effective electrode array in mapping karst hazards in electrical resistivity tomography when conducting environmental and engineering investigations in karst terranes engineers and geologists often supplement exploratory borehole results with data gathered from surface geophysics to reduce the site characterization cost and establish the most useful locations for borings or samples when conducting resistivity investigations a frequently occurring problem is the need to determine which of the many existing electrode configurations will respond best to the material changes in karst features each array has its advantages and disadvantages in terms of depth of investigation sensitivity to horizontal or vertical variations and signal strength in the application presented in this paper numerical forward modeling was conducted of dipole dipole schlumberger and wenner arrays and they produced markedly different anomaly shapes for a conceptual model of the development of a cover collapse sinkhole the resolution of the three above mentioned arrays was further evaluated along a section of i 70 near frederick maryland where a sinkhole had occurred in the median of the highway the image from the dipole dipole array appeared to be better than those from the wenner and schlumerger arrays in displaying the sinkhole collapse area however they are all less effective than a mixed array in which apparent resistivities from all the three arrays are combined and processed together in the model because the mixed array requires a significant increase in data collection the dipole dipole array appears to be the most effective and less costly configuration in mapping karst hazards areas this conclusion was then confirmed by two case studies

geomorphology and natural hazards in karst areas a review 1 introductionsince human beings started to colonise the world slowly migrat ing in multiple directions from the african rift and ultimatelyreaching the southernmost territories of the americas they haveinteracted with the natural environment using its resources and suf fering from its hazardous processes survival of mankind was possiblethanks to its ability to adapt to an ever changing environment and itscapability to learn and communicate the new ndings from the ear liest times geomorphic features and processes were an essential partof social survival crozier et al 2011 in karst terrains caves wereused as shelters as well as burial and sacred places playing an instru mental role in the day to day struggle for survival especially duringthe ice ages fig 1 spectacular karst landmarks such as big cave en trances blue karst springs deep collapse sinkholes cenotes or rockarches just to name a few have often become part of the naturaland supernatural heritage of our ancestors in prehistoric times the human impact on the karst environmentwas very limited like the probability of properties and people beingdamaged by karst processes e g subsidence ooding both impactsandhazardsinkarstterrainshaveincreaseddramaticallyover thelasttwo centuries along with the exponential increase in population andour capability to modify the natural environment largely related tothe economic and technological development of the societies an in creasing number of scientists consider that humans are nowadaysthe most effective geomorphic agent and a prime factor in landscapeevolution zalasiewicz et al 2010 price et al 2011 in fact the for mal de nition of the anthropocene as a new epoch of the geologicaltime scale characterised by a signi cant and global human impact onthe earth s ecosystems is being debated at the present time around25 of the earth s population lives on or nearby karst areas ford andwilliams 2007 and the increasing exploitation of karst resources such as water and building material is leading to severe environmen tal impacts and unsustainable situations drew and hotzl 1999 gunn 2004 unfortunately the number of karst areas affected bywater pollution landscape degradation and other impacts is growingveryrapidly additionally thedamagecausedbyhazardouskarstpro cesses especially subsidence sinkholes beck 2003 waltham et al 2005 gutierrez et al 2008a will most likely keep on increasing exposed human elements augment and anthropogenic changes inthe karst systems frequently result in hazard enhancement karstgeomorphologists and hydrologists can play a decisive role in pre venting natural disasters in karst areas particularly those inducedby human activities dams with leakage and sinkhole problems milanovic 2000 cooper and gutierrez 2011 mines and tunnelsaffected by ooding and subsidence li and zhou 1999 autin 2002 casagrandeet al 2005 luchaetal 2008 high speedrailwaysbuilt in sinkhole prone areas guerrero et al 2008 or developmentof sinkholes at huge rates induced by lake level yechieli et al 2006 or water table sprynskyy et al 2009 declines the importance of properly managing karst areas and mitigatingthe detrimental effects caused by human activities on these inherentlysensitive environments has been boosted by a series of conferencesand projects since the early 1990s ford 1993 williams 1993 pariseet al 2008 2009 raising public awareness on the need to protectour endangered natural resources especially in developed countries has promoted the production of karst speci c environmental impactassessments veni 1999 recently severalapproacheshavebeenpro posedtoassessthedegreeofhuman induceddisturbanceinkarstareas van beynen and townsend 2005 calo and parise 2006 de waele 2009 north et al 2009 although these studies are essential for apropermanagementofthekarstresources theymaybefutileifnotfol lowed by adequate administrative decisions and regulations 2 karst geomorphology2 1 karst processeskarst is characterised by the predominance of rock dissolution overmechanical erosion and is typical of present temperate cold andwarm and tropical environments ford and williams 2007 in karstterrains surface and subsurface geomorphology and hydrology arelargely governed by dissolution of carbonate and or evaporite rocks in the most classical common situation surface waters acidi ed byco

