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Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That sheet is a thin coating of calcium carbonate formed on walls, shelves, benches, and terraces by trickling water [10].?

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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
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Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for cevennes (Keyword) returned 11 results for the whole karstbase:
Traits gnraux de l'hydrologie karstique en Basse Cvenne, 1984, Fabre, G.
GENERAL FEATURES OF KARSTIC HYDROLOGY IN BASSE CEVENNE (FRANCE) - N to the town of Als (SE Massif Central and Cvennes), a very fractured carbonated belt outcrops. The karst concerns some facies of Trias, Lias-Dogger, Upper Jurassic and Lower Cretaceous. Karstic flows are of two types: toward W, convergent to the important springs of la Tour-Dauthunes, and toward E and divergent. Ggeneral characteristics are presented. Economic aspect is pointed out, just as karstic stream piracy.

Karsts et palokarsts du bassin de Mialet (Bordure cvenole, Gard) : formation et volution dun karst dmantel, 1997, Bruxelles, Laurent
The Mialet basin is a limestone massif of 62 km2 on the edge of the Cevennes Mountains, made of 400 m of limestones and dolomites. Two allochtonous rivers (Gardons) cross and dissect it. Many caves are to be found at each level and their formation cannot be explained with today's topography. Surface karstic features (dolines) are rare but karstic fillings and many speleothems can be observed on the surface. These deposits are former karst (paleokarst) cut by rivers incision. Recent karstic systems are organized differently but new subterranean circulations sometimes flow in old galleries and declog them.

Quelle est la dimension du massif karstique de la Sainte-Baume ? Elments pour une thorie spatiale et fractale du karst, 2000, Martin, Philippe
The dimension of the surface of Sainte Baume and its neighbourhood is close to 2,2. This value has been obtained the study of 5 contour lines (from 400 to 800 m) and 5 topographic profiles (3 N - S and 2 E - W). 3 methods were used for contour lines: box counting (DB); the information dimension (Di) and surface - perimeter relation (D(P)). Three methods have been used for topo_graphic profiles: the power spectrum (DSPEC); statistics R/S (DR/S) and vario_gramme (DVAR). Average results are: (DB) = 1.20; Di = 1.23; (D(P)) = 1.32; DSPEC = 1.17; DR/S = 1.24; DVAR = 1.23. Thus, the surface of Sainte Baume and its neighbourhood is fractal. It means, theoretically, that Sainte Baume can be characterised by an infi_nite surface in a bounded volume. This first approach focuses on karst surface approach, cave systems approach will be presented in a following paper (in this review). This result raises numerous geomorpho_logic questions. How to calculate a specific erosion? How to think forms in a theoretical frame, which could develo_ped out of the Euclidean geometry conventions? How to think an essential_ly irregular morphology? Elements of answer are brought on a theoretical plan. They constitute the first elements of a karst geometrical theory. Calculation of the specific erosion points out the problem of the size of the surface used. Due to fractal theories, this size is relative to the observation scale used. To be significant, specific erosion calcula_tion needs the use of an efficient scale, in regard of the erosion processes studied. Furthermore, specific erosion expresses only a balance of mass, not a morphoge_nesis. It corresponds to a chronological approach of the karst. Two dynamics can be distinguished in surface morphogenesis. In one hand, increase of the mean slopes is named spatial differentiation, in another hand, decrease of this value is classically called: aplanation or levelling. These 2 dynamics imply the wearing away of spatially various materials. It takes place essentially around thalwegs during the differentiation stage, around the crest during levelling. Thus morphology, space are important factors of the dynamics in the work. Space is not only a support, but an actor in morphogenesis.

