Publications of Luc Willems
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See detailPoint Dilution Tracer Test to Assess Slow Groundwater Flow in an Auxiliary Karst System (Lake of Fontaine de Rivîre, Belgium)
Meus, Philippe; Flament, Jérémy; Willems, Luc ULiege et al

in Eurokarst 2018 Proccedings (2018)

The quantification of mass transfer through auxiliary karst systems is addressed by using a specific point dilution long-term tracer test. The physical functioning of such systems is usually only inferred ... [more ▼]

The quantification of mass transfer through auxiliary karst systems is addressed by using a specific point dilution long-term tracer test. The physical functioning of such systems is usually only inferred by hydrodynamical and environmental tracer data, whose interpretation often relies on invalidated assumptions. The new approach is a way for experimentally validating or complementing the classical approaches. The lake of Fontaine de Rivîre is an auxiliary karst system in the Frasnian limestones of the Ourthe Valley in Belgium. Its particular confinement was studied by conjunctional use of natural responses and single-point dilution tracer test, with an injection of 41 g of uranine on 22 March 2017. The tracer test was monitored during one year using fluorometers, water and charcoal samplings at five points in the lake and six points at the surface (no connection having been established outside). [less ▲]

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See detailLe vallon « Schmerling » et ses alentours Un site géo-archéologique exceptionnel
Willems, Luc ULiege

Scientific conference (2017)

Si le site des Awirs est célèbre pour les cavités explorées par le docteur Schmerling et sa découverte du premier Néandertalien, il présente d’autres aspects remarquables liés à la fois de la géologie ... [more ▼]

Si le site des Awirs est célèbre pour les cavités explorées par le docteur Schmerling et sa découverte du premier Néandertalien, il présente d’autres aspects remarquables liés à la fois de la géologie locale et de son exploitation par l’homme et aux processus d’altération qui s’y sont déroulés au cours des millions d’années. Une nouvelle prospection essentiellement géomorphologique et karstologique de la zone a permis d’identifier de nouvelles cavités. Elle en précise les modes de formation qui, pour certaines, sont liés à l’altération de schistes et à la libération d’acide sulfurique qui l’accompagne. Les anciennes exploitations d’alun et l’exploitation d’une carrière ont laissé de nombreuses traces d’une archéologie industrielle aujourd’hui partiellement disparue. Le dégagement des terrains de surface par ces activités permet une observation privilégiée des phénomènes souterrains. Une réflexion globale sur ce site unique précise les avantages qui ont conduit l’homme à l’utiliser de façon préférentielle durant des siècles. [less ▲]

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See detailThe Rio Peruaçu Basin, an impressive multiphased karst system
Rodet, Joël; Willems, Luc ULiege; Pouclet, André

in Carvalho Vieira, Bianca; Salgado,, André Augusto Rodrigues; Cordeiro Santos, Leonardo José (Eds.) Landscapes and Landforms of Brazil (2015)

The Rio Peruaçu basin is located on the left bank of the Rio São Francisco, in the north of the state of Minas Gerais. While its upper portion collects the waters flowing from the sandstone formations of ... [more ▼]

The Rio Peruaçu basin is located on the left bank of the Rio São Francisco, in the north of the state of Minas Gerais. While its upper portion collects the waters flowing from the sandstone formations of the Urucuia, its lower part cuts into the Bambuí limestones, carving out a narrow canyon about 200 m deep for which the site is known. Over more than 17 km, the stream opens a bed that disappears underground six times. These underground sections are the remainders of an extensive and complex primitive karst network. Although some segments consist merely of simple but majestic arches, others, such as the Brejal and especially the Janelão, offer kilometers of underground galleries that can attain exceptional dimensions. For example, the Janelão cave reaches a ceiling height of 106 m and a width of 60 m. This ensemble is punctuated by large, flat areas that function as reservoirs, such as the poljes of Silu and Terra Brava, or constitute the confluence with the Rio dos Sonhos. The system results from a complex Cenozoic evolution, including several spectacular episodes. As currently reconstituted, this evolution comprises at least three main episodes. The impressive landscapes of this region are not its only interesting feature: humans have occupied the basin since prehistoric times, as attested by about a hundred rock shelters and open-air dwelling sites that have not yet revealed all their secrets. [less ▲]

