillic and advanced argillic alteration including hydrolysis of elemental sulfur 5 a combination of several of the listed processes criteria to assess the nature of such waters using their chemical and isotopic composition are based on the relative abundances of major species and trends in isotopic compositions generally controlling by mixing of magmatic host rock meteoric endmembers an overview of available data on temporal chemical variations of such waters shows that usually volcanic activity is marked by an increase in the so4 cl ratio during or after the eruptive event the response on the volcanic activity depends on hydrogeological conditions that control the appearance of the asc springs

color and temperature of the crater lakes at kelimutu volcano through time we investigated the color and temperature of three volcanic crater lakes that co exist at kelimutu volcano indonesia using 30 years of landsat data these satellite data were obtained through google earth engine time series of surface reflectance visible wavelengths and brightness temperature above background thermal infrared wavelengths were calculated color was defined in the rgb red green blue and hsv hue saturation value color spaces and we introduce a visualization concept called hue stretch to consistently represent hue through time these parameters display long term trends seasonal cycles and short duration bursts of activity at the lakes we demonstrate that the color of the lakes are related over a period of months to years and discovered a previously unreported but significant episode around 1997 which included large agglomerations of floating elemental sulfur globally speaking these techniques could reveal trends at any of the 100 crater lakes on active volcanoes furthermore they could apply to any target whose color changes through time e g forests crops and non volcanic water bodies we have open sourced the code necessary to perform these analyses

geochemistry mineralogy and chemical modeling of the acid crater lake of kawah ijen volcano indonesia the kawah ijen volcano with a record of phreatic eruptions has its 1000 m wide crater filled with a lake that has existed for at least one century at present the lake waters are hot t 37 c strongly mineralized tds 105 g l and extremely acidic ph 0 4 by its volume the javanese lake is probably the largest accumulation in the world of such acidic waters mineralogy of the suspended solids within the lake waters suggests that concentrations of si ca ti and ba are controlled by precipitation of silica gypsum anatase and barite lake sediment is composed of chemical precipitates with composition similar to the suspended solids thermodynamic calculations predict that the lake waters have reached equilibrium with respect to cristobalite barite gypsum anglesite celestite and amorphous silica in agreement with the analytical observations significant concentrations of ferric iron suggest that the current lake waters are fairly oxidized sulfides are absent in the water column but are always present in the native s spherules that form porous aggregates which float on the lake the presence of native s provides direct evidence of more reduced conditions at the lake floor where h 2 s is probably being injected into the lake with progressive addition of h 2 s to the acid waters native s pyrite and enargite are theoretically predicted to be saturated reactions between upward streaming h 2 s bearing gases discharged by subaqueous fumaroles and metals dissolved in the acidic waters could initiate precipitation of these sulfides a model of direct absorption of hot magmatic gases into cool water accounts for the extreme acidity of the crater lake results show that strongly acidic sulfate rich solutions are formed under oxidizing conditions at high gas water ratios reactions between the acidic fluids and the ijen andesite were modeled to account for elevated cation concentrations in lake water current concentrations of conservative rockforming elements are produced by dissolution of approximately 60 g of andesite per kg of acid solution complete neutralization of the acid lake waters by reaction with the wallrock produces a theoretical alteration assemblage equivalent to that observed in volcano hosted acid sulfate epithermal ore deposits

effect of massive gas hydrate formation on the water isotopic fractionation of the gas hydrate system at hydrate ridge cascadia margin offshore oregon because gas hydrate is preferentially enriched in the heavy water isotopes the 18o and d values of pore waters collected from gas hydrate bearing sediment can provide information on the abundance and mechanisms of gas hydrate formation pore waters sampled from deep seated 40 to 125 mbsf gas hydrate deposits in hydrate ridge during odp leg 204 show depletion in dissolved cl and enrichments in 18o and d due to gas hydrate destabilization during core recovery the oxygen and hydrogen isotopic fractionation factors o 1 0025 and h 1 022 estimated from an extensive data set n 30 samples correspond to experimentally determined values in contrast pore waters from shallow samples 25 mbsf at the ridge summit n 32 are highly enriched in dissolved cl and depleted in 18o and d consistent with formation of massive gas hydrate deposits at rates faster than those at which these anomalies would be removed by advection or diffusion the water isotopic fractionation factors in the brine are significantly lower than those experimentally determined with o of 1 0010 average value of 1 0012 and h of 1 008 average value of 1 008 we discuss several factors that may be causing this anomalous fractionation and suggest that low gas occupancy in hydrate lattice high hydration number may be responsible for the observed small fractionation if this were the case the oxygen and hydrogen fractionation may serve as an indicator of hydration number during formation of gas hydrate in natural systems

