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NUMERO 3 2006:Maquette Geomorpho Géomorphologie : relief, processus, environnement, 2006, n° 3, p. 165-174 The changing nature of periglacial geomorphology La nature mouvante de la géomorphologie périglaciaire Hugh French* and Colin E. Thorn** Abstract Periglacial geomorphology faces the prospect of being consumed or by-passed by the growth of geocryology, the changing nature of geomorphology, and the sophistication of Quaternary studies. Identification of typical ‘periglacial’ landscapes is tenuous. The core of periglacial geomorphology concerns the study of freezing processes, associated ground ice, and related landforms. Such an approach places permafrost in a central, but not defining position, within periglacial geomorphology. Likewise, cold-region geo- morphology, an areal or regional concept, embraces a mix of glacial, periglacial, and azonal processes that assume distinct characteristics in the cold non-glacial regions of the world. Because the ultimate aim of periglacial geomorphology is to create mod- els of cold-climate landscape evolution, continued growth of the discipline depends upon it maintaining a bridging position between geomorphology, geocryology, and Quaternary science. Periglacial geomorphology must always change in response to the larger sci- entific context of which it is part. Key words: periglacial geomorphology, geocryology, Quaternary science, cryospheric sciences, geomorphology. Résumé La géomorphologie périglaciaire doit faire face à la perspective prochaine d’être incorporée ou supplantée par la géocryologie qui connaît un retour en grâce depuis quelques décennies, par l’évolution même de la géomorphologie ou par la sophistication des études sur le Quaternaire. L’identification d’un paysage « périglaciaire » typique est délicate. Le noyau de la géomorphologie périglaciaire se concentre sur l’étude des processus liés au gel, sur la glace du sol et les modelés associés. Une telle approche place le pergélisol en position centrale, mais non définie, au sein de la géomorphologie périglaciaire. Au contraire, la géomorphologie des régions froides, concept spatial, englobe à la fois les processus glaciaires, périglaciaires et azonaux qui produisent des modelés caractéristiques dans les régions froides non englacées de la planète. Puisque la finalité de la géomorphologie périglaciaire est de créer des modèles d’évo- lution des reliefs des zones froides, la croissance continue de la discipline est inféodée au maintien d’un pont entre la géomorphologie, la géocryologie et les sciences du Quaternaire. La géomorphologie périglaciaire doit constamment évoluer en réponse à l’élargisse- ment permanent du champ scientifique dont elle fait partie. Mots clés : géomorphologie périglaciaire, géocryologie, sciences du Quaternaire, cryosciences, géomorphologie. Version française abrégée évolution historique différente, la confusion s’est installée La géomorphologie périglaciaire est une sous-discipline entre la géocryologie et la géomorphologie périglaciaire à de la géomorphologie qui s’intéresse aux modelés et aux cause de relations académiques complexes entre les Acadé- processus des régions froides non englacées de la Terre mies des Sciences et les départements universitaires en (French, 1996). Aujourd’hui, deux questions primordiales Russie et en Chine, et entre les départements de géographie, émergent au sein de cette sous-discipline : premièrement, il géologie, sciences de la Terre, géophysique et ingénierie existe un conflit d’intérêt vis-à-vis du développement rapide dans de nombreux pays du monde. La confusion a atteint de la géocryologie ; deuxièmement se pose le problème de son comble en Russie où les activités de recherche se che- la définition exacte des régions périglaciaires et de l’évolu- vauchent dans des départements entièrement consacrés aux tion de leur nature avec le temps. Cet article s’intéresse à études cryologiques. Il apparaît que la géomorphologie ces deux questions. périglaciaire (et peut-être la géomorphologie en général) se La géocryologie existe depuis au moins 1924 en Russie, sépare à présent de la géographie. Une partie de ce divorce mais apparaît plus tardivement (aux environs de 1940) en repose sur la révélation que de nombreuses notions Amérique du Nord et encore plus tard en Chine. Outre cette anciennes de la géomorphologie périglaciaire n’étaient pas * Departments of Geography and Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. E-mail: [email protected] ** Department of Geography, University of Illinois, Urbana, Illinois 61801, USA. E-mail: [email protected] Hugh French and Colin E. Thorn très argumentées et que plusieurs processus azonaux crédibilité de la géomorphologie périglaciaire. Une telle devaient être inclus dans l’examen des régions traditionnel- perspective