References of "Demoulin, Alain"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailAmount and controls of the Quaternary denudation in the Ardennes massif (western Europe)
Demoulin, Alain ULg; Hallot, Eric ULg; Rixhon, Gilles ULg

in Earth Surface Processes & Landforms (2009), 34

It is still debated whether the primary control on the middle Pleistocene denudation of the uplifted Ardennes massif (western Europe) is tectonic or climatic. Here, based on geomorphological observations ... [more ▼]

It is still debated whether the primary control on the middle Pleistocene denudation of the uplifted Ardennes massif (western Europe) is tectonic or climatic. Here, based on geomorphological observations, we calculate the amount of river incision and interfluve denudation in the Meuse basin upstream of Maastricht since 0·7 Ma and we show that the main response to tectonic forcing was incision. This allows us to provide first-order estimates of the tectonic and climatic contributions to the denudation of the Ardennes. From a dataset of 71 remnants of a terrace level dated ~0·7 Ma, we first derive a basin-scale functional relationship linking incision with distances to the regional base level (Lc) and to the source (Ls) in the Ourthe basin (pertaining to the Ardennian part of the Meuse basin). Expressed as I = I0*(1 – a*Lcb/Lsc), I0 being the incision measured at the basin outlet, this relationship calculates that river incision has removed 84 km3 of rock in the Meuse basin upstream of Maastricht since 0·7 Ma. In the same time, 292 km3 were eroded from the interfluves. A comparison of these volumes shows that the tectonically forced river incision accounts for ~22% of the total post-0·7 Ma denudation. Furthermore, the mean denudation rate corresponding to our geomorphological estimate of the overall denudation in the Meuse basin since 0·7 Ma amounts to 27 mm/ky, a figure significantly lower than the ~40 mm/ky mean rate derived from 10Be studies of terrace deposits of the Meuse (Schaller et al., 2004). This suggests that, taken as a basin average, the 10Be-derived rate is overestimated, probably due to an overrepresentation of the erosion products of the rapidly incising valleys in the alluvial deposits. [less ▲]

Detailed reference viewed: 38 (5 ULg)
Full Text
Peer Reviewed
See detailTracking landslide displacements by multi-temporal DTMs: A combined aerial stereophotogrammetric and LIDAR approach in western Belgium
Dewitte, Olivier ULg; Jasselette, J. C.; Cornet, Yves ULg et al

in Engineering Geology (2008), 99(1-2), 11-22

Detailed reference viewed: 72 (21 ULg)
Full Text
Peer Reviewed
See detailAn automated method to extract fluvial terraces from digital elevation models: The Vesdre valley, a case study in eastern Belgium
Demoulin, Alain ULg; Bovy, Benoît ULg; Rixhon, Gilles ULg et al

in Geomorphology (2007), 91(1-2), 51-64

Fluvial terraces are a powerful tool for unraveling the combined tectonic and climatic conditions that controlled, directly or indirectly, the Quaternary incision of rivers. Terrace long profiles are ... [more ▼]

Fluvial terraces are a powerful tool for unraveling the combined tectonic and climatic conditions that controlled, directly or indirectly, the Quaternary incision of rivers. Terrace long profiles are usually retrieved from sparse traces of ancient floodplains preserved in the present topography. However, when these traces classically collected from topographic maps, aerial photographs, and field analyses are too few, the inferred profiles may be questionable. Yet the now available high quality and high resolution digital elevation models (DEMs) offer an opportunity to increase greatly the quantity of information usable to reconstruct terrace profiles. Therefore, the purpose of this study was to develop a new DEM-based method of terrace recognition in order to create a larger database and better constrain the profile reconstruction. Moreover, particular procedures of image and numerical processing were defined to fully automate the analysis. Basically, our method relies on the production of bivariate scatter plots depicting the relation between slope and relative altitude (i.e., the altitude above the current alluvial plain) for all pixels of successive sections of the valley. For each scatter plot, the curve of the lowest slope values observed at every relative altitude is smoothed and its minima are assumed to locate the altitudes of the "terrace" elements preserved in the section. We successfully tested this method in the Vesdre valley, incised in the NE Ardenne massif (E Belgium), notably identifying fault deformation of the profiles. The main advantages of our approach are its objectivity, exhaustiveness, and rapidity, allowing fast and coherent analysis of many rivers over extended regions. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 121 (33 ULg)
Full Text
Peer Reviewed
See detailCharacteristics of the size distribution of recent and historical landslides in a populated hilly region
Van den Eeckhaut, M.; Poesen, J.; Govers, G. et al

in Earth and Planetary Science Letters (2007), 256(3-4), 588-603

Despite the availability of studies on the frequency density of landslide areas in mountainous regions, frequency-area distributions of historical landslide inventories in populated hilly regions are ... [more ▼]