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See detailBacteria, bonds between classical karsts and karsts in silicated non carbonated rocks ?
Willems, Luc ULiege

Poster (2014, June)

For several years, similar karsts to those found in the limestone have been observed in various silicated non-carbonated rocks. Several morphological arguments show that a complete dissolution of rocks is ... [more ▼]

For several years, similar karsts to those found in the limestone have been observed in various silicated non-carbonated rocks. Several morphological arguments show that a complete dissolution of rocks is necessary to explain the formation of some caves and other related forms independently of hydrotermalisme phenomena. However, the physico-chemical processes generally considered do not provide a satisfactory explanation to this dissolution. Bacterial activity found deep in many lithologies provides a solution to this apparent contradiction. [less ▲]

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See detailEndokarsts and cryptokarsts in Cretaceous coarse and higly porous chalk at the Belgian-Dutch border
Willems, Luc ULiege; Rodet, Joël

in Filippi, Michal; Bosák, Pavel (Eds.) Proceedings of the 16th International Congress of Speleology, July 21–28, Brno. Volume 3, p. 499. Czech Speleological Society. Praha. (2013, July 21)

Since 2003, the study of several quarries at the Belgian-Dutch border has made it possible to identify numerous karsts essentially developed in coarse chalk (calcarenites) of the Maastricht Formation ... [more ▼]

Since 2003, the study of several quarries at the Belgian-Dutch border has made it possible to identify numerous karsts essentially developed in coarse chalk (calcarenites) of the Maastricht Formation (Upper Cretaceous). This lithology is highly porous and is often considered unfavorable to karstification. However, caves, solution pipes, sponge networks, roof channel, pockets (alveoli) several meters in diameter developed inside without connection to fractures. These karsts belong to flooded karsts (caves and pockets) or to younger cryptokarsts (input karst type – thousands of solution pipes). When the endokarsts dewater, the high porosity of calcarenites inhibits closed caves from evolving. Tubular solution pipes are produced by the seepage water under fluvial terrace gravels and can exceed 30 m deep under the surface plateau. Sometimes, they encounter caves which are consequently filled and fossilized. By this process, they preserve caves from further collapsing inside a crumbly lithology. [less ▲]

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See detailMicroorganisms in Karsts: a case study in St Anne cave, Belgium
Carnol, Monique ULiege; Willems, Luc ULiege; Malchair, Sandrine ULiege

Poster (2011, September 30)

Despite the importance of microorganisms as geochemical agents over geological times, their extended metabolic diversity and their essential role in element cycles (i.e. mineral dissolution, precipitation ... [more ▼]

Despite the importance of microorganisms as geochemical agents over geological times, their extended metabolic diversity and their essential role in element cycles (i.e. mineral dissolution, precipitation, oxido-reduction processes), microbial community composition and processes as well as their ecological role in karst environments are poorly known. While little was published on cave-dwelling microorganisms until the early 1990s, it is now recognized that microorganisms may mediate many important mineral transformations, originally considered to be inorganic in nature. Indeed, recent evidence (Northup & Lavoie, 2001) proved the implication of microorganisms in karstification through precipitation and dissolution processes, resulting in the deposition of carbonate speleothems, silicates, iron or manganese oxides, sulphur compounds and nitrates and in the breakdown of limestone walls. In this poster, we review some potential processes and signs of microbial activity in caves. We present results of a study on the microbial diversity in the ‘St Anne’ cave, Belgium. We focused on ammonia-oxidizing bacteria (AOB), which are responsible for the first, acidifying step of the nitrification process. Chemical composition of the water, numbers of cultivable bacteria (free and particle-associated bacteria) and the diversity of AOB were studied in waters and sediments of the ‘Chawresse’ (underground river in St Anne), on the cave wall and in the soil aboveground. The use of molecular techniques, based on direct ADN extractions, provide more detailed information on the microbial diversity of an environment, as culture-based techniques retrieve only about 1% of bacterial species present in the environment. Bacterial counts showed that most cultivable bacteria were associated with suspended particles and that their numbers decreased underground. Molecular analyses revealed the presence of AOB in the karst system. Comparison of aboveground and belowground diversity also indicated the possibility of a specific endokarst AOB community. Further research perspectives will be discussed. <br /> <br /> <br />Northup, D.E. and Lavoie, K.H. 2001. Geomicrobiology of caves: A review. Geomicrobiology Journal, 18(3):199-220. [less ▲]