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

a multiscale study of the permeability of a thick clayey till we describe and evaluate two previously undocumented methods of bulk permeability k determination and compare results obtained with results of conventional smaller scale tests on the same thick clayey till deposit analysis of the downward propagation of seasonal water table fluctuations yielded bulk k of approximately 10 10 m s 1 in close agreement with results of laboratory consolidation and permeameter tests slug tests and distribution of vertical hydraulic gradient with depth in the deposit this agreement suggests that for such materials high gradient tests conducted at small scales of distance and time can provide reasonable estimates of bulk k the results also imply groundwater residence times in the till of thousands of years the flow pattern observed near a large excavation in the till was consistent with the initial recoveries of piezometers installed in much smaller boreholes assuming perturbation of hydraulic head in the formation due to borehole excavation time scales of these perturbations which prevent interpretation of measured hydraulic head using conventional well hydraulic methods varied from months to tens of years

surface hydrology iv flow in sloping layered soil in a nonuniform soil with rotational symmetry the properties change along a coordinate n that forms an angle ia n with the vertical during infiltration there will be a flow component in the parallel direction s downstream which is proportional to the rain itself and the slope the horizontal flow is proportional to the vertical flow the slope and the coefficient of anisotropy the last has been calculated for a soil made up distinct layers in the limiting case of very thin layers or near the saturation point the vertical and horizontal conductivities are respectively the expected arithmetic and harmonic means familiar from saturated flow the coefficient of anisotropy increases with the rate of vertical flow to a power greater than unity the horizontal flow component can be many times the vertical one it finds application in pollution problems and in the study of the underground water regime

surface and subsurface environmental degradation in the karst of apulia southern italy karst environments are highly vulnerable to a variety of degradation and pollution problems geology fractured carbonate rocks morphology presence of a network of cavities produced by karst processes and hydrogeology rapid concentrated flow through fractures and conduits of karst carbonates strongly favour the movement of contaminants towards the water table in particular poor quality of subsurface water can derive from polluting substances flowing at the surface and or by direct immission of liquid and solid waste into the water table through the systems of conduits and joints in the rock mass as a consequence water quality can deteriorate severely which implies very high economic and social costs in order to clean the polluted sites and restore the original situation in some cases such as when the original karst morphology is changed because of anthropogenic interventions the variations created in the landscape are not recoverable and a loss of sites of naturalistic interest has to be registered high vulnerability of a typical karst region of the mediterranean area is illustrated in this paper by describing some case studies from apulia southern italy the apulia region where karst processes have had a prominent role in the development of the present landscape is mostly underlain by intensely karstified limestone two cases of pollution due to solid waste into karst cavities grave di s leonardo in the gargano promontory and grave pelosello in the murge plateau landscape transformation in the minervino murge area and degradation of gravina monsignore a typical karst valley in southeastern murge are described in the paper in two out of four cases degradation of the sites was discovered thanks to activity from local speleologists who also acted as promoters for cleaning and safeguarding the polluted sites these examples underline well the mismanagement of karst territories in particular the common practice to dump refuse into sinkholes and caves the pollution of limestone aquifers and the effects that such pollution in karst areas might have in terms of the risk to public health