fluids in early stage hydrothermal alteration of high sulfidation epithermal systems a view from the vulcano active hydrothermal system aeolian island italy abstract high sulfidation hs epithermal systems have elements in common with passively degassing volcanoes associated with high t acid fumarole fields or acid crater lakes they are considered to form in two stages the first of which involves advanced argillic alteration resulting from intense strongly acidic fluid rock interaction the la fossa hydrothermal system vulcano island represents a classic example of such an active hs system and can be considered as a modern analogue of this early stage of alteration resulting in a core of intense silicic 90 95 pure sio2 alteration surrounded by alunitic alteration zones this paper focuses on a geochemical and stable isotope study of the surficial alteration facies of vulcano particularly the horizon characterized by strong silicic alteration and on deep seated xenoliths ejected during the last eruption of la fossa volcano 1888 90 that can be considered as representative of fragments of the deep conduit system of la fossa volcano using directly measured temperatures at the sites of sampling we have calculated fluid composition in isotopic equilibrium with the alteration products the large range of measured silica 18o 12 3 to 29 reflects the wide range of formation temperatures 80 240 c the fluid compositions calculated for intense silicic alteration vary from 0 9 to 6 5 these are significantly heavier than local meteoric water 6 and are consistent with derivation from the condensation of high temperature fumarolic gases dominated by magmatic fluids and rich in acid gases so2 h2s hcl hf into shallow groundwaters of meteoric origin with dynamically variable ratios of fumarolic steam meteoric water the calculated 18o and d of water in equilibrium with alunite also suggest the mixing of magmatic and meteoric waters for the fluids involved in the genesis of advanced argillic alteration facies the calculated 18o of water in equilibrium with hedenbergitic clinopyroxene found in a veinlet in a metasomatized xenolith is 8 9 this value cannot reasonably result from water rock interaction between the host volcanic rocks and surface water instead it most likely represents a fluid brine exsolved from magma which was responsible for high temperature metasomatism in the deep conduit system

alluvial dolines in the central ebro basin spain a spatial and developmental hazard analysis abstract alluvial dolines are abundant in quaternary terraces and pediments overlying neogene gypsum in the zaragoza area central ebro basin spatial analysis and experimental simulation show that sulphate content in the groundwater grain size of the detrital cover topography of the tertiary quaternary boundary annual variation of the water table and thickness of the detrital cover are the main factors controlling their development taking into account these variables a theoretical spatial hazard model has been elaborated expressed as a mathematical equation and a hazard map both experiments and field data show a high correspondance between two basic mechanisms of evacuation and subsidence dragging slow subsidence and collapse of cavities and two basic types of morphology and internal structure of dolines basin doline funnel structure and well doline vault structures respectively a genetic classification of dolines and some evolutionary patterns based on these criteria are developed historical changes observed in doline distribution as well as field surveys of urban damage and microtopographic profiles allow us to evaluate the present day activity of dolines local subsidence rates measured in urban areas range from 2 5 to 10 cm year although doline generation and reactivation in the whole area tend to be compensated by filling by human activity

geochemical constraints for the formation and dissociation of gas hydrate in an area of high methane flux eastern margin of the japan sea abstract the umitaka spur in the joetsu basin on the eastern margin of the japan sea is characterized by a number of features indicative of high methane flux such as a bsr and gas plumes rising through the water column these are likely linked to the presence of hydrocarbon source rocks underneath the spur the interstitial water chemistry at the spur was measured in order to delineate the behavior and evolution of the gas hydrate system across the region the sulfate depth profiles indicate that the smi depths become shallower toward the crest of the spur and are shallowest less than 200 cmbsf at two plume sites suggesting that the methane fluxes are highest around the plumes depth profiles of dissolved cl all fall into one of four distinguishable trends type i where concentrations linearly increase with sediment depth type ii where concentrations linearly decrease with depth type iii where concentrations remain constant and type iv where concentrations exhibit negative spikes caused by dissociation of gas hydrate during core recovery and handling type i cores commonly recovered at central plume site are characterized not only by steep cl gradients 13 2 to 51 0 mm m but also extreme depletions in d and 18o 0 97 to 0 54 vsmow m for dh2o and 0 16 to 0 10 vsmow m for 18oh2o suggesting gas hydrate formation at shallow depth the cl gradients of type ii cores recovered from the southern part of the spur have little variation 14 8 to 8 3 mm m gas hydrate dissociation along base of the gas hydrate stability zone best explains both the similar pattern of freshening with depth and the widespread distributions of type ii cores although gas hydrate dissociation is known to release isotopically heavy water type ii cores show progressive depletions of both d and 18o with downward depth the apparent contradiction between cl concentrations and the isotopic compositions of type ii cores is likely due to re equilibration by strong burial diagenesis observed all over the japan sea sediments regional dissociation of gas hydrate is likely to have been triggered by sea level drop which facilitated dissociation of subsurface gas hydrate

