Soil production and hillslope transport in mid‐latitudes during the last glacial–interglacial cycle: a combined data and modelling approach in northern Ardennes

Abstract

The relative efficiency of various hillslope processes through Quaternary glacial-interglacial cycles in the midlatitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate-dependent hillslope evolution with an inversion algorithm in order to get deeper insight into the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a~2500 km 2 real area under a simple two-stage 120kyr-long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges. We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first-order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm-cold and cold-warm transitions, when the mean annual temperature passes through the [0, À5°C] range. We also point to the overwhelming importance of solifluction in shaping hillslopes and transporting soil, and the role of depth-dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor.

Applying Pattern Oriented Sampling in current fieldwork practice to enable more effective model evaluation in fluvial landscape evolution research

“…By comparing the degree of spatial clustering between channel units observed in late Cretaceous-age rocks and a flume experiment, they conclude that the patterns observed could have formed as a result of self-organization within the system rather than due to external forcing (Humphrey and Heller 1995). A similar approach is taken with Quaternary age sequences by Bovy et al (2016).…”

“…Bovy et al 2016), as can use of geotechnical borehole data. Whilst this may involve more fieldwork, it may rather involve creatively using existing datasets for this new purpose.…”

“…It is for example equally relevant to know where sediments occur and where they do not. A similar approach is taken with Quaternary age sequences by Bovy et al (2016). Too often we have much data from particular locations while at the same time we have almost no data outside these unique locations (often boreholes and quarries).…”

“…The narrative favoured for explanation is then adopted from the modelled scenario with the best fit to the present day (e.g. Bovy et al 2016). Where only one scenario fits the geological data available for evaluation, equifinality is avoided.…”

“…Good pedological maps can be invaluable in achieving this aim (e.g. Bovy et al 2016), as can use of geotechnical borehole data. These datasets can also be usefully used for making volumetric comparisons of various types, as noted in Table II.…”