Forme et rugosit des surfaces karstiques. Consquences pour une thorie spatiale et fractale de linterface terrestre, 2000, Martin, Philippe
This text proposes a theoretical, hypothetical and speculative approach of the transformation of earth's surfaces. This reflection is based on the notion of otherness. Our approach uses two oppositions: levelled/ roughness and karstic/ non karstic. The dimension of the roughness surfaces is understood between 2 and 3. The dimension of the surfaces of levelling is close to 2. Quantifications showed that massifs are limited by surfaces more or less irregular. In certain cases, the erosion transforms so a surface of levelling into rough surface. In that case initial shape is not preserved. The levellings on the karstic massifs (outliers often) seem better preserved (karstic immunity) than on the other rocks. This conservation would explain a weak value of the fractal dimension of air surfaces of karsts tested always with the same protocol (relation S PD). They were compared with the surfaces of reliefs of basal complex. Three ideas summarise obtained results: [1] The average of fractal dimensions of karsts are smaller than those of the relief of basal complex. [2] The dispersal of the mean values of surface of karst is lower to the dispersal of the mean values of basal complex. [3] Distance between minimal and maximal values for karsts is much bigger than distance between minimal and maximal values for basal complex. To explain the weak roughness of karsts we made three hypotheses: [a] These fragments would correspond to zones still not affected by the erosion (time problem) [b] In such a system some changes on a plan would prevent changes on the another plan (spatial problem) [c] Initial shape is replaced by a similar shape (Platon's Parmnide). The endokarst is described empirically and by analogy with the fractal model of Sierpinski's sponge as a unique surface infinitely folded up in a limited volume. So the growth of the karstic spaces in the endokarst, increases almost until the infinity, the size of the internal surface of the karst. To find a theoretical base at the roughness and at the extreme size of these surfaces, we studied the report between the growth of a volume and the growth of the surface, which limits this volume. Three theoretical models show that if surfaces do not change, volume to be affected by unity of surface grows strongly. Eroded volume depends on the size of the exposed surface. If the eroded volume depends on the size of the exposed surface, then time to erase a mountain could be, in theory, infinite. This is not acceptable because a massif can be erased in about 200 Ma. According to analogies with different morphogenesis (physical, biologic), we make the hypothesis that fractal character, of surfaces of the massifs corresponds to the necessity of increasing, as much as possible, the size of the surface subjected to the erosion so as to decrease the time of destruction of the relief. This is coherent with the idea of a system far from the balance, which tends to join the state of balance as quickly as possible by developing specific morphologies. Distance between the relief and the lower limit of the potential of erosion is then introduced as a factor being able to explain the small roughness of high continental surfaces. The reduction of the volume by erosion is cause (and not consequence) of the decrease of the roughness. The surface can become less rough because volume decreases. The surface of levelling constitutes the final morphology, which is transformed only very slowly. In this perspective the dynamics allows only the fulfillment of spatial rules. In the case of the karst, because of the existence of the subterranean part of the karstic surface and its roughness, it is not useful that air part becomes very rough. Levellings would be preserved by geometrical uselessness to destroy them. They would not correspond to forms in respite as implies him the temporal analysis (hypothesis [a]), but to forms corresponding to a particular balance (hypothesis [b]) who would even be locally transformed (karstic levelling) into the same shape (hypothesis [c]). This theoretical plan supplies with more an explanation on the visible contradiction between the speed of the karstic erosion and the durability of levellings.

Pedogenic and Karstic Features at the Boundaries of Bathonian Depositional Sequences in the Grands Causses Area (Southern France): Stratigraphic Implications, 2000, Charcosset P, Combes Pj, Peybernes B, Ciszak R, Lopez M,
Several exposure surfaces (D1 to D6) underlain by paleosols, paleokarstic surfaces, and subsurface paleokarsts were identified in the Middle to Upper Bathonian Calcaires a Stipites and Dolomies II Formations in southern France. Two kinds of paleosols with different degrees of maturity were recognized: simple ferruginous crusts, capping very irregular bed surfaces, and a rooted horizon. The paleokarstic surfaces are marked by nodular horizons and paleocaves. On the Cevennes shoal, the paleokarsts discontinuities are associated with synsedimentary tectonic processes, which did not extend into the overlying Dolomies II Formation. Subsurface paleokarsts were observed in the Cirque du Bout du Monde (on the Cevennes shoal) within the Calcaires a Stipites Formation, just beneath surface D5. They are characterized by stronger brecciation of the beds. Most of the paleokarstic discontinuities described in this study correspond to the boundaries of four third-order depositional sequences, Bt 1 to Bt 4 (D1 at the base of Bt 1; D2, D3, D4, and D5 capping Bt 1, Bt 2, Bt 3, and Bt 4, respectively; D6 at the top of the Dolomies II Formation). D1, D2, and D3 paleokarsts are geographically limited to the Grands Causses Graben, whereas D4, D5, and D6 are present only on the Cevennes shoal. Geographic trends of paleokarsts confirm the transgressive trend of sequences Bt 3 and Bt 4, and of the overlying Dolomies II Formation towards the shoal. D6 paleokarstic features were also observed within the uppermost part of the Dolomies II Formation in the Horst de Saint-Bresson. The latter transgressive process provides evidence for subaerial exposure of this paleostructure during the latest Bathonian-Callovian interval, induced by tectonic uplifts

