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Past landslides have been recognized in the Battice area in E-Belgium. In contrast to the other inactive landslides, the Manaihan landslide responded immediately to heavy rainfall events in the last two decades. This study aims to map its spatial extent and the dominant surface features; to measure surface displacement using GPS; to investigate subsurface structure with Cone penetration test (CPT) and corings; and to determine the depth of the shear surface by inclinometers. Results show a partial landslide reactivation. Surface velocities range between 20 and 40 cm/year and are strongly dependent on winter rainfall. CPT results give clear boundaries between the landslide mass and the undisturbed bedrock in the head scarp. Distinct shear surfaces have been determined with displacement rates up to 15.8 mm in 21 days. Further research should apply geophysical methods for two-dimensional information on the ground, investigate geotechnical properties of the landslide mass, model slope instability, and determine the influence of a sewage pipe crossing the central landslide mass as a potential cause for landslide activity.

Tectonic motion rates of individual faults and regional deformation in an intraplate setting are estimated, based on the analysis of ten yearly surveys of a regional levelling network in NE Ardenne (W Europe). Owing to the frequency and number of measurement epochs, much greater than in classical comparisons of general surveys, the tectonic and near-surface components of ground motion are clearly separated. The marked temporal variability in ground motion strongly depends on the amount of precipitation fallen during the six months preceding each survey and the subsequent drying off of the subsoil at the time of the surveys. Moreover, the ground response to this influence varies from place to place, leading to high differential movements at the local scale. Taking into account the percentage of surveyed faults which moved tectonically during the time of the study, I calculate fault motion rates of 0.06–0.09 mm/yr, similar to geological rates. Moreover, the data indicate that one way for intraplate normal faults to accommodate tectonic strain aseismically is intermittent fault creep, with short episodes of a few mm displacement separated by many year-long time intervals of fault quiescence. A flexural deformation shows the superposition of a tilt event on a trend corresponding to a tilt rate of 0.16 μrad/yr for a 2.8-km-long segment.

A series of palaeolandslides is described in eastern Belgium, with geophysical investigations, trench analysis and a number of 14C dates complementing the field description. The proposed sliding mechanism stresses the importance of initial liquefaction of the upper Cretaceous Aachen sands underlying the ~30-m-thick Vaals Clay Formation, in which all landslides are developed. Slope-stability analyses support the hypothesis of sudden landsliding and yield further useful information to discuss their origin. A main difficulty in determining the landslide trigger arises from insufficient absolute dates. Assuming that all landslides occurred simultaneously, we weigh the probabilities, respectively, of a climatic and a seismic trigger. Although the 150 a.d. possible date of landslide initiation falls close to one of the wettest periods of the Holocene, the spatial distribution of the deep slides and their proposed mechanism strongly suggest a seismic origin in connection with a rupture of the nearby Ostend segment of the active Hockai fault zone. However, considering that the nearby 1692, Verviers earthquake apparently caused no ground failure, it is probable that both the climatic and seismic triggers were jointly needed to provoke such deep and extended landsliding on moderate, generally stable slopes.

In order to get a better insight into the temporal pattern of height change variations in a moderately seismic intraplate area, a 1 km long section has been weekly leveled from April, 21, 1997 to January, 12, 1998 in NE Ardenne (Belgium). As this section is located very close to a small reservoir of 25U10 6 m 3 , it also allowed the influence of lake level variations on the nearby ground motion to be studied. The measured height difference variations show a maximum amplitude of 3.45 mm, with weekly values not exceeding 1 mm. A two-dimensional (2D) finite element modeling confirms that waterload variations in the lake are the primary cause of movement of the section, inducing maximum ground subsidence of about 2 cm and seasonal tilting of 3^4 Wrads within a range of 2^3 km. We also show that a fault passively alters the spatial distribution of the waterload-dependent movements. The removal of this component from the observed ground motion leaves oscillating residual displacements characterized by an amplitude of 1^1.5 mm and a ‘period’ of about 2 months. We demonstrate that these displacements are independent of rainfall and probably of groundwater fluctuation too. Although most of the residual motions take place on the fault straddled by the leveling section, no credible mechanism can be found to ascribe these motions to a tectonic process. fl 2000 Elsevier Science B.V. All rights reserved.

