We would like to express our gratitude to the entire organising committee (Antoine Chabrol, Etienne Cossart, Aurélien Christol, Emilie Ecochard, Franck Lavigne, Eric Le Breton, Charles Le Cœur, Irina Pavlova, and Nathalie Thommeret) of the 2010 Young Geomorphologists colloquium of the French Group of Geomorphologists. The organisation received financial support from the University Panthéon-Sorbonne (Paris 1) and the PRODIG (UMR 8586 CNRS) and LGP (UMR 8591 CNRS) research laboratories, as well as logistical support from the Department of Geography of the University Panthéon-Sorbonne (Paris 1). We also acknowledge with thanks the 16 reviewers who commented the former drafts of the papers, and Natasha Shields who carefully translated in English the introduction of this issue.
1Through studying the evolution of terrestrial relief, geomorphologists seek to understand and model the dynamics of physical environments. The time-scale is therefore at the heart of the geomorphological approach. Indeed, it would be impossible to provide an exhaustive account of all of the studies that quantify erosion data or reconstruct the rhythms of evolution. Thus, the presentations made by the 'young geomorphologists' on the 4th and 5th of February 2010 at the University Panthéon-Sorbonne (Paris 1) integrated this temporal dimension, according to the three principal time scales classically used in geomorphology (fig. 1): 'the present-day morphological time-scale and the two scales of past geomorphological transformations as recorded by sedimentary archives or landforms' (Allée and Muxart, 2007). These three themes, however, were not equally represented in terms of the number of communications referring to each.
Fig. 1 – Lateglacial/Holocene transition in the Upper-Durance catchment
A: Volumes of relief and structural landforms. Example of the Hofdaholar escarpment (Skagafjörður, North Iceland): the escarpment, dipping slightly in accordance with the layers of basalt provides a large amount of debris. Its chronic instability was the cause of several generations of mass movements (Mercier et al., 2011), not visible in the photograph. Acquired by É. Cossart (July 2010).
B: Geomorphology and past environments remnants. Example of glacially-polished knobs, preserved here on a basalt outcrop (Bakkaflöt, Skagafjörður, North Iceland), inventory and mapping allows to reconstruct the extent of the paleo-glacier; striae indicate the direction of the ice-flow. Acquired by É. Cossart (July 2010).
C: Geomorphology and current morphodynamics. Outcrops of schists, easily gullied, provide debris made of fine particles and elongated boulders. This abundant supply favors a high sediment load of water; during high intensity rainfall events, hyper-concentrated flows or debris-flows may occur, threatening the infrastructures of the village and the ski resort of La Grave (Hautes-Alpes, France).
Acquired by É. Cossart (July 2007).
2Studies on structural geomorphology over long time scales (greater than one million years), that reconstruct erosion rhythms and erosion data through records that are often incomplete and difficult to interpret (relief, superficial landforms, paleosols, etc.) are less well-represented. The small number of studies presented on this theme is, of course, regrettable as this branch of the discipline has largely contributed to the growth of geomorphology, as demonstrated by the numerous evolutionary diagrams in contemporary textbooks, and as one may consider that 'structure is the basis of everything' (Dewolf, 1981). Without entering into the details of a complex debate, this may perhaps be the result of recent reforms in research (which is more focused on 'applied' studies), and also the effects of new academic formats (three-year thesis and then a reduced habilitation thesis ; Lageat and Le Coeur, 2007) which encourage the acquisition of results that may be published rapidly. The article by A. Poiraud et al. (in this volume) shows that while studies of structure and lithology are indeed fundamental, their applications are real. In the case presented, the initiation and the functioning of landslides in the Puy catchment cannot be understood without a thorough study of the structural framework.
3The 2010 Young Geomorphologists colloquium showed that the reconstruction of past dynamics through sedimentary records is an expanding area of the discipline with renewed applications, particularly in geoarchaeology. Recent improvements in geophysical prospection methods as well as dating methods may explain this dynamism. Generally focused on the Holocene, studies in this area concern scientific interactions between the domain of Earth science and disciplines focusing on the activities of past human societies. In this way, the article by C. Flaux et al. (in this volume), through the case study of the Nile Delta, shows how chronostratigraphic markers allow the environmental conditions of past societies to be defined.
4'Present day morphodynamics', meanwhile, remains the most productive field in our discipline in terms of the number of publications proposed in 2010. In this context, the term 'present day' is associated with multiple different time scales ranging from the instantaneous event (typically the natural hazard) to the slow yet relentless evolution of a system as it reacts over many decades or centuries to climatic and human impacts. Two types of contributions have shown how geomorphology continues to progress in the domain of present-day dynamics. Firstly, the description and interpretation of markers (particularly sedimentary markers) of certain events is more and more precise, as shown in the case study on tsunami deposits (article by P. Wassmer and C. Gomez, in this volume) or on fluvial deposits (article by G. Brousse and G. Arnaud-Fassetta, in this volume). In addition, the systematic use of geomatic methods in synthesising a rich (yet often disparate and heterogeneous) iconographic documentation, allows not only unique events but also successions of events over a period of several decades to be reconstructed, as presented in the article by G. Brousse et al. (in this volume).
5Faced with these different time scales, which are almost intuitively integrated by geomorphologists according to their study objective(s), geographers involved in 'modelling' have been able to adopt extreme solutions such as 'la mise entre parenthèses du temps' ('isolating time periods' ; Durand-Dastès, 2001), thus using an approach that focuses on explaining of how a given situation is allowed to last. These 'models' are based on the hypothesis of equilibrium, and even stable equilibrium, relating to the process or the phenomenon studied. This isolation of time periods, may be partly found in the approach adopted by Siegfried Passarge (1867-1958) in his definition of 'landscape theory'. G. Hallair (in this volume), in an article that is epistemological in scope, traces the construction of this theory which prefigured a typical approach to geographical information systems, emphasising so-called “vertical” interactions (sensu Pumain and Saint-Julien, 1997) between sites.
6In conclusion, the temporal dimension shows, firstly, the interest that research on markers of environmental change, whether of climatic, human or tectonic origin, holds for the study of geomorphology. In addition, taking account of time scales is in itself a rich field of research, which encourages advances in modelling approaches in our discipline. Indeed, beyond 'discrete' diachronic reconstructions undertaken based on simple static states, modelling and simulation software now offer many applications to take account of 'continuous' time. This opens many perspectives for modelling possible equilibria within the functioning of systems, and understanding why one particular equilibrium is achieved instead of another. These approaches complement those of many other geographers and in the future may constitute one of the 'core areas' of our discipline.