a systematic engineering geological evaluation of diabase dikes exposed at the underground caverns of dagangshan hydropower station southwest china dagangshan hydropower station is located in the middle of dadu river southwest china many diabase dikes were exposed in the adamellite granite body during excavation of the underground caverns the dikes are highly directional have crushed interiors exhibit strong alteration and have poor contact relationships with surrounding rocks all of which is inconsistent with the characteristics of typical diabase this paper describes systematic research that focused on the dikes spatial distribution macroscopic characteristics physical and mechanical properties and common instability modes factors influencing their stability and their corresponding control measurements are discussed in the context of the site and its conditions results show that most of the dikes located in the underground caverns are the branches of the main dike 9 which produced from a strong basic magma extrusion overflow event happened in between the permian and triassic due to multiple strong tectonic activities the chlorite alignment of these dikes generally tended to be significant and leaded the physical and mechanical properties to be poor then excavation and repetitive blasts resulted in strong disturbances to the original dikes and even caused rock unloading collapse rock block fall and groundwater runoff system water inflow change according to the common instability modes and reasons of diabase dikes some specific control measures including solidified rubbles reinforcement methods pre grouting and small ducts are implemented in order to keep the surrounding of diabase safety and the results show that the control methods perform a proper effect on these engineering problems

application of field geophysics in geomorphology advances and limitations exemplified by case studies abstract during the last decade the use of geophysical techniques has become popular in many geomorphological studies however the correct handling of geophysical instruments and the subsequent processing of the data they yield are difficult tasks furthermore the description and interpretation of geomorphological settings to which they apply can significantly influence the data gathering and subsequent modelling procedure e g achieving a maximum depth of 30 m requires a certain profile length and geophone spacing or a particular frequency of antenna for more than three decades geophysical techniques have been successfully applied for example in permafrost studies however in many cases complex or more heterogeneous subsurface structures could not be adequately interpreted due to limited computer facilities and time consuming calculations as a result of recent technical improvements geophysical techniques have been applied to a wider spectrum of geomorphological and geological settings this paper aims to present some examples of geomorphological studies that demonstrate the powerful integration of geophysical techniques and highlight some of the limitations of these techniques a focus has been given to the three most frequently used techniques in geomorphology to date namely ground penetrating radar seismic refraction and dc resistivity promising applications are reported for a broad range of landforms and environments such as talus slopes block fields landslides complex valley fill deposits karst and loess covered landforms a qualitative assessment highlights suitable landforms and environments the techniques can help to answer yet unsolved questions in geomorphological research regarding for example sediment thickness and internal structures however based on case studies it can be shown that the use of a single geophysical technique or a single interpretation tool is not recommended for many geomorphological surface and subsurface conditions as this may lead to significant errors in interpretation because of changing physical properties of the subsurface material e g sediment water content in many cases only a combination of two or sometimes even three geophysical methods gives sufficient insight to avoid serious misinterpretation a good practice guide has been framed that provides recommendations to enable the successful application of three important geophysical methods in geomorphology and to help users avoid making serious mistakes

field experiments in a fractured clay till 1 hydraulic conductivity and fracture aperture field values of horizontal hydraulic conductivity measured in the upper 1 5 5 5 m of a weathered and fractured clay rich till were strongly influenced by smearing around piezometer intakes which occurs during augering and by the physical scale of the measuring device values measured in conventional augered piezometers were typically 1 2 orders of magnitude lower than those measured in piezometers designed to reduce smearing measurements of hydraulic conductivity in small scale seepage collectors or piezometers which typically intersect fewer than 10 fractures vary over a much greater range 10 10 to 10 6 m s than large scale values based on infiltration into 5 5 m deep trenches which intersect thousands of fractures range 10 7 to 3 10 7 m s values of hydraulic fracture aperture 1 43 m and fracture porosity 3 10 5 to 2 10 3 were calculated using the cubic law with fracture orientation distribution measurements and the small scale hydraulic conductivity measurements this paper provides the first reliable determination of the magnitude and spatial distribution of hydraulically derived fracture parameters in a clay deposit the absence of such data has until now severely limited the application of quantitative groundwater flow and contaminant transport models in this type of deposit