Despite the availability of studies on the frequency density of landslide areas in mountainous regions, frequency-area distributions of historical landslide inventories in populated hilly regions are absent. This study revealed that the frequency-area distribution derived from a detailed landslide inventory of the Flemish Ardennes (Belgium) is significantly different from distributions usually obtained in mountainous areas where landslides are triggered by large-scale natural causal factors such as rainfall, earthquakes or rapid snowmelt. Instead, the landslide inventory consists of the superposition of two populations, i.e. (i) small (<1-2 . 10(-2) km(2)), shallow complex earth slides that are at most 30 yr old, and (ii) large (> 1-2 . 10(-2) km(2)), deep-seated landslides that are older than 100 yr. Both subpopulations are best represented by a negative power-law relation with exponents of -0.58 and -2.31 respectively. This study focused on the negative power-law relation obtained for recent, small landslides, and contributes to the understanding of frequency distributions of landslide areas by presenting a conceptual model explaining this negative power-law relation for small landslides in populated hilly regions. According to the model hilly regions can be relatively stable under the present-day environmental conditions, and landslides are mainly triggered by human activities that have only a local impact on slope stability. Therefore, landslides caused by anthropogenic triggers are limited in size, and the number of landslides decreases with landslide area. The frequency density of landslide areas for old landslides is similar to those obtained for historical inventories compiled in mountainous areas, as apart from the negative power-law relation with exponent -2.31 for large landslides, a positive power-law relation followed by a rollover is observed for smaller landslides. However, when analysing the old landslides together with the more recent ones, the present-day higher temporal frequency of small landslides compared to large landslides, obscures the positive power-law relation and rollover. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 22 (3 ULg)
Full Text
Peer Reviewed
See detailSeasonal height change influence in GPS and gravimetric campaign data
Demoulin, Alain ULg; Ducarme, B.; Everaerts, Michel ULg

in Journal of Geodynamics (2007), 43(2), 308-319

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 ... [more ▼]

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 mu gal, 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. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

Detailed reference viewed: 18 (2 ULg)
Full Text
Peer Reviewed
See detailTracking landslide evolution over decades: application of aerial digital photogrammetry to the Oudenaarde area (W Belgium)
Dewitte, Olivier ULg; Jasselette, Jean-Claude; Cornet, Yves ULg et al

(2007)

In order to include some kinematic information within landslide hazard prediction models, we estimated landslide motion in the medium term (i.e. a few decades) by comparing precise landslide topography ... [more ▼]

In order to include some kinematic information within landslide hazard prediction models, we estimated landslide motion in the medium term (i.e. a few decades) by comparing precise landslide topography reconstructions at different dates. Precise multitemporal 3D data of the 13 old deep-seated landslides developed on two hills close to the town of Oudenaarde (W Belgium) were obtained by digital stereophotogrammetry using aerial photographs of three different periods (1996, 1973 and 1952). From these data, six DTMs (3 different dates for each investigated hill) were produced with an overall RMS error of ~50 cm. The obtained DTMs were subtracted from each other in order to determine the vertical displacement of each pixel during the considered time interval. Globally, movements are observed in all the landslides and they generally correspond to a rotational pattern. [less ▲]

Detailed reference viewed: 73 (10 ULg)
Full Text
Peer Reviewed
See detailStrategies to estimate ground susceptibility to landslide reactivation. A probabilistic application in W Belgium (Oudenaarde)
Dewitte, Olivier ULg; Chung, Chang-Jo; Cornet, Yves ULg et al

(2007)

In the hilly region of the Flemish Ardennes in western Belgium, no new big deep-seated landslides have occurred for decades, whereas several reactivation episodes were recently observed in ancient ... [more ▼]