Evolution of river network at the 'Cevennes-Grands Causses' transition: Consequences for the evaluation of uplift, 2001, Camus H,
The Mediterranean catchment of the Cevennes (S. France) presents deep incision of the river network (fig. 1 and 2). Combined geomorphology and analyses of the residual sedimentary formations allows to reconstruct a complex history of river network evolution, including capture of tributaries of the Herault River (fig. 1, 2 and 3). The history of uplift of the upstream drainage area could be estimated from the provenance studies of the fluvial and karstic deposits, however river incision is also controlled sea-level changes and differential erosion, which makes reconstruction more complex. Allochthonous clasts types Analyses of allochtonous deposits on the Grands Causses surface reveals different origin for sediments from the hill top and the Airoles valley (fig. 4b), which was previously unrecognised. Facies 1 is found on the highest points of the Grands Causses surface (well sorted rounded quartz pebbles in red shale matrix) it corresponds to a weathered residual sediments (dismantling of an ancient cover). Facies 2 is found on the slope of the Airoles Valley (fig. 7). It consists of alluvial crystalline poorly sorted clasts with outsized clasts (up to 50cm) of quartz-vein, schists in a matrix of shales and sand (weathered granite). Between the hill tops and the Airoles Valley, karstic network presents a sediment fill with clasts reworked from facies I and facies 2 (fig. 6). Airoles valley model : an example of diachronic formation of drainage network The Airoles dry valley stretches on the Grands Causses from the north (700 m) to the south into the present thalweg line of the Vis canyon (500 m) (fig. 1b & 3). Crystalline deposits witness an ancient catchment in the Cevennes. Presently, the catchment in the crystalline basement is disconnected and captured by the Arre River flowing eastwards (fig. 3 & 4a). The profile of the Airoles abandoned valley connects with the present Vis Canyon, therefore, at the time of capture, incision of the Vis canyon had reached its present altitude (fig. 4a). The geomorphologic evolution of this area took place in three stages (fig. 8). 1) The Grands Causses acted as piedmont for the crystalline highlands of the Massif Central (fig. 8A). A latter karstic evolution (tropical climate) allowed the weathered residual sediments (facies 1) (fig. 8A). 2) Incision of the Vis karstic canyon implies that the Herault incision and terraces (facies 2) (fig, 8B) of the Airoles valley occurred during this stage. 3) The Arre valley head propagates westward by regressive erosion and finaly captured the Airoles river crystalline catchment (fig. 8C). Consequence for the Cevennes uplift and hydrographic network development Although the values of present vertical incision in the Vis canyon and in the Arre valley are similar, but they achieved at different time. In addition, the narrow and deep canyon of the Vis is due to vertical incision from the karstic surface of the Grands Causses, whereas the Arre wide valley results from (a younger) lateral slops retreat from a low Herault base-level. The Vis karstic canyon developed in a similar way to the major karstic canyons of both Mediterranean and Atlantic catchment (i.e. Tarn). This rules out a Messinian Mediterranean desiccation as incision driving mechanism and suggests tectonic uplift of the Cevennes and surrounding areas. The Tam being already incised by 13 My [Ambert, 1990], it implies a Miocene age for the incision. Conclusion The amplitude of the vertical incision cannot therefore be used in a simple way to interpret the uplift history of the basement. Consequently, geomorphologic analysis appears to be a prerequisite to distinguish the part played by each factor, and to select the site of uplift measurement

