References of "Alexandre, Jean"
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See detailLa climatologie
Erpicum, Michel ULg; Alexandre, Jean ULg

in Bulletin de la Société Géographique de Liège (2003), 43(2003), 79-88

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See detailLes cuirasses latéritiques et autres formations ferrugineuses tropicales : Exemple du Haut Katanga méridional
Alexandre, Jean ULg

in Annalen. Geologische Wetenschappen = Annales - Musée Royal de l'Afrique Centrale. Sciences Géologiques (2002), 107

In Southern High Katanga, the ferruginous formations such as iron duricrusts and stone lines with lateritic nodules show a diversity as broad as in Western Africa. Bauxites are nevertheless almost absent ... [more ▼]

In Southern High Katanga, the ferruginous formations such as iron duricrusts and stone lines with lateritic nodules show a diversity as broad as in Western Africa. Bauxites are nevertheless almost absent proving that, here, aluminium does not contribute to the genesis of duricrust, leaving iron as the only responsible. Among that wide diversity, the indurated sands form a special case because of their dual origin. Because of a large porosity favouring a fast iron penetration and fixation, some of the sandy concretions or duricrusts may have a short history and some of them may even be very recent. Nevertheless the others have a genesis that fits in with the general longer scheme. The most frequent type of laterite crust is also the most complex one. Its facies is both nodular and vermicular. Several agents and climatic phases are involved in its formation : • A first planation surface with wide-open valleys where the water table lies near the surface induces favourable circumstances for the next step; • In such circumstances, nodules are shaped in the mottled soil horizon. One exceptionally well-preserved site evidences the proximity between mottles (the nodules to be) and water table level at the end of the dry season; • A revival of erosion enhances river down cutting which in turn lowers the water table so that termites can reach the mottled horizon; • Nodules are mechanically concentrated by elimination of the non-indurated zones (relative accumulation): within the soil, by termites (on shaly rocks), at the surface by run off (often, on sandy rocks, unfavourable to termites activity); X • Finally the ran off extends to both types of rock and denudes the indurated zone; • A ferruginous coating forms on different substrates : upper laterite surface, internal joints, termite galleries as well as on any gravel at the soil surface. The coating lies unbroken from one object to the other but the outer surface is frequently eroded. The superficial coating could be a rock varnish formed by bacteria during a desertic period. The coating of galleries partly inhibits bioturbation because they collapse no more. The network of the strengthened galleries constitutes an internal skeleton reinforcing the laterite mantle; • With the return of a less severe climate, termites from below the laterite mantle again bring up material. The resulting upper fine deposit often exceeds 2 meter. All those processes imply important climatic variations : • A steppe vegetation with a scanty grass cover favouring run off and planation; • A relatively arid climate for the coatings formation; • A contrasted seasonal regime, not so different from the present day climate (six months dry season) for vertical erosion and intense termite activity. The weathering of rocky materials except for the iron impregnated ones (nodules, ferricretes and so on) requires a humid climate. This is happening nowadays but the more humid Quaternary phases were more effective in that respect. The characteristics of the outer coatings (thickness, colour, conservation state of the included quartz grains) allow us to identify four levels of ferricrete. Their succession is confirmed by the relative position of the coatings between them and by the correlated continental deposits. Because of their coatings, all those ferricretes are dated back to the Tertiary (because of the desertic climate needed for the formation of the rock varnish). Their levels overlook the Quaternary river terraces. The oldest ferricrete is quite different from the others. It shows neither nodules nor termite galleries. Its facies is thus very different from the nodular/vermiform of the three younger ones. It shows three facies, sometimes superimposed : pisolithic, massive or breccia-like. Moreover, the ferricrete of the corresponding level in West Africa contains bauxite. Its genesis is the result of a very different sequence of processes, some aggressive and linked to a humid climate with a great supply of iron and others resulting from more arid conditions producing the thick pisolith coatings. Ferruginous stone-lines present a wider variety of concretions than duricrast. Their upper part is the result of a concentration mainly by run off that occurred during several periods of the Quaternary. Cover loam is each time built up again by the termites from weathered rocks below the stone-line. The same phenomenon is seen on ferricretes. The soil profile where ferruginous formations can be seen consists of horizons of different ages. Weathering of saprolite and soil lifting are still active nowadays. Whereas some stone-line profiles are renewed at each Quaternary dry phase, the ferricrete profiles are build up during a long period of time extending from the Tertiary till now. A new definition of iron duricrast is proposed that is not based on weathering in depth or on the presence of aluminium [less ▲]