natural and human induced sinkholes in gypsum terrain and associated environmental problems in ne spain the central ebro basin comprises thick evaporite materials whose high solubility produces typically karstic landforms the sinkhole morphology developed in the overlying alluvium has been studied using gravimetry and ground penetrating radar gpr on stream terraces as well as analyzing the evolution of sinkhole morphologies observed in aerial photographs taken in 1928 1957 and 1985 the sinkhole morphologies give some idea of possible subsurface processes as well as an indication of the final mechanisms involve in sinkhole development on stream terraces and cover pediments the most commonly encountered dolines are bowl shaped in their morphology with both diffuse and scarped edges in contrast dolines developed in the gypsiferous silt infilled valleys have a funnel and well shaped morphology the diffuse edged bowl shaped dolines are developed through the progressive subsidence of the alluvial cover due to washing down of alluvial particles through small voids and cracks into deeper subsurface caves resulting in a decrease alluvial density future compaction of the alluvial cover will produce surface subsidences this type of dolines are associated with negative gravity anomalies in contrast the scarped edge dolines are formed by the sudden collapse of a cavity roof the cavities and cracks formed in the gypsum karst may migrate to the surface through the alluvial deposits by piping and they may subsequently collapse in this instance the cavities can be detected by both gravity and gpr anomalies where the voids are not deeper than 4 5 m from the surface these processes forming sinkholes can be enhanced by man induced changes in the groundwater hydrologic regime by both inflows due to irrigation ditch losses or pipe leakages and by outflows from pumping activities

hydrological evolution and chemical structure of a hyper acidic spring lake system on whakaari white island nz abstract white island has a long and varied history of acid spring discharge and shallow ephemeral lake formation on its main crater floor in the 12 months prior to the onset of the 1976 2000 eruptive episode mass discharge from the spring system increased ca 10 fold pointing to a strong coupling of the hydrothermal environment to the evolving magmatic system between 1976 and 1978 the formation of numerous eruption vents to 200 m depth in the western sub crater abruptly changed the hydraulic gradients in the volcano resulting in the reversal of groundwater flow in the massif towards the newly formed crater s this affected not only the style of volcanic activity leading to phreatic phreatomagmatic magmatic eruption cycles but also led to the demise of the spring system with discharge from the main crater declining by a factor 100 by 1979 eruptive activity ended shortly after a moderate strombolian eruption in mid 2000 after which ephemeral lakes started to form in the eruption crater complex between 2003 and 2015 there were three complete lake filling and evaporative cycles reflecting varying heat flow through the conduit system beneath the lake over these cycles lake water concentrations of cl and so 4 varied between ca 35 150 and 5 45 g l respectively with ph values temporally ranging from 1 5 to 1 springs appeared on the main crater floor in 2004 and their discharges varied with lake level pointing to the lake level being a primary control over the piezometric surface in the crater area springs closest to the crater complex show direct evidence of crater lake water infiltration into the crater floor aquifer whereas distal spring discharges show compositional variations reflecting vertical displacement of the interface between shallow dilute condensate and underlying acidic brine fluids source components for the spring fluids include magmatic vapour dissolved andesitic host rocks seawater and meteoric water lake waters on the other hand consist predominantly of magmatic vapour meteoric water and solutes derived from host andesites and their altered derivatives 2 h and 18 o signatures of the enclosing acid brine fluids indicate they are predominantly seawater which have been affected by both vapour loss but also mixing with arc type vapour an interesting finding of this study is that crater floor deformation correlates directly to both lake level and volatile emissions in an apparent poroelastic response to the establishment of a hydrostatic water column in the eruption crater complex and a net decrease in permeability owing to hydrothermal mineralization in the conduit predominantly elemental sulfur and sulfate minerals the hydrostatic pressurization of the vent environment also leads to increased gas pressures and flows through fumarolic channels and consequent expansion of fumarolic areas on the main crater floor a period of unrest which commenced in august 2012 and lasted until october 2013 included the extrusion of a small dome into the eruption crater complex this activity and related high heat flow led once again to evaporation of the lake and ongoing phreatic eruption activity which has provided interesting insights into the role which elemental sulfur associated hydrothermal alteration minerals and of course water play in regulating pressures in the magmatic hydrothermal environment