In the hilly region of the Flemish Ardennes in western Belgium, no new big deep-seated landslides have occurred for decades, whereas several reactivation episodes were recently observed in ancient landslides. We selected a test area comprised of 13 rotational landslides located close to the town of Oudenaarde in order to predict the susceptibility of their main scarp to retreat. We propose here two probabilistic models based on a fuzzy set approach. The models use empirical distribution functions (EDFs) as favourability values to build membership values and combine them by using the fuzzy Gamma operator. Based on Kolmogorov-Smirnov tests applied to these EDFs to select the most relevant data, a first model was obtained bases on a combination of 5 quantitative variables: slope angle, distance from cultivation located upstream of the main scarp, slope aspect, elevation and profile curvature. Another, more empirical approach based on the a posteriori analysis of the prediction-rate curves was applied to select the 4 variables of a second model: slope aspect, plan curvature, vegetation index and focal flow. According to the prediction-rate curves and the resulting susceptibility maps, the empirical model appears more efficient in locating the main scarp areas most prone to reactivation. [less ▲]

Detailed reference viewed: 37 (8 ULg)
Full Text
Peer Reviewed
See detailMapping landslide susceptibility from small datasets: A case study in the Pays de Herve (E Belgium)
Demoulin, Alain ULg; Chung, C. J.

in Geomorphology (2007), 89

A landslide susceptibility map is proposed for the Pays de Herve (E Belgium), where large landslides affect Cretaceous clay outcrop areas. Based on a Bayesian approach, this GIS-supported probabilistic ... [more ▼]

A landslide susceptibility map is proposed for the Pays de Herve (E Belgium), where large landslides affect Cretaceous clay outcrop areas. Based on a Bayesian approach, this GIS-supported probabilistic map identifies the areas most susceptible to deep landslides. The database is comprised of the source areas of ten pre-existing landslides (i.e. a sample of 154 grid cells) and of six environmental data layers, namely lithology, proximity to active faults, slope angle and aspect, elevation and distance to the nearest valley-floor. A 30-m-resolution DEM from the Belgian National Geographical Institute is used for the analysis. Owing to the small size of the sample, a special cross-validation procedure of the susceptibility map is performed, which uses in an iterative way each of the landslides to test the predictive power of the map derived from the other landslides. Four different sets of variables are used to produce four susceptibility maps, whose prediction curves are compared. While the prediction rates associated with the models not involving the “proximity to active fault” criterion are comparable to those of the models considering this variable, strong weaknesses inherent in the fault data on which the latter rely suggest that the final susceptibility map should be based on a model that excludes any reference to fault. This highlights the difference between a triggering factor and determining factors, and in the same time broadens the scope of the produced map. A single reactivated slide is also used to test the possibility of predicting future reactivation of existing landslides in the area. Finally, the need for geomorphological control over the mathematical treatment is underlined in order to obtain realistic prediction maps. [less ▲]

Detailed reference viewed: 26 (5 ULg)
Full Text
Peer Reviewed
See detailMonitoring and mapping landslide displacements: a combined DGPS-stereophotogrammetric approach for detailed short- and long-term rate estimates
Demoulin, Alain ULg

in Terra Nova (2006), 18(4), 290-298

Although desirable for a reliable hazard assessment, rate estimates of landslide motion rarely combine a good time resolution and a sufficiently long time of observation. Here, both angles are tackled for ... [more ▼]

Although desirable for a reliable hazard assessment, rate estimates of landslide motion rarely combine a good time resolution and a sufficiently long time of observation. Here, both angles are tackled for the Manaihan landslide (East Belgium), dramatically reactivated in September 1998. I monitored the landslide displacements by repeated Global Positioning System (GPS) surveys from 1999 to 2005. Two digital elevation models were also produced, one of the landslide topography in 1999 by GPS and a second by stereophotogrammetry from aerial photographs of 1953. Subtracting one model from the other, I mapped the height changes within the landslide over the 1953-1999 period. All measurements consistently showed that, beyond the sudden similar to 1.5 m slip of September 1998, the landslide moved at a mean rate of c. 20 cm yr(-1) since 1980. Most displacements occurred around the winter's end, when long-lasting precipitation combined with minimal evaporation and occasional intense daily rainfall. The motions are spatially determined by seepage from a broken sewage pipe inducing local high pore pressures. [less ▲]

Detailed reference viewed: 26 (2 ULg)
Full Text
Peer Reviewed
See detailSlip rate and mode of the Feldbiss normal fault (Roer Valley Graben) after removal of groundwater effects
Demoulin, Alain ULg

in Earth and Planetary Science Letters (2006), 245(3-4), 630-641

The Feldbiss fault is the main active fault bounding to the southwest the Roer Valley Graben of NW Europe. In order to investigate the reasons of the discrepancy between its short- and long-term slip rate ... [more ▼]

