Abstract:
This study investigates sediment transport processes and sediment-landform
development at two small valley glaciers of contrasting basal thermal-regime.
A range of innovative techniques are applied to characterize and quantify
glacier structure, glacially transported sediment facies and sediment-landform
assemblages at Glacier de Tsaneuron, Switzerland, and Midre Lovénbreen,
Svalbard. Sediment transport at Glacier de Tsaneuron is dominated by a
rockfall-derived supraglacial debris stripe and abrasion-derived subglacial debris
planes. Modeled sediment transport rates are equivalent to a glacier-wide erosion
rate of 0.5 mm a -1. Subglacially transported sediment ablates to form
a complex network of debris stripes, the texture and morphology of which are
consistent with sediment supply from palaeokarst sinkholes. These sinkholes
dominate the limestone plateau on which the glacier is situated and also restrict
glaciofluvial sediment transport by rerouting much of the glacier's meltwater
though the karst system. This results in a landsystem that is atypical of valley
glaciers in the Alps. Sediment transport at Midre Lovénbreen is strongly
influenced by glacier structure, identified at the glacier surface and in digital
optical televiewing borehole logs. Glacier structure is successfully reconstructed
in three-dimensions, revealing several visually distinctive englacial ice properties
and deformation structures. Basally derived englacial sediment layers are
found to be intercalated with primary stratification, elevated into near-vertical
planes around a gently upglacier dipping central fold axis by large-scale lateral
folding. Sediment analysis also allows supraglacial longitudinal debris ridges to
be sub-classified into two types, with a new (Type II) form experiencing secondary
deformation by small-scale flow parallel recumbent folding in association
with vertical displacements across arcuate shear planes near the glacier terminus.
Non-structurally controlled sediment transport at Midre Lovénbreen is
dominated by low-intensity deformation of subglacial till, and is also characterized
by the formation of supraglacial debris cones and proglacial flutes. Flutes
at Midre Lovénbreen are interpreted to form beneath warm-based ice by the
squeezing of partially fluidized till into cavities where freeze-on occurs due to a
'heat-pump' effect across subglacial boulders. The results of this investigation
demonstrate that, while basal-thermal regime may exert a strong influence on
glacial sediment-transport processes that operate at the small-scale, bedrock
physiography ultimately defines glacier morphometry and resulting large-scale
flow structures. Additionally, although some of the sediment-landform types
identified in this study are exclusive to a particular set of basal-thermal conditions,
the composition and morphology of these sediment-landform assemblages are such that they are unlikely to be preserved in the geological record.