a hillslope scale experiment to measure lateral saturated hydraulic conductivity 1 one of the most challenging parameters in hillslope and watershed scale distributed hydrologic models is the lateral saturated hydraulic conductivity ks in this paper we present a methodology to determine the hillslope scale lateral ks above a moderately deep sloping restrictive layer in an 18 35 m hillslope plot using perched water level measurements and drain tile outflow data the hillslope scale lateral ks was compared to small scale ks measured with small soil cores and the guelph permeameter our results show that small scale ks measurements underestimate the actual hillslope scale ks the hillslope scale ks measurements were 13 7 4 1 and 3 2 larger than small soil core measurements in the a b and e horizons respectively we argue that the gap between small scale and hillslope scale ks within the same porous medium is foremost a measurement problem data analysis provided the ks distribution with depth showing a sharp decrease in ks within the first 0 1 m of the soil and an exponential decline in ks below 0 1 m the distribution of ks with depth was best described by a double exponential relationship overall results indicate the importance of macroporosity perhaps of biological origin in determining ks at a hillslope scale

multi scale permeability estimation for a tropical catchment physically based and spatially distributed modelling of catchment hydrology involves the estimation of block or whole hillslope permeabilities invariably these estimates are derived by calibration against rainfall runoff response rarely are these estimates rigorously compared with parameter measurements made at the small scale this study uses a parametrically simple model topmodel and an uncertainty framework to derive permeability at the catchment scale the utility of expert knowledge of the internal catchment dynamics i e extent of saturated area in constraining parameter uncertainty is demonstrated model derived estimates are then compared with core based measurements of permeability appropriately up scaled the observed differences between the permeability estimates derived by the two methods might be attributed to the role of intermediate scale features natural soil pipes an alternative method of determining block permeabilities at the intermediate or hillslope scale is described this method uses pulse wave tests and explicitly incorporates the resultant effects of phenomena such as soil piping and kinematic wave migration the study aims to highlight issues associated with parameterizing or validating distributed models rather than to provide a definitive solution the fact that the permeability distribution within the borneo study catchment is comparatively simple assists the comparisons the field data were collected in terrain covered by equatorial rainforest combined field measurement and modelling programmes are rare within such environments

vadose zone permeability tests unsteady flow saturated unsaturated flow models are used to simulate transient conditions in four soils during constant head borehole infiltration tests in the vadose zone infiltration rate varies directly with saturated hydraulic conductivity and is also influenced by unsaturated soil properties antecedent moisture conditions anisotropy and borehole conditions the method recommended by the u s bureau of reclamation to determine when to terminate a test may lead to overestimating saturated hydraulic conductivity simple graphical procedures are developed to overcome field problems associated with large water volume requirements or long time required to reach steady state by using early time date to estimate the steady infiltration rate

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

regression models for hydraulic conductivity and field test of the borehole permeameter the saturated hydraulic conductivity ks of sediments in the vadose zone is an important parameter in predicting the seepage rates of water and contaminants the borehole permeameter is an in situ technique to test a relatively large sample size at any depth solutions are presented which account for the effects of unsaturated flow these solutions are derived from a regression analysis of results of numerical simulations in which unsaturated hydraulic conductivity is represented by one or two parameters the results of a borehole permeameter test in a uniform sand are compared with field ponding tests and air entry permeameter tests the regression based solutions for the borehole permeameter which account for capillarity provide very good agreement with other permeameter results depending upon the approach used to solve the borehole problem ks values determined by methods which neglected and included capillary effects varied by a factor of only about two for the soil tested

comparison of methodological uncertainties within permeability measurements permeability measurements are critical to the calculation of water flow within hillslopes despite this errors in permeability measurements are often ignored and can be very large particularly in disturbance sensitive gley soils this work compares the uncertainties associated with six field methods of permeametry applied to a gleyed soil in upland britain slug tests constant head borehole permeametry and falling head borehole permeametry were undertaken on established piezometers additionally ring permeametry and two types of trench tests were evaluated method related uncertainty due to proximity of impeding layers of high sorptivity soils produces under and over estimates of permeability by a factor of up to 0 2 and 5 respectively this uncertainty band is smaller than the observed effects of anisotropy and temporal variability had smearing and soil ring leakage errors not been minimized the methodological uncertainties would have been so large that they would have distorted the true spatial field of permeability and its estimated impact on the balance of vertical and lateral flow