The Feldbiss fault is the main active fault bounding to the southwest the Roer Valley Graben of NW Europe. In order to investigate the reasons of the discrepancy between its short- and long-term slip rate estimates, we have repeatedly surveyed a 2.3 km-long line by levelling at Sittard (The Netherlands) from April 2001 to December 2004. Simultaneously, three superposed aquifers were monitored on both sides of the fault. The across-fault differential groundwater variations are shown to be responsible for a seasonal 0.87 mm/m vertical motion of the fault, mainly through the effect of pore pressure changes in confined aquifers. After removal of this effect, I get a residual trend of -0.60 +/- 0.11 mm/yr for the relative motion of the hangingwall. This trend was disturbed in the summer of 2002 by transient millimetre-level up and down motions temporally associated with the small Eschweiler earthquake that occurred on July 22, 2002 on the Feldbiss fault at a distance of 35 km from Sittard. I explain this as a creep event triggered by the passage of trapped seismic waves. The subsisting discrepancy between the long-term slip rate of 0.06 mm/yr and short-term rates of similar to 1.5 mm/yr (from 1962 to 2001) and 0.6 mm/yr (from 2001 to 2004) is tentatively interpreted as resulting from the current occurrence of a decade-long episode of aseismic slip involving a large part of the fault plane. Occasionally associated with minor seismicity, this aseismic slip event could betray a thickening of the transitional region located below the upper crustal zone of stable sliding. It causes a total fault slip of 5-10 cm in a few tens of years, releasing smoothly all, or a great part of, the strain accumulated during the previous 1-2 ky of fault quiescence. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 19 (1 ULg)
Full Text
Peer Reviewed
See detailRecent landslide activity in Manaihan, E Belgium
Demoulin, Alain ULg; Glade, T.

in Landslides (2004), 1

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 ... [more ▼]

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. [less ▲]

Detailed reference viewed: 26 (2 ULg)
Full Text
Peer Reviewed
See detailReconciling geodetic and geological rates of vertical crustal motion in intraplate regions
Demoulin, Alain ULg

in Earth & Planetary Science Letters (2004), 221

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 ... [more ▼]

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 Wrad/yr for a 2.8-km-long segment. [less ▲]

Detailed reference viewed: 17 (1 ULg)
Full Text
Peer Reviewed
See detailTectonic vs. shallow origin of geodetically inferred ground movements: an NE Ardenne (Belgium) case
Demoulin, Alain ULg; Vliegen, Bernard; Charlier, Robert ULg

in Earth and Planetary Science Letters (2000), 181(1-2), 217-228

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 ... [more ▼]

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 25 X 10(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 mu rads 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. (C) 2000 Elsevier Science B,V. All rights reserved. [less ▲]

Detailed reference viewed: 38 (8 ULg)
Full Text
Peer Reviewed
See detailTesting the tectonic significance of some parameters of longitudinal river profiles: the case of the Ardenne (Belgium, NW Europe)
Demoulin, Alain ULg

in Geomorphology (1998), 24

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 ... [more ▼]

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 bedloadrdischarge 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. [less ▲]

Detailed reference viewed: 13 (6 ULg)
Full Text
Peer Reviewed
See detailNeotectonic implications of a lineament-coplanarity analysis in Southern Calabria, Italy
Cornet, Yves ULg; Demoulin, Alain ULg

in Special Publication - Geological Society of London (1998), 146

Detailed reference viewed: 24 (7 ULg)
Full Text
See detailThe Stavelot Massif from Cambrian to recent. A survey of the present state of knowledge
Bless, M. J. M.; Bouckaert, J.; Camelbeek, L. et al

in Annales de la Société Géologique de Belgique (1990)

Detailed reference viewed: 44 (8 ULg)
See detailLes surfaces d'érosion crétacique et paléogènes du nord de l'Ardenne-Eifel
Demoulin, Alain ULg

in Zeitschrift für Geomorphologie (1986), 30

Detailed reference viewed: 48 (11 ULg)
Peer Reviewed
See detailNote sur le dépôt caillouteux de G'doumont (Malmedy)
Demoulin, Alain ULg

in Bulletin de la Société Géographique de Liège (1982)

Detailed reference viewed: 38 (19 ULg)