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See detailLe système karstique de la Lomme. Quelques points d'observation remarquable
Willems, Luc ULiege; Ek, Camille ULiege

in Professional Paper (2011), 2011/2(309), 11-26

Présentation de quelques sites karstiques remarquables situés sur la commune de Rochefort

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See detailLe système karstique de la Lomme, région de Rochefort, cadre général
Willems, Luc ULiege; Ek, Camille ULiege; Marion, Jean-Marc ULiege

in Professional Paper (2011), 2011/2(309), 3-10

“La Calestienne” is the strip of Devonian limestones which separates the Ardennes from the Famenne and Condroz regions. It contains the most important karstic phenomena in Belgium. The karst system ... [more ▼]

“La Calestienne” is the strip of Devonian limestones which separates the Ardennes from the Famenne and Condroz regions. It contains the most important karstic phenomena in Belgium. The karst system developed over 10 kilometers along the river Lomme (Lhomme) and its main tributary, the Wamme, in the region of Rochefort, illustrates the main characteristics of the Calestienne. The Calestienne around Rochefort is bordered to the northwest by the wide depression of the Famenne shales, the altitude of which oscillates between 150 and 200 meters. In the southeast of this limestone strip, the Ardenne, a region composed of more resistant rocks, rises to altitudes often greater than 400 m. In the landscape, the Calestienne forms a real step at an intermediate altitude. To the Northeast of Rochefort, the limestone strip widens out considerably due to the Gerny anticline. [less ▲]

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See detailKarsts in silicated and non carbonated rocks
Willems, Luc ULiege

Conference (2011)

Karsts in silicated and non carbonated rocks refer to morphologies similar to those found in limestones (caves, lapies, polje…) as being equally generated by predominantly dissolution processes. Their ... [more ▼]

Karsts in silicated and non carbonated rocks refer to morphologies similar to those found in limestones (caves, lapies, polje…) as being equally generated by predominantly dissolution processes. Their discovery in allegedly not very soluble rocks raises the question of existing water resources in lithologies which are rarely considered from this point of view. A rough inventory of this kind of karsts shows that they essentially develop in sandstones and quartzites. Other silicated lithologies such as granites or gneisses seem to contain only a few examples. Karsts in silicated and non carbonated rocks are found at all latitudes, though mainly in the warm and temperate climate zones of the world. Nevertheless, these conclusions may result from the lack of systematic prospecting in numerous regions of the world. Typically, most studied cavities are located in Paleozoic to Proterozoic rocks. Underground networks can stretch for several kilometers. Two types of cavities can be identified. The first one is characterized by cave entrances located in a cliff or in a raised hillside. These subhorizontal cavities end blind within the rock massif. No trace of fracturing authorizing mechanical erosion by flows, which would explain their genesis, was ever recorded. The second type of cavities is characterized by the presence of an underground stream which disappears in a siphon or in some impenetrable passages. In some cases, an important granular disintegration of the surrounding rock produces quantities of sand which seal large pre-existent voids. The latter were formed in different physico-chemical conditions than those present in the open air environment. An initial deep karstification is possible despite the surface environment. Secondary morphologies on the cave walls (alveoli, pillars of dissolution, passages with “key hole” section, ceiling bells …) enable us to partially reconstitute the genesis of these caves. It would start in a phreatic environment with the development of spots of dissolution along deep water circulations. Initially, independent cavities grow and interconnect to form embryonal karst networks. The incision of valleys and the weathering processes progressing from the surface can intersect these. Physical erosion then becomes more prominent than chemical erosion. The pre-existent forms, depending on their organization, can either be dismantled or contribute to the evolution of a complex karst network. A comprehensive study of karsts in silicated and non carbonated rocks is an opportunity to a better understanding of generally inaccessible deep karstification, including in the carbonated rocks. Moreover, the presence of these karsts and sometimes of underground rivers in regions hit by chronic droughts represents a potential of water resources disregarded today. [less ▲]