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

morphometric analysis of sinkholes in a karst coastal area of southern apulia italy salento the southern portion of apulia region se italy is a narrow and elongated peninsula in carbonate rocks with prevailing low coastlines locally interrupted by high rock cliffs the long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes as observed in many other karst coastal settings worldwide development of sinkholes may be particularly severe along the coasts where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes even influencing the coastline evolution following a previous study where the main features of sinkholes at torre castiglione taranto province were investigated and described and a preliminary susceptibility map produced at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes the main morphometric parameters generally used for sinkhole characterization have been considered in this study shape of the sinkhole azimuth and length of maximum and minimum axes depth elongation ratio and distance from the shorelines each of them is described both as individual parameter and in conjunction with the others in the attempt to identify the main factors controlling development of sinkholes in the area and their evolution as well with regard to this latter aspect beside simple morphometry of the sample of sinkholes at torre castiglione we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities to investigate the matter a three stage analysis has been carried out in this study by means of field measurements of the fractures bounding the sinkholes field measurement of the long axes azimuth of the elongated sinkholes comparison of the previously described sets with the strikes of the main regional geological structures the obtained results show in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays eventually the approach here presented may be applied in other karst coastal sinkhole prone areas to gain new knowledge on the genesis and evolution of coastal sinkholes and to properly evaluate the hazard they pose to the anthropogenic environment

karst geosites at risk of collapse the sinkholes at nociglia apulia se italy this paper focuses on the impacts of contemporary geomorphological processes on fruition activities in a karst area of salento apulia southeastern italy the work illustrates the results of studies in a sinkhole field at nociglia in the lecce province recently recognized as a geosite and where shallow phreatic speleogenesis operates close to the water table level with the formation of karst caves successive roof collapse formation of wide caverns and sinkhole development at the surface all these features threaten the nearby infrastructures including a province road salento has a great number of active sinkholes related to natural and anthropogenic cavities their presence is at the origin of several problems in the built up environment due to increasing population growth and development pressures in such a context the detection of cavities and the assessment of sinkhole hazards present numerous difficulties to assess the potential danger from sinkholes it is important to identify and monitor the main factors contributing to the formation process a multi disciplinary approach comprising geological geomorphological and geophysical analyses is necessary to obtain a comprehensive knowledge of these complex phenomena in karst areas geophysical methods can be of great help to monitor the processes and for identifying and mapping features related to the underground voids by detecting contrasts in physical properties such as density and electrical resistivity with the surrounding sediments at the same time recognition of the presence of sinkholes by geophysical methods has to adapt to the local geological conditions and take advantage of the integration of the several methodologies available the territory of nociglia demonstrates that monitoring is essential for the safe exploitation of these type of geomorphosites

cave detection using multiple geophysical methods unicorn cave harz mountains germany unicorn cave in the southern harz mountains of germany is a show cave in dolomitic rocks of the zechstein formation the cave s trunk passage is interrupted by larger rooms the overburden is only around 15 m the passages are filled with sediments that can be up to 50 m thick we used gravimetry and electrical resistivity imaging over the cave area to identify the subsurface voids and the extent of the sediment infill of the cave passages our choice of methods was based on several conditions unique to the cave 1 well surveyed 2 shallow overburden 3 large air filled passages and 4 thick sediment cover concealing true passage size using the cave survey as an initial model for the subsurface structure we successfully identified the air filled cave with both methods we then inferred the thickness of the sediment infill by forward modeling and identified a possible southward continuation beyond the currently explored passages