fait du pergélisol un élément central, mais non lement définies comme périglaciaires. limitant, de la géomorphologie périglaciaire. De même, de La géomorphologie périglaciaire s’est rapidement déve- nombreux éléments d’étude qui constituent la géomorpholo- loppée après la Seconde Guerre mondiale, mais elle a gie périglaciaire contemporaine doivent également être véhiculé deux pièges importants. Le premier est la suresti- considérés comme une composante de la géocryologie. mation de la météorisation liée au gel/dégel et de son Néanmoins, d’autres composantes de la géomorphologie occurrence, ce qui sera débattu dès les années 1970. périglaciaire englobent l’impact du gel saisonnier ou le rôle Aujourd’hui, on sait que la météorisation en régions froides du manteau neigeux et des couvertures de glaces marine, est complexe, car elle englobe également des mécanismes fluviale et lacustre (Thorn, 1978). En outre, la géomorpho- biologiques et chimiques. Le second piège réside dans le logie des régions froides non englacées doit prendre en fait que cette sous-discipline a insuffisamment pris en considération l’étude, non seulement de la géocryologie et considération, non seulement la lithologie, mais aussi la de la géomorphologie périglaciaire comme définies ici, durée et l’efficacité des conditions climatiques froides. mais également les processus azonaux qui montrent des Nous pensons que la géomorphologie périglaciaire contem- fonctionnements et/ou une fréquence ou une magnitude dif- poraine devrait être perçue comme une sous-discipline férents dans les régions froides. Au cours de notre époque consacrée aux processus géomorphologiques, sur le modè- caractérisée par des changements scientifiques rapides, la le de la géomorphologie fluviale ou éolienne, par exemple. géomorphologie périglaciaire, comme toute autre science, Ainsi définie, une géomorphologie périglaciaire s’attachant doit s’adapter à de nouvelles attentes plus rigoureuses, afin principalement aux modelés ne manquera pas de chevau- d’éviter le risque de flétrir puis de disparaître. cher considérablement la géocryologie dont le champ d’étude est consacré aux conditions thermiques dans le sol Introduction et à la glace du sol. Cependant, de tels chevauchements thé- matiques sont fréquents dans le monde scientifique et des Periglacial geomorphology is the sub-discipline of geo- disciplines connexes s’appuient clairement sur leurs exper- morphology concerned with the landforms and processes of tises respectives pour permettre, grâce à cette fertilisation the cold non-glacial regions of the world (French, 1996). croisée, de renforcer le progrès scientifique. However, while this definition captures the traditional Nous pensons que la géomorphologie périglaciaire doit essence of the sub-discipline, it does not reflect, nor address, désormais se concentrer sur : 1) la nature des processus liés two important emergent issues within periglacial geomor- au pergélisol, à la glace du sol et aux modelés associés ; 2) phology. The more fundamental is the relationship between les processus azonaux qui opèrent dans les environnements the older sub-discipline of periglacial geomorphology with froids mais non englacés ; 3) les espaces à la périphérie des its roots in climatic geomorphology, and more broadly geog- glaciers (zone proglaciaire) et les transitions paraglaciaires raphy; and the younger, presently more vigorous discipline qui leurs sont associées ; 4) les environnements alpins of geocryology, here defined simply as permafrost science. (montagnards) ; 5) les reconstructions paléoenvironnemen- The latter discipline is one of the cryospheric sciences and tales des climats froids pléistocènes, et enfin ; 6) les études has a sharply different disciplinary heritage to that of géotechniques et environnementales associées au sols gelés, periglacial geomorphology. These overlapping, even con- au gel du sol et au changement climatique global. flicting, interests can be viewed as an illustration of Le but fondamental de la géomorphologie est l’élabora- M. Church’s (2005) recent observation of the drift of geo- tion de modèles d’évolution des paysages. Cependant, la morphology away from geography. Probably, the situation nature de l’évolution des paysages sous conditions froides et also reflects the normal ecological development of any sci- non englacées reste largement négligée en réalité. Une telle entific discipline that sees it invading new territory tâche est certainement ambitieuse. Pourtant, elle doit être opportunistically, dying back when the prevailing paradigm entreprise car actuellement les progrès les plus substantiels appears stale, and dying out when it has been exhausted. At nous viennent de la géocryologie et des sciences du Quater- the disciplinary scale these steps seem
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