Jan Boelhouwers

Geomorphological characteristics of small debris flows on Junior's Kop, Marion Island, maritime sub ‐ Antarctic

The geomorphological characteristics of small debris flows in a maritime sub-Antarctic environment are described. The morphological and sedimentological characteristics of the debris flows are comparable to debris flows documented for other parts of the world; their initiation appears closely linked to the unusual environment in which they are found. Sediment supply is generated by diurnal frost heave of loamy sediment associated with Azorella selago. The debris flows are triggered by sediment mobilization upon saturation of the frost-heaved surface gravel and overland flow over the low-permeability and frost-susceptible slope materials. Morphological effects of the flows are short-lived due to obliteration by subsequent frost heave activity. Copyright

New Perspectives on Autochthonous Blockfield Development

The development of coarse blocky mantles in cold regions has played a central role in both the original definition of the periglacial facies by Lozinski and the establishment of a perception on the widespread efficacy of frost weathering among peri glacial geomorphologists. This paper challenges these notions as simplistic “geomyths” that limit the understanding of blocky weathering and blockfield development, whether in cold or warm regions. Mechanisms of block production increasingly appear to be the result of azonal weathering processes such as chemical weathering and thermal stress fatigue, with bedrock fractures a prequisite rather than an outcome of frost action. Observations from outside cold regions and the long-term landscape development associated with many blockfields further lead to broaden perspectives beyond simplistic frost action. Instead blockfields appear to be the result of complex process interactions and climatic histories that defy straightforward palaeoclimatic interpretations.

Relict periglacial slope deposits in the Hex River Mountains, South Africa: observations and palaeoenvironmental implications

Abstract Shattered bedrock near the summit of Matroosberg, Western Cape Mountains, is closely associated with several blockstreams which grade downslope into broad terraces. With an increase in slope angles the regolith grades into broad bands of coarse but sorted material parallel to the maximum gradient. The width of the coarse stripes increases in the downslope direction, where they merge into openwork block deposits several tens of metres long and wide. Whereas the terraces near the summit plateau closely resemble gelifluction sheets, the large sorted stripes and coarse debris mantles are analogous to the stone-banked terraces described for the Colorado Front Range. The landforms are primarily related to seasonal frost creep at the Last Glacial Maximum (LGM) when mean annual temperatures are estimated to have been around 0°C, i.e., winter temperatures 7–8°C lower than present. Snowcover must have been limited to allow deep frost penetration.

Block deposits in southern Africa and their significance to periglacial autochthonous blockfield development

Abstract Autochthonous blockfields are generally considered landforms indicative of periglacial environments. This paper presents observations from the semi‐arid Karoo and afro‐montane Drakensberg and Lesotho highlands, southern Africa, on non‐periglacial autochthonous block mantles on dolerite sills and basalt. Subsurface weathering in resistant lithology with subsequent removal of fines is argued to result in autochthonous blockfields. It is proposed that blockfields may develop under a wide range of environments wherever resistant lithologies are present. The paleoenvironmental significance of blockfields depends entirely on establishing a more reliable analysis of weathering environments under which blocks developed and, where fines are produced, subsequent block concentration.