We would like to especially thank the 2014 JJG organizing committee (S. Costa, R. Davidson, D. Delahaye, A. Beauchamp, M. Fressard, A. Glais, P. Letortu, O. Maquaire, A. Marone, B. Parey, T. Preux, R. Reulier and A.-J. Rollet) and the geography faculty of the Caen Basse Normandie University for the assistance provided during these days and their organization stage. We also thank the Caen Basse Normandie University for their financial support. Finally, our thanks also go to all the reviewers who gave us their time to help improve the scientific quality of the articles published in this issue.
1The 2014 edition of the young geomorphologists’ Days (the 2014 JJG), held by GFG (Groupe Français de Géomorphologie / French Group of Geomorphology) was held in Caen on 31 January and 1 February 2014. This event was organized by the LETG Géophen Caen (UMR CNRS 6554) laboratory and the University of Caen Basse-Normandie. These Days were an opportunity for 14 geomorphologists doctorate students (11 communications and 3 posters) to present their works in four thematic sessions: fluvial geomorphology (2 papers), coastal geormorphology (2 papers), slopes dynamics (4 papers) and geoarcheology (3 communications). This year again, these PhD students come from all over France (Paris, Caen, Toulouse, Brest, Grenoble, Reims and Lyon). The day was followed by a morning spent in the field, at the heart of the Seulles watershed, one of the LETG Caen-Géophen laboratory’s study sites. The topics presented here include agricultural plots erosion, transfers and sedimentary connections between catchment and waterways, management of waterways in lower Normandy, etc.
2The 2014 JJG confirm the main thematic orientations of French geomorphology observed in the context of previous editions. Temporally, presentations mainly analyze current or Holocene dynamics and, again this year, structural studies conducted over a long time are little represented, which is noteworthy. Spatially, the surveyed plots continue to cover diverse geographical contexts, from the French coast (Brittany, Normandy) to desert environments (Egypt), through the Paris basin, the Garonne basin, the Alps, Italy and Armenia.
3This special issue brings together 5 articles drawn from these presentations. While they are not representative of the curiosity French geomorphologists feel towards foreign lands, they all show our common interest in the issue of identifying the contributions of various natural and anthropogenic drivers on the evolution of different morphological systems. Two approaches can be schematically differentiated. The first is based on an analysis at various time scales (Holocene – over several centuries) to observe breaks in the path of the systems studied in connection with the more or less abrupt changes in potential drivers. The second focuses on an events- analysis based on measurements with high spatial and temporal resolution, in order to quantify the relative importance of different drivers.
4Studies integrating the first approach are based primarily on the analysis of sedimentary archives of historical documents and geophysical investigations. Along these lines, M. David et al. and S. Lescure et al. (in this volume) seek to identify the controlling factors that led to a fluvial transformation of the Garonne River. Lescure et al. (this volume) are involved in the recent effort that aims to describe a specific part of the Garonne, namely its river-sea space. They thus demonstrate the complexity of these transitional spaces but still manage to reconstruct the outline of the evolution of this system and to correlate them with those observed in other major European systems (Seine, Rhône and Scheldt).
5Further upstream, M. David et al. (this volume) study the factors influencing the development of the hydro-sedimentary functioning of the Garonne River in Toulouse on a centuries-long time scale. Combining the study of historical maps and field measurements (coring and Electrical Resistivity Tomographies), they identify a succession of phases that are more or less active in terms of hydro- geomorphological processes. While these phases generally follow the established models in other European rivers (especially alpine ones), the authors nevertheless point to a double characteristic feature in their observations: namely a simplification of the channel in the middle of the 19th century, and the lack of braided rivers on the old map data during the Little ice age.
6By working on the reconstruction of historical trajectories, many methodological issues emerge, owing to the diversity of old measures and of their resolution. Thus, M. Jabbar et al. (this volume) point to the difficulty of using historical data quantitatively, and comparing them with current data. Nevertheless, they managed to develop a method to analyze ancient bathymetry (19th and 20th centuries) from surveys conducted over the front ranges of the Île-Tudy island (South Finistère region) – taking into account all the inaccuracies inherent in this type of data – and then compare them to recent profiles (2012). While previous work has only observed an overall agradation phase of of this sector since the early 20th century (Bouffort et al., 2011), these authors identify alternating phases of lowering and raising since the 19th century. From these results, it is then easier to differentiate temporally between the many natural drivers (changes in swell regime; effects of major marine-weather events) and the anthropic ones (sand extraction and polderisation...), who have, alternately or simultaneously, ruled the morphological evolution of this sector.
7Studies using an events-driven approach to current morphological processes require the use of more efficient tools, on measurements’ spatial resolution as well as their accuracy. N. Bollot et al. (this volume) have thus questioned the role of groundwater in the occurrence and distribution of landslides, and the influence of wine-making practices on these aquifers throughout the Semoigne basin (Paris Basin). They then conducted a hydrological study combining an integration gauging pole equipped with a micro-meter, and a multi-parameter probe. Their first results lead to reconsider the issue of landslide susceptibility, by complementing the structural and economic parameters normally included in models (Van den Eeckhaut et al., 2010; Conforti et al., 2014 and Umar et al., 2014) with water resources and their relationship with the spatial distribution of landslides.
8For their part, P. Letortu et al. (this volume) have built on a portion of the many quantitative perspectives offered by the use of TLS (terrestrian lidar scan) in coastal geomorphology: fine quantification of ablation rates; visualization of the spatial and temporal distribution of debris production and the distinction between particules and mass movements. Their high frequency diachronic monitoring (every 4-5 months) and their high spatial resolution of the Normandy chalk cliffs hence contribute to better understanding how cliffs retreat; they thus provide answers to the questions asked by societies that have rashly settled very close to the steep edge.