L’objectif de cette contribution est de comprendre l’impact paysager et écologique diachronique de des fortifications Séré de Rivières et de la guerre, afin d’interpréter les héritages biogéographiques de ces morphologies héritées des conflits. Le secteur considéré correspond au fort de Brimont, situé sur une butte-témoin en avant de la côte d’Île-de-France, s’inscrivant dans la ceinture fortifiée de Reims (Marne ; 7 forts et 5 ouvrages secondaires). Par l’emploi d’une méthode combinant relevé botanique, LiDAR, archives historiques et SIG, une approche géohistorique et biogéographique est proposée afin d’envisager sa trajectoire paysagère, de sa construction en lisière forestière, à son intégration aux réseaux de défense de la Grande Guerre et jusqu’à sa désaffection au cours du XXe siècle. Les résultats témoignent d’une influence mutuelle entre forêt et héritages militaires, tant dans l’influence de la végétation sur les actions militaires que de l’impact de la militarisation et de la guerre sur les milieux forestiers (impacts de la construction du fort et des combats, plantation militaire). La résilience territoriale de ces ouvrages et de ces sites fortifiés est enfin questionnée à l’aune de leur valeur patrimoniale et écologique (îlots de biodiversité, corridors biologique) dans un contexte de fortes pressions agricoles et viticoles.

The slopes of the Champagne vineyards are regularly affected by landslides. Given the high societal and economic stakes, these processes cause significant damage and pose a major challenge for the wine industry, forestry and heritage preservation. Numerous studies have already been conducted to understand their behavior and hydrodynamic functioning. They show varied morphologies and a dominant influence of water resources. However, this forcing does not explain the spatial distribution of current landslides, which occur in upper-slope positions, on the steepest terrain recently planted with vines. Using the two shallow landslides at Reuil, located in the heart of the Marne Valley in the Champagne vineyards, as a study site, recent landslide activity is analyzed through a comparative analysis of three DTMs derived from LiDAR HD data and two UAV photogrammetric surveys. This study reveals the affected areas and displaced volumes, which can reach up to 900 m3. Landslide activity was then correlated with regional climatic data. This research shows that landslides are more likely to occur during a period of excessive rainfall following a drier period. Diachronic analysis of aerial images also demonstrates the influence of land use on landslide activity. In particular, land clearing and vineyard operations on the steepest plots constitute a significant anthropogenic forcing affecting slope stability. Taken together, these results provide greater insight into the changing geomorphological dynamics of the Champagne vineyards. On the one hand, they clarify how landslides occur at vineyard plot scale. On the other hand, they provide initial insights into the resilience of stakeholders (winegrowers, etc.) affected by these instabilities.

Lowland landslides are very common in temperate climates but are less studied than in mountainous regions. Although they are often less spectacular, they can cause considerable damage to the land they affect. In Champagne (France), this is particularly the case in vineyards where land prices are very high. Often, they are the result of the reactivation or resumption of older, often larger and deeper landslides. The recurrence of landslides throughout the Holocene is accepted in the region but not proven. The aim of this contribution was to characterize the temporal evolution of instabilities using two LiDAR images and to understand the impact of the climate on the temporal distribution and activity of landslides. In the upper part of the landslide, displacements affect a surface area of 5500 m2 during a period of strong climatic variations. Moreover, the entire slide, 30 m deep, still appears to be moving. A comparison of two LiDAR images, therefore, enabled us to analyze the displacements with precision and to assess the associated risk management.

The Quaternary saw numerous reorganizations of the hydrographic network, greatly modifying the hydrological network of these rivers. Eastern France is well known for many stream captures, described as early as the late 19th century. The oldest of these have been dated to the Middle Pleistocene. It is interesting to note, however, that these sites, located in the heart of vast limestone plateaus, have systematically become peatland zones, and understanding their functioning is fundamental to wetland restoration and renaturation programs. In addition to serving as biodiversity reservoirs, these peatlands also represent substantial carbon storage potential in the context of global climate change. Using two examples—the Marais de Saint-Gond and the Bar peatland—we propose to provide the key to understanding the origin of their sedimentary filling and the consequences of their current hydrogeological functioning.