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See detailKarsts des calcarénites de la carrière du Romont (Eben – Belgique)
Willems, Luc ULiege; Rodet, Joël

in Bulletin de la Société Royale Belge d'Études Géologiques et Archéologiques (2010), (hors-série n°3), 119-134

Th e quarry of Romont (Eben/Bassenge, near the Belgian-Dutch border) intersects many endo and exokarsts developing essentially in coarse chalk (calcarenites) of the Maastricht Formation (Upper Cretaceous ... [more ▼]

Th e quarry of Romont (Eben/Bassenge, near the Belgian-Dutch border) intersects many endo and exokarsts developing essentially in coarse chalk (calcarenites) of the Maastricht Formation (Upper Cretaceous). It is an appropriate place to study deep and superficial karstification in highly porous rocks. Th e porosity partially inhibits the further development of closed caves (endokarsts) aft er they dewatered. Caves are later fi lled-up by collapsing or when they are cut by solution pipes (exokarsts), and thus partially sealed and preserved in a soft lithology. Th ese solution pipes are generated under river gravels and can go tens of meters deep through calcarenites. [less ▲]

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See detailKarsts dans les gneiss - alvéoles géantes et micro-alvéoles dans la région de Milagres, état de Bahia, Brésil
Rodet, Joël; Willems, Luc ULiege; Auler, Augusto

Conference (2009, December 05)

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See detailProblème des karsts en roches silicatées... lacunes d’observation et paradigme du karst
Willems, Luc ULiege; Ek, Camille ULiege; Rodet, Joël et al

Conference (2009, December 05)

Depuis le développement de la karstologie, la grande majorité des cavités prospectées l'ont été dans les roches carbonatées ou apparentées, réputées fort solubles. Partant de ce principe, les autres ... [more ▼]

Depuis le développement de la karstologie, la grande majorité des cavités prospectées l'ont été dans les roches carbonatées ou apparentées, réputées fort solubles. Partant de ce principe, les autres lithologies n'ont été à ce jour que partiellement investiguées puisque réputées peu ou pas solubles. Pourtant, depuis plusieurs siècles, des grottes et autres formes apparentées sont mentionnées notamment dans des grès, des granites ou les quartzites. Très rapidement, elles ont été catégorisées comme pseudokarst en se basant sur deux principes, le premier, la convergence de forme, le second, les processus physico-chimiques qui présideraient à leur formation seraient différents de ceux rencontrés dans les calcaires. L'évolution des recherches et des techniques de ces vingt dernières années ouvre de nouvelles perspectives sur une réalité karstique commune qui transcenderait les lithologies tant carbonatées que non carbonatées. Peu à peu, elle oblige les chercheurs à se repositionner quant à la notion de karst. [less ▲]

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See detailAbordagem geomorfológica da bacia do rio Peruaçu e implicações geoarqueológicas
Rodet, Joël; Rodet, Jacqueline; Willems, Luc ULiege et al

in Arquivos do Museu de História Natural (2009), 19(1), 75-103

The Rio Peruaçu Basin is the object of a geomorphological redifinition starting from a multi-field approach carried out for over ten years. Based on the works of the Minas Gerais archaeologists and ... [more ▼]