Polyphased uplift and erosion of the Cevennes (southern France). An example of slow morphogenesis, 2002, Seranne Michel, Camus Hubert, Lucazeau Francis, Barbarand Jocelyn, Quinif Yves,
The Cevennes are bordering the French Massif Central and the Gulf of Lion margin. The morphogenesis of this area results from an interaction between deep-seated and superficial processes, whose origin and timing is still discussed. We attempt a reconstruction of the surrection and erosion history of the area through a multidisciplinary approach including geology, geomorphology, thermochronology and geochronology. Thermochronology shows that the Cevennes basement underwent some 2 km denudation in mid-Cretaceous time. Analyses of the sediments preserved on uplifted surfaces and in peripheral sedimentary basins indicate a differential surface uplift of the Cevennes, of the surrounding calcareous plateaus, and of the coastal plain, that occurred in several stages during the Tertiary. Early Miocene rifting of the Gulf of Lion margin and opening of the NW Mediterranean drastically modified the drainage network. Geomorphology analyses of the incised rivers and karst network suggest that most of the incision results from uplift that occurred sometime in the Serravalian-Tortonian interval. U/Th dating of calcite concretions in karsts allows to chronologically bracket the formation of some fluvial terraces, and to find very low incision rates during the Pleistocene. Most of the morphogenesis predates the Quaternary. This ongoing study shows an example of polyphased and very slow morphogenesis, with present-day landscape including elements as old as Cretaceous

Speleothem rupture in karst: tectonic or climatic origin? U-Th dating of rupture events in Salamandre Cave (Gard, southeastern France), 2004, Ponsbranch, Hamelin B. , Brulhet J. , Bruxelles L. ,
Caves are relatively protected from the main external erosional factors. Therefore, they constitute potentially reliable places for long-term conservation of continental history. Moreover their secondary carbonated deposits, the speleothems, can be dated precisely on the 0-500 ka time-scale using U-series isotopes measured by thermo-ionisation mass spectrometry (TIMS). Tectonic events (tectonic displacements and earthquakes) may change cave morphology and induce speleothem breaking or displacement as has been shown by previous studies performed mainly in Italy [Forti et Postpischl, 1984; Postpischl et al., 1991 for example]. Nevertheless, collapses of speleothems observed today in caves are difficult to interpret as their origin may be linked to several other natural processes. We studied the Aven de la Salamandre cave located in southeastern France (Gard), an area between the Cevennes fault and the Nimes fault, where evidence of Quaternary vertical movements was previously described. However, this region is not considered to be a seismic active zone. The Aven de la Salamandre cave is characterized by numerous broken speleothems. Some of them are very large and a lot of them are covered by growth of new calcite or new speleothem generation. We report here 13 TIMS U/Th analysis performed on two broken speleothems recovered by second generation calcite growth. Dating results are discussed through time corrections due to detrital content of calcite. In the first sequence, a 7 0.35 ka fracture event is identified. In the second sequence, the age of the breakdown is between 1.1 0.1 and 6.3 2 ka. These events could thus be contemporary. Hypotheses for the origin of this fracture event are presented and discussed: (i) karstic catastrophic event due to intense climatic changes or to cavity collapse (break down of hanging wall, gravity, landslide...); (ii) co-seismic ruptures. The first conclusion of this study is that these collapse episodes in the Aven de la Salamandre cave cannot be due to the direct effect of an earthquake or climatic event. Only indirect effects of flooding (by mobilization of the argillaceous components of the floor and consecutive destabilization of the speleothems growing upon it) or earthquake effects (more likely by local effects than by wave front passage) are privileged. By comparing our dating with regional destructive known events (in other karsts, in cliffs and scarps), dated by relative chronology, we are lead to propose a regional generalized event precisely dated here at 7 ka. This second conclusion doesn't contradict the presence of unbroken speleothems older than 100 ka found in other caves in the neighborhood as local effects is one of the predominant factors relative to speleothem stability. As a final conclusion, this paper promotes the use of speleothems as reliable datable tools for assessing regional stability problems (sensitivity to seismic hazards, to destructive intense climatic events...) as is done for paleoclimatic reconstruction