integrated geophysical approach in assessing karst presence and sinkhole susceptibility along flood protection dykes of the loire river orleans france abstract non invasive geophysical methods are often used for detecting near surface defects and monitoring seepage in river dykes or dams between 2008 and 2009 a series of geophysical experiments was conducted to detect karst features below the dykes of the loire river orleans france multi channel analysis of seismic surface waves masw was used to obtain the shear wave velocity vs profile of the subsurface below the dykes as an effective approach to investigating the structure of the dykes multi channel resistivity surveys were also used to evaluate the electrical properties of material inside and under the dykes this study discusses the exploration strategy and results for several sections of the dyke system based on the experimental data vs contours are used to geometrically and qualitatively describe the subsurface under the dykes and identify areas of mechanical weakness corresponding to karst features while resistivity contours allow distinguishing interactions between the karst and the dykes through the identification of areas of downward material movement known and unknown anomalies are identified a practical approach that combines seismic and electric resistivity results is proposed to assess karst presence and sinkhole hazards along the investigated dykes using a susceptibility index referring to the likelihood level of the events as a validation method areas of strong karst susceptibility index along the dykes are compared to known collapse event sinkholes dyke breaches etc locations available in databases

a preliminary analysis of failure mechanisms in karst and man made underground caves in southern italy abstract natural and anthropogenic caves may represent a potential hazard for the built environment due to the occurrence of instability within caves that may propagate upward and eventually reach the ground surface inducing the occurrence of sinkholes in particular when caves are at shallow depth the effects at the ground surface may be extremely severe apulia region southern italy hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities the latter being mostly represented by underground quarries the pliocene pleistocene calcarenite a typical soft rock was extensively quarried underground by digging long and complex networks of tunnels with time these underground activities have progressively been abandoned and their memory lost so that many apulian towns are nowadays located just above the caves due to urban expansion in the last decades therefore a remarkable risk exists for society which should not be left uninvestigated the present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties aimed at exploring the progression of instability of the cavities numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass and the distinct element method for jointed rock mass conditions both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated along with the consequent failure mechanisms in particular degradation processes of the rock mass as a consequence of wetting and weathering phenomena in the areas surrounding the caves have been simulated the results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes as detected in situ has been noticed

a spatial filter approach to evaluating the role of convection on the evolution of a mesoscale vortex abstracta new spatial filter is proposed that exploits a spectral gap in power between the convective scale and the system vortex scale during tropical cyclone tc genesis simulations using this spatial separation this study analyzes idealized three dimensional numerical simulations of deep moist convection in the presence of a symmetric midlevel vortex to quantify and understand the energy cascade between the objectively defined convective scale and system scale during the early stages of tropical cyclogenesis the simulations neglect surface momentum heat and moisture fluxes to focus on generation and enhancement of vorticity within the interior to more completely close off the energy budget and to be consistent for comparison with prior benchmark studies of modeled tc genesis the primary contribution to system scale intensification comes from the convergence of convective scale vorticity that is supplied by vortical hot towers vhts they contribute more than the convergence of system scale v

identification of sinkhole development mechanism based on a combined geophysical study in nahal hever south area dead sea coast of israel seismic refraction magnetic resonance sounding mrs and the transient electromagnetic tem method were applied to investigate the geological and hydrogeological conditions in the nahal hever south sinkhole development area at the dead sea ds coast of israel microgravity and mrs results reliably reveal large karst cavity in the central part of investigated area the map of the seismic velocity shows that sinkholes in nahal hever can be divided into two major groups sinkholes close to the salt edge and sinkholes over compact salt formations between a few tens to a hundred meters from the major cavern the present study shows that the formation of sinkholes of the first group is caused by soil collapsing into the cavern in the area occupied by sinkholes of the second group karst was not detected either by mrs or by seismic diffraction methods tem results reveal shallow clay layer saturated with ds brine underlain sinkholes of this group it allows suggestion that the water drainage and intensive water circulation during rain events wash out fine rock particles from the unsaturated zone into the pre existing cavern initiating the formation of sinkholes of the second group karst development takes place at a very low bulk resistivity 1 m of the ds aquifer attesting to the fact that pores are filled with a highly saline solution refilling of the karstic cavities with collapsing and flushed soil slows down sinkhole development in the area the sinkhole formation cycle at the site is estimated at 10 years sinkhole development throughout the studied area is triggered by a drop in the level of the ds which reduces the head of the confined aquifer and the strength of the overlain sediments

