The Youth Geomorphologists Colloquium of Strasbourg has benefited from the assistance and financial supports from the laboratory LIVE – UMR 7362, the Faculty of Geography, and the University of Strasbourg. Beta Analytics also provided financial assistance. The organisers of this colloquium, Jean-Michel Carozza, Damien Eartlen and Laurent Schmitt, especially thank F. Kolb, who has provided financial management, and J. Humbert for his support in the process. We thank all the reviewers who have agreed to evaluate these papers and, by their meticulous work, have contributed to the quality of this issue.
1The Youth Geomorphologists Colloquium (JJG) are an opportunity to sound out the discipline, to measure its dynamics and to assess its innovative dimensions regarding the tools, the methods or the thematic investment into new territories. As recalled by M.-J. Penven et al. (2011) by introducing the Rennes JJG 2010, the original purpose of this biennial meeting until 2000, yearly since then, was twofold: to raise awareness of the recent works and encourage exchanges between young Ph.D students. The proliferation of the meetings, conferences and seminars and alternative modes of research dissemination – web pages, scientific blogs... – could have made partially out of date the value of such a meeting. That is not the case, as evidenced by the stability of the contribution level around thirty papers each year. The attractiveness of the JJG is maintained to a high level by the dynamism of the successive organiser teams and the innovations they have bring: in addition to the traditional one day field trip, the spreading over two days of communications, the large amount of time left for exchanges, the introduction of keynote lectures on specific topics of geomorphology or related disciplines (geology, soil science, sedimentology...) or the invitation of foreign students, have contributed to makes the JJG a full part conference. The backing of the JJGs to the journal Géomorphologie: relief, processes, environment and the publication of the best papers in a special issue, also helps to maintain this success.
2The Strasbourg JJG took place on 26, 27 and 28 January 2012. They brought together more than sixty participants. Four thematic sessions were proposed: Palaeoenvironments (6 communications); River dynamics (6); Geomorphological hazards (7); and Soils and soil erosion (5). In addition, two communications of invited foreign students on landslides modelling were also presented. Two keynote speeches, on time dynamics in soils (D. Schwartz, Professor at the University of Strasbourg), and on the particle size analysis (J.-L. Mercier, Emeritus Professor at the University of Strasbourg) have introduced each of the conference day. The geographical distribution of study areas shows an equal distribution between metropolitan France (12 communications) and foreign countries (South America: 3; Maghreb: 5; Turkey: 1; Pakistan: 1; Mongolia: 1; Indonesia: 1).
3This brief review confirms that Strasbourg JJG are in the trend highlighted by E. Cossart et al. (2011). The long-time evolution of geomorphic systems, which was the heart of the construction of the discipline, is now at its lower. In parallel, the structural and tectonic thematics have vanished and have given the way to surface process geomorphology. The emergence of an applied geomorphology more in line with social expectation as hoped by J. Tricart (1978), is probably one of the explanatory factors. The shift of these thematic to geological discipline, the higher degree of specialisation of teaching as well as professionalisation in order to respond to growing demand also contribute equally. The “epidermis of the Earth”, according to Tricart (1962)’s expression may have lost its thickness and congruence, isolated from its “hard basement”. This thematic tightening that we regret, is accompanied by a real capacity to gain new tools and techniques that are used by young geomorphologists to redefine objects and thematic studies on one hand and to the definition of new working methodologies on the other. Thus, the reduction of the geomorphology’s field of intervention, as perceived through JJG, is accompanied by an increasing complexification in methods and tools used. Through this new prism, some of the classical problems of geomorphology are reread and renewed.
4This volume is introduced by the text from the keynote speech provided by J.-L. Mercier on grain-size analysis. This text is in the direct lineage of seminal work performed in Strasbourg by A. Cailleux and J. Tricart (1959). J.-L. Mercier shows that, as many methods in geomorphology, particle-size analysis must be renewed in order to incorporate updated knowledge, as the data acquisition (laser grain-size analysis) has evolved too. This renewal is the condition for an optimal use of these indicators that have not been yet explored and exploited, especially in the context of surface processes or palaeoenvironmental geomorphology.
5The following three sections deal with changes in geomorphic systems over the last few millennium, which is today one of the privileged time-scale for many geomorphological studies. Despite their common time-scale, these works differ as well by their objects as by the methods they used. A. Christol et al. document the evolution of a high-amplitude lake system, the Lake Van in Turkey. They reconstruct the high lake levels by the mean of a coupled stratigraphic and geomorphologic approach that complements the purely sedimentological approaches from lake core data. These authors show the potential of a coupled landforms-sedimentary formation approach to document the evolution of large continental lake system like in the mega-lake Chad (Bouchette et al., 2010) or in lake Lisan (Lisker et al., 2009). Landforms are also at the heart of the work of M. David and J.-M. Carozza, but erosional one. The origin of enclosed depressions from Languedoc-Roussillon is still debated. Here, the origin of these landforms is discussed from the quantitative point of view, i.e. by geomorphometric and statistical approach. Here again, if the method is not entirely new, but the sequence of analysis, PCA and CAH in succession, reveals its potential in order to discuss the origin of these landforms. Finally, the papaer by J. Goslin et al. develop a reconstruction of Holocene sea-level changes in tidal context from stratigraphic and geochemical markers (δ13C), which is a promising alternative to more traditional biological indicators.
6Over middle time-scale (centennial time-scale), the paper by M. Forget shows the usefulness of geo-historical methods to document the evolution of a large river, the Parana River. The size of the hydrographical system studied and the available documentation sources have required an adaptation of the classical methods of the historical geography. Beyond the studied case, this article opens the way for more qualitative approach of historical sources with low geometric quality and their transposition to other contexts.
7Finally, two papers address the issue of geomorphologic changes during short time to very short time-scale. E. De Belizal focuses on post-eruptive adjustments of the hydrographical network that occurred after 2010 on the Merapi volcano. He shows how people have adapted to the new rate of river-torrential system evolution on the volcanic slopes. A. Nicolae Lerma shows all the interest of an unconventional documentary source, the video record, to calibrate and validate a model of coastal flooding in the case of March up to the Caribbean coast of Colombia.
8Ultimately, these papers reveal the development of tools, techniques and methods in geomorphology centred on the intermediate and short times. This shows the ability of young geomorphologists to adapt and innovate in the context of current research. Thus, they contribute to the definition of new paradigms of the geomorphology.