The longitudinal profiles of 24 rivers of 3rd to 5th order have been analyzed in order to recognize the regional tectonic differentiation pattern of the Ardenne, a Paleozoic massif of NW Europe. Data collected exclusively from 1/25,000 topographic maps were used to define a set of parameters related to the geometry of the profile and proxies for river bedload and drainage area. Validation of the proxy defined for the bedload/discharge ratio demonstrates its potential use for inter-river comparison based on its value at the river mouth; it is however inadequate to estimate the ratio changes along a given stream course. This proxy has been computed to estimate the portion accounted for by hydrodynamic factors in the river bed profiling. Thus, outliers to the correlation function linking it to the river bed gradient have been considered as undergoing other influences, principally of lithologic or tectonic origin. Most indicative of the computed profile parameters are those related to the concavity of the profile. Four more or less regional longitudinal profile types are recognized which are partly determined by differential tectonic movement. The combined analysis of all the parameters confirms the current uplift of the NE Ardenne and points to a subsidence of the Namur area with respect to its SW and SE surroundings. Whether periglacial or tectonic in origin, the Upper Pleistocene lowering of a local base-level has also been identified in the Famenne. Another conclusion of this study is that in order to evidence tectonic influences and to avoid any misinterpretation in a region of complex geologic and geomorphic history and moderate tectonic activity, it is essential to consider a number of parameters and to consider their significance within the framework of detailed geologic setting and morphogenetic history.

Precise levelling data are examined in the southern Black Forest massif by comparing them analytically along levelling profiles. Instead of generalizing regional vertical motion trends, the method emphasizes the current activity of accurately located individual structural elements. Measured recent crustal movement rates range from 0.2 to 1.1 mm/year for the 1930–1961 (1972) period, the inferred motions corresponding to aseismic fault creep. Based on the near infrared band image of a Landsat MSS scene, a lineament map of the study area is compared with the recent crustal movement (RCM) map. The Upper Rhine graben eastern border fault between Badenweiler and Freiburg displays the highest RCM: these displacements are consistent with the geological motion and the topographic expression of that structure. Within the massif, both the lineament map and the RCM map demonstrate the predominant role played by WNW/ESE- to NW/SE-striking structures in accommodating the deformation. Moreover, with the seismic dislocations in the southern Black Forest taking place also mainly on N120 and N20 faults, it is most probable that these active structures are deep-reaching zones of crustal weakness. To some extent, seismicity and RCM appear, however, to be mutually exclusive in their spatial distribution, the seismic Black Forest flexure and Dinkelberg block being opposed to the aseismically moving eastern and northern parts of the study area.

Fissures of seismic origin are described from terrace deposits of the Meuse river in the Liege-Maastricht area, west of the Lower Rhine–Roer rift segment. Though associated with hydroplastic deformation of the sediments, they are not injection structures. They are interpreted as tension cracks resulting from local deformation of susceptible layers inferred to be due to cyclic loading by seismic waves: the fissures have been tilled afterwards from above by vertically laminated sands and silts. The distribution of the fissured areas and the special features of some ground cracks suggest that they could be linked to more than one earthquake between 650 and l00 ka bp. By comparison with liquefaction phenomena described in relation to actual earthquakes, the failure of the Meuse terrace deposits could have been produced by seismic events of M L > 6.5.

Precise levelling data are re-examined in the southwestern Rhenish shield and its foreland by comparing them analytically along levelling profiles. Instead of generalizing regional vertical movement trends, this method emphasizes the activity of individual structural elements, which can be located with a high accuracy. It is shown that present-day vertical motions concentrate on fractures which cut the massif into a number of tectonic blocks. These undergo more or less independent movements. Significant measured displacements range from 1 to 3.5 cm over an average 20-year period and correspond mostly to aseismic slip. High displacements are found near pre-existing faults, sometimes also zones of joint concentration which are favourably oriented with respect to the current regional stress field. In the Mosel area, SW-NE-trending faults are predominantly reactivated as reverse faults. The motion inferred for the Hunsruck border fault is also consistent with the compressive regime presently observed in that area, with σ1 oriented to the northwest. The direction of vertical motions along the western border fault of the upper Rhine graben changes from south to north in relation to the different azimuths of the central and northern segments of the graben, inducing a S-N-oriented transition from compressional to extensional shear. Within the graben itself, some N160°E-trending normal faults are identified, one of them having probably ruptured in a swarm of microearthquaks not long before the second survey was performed. The western Saar-Nahe trough is characterized by N-S-oriented fractures which cannot be related to mapped faults but show a close connection with photolineaments.

