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Liquid water is generally only meta-stable on Mars today; it quickly freezes, evaporates or boils in the cold, dry, thin atmosphere (surface pressure is about 200 times lower than on Earth). Nevertheless, there is morphological evidence that surface water was extensive in more ancient times, including the Noachian Epoch (∼4.1 Ga to ∼3.7 Ga bp), when large lakes existed and river-like channel networks were incised, and early in the Hesperian Epoch (∼3.7 Ga to ∼2.9 Ga bp), when megafloods carved enormous channels and smaller fluvial networks developed in association with crater-lakes. However, by the Amazonian Epoch (∼3.0 Ga to present), most surface morphogenesis associated with liquid water had ceased, with long periods of water sequestration as ice in the near-surface and polar regions. However, inferences from observations using imaging data with sub-metre pixel sizes indicate that periglacial landscapes, involving morphogenesis associated with ground-ice and/or surface-ice thaw and liquid flows, has been active within the last few million years. In this paper, three such landform assemblages are described: a high-latitude assemblage comprising features interpreted to be sorted clastic stripes, circles and polygons, non-sorted polygonally patterned ground, fluvial gullies, and solifluction lobes; a mid-latitude assemblage comprising gullies, patterned ground, debris-covered glaciers and hillslope stripes; and an equatorial assemblage of linked basins, patterned ground, possible pingos, and channel-and-scarp features interpreted to be retrogressive thaw-slumps. Hypotheses to explain these observations are explored, including recent climate change, and hydrated minerals in the regolith ‘thawing’ to form liquid brines at very low temperatures. The use of terrestrial analogue field sites is also discussed. [ABSTRACT FROM PUBLISHER]

A selection of subaerial slope processes is discussed together with the morphological and sedimentological traces that are left by the processes. Emphasis is on mass transfers related to (coarse) blocky slopes and to scree accumulations, either on steep or on gentle slopes. New developments in the interpretation of more or less clearly stratified slope deposits are discussed in the light of the findings of research focusing on present-day process-form (process-material) relationships. The question of the climatic (and, more specifically, the periglacial) significance of the different processes and their morpho-sedimentary expression is a returning theme in this paper. It is concluded that many deposits are formed by azonal processes, although their activity (in terms of magnitude-frequency combinations) is often relatively high under periglacial conditions. Some of the deposits point to (cold-climate) extreme events. This especially is the case for frost-coated clast flows, aeolian transport of large platy clasts, and to a lesser extent debris flows. [ABSTRACT FROM AUTHOR]

Abstract: Palsas are true perennial permafrost mounds. It is generally accepted that there are at least three mechanisms which might contribute to the initiation of their formation, although these are not necessarily mutually exclusive. These mechanisms can be termed: the ‘snow cover’ hypothesis; the ‘vegetation succession’ hypothesis; and the ‘buoyancy’ hypothesis. Furthermore, there are at least three types of palsas recognized, although the terminology relating to these different varieties is varied and disputed. It is clear that palsas are potentially extremely useful features for monitoring permafrost growth and decay in certain areas, and that a unified understanding of their growth and decay processes would aid this. [ABSTRACT FROM AUTHOR]

Pingos are true perennial permafrost mounds. It is generally accepted that there are two main types of pingos in terms of genesis: hydrostatic (closed system) and hydraulic (open system). It is here proposed that a third category of ‘polygenetic’ (or ‘mixed’) pingos should also be recognized in the light of published work and recent investigations. The lack of comprehension of hydraulic pingo genesis would seem to add weight to this proposal. Since suitable conditions for the formation of pure hydrostatic pingos are rarely met outside the Mackenzie Delta/Tuktoyaktuk Peninsula area the ‘world’ type of pingo is most likely to be of an hydraulic or ‘polygenetic’ variety and thus further investigation is warranted, particularly for the elucidation of the palaeoenvironmental inferences of ‘relict pingos’. [ABSTRACT FROM AUTHOR]