As part of the national "Séré de Rivières" defensive system established after the Franco-Prussian War (1870-1871), 234 forts were constructed ex nihilo (1874-type forts). They are made of geomaterials of diverse origins and covered with massive embankments totaling tens of thousands of cubic meters, forming hybrid landforms associated with the fortifications. The two previous editions of the French Young Geomorphologists Days (2022 and 2023) highlighted the significant influence of geomorphological and geological conditions on the spatial organization and construction of these forts, as well as the morphological imprints resulting from their use during WW1. This paper operates on the premise that, while fundamentally anthropogenic structures embedded in the historical environment, these polemoforms (or war landforms) possess a geoheritage value, warranting their recognition as "polemo-geomorphosites”. Focusing on the Reims fortified belt (7 forts and 5 ancillary fortifications constructed between 1875 and 1885), this study aims to explore conservation challenges by examining the causes and processes of erasure to which these morphologies, like all landforms, are subjected. This approach draws inspiration from prior works on WW1 polemoforms, particularly the geography doctoral theses of De Matos-Machado (2018) and Taborelli (2018). To this end, microtopographic data from IGN's LiDAR HD survey (2021-2026) were processed within a Geographic Information System (GIS) to identify erasure indicators ­ such as ruggedness indices and slope distribution analyses ­ that can be generalized across all 12 structures. These findings were cross-referenced with archival and field data to analyze the underlying causes. The "Séré de Rivières" polemoforms demonstrate considerable complexity, encompassing hectometric scales (geofacies) and a much more elaborate internal morphological organization compared to traditionally studied polemoforms (e.g., trenches, shell craters). Despite this, the results allow for a classification of the Reims forts based on their degree of erasure, ranging from virtually intact morphologies to those attenuated or leveled by erosion (abrasion, transport, deposition). The geomorphological approach of polemo-landscapes puts emphasis on the forms, formations, and processes contributing to their genesis and destruction. This perspective supposes the use of the paradigm of geomorphological evolution applied to polemoforms ­ not on the geological timescale, but within the Anthropocene timescale (protohistoric and historical periods) ­ defining primitive, derived, and degraded/leveled landforms. Finally, this analysis highlights various anthropogenic and natural processes contributing to their erasure, including warfare, geomaterial reuse, and gravitational hazards.

Investigations of hydric and hydrogeological mechanisms that contribute to the current reactivation of mass-movements feed predictive models that can be useful for risk management. Our model is based on an approach combining (1) a large-scale analysis of the landforms, using LiDAR imagery and field observations, (2) a characterization of the groundwater (piezometry, conductivity and temperature), both in the landslide and in the stable slope, and (3) electrical resistivity profiles. These combined data allow the reconstruction of the structure of the landslide to determine its influence on groundwater flow. The Saint Maur landslide bars the main aquifer of the Upper Ypresian sands whose slow flow results in lower piezometric level fluctuations and stronger mineralization than found in the unconfined aquifer on either side of the slip. The confined aquifer emptying occurs through the sliding plane so that the landslide aquifer is fed essentially by capillary rise from the shear plane and to a lesser extent by surface infiltration. Therefore, the amount of water in the landslide and the resulting probability of mass movement are weakly correlated with rainfall events. In addition, the wide dispersion of the conductivity values of the landslide aquifer reflects a weak mixing of the water. Groundwater circulation modelling allows us to correct in situ (i.e. underground) the flows causing reactivations, and confirms that stabilization by hydrogeological action is more efficient than a surface drainage. Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/role-of-water-in-destabilizing-slopes

The Jacotines landslide is representative of the large mass movements that affect the Champagne vineyards. Understanding the subsurface structure of these slopes and the mechanisms leading to sliding events is of a great interest, particularly for winegrowers who produce Champagne. This knowledge is generally used to elaborate accurate hazard assessment maps, which is an important feature in land use planning. The approach presented is based on the integration of geophysical imaging (seismic wave velocity and electrical resistivity), lithostratigraphic analysis (drilling core) and geomorphological investigations (surface landforms) to reconstruct the relations between the landslide structure, surface water flow, groundwater regime and the overall slope stability. A first phase of instability resulting in a large rotational slip probably occurred during the Late Glacial Period in morphoclimatic conditions characterized by an excess of water. A second one, still active, leading to superficial reactivations and relates to present hydrogeological conditions determined by the internal structure of the landslide.