While climatic models of valley downcutting discuss the origin of terrace staircases in valleys of middle Europe within the frame of alternating cold and temperate periods of the Quaternary, other models, starting from a base level fall imposed by an initial tectonic signal, describe the response of the drainage network mainly as the propagation of an erosion wave from the place of base level fall (the margin of the uplifted region) toward the headwaters, the two types of model being rarely confronted. In the Ardennes (West Europe), cosmogenic10Be and26Al ages have recently been calculated for the abandonment of the Younger Main Terrace (YMT) level, a prominent feature at mid-height of the valleysides marking the starting point of the mid-Pleistocene phase of deep river incision in the massif. These ages show that the terrace has been abandoned diachronically as the result of a migrating erosion wave that started at 0.73 Ma in the Meuse catchment just north of the massif, soon entered the latter, and is still visible in the current long profiles of the Ardennian Ourthe tributaries as knickpoints disturbing their upper reaches. At first glance, these new findings are incompatible with the common belief that the terraces of the Ardennian rivers were generated by a climatically triggered stepwise general incision of the river profiles. However, several details of the terrace staircases (larger than average vertical spacing between the YMT and the next younger terrace, varying number of post-YMT terraces in trunk stream, tributaries and subtributaries) show that a combination of the climatic and tectonic models of river incision is able to satisfactorily account for all available data. The cosmogenic ages of the YMT also point out a particular behaviour of the migrating knickpoints, which apparently propagated on average more slowly in the main rivers than in the tributaries, in contradiction with the relation that makes knickpoint celerity depend directly on drainage area. We tentatively suggest a process accounting for such anomalies in migration rates.

[1] Despite constant progress in numerical and field studies of landscape evolution, time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low temperature thermochronology, especially outside high relief mountainous areas. Here, I show that regional statistics of the landscape metric R involving hypsometric integrals at three nested levels of a catchment are able to isolate the time effect on landscape geometry during the latter's transient response to a tectonic perturbation. Analysis of 210 catchments from 9 regions of known uplift age worldwide shows that the regionally characteristic, R-derivedSRindex is in inverse power law relation with the time elapsed since a base level lowering. Suggesting a response time of ∼5 My, this finding has important implications for quantifying the rate of landform evolution and determining whether a landscape has reached steady-state form.

Although it constitutes a main tool to unravel the regional recent tectonics, the chronology of the Pleistocene river incision is still poorly constrained within the uplifted Ardennes massif (Western Europe). Here, we use in situ produced cosmogenic 10Be and 26Al concentrations from depth profiles in terrace sediments of several Ardennian rivers (Meuse, Ourthe and Ambleve) in order to date the so-called Younger Main Terrace (YMT), a key-level in the drainage network evolution. We present the first absolute dating of the YMT in the lower Meuse valley, where we obtained an age of 725 ± 120 ka for a terrace deposit buried beneath 3 m of Weichselian loess at Romont. This age is consistent with some previously published estimates based on paleomagnetic data and MIS correlations. However, the ages we obtain for the same terrace level in Ardennian tributaries of the Meuse are significantly younger: 390 ± 35 ka in the lower Ourthe, and only 220 ± 31 ka still farther upstream, in the lower Ambleve. We thus demonstrate that the post-YMT incision occurred diachronically in NE Ardennes. The ∼0.5 Ma timespan needed by the erosion wave to propagate from the lower Meuse towards the Ardennian headwaters contradicts the long-held statement of a climatically driven incision that would have been synchronous throughout the catchments. Finally, we interpret the strong 10Be enrichment displayed by the lower half of the Belle–Roche (lower Ambleve) profile as betraying the long-lasting, slow accumulation of the ∼8 m thick terrace deposit in that place.

The geomorphological analysis of the terraces of the Amblève, an Ardennian subtributary of the Meuse, allows us to reconstruct eleven distinct levels (T1 to T11). Like those of most rivers draining the Ardennes massif, the Amblève terrace profiles also converge in the upstream direction. Moreover, the “Main Terrace” complex, widely recognized in the Rhine and Meuse systems (including their major tributaries draining the Ardennes-Eifel massif), has also been identified in the Amblève valley. However, the lack of terrace remnants in the ~ 10- km-long reach of the Quarreux gorge, combined with the knickpoint observed in the presentday long profile in this reach, leaves some uncertainty in the overall profile reconstruction. Despite the presence of a paleokarst filled by alluvial material in the lower Amblève and diversely dated between ~ 0,5 and ~ 1 Ma, firm chronological data about the Quaternary evolution of the Amblève are still lacking. Therefore, we base our discussion of the temporal evolution of the Amblève incision on geometrical correlations with dated terraces of the Meuse downstream of Liège.