The effect of the Messinian Deep Stage on karst development around the Mediterranean Sea. Examples from Southern France, 2004, Audra P, Mocochain L, Camus H, Gilli E, Clauzon G, Bigot Jy,
It is difficult to explain the position and behaviour of the main karst springs of southern France without calling on a drop in the water table below those encountered at the lowest levels of Pleistocene glacio-eustatic fluctuations. The principal karst features around the Mediterranean are probably inherited from the Messinian period ('Salinity crisis') when sea level dropped dramatically due to the closing of the Straight of Gibraltar and desiccation of the Mediterranean Sea. Important deep karst systems were formed because the regional ground water dropped and the main valleys were entrenched as canyons. Sea level rise during the Pliocene caused sedimentation in the Messinian canyons and water, under a low hydraulic head, entered the upper cave levels. The powerful submarine spring of Port-Miou is located south of Marseille in a drowned canyon of the Calanques massif. The main water flow comes from a vertical shaft that extends to a depth of more than 147 in bsl. The close shelf margin comprises a submarine karst plateau cut by a deep canyon whose bottom reaches 1,000 in bsl. The canyon ends upstream in a pocket valley without relation to any important continental valley. This canyon was probably excavated by the underground paleoriver of Port-Miou during the Messinian Salinity Crisis. Currently, seawater mixes with karst water at depth. The crisis also affected inland karst aquifers. The famous spring of Fontaine de Vaucluse was explored by a ROV (remote observation vehicle) to a depth of 308 in, 224 m below current sea level. Flutes observed on the wall of the shaft indicate the spring was formerly an air-filled shaft connected to a deep underground river flowing towards a deep valley. Outcroppings and seismic data confirm the presence of deep paleo-valleys filled with Pliocene sediments in the current Rhone and Durance valleys. In the Ardeche, several vauclusian springs may also be related to the Messinian Rhone canyon, located at about 200 in below present sea level. A Pliocene base level rise resulted in horizontal dry cave levels. In the hinterland of Gulf of Lion, the Cevennes karst margin was drained toward the hydrologic window opened by the Messinian erosional surface on the continental shelf