The Rio Peruaçu Basin is the object of a geomorphological redifinition starting from a multi-field approach carried out for over ten years. Based on the works of the Minas Gerais archaeologists and speleologists, this study defines four geomorphological compartments from the springs to the juction with the Sao Francisco river,namely: the zone of the upper valley, the zone of the geological transition, the zone of the karstic canyon and the zone of the alluvial plain. The main stages of the geomorphological evolution of the system were released and make it possible to define the space distribution of the mineral resources potentially usable by the prehistoric groups, and also to work out a typology of the raw material deposits. This approach contributes to the definition of the perception of the space by the first human settlements. [less ▲]

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See detailEXEMPLOS BRASILEIROS DE CARSTE EM ARENITO: CHAPADA DOS GUIMARÃES (MT) E SERRA DE ITAQUERI (SP)
Hardt, Rubens; Rodet, Joël; Dos Anjos Ferreira PintoI, Sergio et al

in Espeleo-Tema - Sociedade Brasileira de Espeleologia (2009), 20(n. 1/2), 7-23

The issue of non-carbonate karst is still controversial in academic circles, there is resistance from classical karst researchers. However, in many studies throughout the world, the karst in non-carbonate ... [more ▼]

The issue of non-carbonate karst is still controversial in academic circles, there is resistance from classical karst researchers. However, in many studies throughout the world, the karst in non-carbonate rocks is a constant. Although their existence is controversial, this is due to the small amount of research conducted in these rocks had not generated a sufficient amount of information that would establish general comparison with the carbonate karst, identifying boundaries and differences. In this article, we attempted to show some of the evolution of the concept through the literature and present two examples of sandstone karst in Brazil. [less ▲]

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See detailINCIDENCES MORPHODYNAMIQUES DE LA TREPANATION DE L'ENDOKARST PAR DES RACINES DU MANTEAU D'ALTERATION. EXEMPLES DANS DES GROTTES DE LA CRAIE EN EUROPE OCCIDENTALE (FRANCE ET BELGIQUE).
Rodet, Joël; Willems, Luc ULiege; OGIER-HALIM, Sylvie et al

in White, William B (Ed.) Proceedings : 15th International Congress of Speleology, Kerrville, Texas, United States of America, July 19-26, 2009 (2009)

Le débouché de la zone des puits dans les galeries du karst est considéré traditionnellement comme une suite logique de la pénétration des eaux de surface vers les collecteurs souterrains. C'est pourquoi ... [more ▼]

Le débouché de la zone des puits dans les galeries du karst est considéré traditionnellement comme une suite logique de la pénétration des eaux de surface vers les collecteurs souterrains. C'est pourquoi les observations se limitent généralement à de simples descriptions morphologiques. La mise en évidence de deux ensembles dynamiques distincts, l'introduction des eaux superficielles (karst d’introduction) et la collecte/concentration/restitution aux exsurgences des eaux souterraines (karst de restitution), et l’absence de connexion systématique entre karst d'introduction et karst de restitution permettent d’envisager une évolution initialement séparée, voire diachronique, de ces deux ensembles dynamiques. Afin de vérifier cette hypothèse, nous avons étudié l’impact de la trépanation de grottes dans deux réseaux karstiques d’Europe occidentale. Le premier en Normandie (France) se développe dans des craies fines où la porosité de la roche peut atteindre 10 à 15 %. Le second se situe en Basse Meuse liégeoise (Belgique) dans des calcarénites pouvant dépasser 50 % de porosité efficace. La cavité normande, mature et fossile, est largement comblée de sédiments quaternaires (loess). Elle est reconnue sur plus de 600 m, dont un collecteur de 450 m de développement. La trépanation du collecteur fossile et comblé et son fonctionnement séquentiel ont entraîné une ablation de la partie supérieure du comblement et sa substitution par la charge terrigène introduite par les épisodes d'introduction, avec une sédimentation conforme à la dynamique de l'introduction. Mais l'incidence majeure de ces épisodes est la mise en place d'une morphologie spécifique, organisée de l'amont vers l'aval : effet barrage vers l'amont du drain avec une altération profonde de l'encaissant, ouverture d'une rampe de connexion en toit avec le drain, développement d'un chenal de voûte pénétrable, ouverture d'un grand volume vide - réservoir d'équilibre, creusement d'un chenal de voûte plus petit, qui se réduit en aval au fur et à mesure de l'absorption du flux aqueux par le remplissage et les parois du collecteur. La cavité belge, reconnue sur quelques dizaines de mètres de développement, est comblée de sédiments terrigènes, sans qu’aucune liaison karstique ne soit établie avec une quelconque émergence. L'absence de continuité karstique aval interdit le creusement du chenal de voûte, mais on retrouve le comblement terrigène granoclassé, retouché par les épisodes plus récents, et en aval le développement d'une grande chambre réservoir où la porosité élevée des calcarénites encaissantes absorbe l'eau introduite. Ces deux exemples montrent très clairement que la connexion entre l'introduction des eaux et la restitution karstique n'est pas toujours assurée et surtout que le creusement des formes d'introduction peut se réaliser indépendamment du drainage de restitution. Lorsque que ce dernier est trépané alors qu'il n'est plus fonctionnel, il enregistre les effets d'une dynamique d'introduction. La recherche de ces morphologies dans les collecteurs peut alors livrer de sérieuses indications sur l'évolution du système karstique. [less ▲]