International audience; A number of motored auger holes have been drilled in 2002 and 2006 in four sand-clay deposits preserved in dissolution pockets within the Dinantian limestones of the watershed north of the Vesdre valley. These deposits of unknown age are currently classified as (Tertiary) SBL in the new geological map of Wallonia. We present detailed lithostratigraphic logs of the deposits and describe the results of sedimentological and mineralogical analyses. In particular, K-Ar dating of neoformed Mn oxides found at the base of one augerhole at Rechain yielded ages ranging from Cenomanian to Santonian, allowing us to place the Rechain and Andrimont deposits within the early Late Cretaceous. This is fully consistent with their topographic location very close beneath the trace of the pre-Cretaceous erosion surface and makes them the westernmost remains of the Hergenrath Member of the Late Cretaceous Aachen Formation. To the west, the Magnée deposit is more “typical SBL”, probably corresponding to the Late Neogene filling of a dissolution pocket by reworked weathering products of the local Cretaceous cover

A key issue in landslide susceptibility mapping concerns the relevance of the spatial data combination used in the prediction. Various combinations of high-resolution predictor variables and possibilities of selecting them from a larger dataset are analysed. The scarp reactivation of several landslides in a hilly region of W Belgium is investigated at the pixel scale. The susceptibility modelling uses the reactivated scarp segments as the dependent variable and 13 factors at a 2. m-resolution related to topography, hydrology, land use and lithology as potential independent variables. The modelling uses a likelihood ratio approach based on the comparison, for each independent variable, between two empirical distribution functions (EDFs), respectively for the reactivated and non-reactivated areas. It uses these EDFs as favourability values to build membership values and combine them with a fuzzy Gamma operator. Five different data combinations are tested and compared by analysing the prediction-rate curves obtained by cross-validation. The geomorphological value of the resulting susceptibility maps is also discussed. This research shows relevant results for predicting the susceptibility to scarp reactivation. We highlight the need for testing several data combinations and underline that combining quantitative criteria with expert opinion is an asset for reliable predictions., JRC.H.7-Climate Risk Management

Low motion rates, typical of intraplate settings, make it particularly difficult to isolate a tectonic signal in vertical displacements of the ground dominated by near-surface influences. Since the spring 2003, we have performed half-yearly GPS and gravimetric campaigns in NE Ardenne in order to evaluate the seasonal changes imposed to the ground height by groundwater variations. The GPS height data show an excellent negative correlation with a proxy for groundwater variations, based on rainfall in the 6 months before the survey, that allows a reliable correction of the measured height changes. During the 2003–2005 time span, the seasonal groundwater-dependent height changes have amounted to a maximum 7.5 mm. The gravimetric campaigns were able to detect reliably only gravity changes larger than 10 μgal, which corresponds to the upper limit of the gravity changes associated with the proposed groundwater-GPS model. No conclusive result may therefore be derived from the gravity observations.

Several examples in western Europe have shown that, at least for deep-seated rotational slides, reactivation of formerly slipped masses is a more frequent phenomenon than the occurrence of new landslides, therefore representing a higher hazard. We selected a study area comprised of 13 landslides located in the Flemish Ardennes (West Belgium) and predicted the hazard related to scarp retreat. The scarp reactivations were identified from the comparison of DTMs produced for 1952 and 1996. Robust results were obtained with the Gamma operator of a fuzzy set approach and a combination of geomorphic, topographic and land use data. We built first a prediction model from the relations linking the 1952–1996 retreat events to the conditioning parameters of 1952. The prediction rate of the resulting susceptibility map is estimated by a cross-validation procedure. We then applied the statistics of this model to the data of 1996 in order to produce a susceptibility map responding to the present-day conditions. Finally, we estimated the conditional probabilities of occurrence of future reactivations for the period 1996–2036.