Etude des palokarsts des environs de Saint-Remze (Ardche, France) : mise en vidence dune rivire souterraine fossilise durant la crise de salinit messinienne, 2005, Martini, Jacques
Paleokarst investigation near Saint-Remze, Ardche, France discovery of an underground river fossilized during the Messinian salinity crisis - The paleokarst features studied in this paper are hosted in Lower Cretaceous limestone and generally appear as filled caves, subsequently de-roofed by denudation. The most important of them forms a sequence of segments developed at a relatively constant elevation of 360-380 m above sea level and can be traced over a length of 5.2 km. The ancient cave passages generally appear as soil covered bands, 5 to 20 m in width and limited on both sides by limestone outcrops. At surface the nature of the cave filling is revealed mainly by scattered blocks: calcite from speleothems and calcified clay, silt, sand and breccia. In the best preserved places, the earth band lies in a trench, where the walls may display a cave morphology and where the filling is often exposed in a undisturbed state. Three types of detrital cave filling have been identified, which in stratigraphical order are as follows: 1) Beige-grey silt, sand and microconglomerate of immature alluvials, with elements of Paleozoic granites and metamorphic rocks, and Upper Miocene volcanics, both originating from the Cvennes Mountains 30 km to the NW. The lithological composition is comparable to the recent alluvials of the Paleokarst investigation near Saint-Remze, Ardche, France discovery of an underground river fossilized during the Messinian salinity crisisArdche River, which is flowing a few kilometers to the SW and is deeply entrenched into a canyon at elevations of 40 to 80 m. The karst context, combined with the biostratigraphical data obtained from rodent molars in the alluvials, suggests an Uppermost Miocene age, comprised between ~5.8 and ~5.45 Ma. 2) Red mature alluvials and colluvials originating from local reworking of surficial karst residuals. At one spot they gave a paleontological age of 3.6 to 3.0 Ma, but from the local karst context one may expect ages from final Miocene to Pleistocene in other spots. 3) Monogenic breccia generated from wall gelifraction, which is Pleistocene after rodent molars found in two places. The paleocave is visualised as formed by an underground stream fed from swallow-holes on the bank of the Ardche River, when it was flowing more than 300 m higher than its actual bed. With regard to its relatively constant elevation and a discordant relationship with the country rock bedding, it is interpreted as a vadose cave controlled by a paleo-water-table. The other fillings (2 and 3) were deposited during subsequent vadose speleogenesis and after considerable water-table lowering. The elevation of this fossilised underground river coincides fairly well with the pre-salinity crisis abandonment surface (5.52 Ma), which is evidenced in the area by high perched gravel relics. The end of the speleogenesis could have taken place just before this event (~5.6 Ma) or at an age not younger than ~5.45 Ma. In the latter possibility, speleogenesis had to be working before the regressive erosion generated by the drastic lowering of the Mediterranean Sea [5.52 to 5.33 Ma, Clauzon et al, 2005 ] reached the area and de-watered the deep karst aquifer. This fossil underground river provides also information about the morphological evolution of the area. For instance the nature of the immature alluvials suggests that the torrential regime of the Ardche was about the same than today. It also indicates that the important and famous cave systems in the area (Grotte de Saint-Marcel, Aven dOrgnac, Systme de Foussoubie, Grotte Chauvet), which are developed at lower elevations, cannot be older than ~5.6 Ma and most likely formed mainly during the Plio-Pleistocene, although most of them have been initiated during the salinity crisis.

The catastrophic flash-flood event of 8-9 September 2002 in the Gard region, France: A first case study for the Cevennes-Vivarais Mediterranean Hydrometeorological Observatory, 2005, Delrieu G, Ducrocq V, Gaume E, Nicol J, Payrastre O, Yates E, Kirstetter Pe, Andrieu H, Ayral Pa, Bouvier C, Creutin Jd, Livet M, Anquetin S, Lang M, Neppel L, Obled C, Parentduchatelet J, Saulnier Gm, Walpersdorf A,
The Cevennes-Vivarais Mediterranean Hydrometeorological Observatory (OHM-CV) is a research initiative aimed at improving the understanding and modeling of the Mediterranean intense rain events that frequently result in devastating flash floods in southern France. A primary objective is to bring together the skills of meteorologists and hydrologists, modelers and instrumentalists, researchers and practitioners, to cope with these rather unpredictable events. In line with previously published flash-flood monographs, the present paper aims at documenting the 8-9 September 2002 catastrophic event, which resulted in 24 casualties and an economic damage evaluated at 1.2 billion euros (i.e., about 7 billion U.S. dollars) in the Gard region, France. A description of the synoptic meteorological situation is first given and shows that no particular precursor indicated the imminence of such an extreme event. Then, radar and rain gauge analyses are used to assess the magnitude of the rain event, which was particularly remarkable for its spatial extent with rain amounts greater than 200 mm in 24 h over 5500 km(2). The maximum values of 600-700 mm observed locally are among the highest daily records in the region. The preliminary results of the postevent hydrological investigation show that the hydrologic response of the upstream watersheds of the Gard and Vidourle Rivers is consistent with the marked space-time structure of the rain event. It is noteworthy that peak specific discharges were very high over most of the affected areas (5-10 m(3) s(-1) km(-2)) and reached locally extraordinary values of more than 20 m(3) s(-1) km(-2). A preliminary analysis indicates contrasting hydrological behaviors that seem to be related to geomorphological factors, notably the influence of karst in part of the region. An overview of the ongoing meteorological and hydrological research projects devoted to this case study within the OHM-CV is finally presented

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