The purpose of this research is to study the place of the “Séré de Rivières” type fortification in the geomorphological dimension of the war landscape. A multiscalar approach is proposed to analyze the geomorphological context of this defensive system. It appears that the rationalization of the relief is effective at all scales: the defensive system is rooted in the eastern mountain massifs and in the cuesta system of the Paris Basin; the strongholds of Reims locks a funnel of consequent valley (Vesle River) by basing itself on the reliefs associated to the cuesta of Île-de-France (reverse side of the cuesta, residual hills, outliers). The cross-analysis under GIS of an airborne LiDAR survey of the Nogent-l'Abbesse fort sector (fortified belt of Reims), and of documentary and field sources, provides a diachronic vision allowing to sort out the forms and to polyphase the “morphogenesis” of this polemolandscape. Its construction and modernization (1875-1892) testify to an architectural standardization, a remarkable adaptation to the reliefs and the reasoned use of local geomaterials. Its integration into the defense networks of the WW1 induced mutual pedological (pedoturbation), morphological (bombturbation) and spatial disturbances between the forts (ramps, tunnels, shelters) and the different components of these networks (trenches, observatories, artillery positions, etc.). This highlights the impact of these fortifications prior to the WW1, which tended to be obscured by this fundamentally morphogenic conflict. Finally, it questions the resilience of these morphologies associated with the war and the patrimonialization of their ecological (islands of biodiversity), geomorphological (“polemogeomorphosite”) and historical wealth.

Research carried out over the last twenty years on local geomaterials in the Reims region, as well as an important collection of Antiquity period archaeological corpuses, currently make it possible to identify the main characteristics of geomaterial supply and use in the Gallo-Roman city of Reims/Durocortorum. The establishment of the town during the late Iron Age (La Tène D), within the chalky plain, not far from the Île-de-France cuesta, strongly shaped future strategies for stone supply. Until the end of the early Roman Empire period, the densification and growth of the urban fabric only served to increase the need for building materials. And, in this area, fundamentally marked by the absence of quality dimension stone in the immediate vicinity of the city, in addition to imports, on the one hand this led builders to turn to soft, local materials, and on the other hand to search for replacements. Thus, the supply of building materials highlights the implementation of multiple strategies, including specific “regional” or extra-regional supplies, but also the optimization of the use of local resources. In this article, we propose to review the geomaterial resources identified in the ancient town of Durocortorum, according to their uses and availability in growing areas, starting from the city center and spreading to areas where investment in material supply was important. This analysis is illustrated by the ways in which these resources have been implemented, depending on context of construction or usage. Indeed, our observations demonstrate that each particular context of use had a specific range of geomaterials associated with it. The chalk on which the city is built is abundantly available, but is also a friable material, from which it is difficult to extract consistent blocks. If its use is widespread, from the stabilization of soils and roads, to its use in small rubble for certain protected spaces (cellars), the high alterability of the material likely did not allow its conservation in all examples of its use. In addition, its modest geotechnical qualities exclude it from use in construction of large complexes, which therefore would have required the importation of other materials. The construction of common facilities, such as residential buildings (mainly urban), or private utility buildings, is characterized by the use of local origin materials or materials extracted directly on site. These would have included: rubble stones, silt intended for the manufacture of adobe bricks, and of course chalk, in all of its various forms. Adobe bricks, locally referred to as earthen tiles, are raw earthen bricks, wherein chalk fragments are bound together with brown silt. Rubble stone of local origin (gritstone, sandstone) are most commonly seen in use for the lower parts of buildings (wall plates, bahut walls). On the other hand, the use of ornamental stones for luxurious residences necessitated the implementation of imported marble from outside the region. Rural peri-urban buildings exhibit almost exclusive use of perishable materials, such as cob and mud bricks or mud tiles, but also relatively abundant use of stone for tools, material goods or larger architectural elements. The utilitarian architectural programs, or those dedicated to the day-to-day life of the city and its surroundings, are marked by a selection of materials requiring specific qualities: relative to water for the aqueduct, or their resistance to the underground environment for the cryptoportici bases. Finally, the construction of monumental adornment for the ancient city, as well as adjacent funerary areas, led to the massive importation of materials from quarries located 30 to 45 km away. The Mars Gate example illustrates this use of large blocks of Lutetian limestone, sourced from a distant area in the region. Thus, the use of geomaterials can be understood as responding just as much to a logic of availability or accessibility, as to a capacity for implementation or requirements in terms of quality, as illustrated by the use of stones with low capillary action in foundations or stem-walls. In Reims, these different requirements required the importation of materials from sources located at a variable distance from the city.