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See detailMorphodynamic incidences of the trepanning of the endokarst by solution pipes. Examples of chalk caves in Western Europe (France and Belgium)
Rodet, Joël; Willems, Luc ULiege; Brown, Joël et al

in Contributed Papers Proceedings 15th International Congress of Speleology (2009)

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See detailKarst in het krijt van Limburg en ombeving
Lagrou, David; Dusart; Willems, Luc ULiege

Poster (2008)

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See detailKarsts in sandstones and quartzites of Minas Gerais, Brazil
Willems, Luc ULiege; Rodet, Joël; Pouclet, André et al

in Cadernos do Laboratorio Xeolóxico de Laxe (2008), 33

The state of Minas Gerais (Brazil) is characterized by significant karst regions, which develop <br /><br />in both sandstone and quartzite terrains and display complex suites of underground and ... [more ▼]

The state of Minas Gerais (Brazil) is characterized by significant karst regions, which develop <br /><br />in both sandstone and quartzite terrains and display complex suites of underground and surfaceforms. In the Espinhaço Ridge, Central Minas Gerais, several caves of up to a few hundred metres long, occur in the surroundings of the town of Diamantina. Some of these caves, such as Salitre actually consist of swallow-holes. Other horizontal caves are characterized by corrosion forms generated in the phreatic zone. In some places, such as in the Rio Preto area, these phreatic forms are overprinted by ceiling tubes, suggesting a polyphase karst evolution, prior to the draining in the cave. Remains of paths, with circular cross section up to one metre in diameter, can be found through residual tower-like surface landforms widely present in the landscapes. Their dissection is due to a generalised karstification in the area, resulting in closed canyons, megakarrens and kamenitzas. In Southern Minas Gerais, close to the Mantiqueira Ridge, the caves of the Ibitipoca state park can reach more than 2 km in length. These caves are associated with a very large hanging geological syncline. Several of these caves contain active streams, which flow for hundreds of metres before disappearing in sand-choked passages. Keyhole cross sections characterize steeply descending passages in these caves, indicatinga chan ge from slow phreatic flow towards a faster vadose flow responsible for the vertical incision of the passage. Such change is probably related to base level lowering and/or to turn in the direction of the water flow. Several generations of wall-pockets, from a few centimetres to over a metre long, occur into the caves. These features are good indicators of the initial phase of speleogenesis, generating the initial conduits by their coalescence. This mechanism is also responsible for cut-off meanders. In the area, the main river flows along the syncline axis and cuts through a rock barrier, generating a tunnel-like passage. This cave drains, through resurgences in its walls, part of the water that flows in other caves located in the flank of the syncline. [less ▲]