poroelastic analysis of cover collapse sinkhole formation by piezometric surface drawdown where the water table is above the soil rock contact in karst regions cover collapse sinkholes in the soil and soft sediment above the rock commonly occur as a result of drawdown of the piezometric surface in the karst aquifer transient stresses and pore pressures around soil voids at the soil rock contact can cause hydraulic fracturing of the soil near the wall of the void after the first such fracture successive sloughing of soil propagates the soil void rapidly to the surface resulting in a cover collapse sinkhole sinkhole formation by this mechanism should be strongly a function of rate and magnitude of piezometric surface drawdown permeability and tensile strength of the soil and the size depth and geometry of the initial soil void large soil voids and those with walls that are partly planar or of low curvature are most susceptible to hydraulic fracture and the resulting progression to sinkhole formation

foundation evaluation of underground metro rail station using geophysical and geotechnical investigations abstract excavations for underground space developments in a thickly populated urban area are sometimes hindered by unexpected formidable consequences like formation of sinkholes or uneven settlement of foundations such troublesome incidences occasionally damage structures in the vicinity of excavations although adequate design guidelines and codes of practices are adopted the disturbance of subsurface regime due to excavation or construction activities often leads to undesired stability issues with resultant appearance of weak zones the reinforcement of weak zones by grouting is one of the common remedies without demarcating the weak or the affected zones becomes counter productive excavation at a location in chennai mega city for metro rail was severely affected by soil piping with development of sinkholes and weakening of the surrounding strata subsequently development of cracks in the adjacent buildings and caused tilting of the nearby taller structures the mandated the geophysical and geotechnical investigations were carried out to demarcate the affected area to avoid further deterioration of the site cross hole seismic p and s wave velocities were estimated between10 pairs of boreholes up to 20 m depth on both the sides of the excavation two electrical resistivity tomography ert profiles each of 141 m in length were carried out in the same location cross hole s wave velocity profiles and resistivity tomograms clearly indicate the presence of weak zones and possible sinkhole locations site specific empirical relationship was established between s wave velocity and standard penetration test spt n value this relationship was further used for determination of spt n values from the measured vs values to compare the subsurface conditions identified under pre and post excavations the results confirmed the presence of weak zones which are responsible for the weakening of the surrounding strata in the foundation geophysical and geotechnical investigations similar to present investigation can be useful for designing metro rail projects in a subsurface environment comprising alluvium sand clay mixed with silt pebbles and boulders lying near a region of ground water pocket in a thickly populated urban area

application of limit plasticity to the stability of sinkholes abstract a solution is obtained using classical plasticity theory and the method of characteristics to evaluate the stability of soils adjacent to a cylindrical void the soil strength contains both cohesive and frictional components which allows the solution to be used to evaluate the drained stability of residual soils overlying cavitose bedrock the method yields a lower bound solution for the magnitude of a surface loading required to cause instability of the system and provides a description of the slip line defining the failure zone the results are compared in dimensionless terms for various combinations of cavity diameter and overburden thickness for a given overburden thickness small cavities are more stable than large cavities however for a given cavity diameter large overburden thicknesses are shown to be more stable than small thicknesses this is contrary to conventional slope stability where stability generally decreases with increasing height the difference is attributed to the role of a circumferential stress component in the axisymmetric solution which may be significant for small diameter cavities equations are suggested for the determinaton of the vertical stress required to generate an instability and for estimation of the size or surface extent of damage these results have significance in soil stability analyses in karst terrain and in the construction of deep foundations such as drilled shafts the improvement of methods to detect and measure voids in soil fischer and canace 1989 will make this method particularly attractive

a preliminary sinkhole raveling chart abstract sinkholes are a major geohazard in karst areas where soluble carbonate bedrock exists downward seepage resulting from the groundwater recharge continuously erode cover soils into cavities within the underlying bedrock resulting in raveling of cover soils identifying these raveled soils or zones is critial in preventing and mitigating the sinkhole collapse in this study a proof of concept was performed to demonstrate the concept of a sinkhole raveling chart that can quantify the severity levels of raveling the raveling chart is constructed based on cone penetration test cpt data collected through multiple sinkhole active sites in central florida a preliminary analysis e g data preparation grouping and zoning was carried out to construct the prototype sinkhole raveling chart this prototype raveling chart as a function of tip resistance qc and sleeve friction fs could delineate not only the raveled and non raveled zones but also the areas that correspond to different levels of raveling severity