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See detailConditions radiatives nocturnes hivernales et température de la chaussée : l’exemple de la station météoroutière de Berloz (Belgique)
Erpicum, Michel ULg; Alexandre, Jean ULg; Etienne, Hugues et al

in Publications de l'Association Internationale de Climatologie (2000), 13

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See detailClimat - Klimaat
Alexandre, Jean ULg; Erpicum, Michel ULg; Vandiepenbeeck, Marc

Cartographic material (1999)

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See detailPrécipitations atmosphériques et altitude. Prélude à une cartographie des montants annuel et mensuels en Belgique
Alexandre, Jean ULg; Erpicum, Michel ULg; Mabille, Georges ULg et al

in Publications de l'Association Internationale de Climatologie (1998), 11

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See detailVariations interannuelles des précipitations mensuelles et leur répartition spatiale en Belgique
Alexandre, Jean ULg; Mabille, Georges ULg; Erpicum, Michel ULg

in Publication Association Internationale de Climatologie (1996), 9

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See detailTypes de circulation atmosphériques, advection des masses d'air et variations climatiques: Le cas des hivers doux et des hivers rudes récents en Belgique
Erpicum, Michel ULg; Mabille, Georges ULg; Alexandre, Jean ULg

in Publications de l'Association Internationale de Climatologie (1993), 6

In Belgium, air masse advections -as it appears at 850 hPa level- are very important for the explanation of the surface air temperature of mild winters. Nevertheless in case of severe winters, radiative ... [more ▼]

In Belgium, air masse advections -as it appears at 850 hPa level- are very important for the explanation of the surface air temperature of mild winters. Nevertheless in case of severe winters, radiative conditions observed at tropospheric lower level and horizontal motion of very thin air masses (below 850 hPa level) seem to be more important for the explanation of ground level temperature. [less ▲]

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See detailAdvection des masses d'air et température de l'air près du sol : recherche d'une méthode d'analyse
Erpicum, Michel ULg; Mabille, Georges ULg; Alexandre, Jean ULg

in Publications de l'Association Internationale de Climatologie (1992), 5

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See detailLe climat
Alexandre, Jean ULg; Erpicum, Michel ULg; Vernemmen, C.

in Denis, J. (Ed.) Géographie de la Belgique (1992)

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See detailClimatology, Fluvial Hydrology and Tropical Geomorphology at the University of Liège
Alexandre, Jean ULg; Erpicum, Michel ULg; Petit, François ULg et al

in Bulletin de la Société Belge d'Etudes Géographiques = Tijdschrift van de Belgische Vereniging voor Aardrijkskundige Studies (1988), 57(1), 91-107

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See detailCaractérisation des types de temps ou ambiances climatiques à l'échelle locale ou régionale : Proposition d'une méthode de travail
Erpicum, Michel ULg; Alexandre, Jean ULg

in Publications de l'Association Internationale de Climatologie (1988), 1

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See detailUne méthode d'analyse des caractéristiques de la saison des pluies en région sahélienne (exemples pris au Sénégal)
Erpicum, Michel ULg; Binard, Marc ULg; Peters, J.-P. et al

in Erpicum, Michel (Ed.) Actes des journées de climatologie (1987)

Starting from the daily data supplied by four stations Saint-Louis. Dakar, Tambacounda and Ziguinchor, a method of characterization of the rainy season in the Sahelian region is proposed. It is founded on ... [more ▼]

Starting from the daily data supplied by four stations Saint-Louis. Dakar, Tambacounda and Ziguinchor, a method of characterization of the rainy season in the Sahelian region is proposed. It is founded on: a) the computation of ten-day amounts of precipitation moving from day to day and being greater than 30 mm; b) the computation of percentages of rainy days and percentages of dry days included in dry spells of 1 to 3, 4 to 7. 8 to 14, 15 to 30 and more than 30 days duration. These percentages are computed for every five-days period (6 per month) of the part of the year during which it can rain. These percentages are computed from forty successive years (1939 - 1978). [less ▲]

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See detailLes processus climatologiques intervenant dans le bilan hydrologique de petits bassins versants boisés
Alexandre, Jean ULg; Petit, François ULg

in Les Ecosystèmes Forestiers en Wallonie (1983)

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