impact of particle transfer on flow properties of crushed mudstones karst collapse pillar kcp is widespread in north china coalfields where coal extraction above the ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure kcp is composed of rock skeleton and fine fillings which can be transferred under the effect of water flow thus kcp usually functions as a channel for groundwater inrush in order to investigate the mechanism of mining induced groundwater inrush of kcp which was caused by fine fillings transfer a self designed particle transfer permeability testing system was used to test the crushed mudstones flow properties which included fine filling particle transfer rate porosity increase rate and permeability under the conditions of varying pore pressure particle size mixture and compaction level initial porosity the tests indicate fine fillings transfer is the essential reason for mining induced groundwater inrush flow instability of kcp the flow properties changeability during fine particle transfer could be divided into four stages i e initial flow stage flow inrush stage continued particle flow stage and stable flow stage and flow inrush stage which is the key point to cause water inrush due to the crushing of edges and corners and the adjustment of the structure the fluctuation of permeability time relationship mainly distributed in the first two stages which make a change to flow channel moreover with the increasing of pore pressure particle size mixture and initial porosity the water inrush time and stable seepage time decreased more rapidly the fine fillings porosity and permeability increased gradually the efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well and not all of the pore structures were in flow this means there was a part of pores that were invalid but the effective porosity in flow can be treated as calculation value approximately

characterization of karst structures using quasi 3d electrical resistivity tomography karst is characteristically complex hydrogeologically due to a high degree of heterogeneity which is often typified by specific features for example cavities and sinkholes embedded in a landscape with significant spatial variability of weathering characterization of such heterogeneity is challenging with conventional hydrogeological methods however geophysical tools offer the potential to gain insight into key features that control the hydrological function of a karst aquifer electrical resistivity tomography ert is recognized as the most effective technique for mapping karstic features this method is typically carried out along transects to reveal 2d models of resistivity variability however karstic systems are rarely 2d in nature in this study ert is employed in valley and hillslope regions of a karst critical zone observatory chenqi watershed guizhou province china using a quasi 3d approach the results from the extensive geophysical surveys show that there is a strong association between resistivity anomalies and known karstic features they highlight the significance of a marlstone layer in channeling spring flow in the catchment and confining deeper groundwater flow evidenced by for example localized artesian conditions in observation wells our results highlight the need to analyze and interpret geophysical data in a three dimensional manner in such highly heterogeneous karstic environments and the value of combining geological and hydrogeological data with geophysical models to help improve our understanding of the hydrological function of a karst system

detecting and characterizing unroofed caves by ground penetrating radar abstract the bare karst surface in the southeastern part of krk island croatia is characterized by different surface karst features such as valley like shallow linear depressions and partially or fully sediment filled depressions of various shapes and sizes they were noticed due to locally increased thickness of sediment and enhanced vegetation but had not yet been systematically studied and defined considering only the geometry of the investigated surface features and the rare traces of cave environments detected by field surveys it was unclear which processes surface karstification and or speleogenesis contributed most to their formation the low frequency ground penetrating radar gpr method using a special 50 mhz rta antenna was applied to study and describe these karst features three study sites were chosen and 5 km of gpr profiles were positioned to include various surface features the results obtained from the gpr investigation lead to the following conclusions 1 an increased thickness of sediment was detected in all the investigated depressions indicating their considerable depth 2 areas between different depressions expressed as attenuated zones in gpr images reveal their interconnection 3 transitions between surface and underground features are characterized by a collapsed passage visible in the gpr data and 4 an underground continuation of surface valley like depressions was detected proving the speleogenetic origin of such features subsurface information obtained using gpr indicates that the valley like depressions irregular depressions completely or partially filled with sediment and some dolines are associated with a nearly 4 km long unroofed cave and developed as a result of karst denudation in the regional context these results suggest long lasting karstification processes in the area in contrast to the pre karstic fluvial phase previously assumed to have occurred here this research is the first application of the gpr method to survey unroofed caves worldwide and the first detailed study of such karst features in croatia the low frequency gpr proved to be an efficient method not only for detecting underground continuations but also for distinguishing and identifying surface features and transition zones between surface and subsurface segments of unroofed caves and can therefore be used for recognizing similar geomorphological features