Title: What was the transport mode of large boulders in the Campine Plateau and the lower Meuse valley during the mid-Pleistocene?
Authors: De Brue, Hanne ×
Poesen, Jean
Notebaert, Bastiaan #
Issue Date: 2015
Publisher: Elsevier
Series Title: Geomorphology vol:228 pages:568-578
Abstract: The Campine Plateau in northeastern Belgium, a remnant of an alluvial fan deposited by the Meuse River during
the mid-Pleistocene, is characterised by the presence of boulders with maximum dimensions of up to 2 m,
embedded in a gravel matrix. These boulders originated in the Ardennes region and are generally assumed to
have been transported by ice-rafting processes. This paper investigates for the first time quantitatively the possibility
of purely hydraulic transport of the boulders, taking into account channel and flow characteristics in
the boulder provenance area during the mid-Pleistocene. Empirical transport relations that describe incipient
motion thresholds in nonuniform river beds as a function of the relative grain size, or the ratio between the
grain size of interest and the median grain size of the channel bed, are applied in order to calculate critical
water depths for transport of boulders of various sizes. Results indicate that hydraulic transport of boulders
with intermediate diameters <1 m could have occurred within limited reaches of the palaeoriver, more specifically
in the palaeo-Amblève tributary; whereas the small slope gradient of the palaeo-Meuse most probably
inhibited boulder movement by hydraulic forces only. Although calculations of the ice volume required to lift a
boulder to the water surface and comparison of the ice floe's dimensions with palaeochannel morphology do suggest
that ice rafting is theoretically possible, several alternative, more probable transport mechanisms for the
larger boulders of the Campine Plateau are proposed, requiring much smaller critical ice volumes and water
depths than ice-rafting processes or purely hydraulic transport. These hypotheses include decreased bed friction
and effective boulder density caused by a limited ice layer attached to the river bed and the boulder, hence lowering
hydraulic transport thresholds, as well as the formation of ice jams and dams inducing catastrophic flooding
and mechanical impacts by ice floes upon failure.
ISSN: 0169-555X
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Division of Geography & Tourism
× corresponding author
# (joint) last author

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