The present-day major relief features of western Europe are to a great extent determined by the underlying geological structures, either passively or actively. To get a comprehensive picture of their morphological evolution and interrelations, this chapter provides an overview of the spatial and temporal characteristics of the larg-escale tectonic framework of the continent. After having described the west European landscape at the end of the Palaeozoic, to which time the oldest preserved landforms date back, an outline of the Mesozoic and Cenozoic history of the major tectonic domains follows. Finally, some denudation estimates highlighting the relationship between tectonics, erosion, and the resulting relief, will be discussed. The three main influences on the present-day topographic patterns are those of the Alpine orogeny, the Cenozoic West European rifting, and the imprint of Variscan structures. They combine within a regional stress field determined by the Africa–Eurasia collision and the Alpine push as well as the mid-Atlantic ridge push. Since the end of the Miocene, this stress field is characterized by a fan-shaped distribution of SHmax along the northern border of the Alpine arc. This gives way to a more consistent NW–SE to NNW–SSE direction of compression further from the chain (Bergerat 1987; Müller et al. 1992). Topographically, western Europe may be roughly divided into a series of belts parallel to the Alpine chain. The Alpine chain culminates in a number of peaks exceeding 4,000 m in elevation (4,810 m at Mont Blanc) but the average altitude is in the order of 2,000 m. To the north, the mountainous Alps are bordered by the Molasse foredeep basin whose surface makes an inclined plane descending northwards from c.1,000 m to c.300 m near the Donau River in the Regensburg-Passau area. To the north-west, the Molasse basin narrows between the Alps and the Jura Mountains and is occupied by several extended lakes inherited from Quaternary glacial activity. Next to the Molasse basin in the north and west is a wide belt of recently more or less uplifted areas between 200 and 1,000 m in elevation (and locally in excess of 1,000 m in the French Massif Central and the Bohemian massif).

Morphological features, under which deformations of Oligocene surfaces are included, demonstrate the varied tectonic activity of the Hautes Fagnes plateau during Cenozoic times. Beyond the general uplift of the region, a local movement raised the Baraque Michel massif by about 100 m above the nearby crest of “La Vecquee”. Moreover, several zones of radial NW-SE faulting are active on the plateau. They are related to the opening of the Lower Rhine Embayment and represent the ultimate SW extension of the fault system associated with this opening.

A number of NW-SE or NNW-SSE trending radial faults are recognized on the northern slope of the Ardenne massif. They have been active since the Oligocene, as depicted by deformations of planation surfaces and other morphological features. The study of river terraces demonstrates their Quaternary activity, with vertical movements ranging from 4 to 10 m during the late Quaternary. This fault activity is related to the opening of the Lower Rhine Embayment.

The study in incident light of the heavy minerals contents of some Oligocene sands in the Hautes Fagnes and the Liege regions (Belgium) clearly shows the successive stages of their weathering: a diagenetic reduction pointed out by the weathering products of ilmenite and ilmenomagnetite, a sulphurization when a lagoonal environment succeeded to the Oligocene regression, a phase of silicification and finally the oxidation of the sediment, more or less intense depending upon the local conditions.

The release of gonadotropin following the injection of synthetic LH- RH was studied in various physiological and experimental circumstances. In the male 25 mcg of LH-RH led to simultaneous release of FSH and LH prior to and during puberty. In adults on the other hand the same dose led only to an increase in LH while FSH levels remained unchanged. At higher doses there was FSH release and an increase in LH proportional to the amount of LH-RH injected. When FSH was released the increase was clearly less than that of LH and often occurred considerably later. In the female 25 mcg of LH-RH led to a clear-cut considerably later. In the female 25 mcg of prior to puberty. After the onset of puberty the degree of response was inverted; the increase in LH was greater than that of FSH. In normally menstruating women the FSH and LH response was greater during the luteal phase than during the preovulatory phase. Treatment with nonsequential hormonal contraceptives blocked FSH and LH release normally produced by the injection of 50 mcg of LH-RH. There was no effect when a dose of 100 mcg was injected. In postmenopausal women only LH rose following the administration of 25 mcg of LH-RH. After 5 days of treatment with 200 mcg ethinly estradiol the same dose of LH-RH led to simultaneous release of LH and of FSH. It is concluded that the secretory response of the gonadotropins to LH-RH is influenced by the endocrine equilibrium and more particularly by the interaction of the gonadal steroids which can alter the synthesis and/or the release of the pituitary gonadotropins.