We thank the organizing committee for the 2015 JJG: Agnès Baltzer, Marie Coquet, Axel Creach, Armelle Decaulne, Paul Fattal, Martin Juigner, Baptiste Le Mauff, Denis Mercier. They all contributed to the scientific success of these days. We also thank the UMR LETG 6654, the University of Nantes, Beta Analysis, BN and biscuit factory Saint Michel for their financial support. Finally, we sincerely thank the ten reviewers who accepted this task, helping to improve the scientific quality of the work presented here.
1On January 29-30 2015 the 16th Youth Geomorphologists Day (JJG 2015) took place in the premises of the Institute of Geography and Regional Planning at the University of Nantes. Organized by the laboratory LETG-CNRS UMR 6554 Nantes-Géolittomer on behalf of the French Group of Geomorphology, the event gathered 55 participants and presented 24 oral communications and three posters. The first day was devoted to scientific presentations on key themes of the discipline: hydrological dynamics, paleoenvironments, slope dynamics and coastal environments at various spatial and temporal scales and in various terrains in France and abroad (Brazil, Greece, Iceland, Italy, Turkey, ...). All presentations showed that measurement techniques and data processing are well mastered by doctoral students and young doctors. Despite a busy schedule, all presentations were followed by scientific discussions, which continued during breaks.
2The next day was spent visiting study sites in Pays de Monts and on Noirmoutier Island, where several of the young researchers of LETG-Nantes-Géolittomer have their study sites. The PhD students led that day. The main themes of the day were the variability of sediment budgets of beaches on either sides of the Fromentine Goulet, south of the Bourgneuf Bay, a historical approach to the Passage du Gois and its direct sedimentary environment, aspects of early development of the site around 6000 BP, the protective measures against dune erosion along the island of Noirmoutier, and diagnosis of vulnerability to hazard of coastal flooding on the municipality of La Guérinière.
3This special issue brings together five papers from the JJG 2015 oral presentations, and illustrates the variety of issues currently addressed in geomorphology, coupling field studies and instrumentation. Two additional papers from JJG 2015 and dealing with Iceland (Coquin et al., Autret et al.) have been published in the special issue dedicated for the first time to this northern island in the 2016-1 issue of the journal Géomorphologie: relief, processus, environnement.
4The paper from Manon Besset and co-authors, dealing with the evolution of the Mekong Delta from a satellite image analyses (1973-2014), emphasizes the significant regression of the coastline over the past decades due to the drastic decrease in sediment supply in connection with the growing human activity.
5Guillaume Brunier and his collaborators applied photogrammetry to a high-resolution geomorphological survey of coastal and river environments. The technique "Structure-from-Motion", tested in different sites of French Guyana, allows developing the morphological variations at a fine scale, noting changes in microforms with a precision reaching 5-10 cm horizontally and 10 cm vertically. The technique offers an interesting compromise between the dynamics of the areas studied; measures reproducibility needed; ease of image post-processing; and involved costs.
6In their study of Holocene paleo-meandering in the alluvial plain of the Cher river at Bigny, Anaëlle Vayssière and co-authors characterize the inherited forms and reconstructed the hydraulic processes of the river from paleoflow rates with bankfull discharge. They also dated the river curves reduction between the Middle Ages and the modern Era and the stability of the Cher river from the mid eighteenth century, linked to human activities.
7With the paper on morphometric slope index (MSI) as an indicator of the landscape evolution, Laura Coco and colleagues rebuild slopes prior to erosion and perform statistical analyzes to assess MSI's influence prior to erosion on the characteristics of existing drainage networks in three Italian-watersheds.
8Finally, Arthur Glais and co-authors reconstruct 3,000 years of detritism in the marshy lowlands of Northern Greece and assess the role of climate fluctuations, as well as that of human impact, through a multi-scalar approach analyzing sedimentary formations at high resolution during the Holocene.