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See detailContribution à l'étude du climat de trois cavités souterraines belges
Piron, Julie; Erpicum, Michel ULiege; Ek, Camille ULiege et al

in Bulletin de la Société Royale Belge d'Études Géologiques et Archéologiques (2007), XLVI

Some temperature and CO2 measures have been made for one year in the cave of Ramioul and in the cave of Comblain-au-Pont, and for six months in the underground quarry of Petit-Lanaye inférieure ... [more ▼]

Some temperature and CO2 measures have been made for one year in the cave of Ramioul and in the cave of Comblain-au-Pont, and for six months in the underground quarry of Petit-Lanaye inférieure. Temperature has been measured by dataloggers. These measures and the comparison between the different caves contributed to a better understanding of their climates. In the cave of Ramioul, closed by non insulated doors, the air movements are relatively low but there are some heat exchanges between the outside and inside air by conduction through the doors. The cave can be divided into two parts each with a different climatic behaviour. High and dangerous CO2 rates have already been measured in this cave. Rates fluctuate in an irregular way and without any connection with the natural seasonal cycle, and the CO2 origins stay uncertain. The cave of Comblain-au-Pont can be divided into two major parts: one enclosed and the other ventilated. The ventilated region is a “wind tube” during the winter, but it doesn’t reverse in the summer. On a larger scale, this region can be considered as a cold air trap despite its two exits, since it has a descendant morphology. <br />In the underground carry of Petit-Lanaye inférieure, the low number of data doesn’t allow a complete diagnosis of the climate organisation, but can give a first idea for the summer period. We can already distinguish some parts that are more or less influenced by the outside temperature fluctuations, probably in relation with some air movements which organised <br />themselves in a complex way in the labyrinthic galleries network. [less ▲]

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See detailKarsts des craies et calcarénites de la Montagne Saint-Pierre (Basse Meuse liégeoise)
Willems, Luc ULiege; Rodet, Joël; Ek, Camille ULiege et al

in Bulletin de la Société Royale Belge d'Études Géologiques et Archéologiques (2007), XLVI

The “Montagne Saint-Pierre” (Sint Pietersberg) is a separate part of the Hesbaye plateau, isolated between the lower valleys of the Geer and the Meuse rivers. It is exploited by a big open-air quarry and ... [more ▼]

The “Montagne Saint-Pierre” (Sint Pietersberg) is a separate part of the Hesbaye plateau, isolated between the lower valleys of the Geer and the Meuse rivers. It is exploited by a big open-air quarry and by numerous underground quarries developing galleries on hundreds of kilometers long. Excavated in Cretaceous chalk and calcarenite, these artificial networks allow an exceptional 3-D observation of karsts inside a very porous and permeable rock, less favourable to a concentrated solution. The most numerous of them are “organ pipes” or “earth pipes”. They are vertical tubular solution pipes that may exceed 60 m in depth. Sponge networks and subhorizontal caves occur, without any visible connection with fracturation. Finally, downwards to at least 20 m below the alluvial plain of the Meuse river, pluridecametric nodes of weathered chalk are found. By their size and rounded morphology, the nodes resemble to the natural caves occurring in the calcarenite and intersected by the underground quarries. All the studied karsts allow us to propose a scenario for the genesis of a polyphase karst system. Independently of surface conditions, caves are generated deeply in the phreatic zone (endokarsts). During the downcutting of theMeuse valley, and related to the fluvial terraces, solution pipes (input karsts) are generated. Due to the valley incision and to the lowering of the aquifer,theses solution pipes progress downward and cut the endokarsts. A concentrated water circulation takes place. In the dewatered upper part of the system, caves cut by solution pipes are rapidly filled by superficial deposits. The high porosity of the calcarenite makes it comparable to a sponge. The rock absorbs quickly the out-flows coming from the surface and causes a rapid deposit of the fine particles transported inside horizontal passages. The sealing of these conduits allows their conservation inside a very crumbly rock. [less ▲]

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