Abstract The Hale impact crater is a large complex crater ( c. 150 × c. 125 km) in the southern hemisphere of Mars. Recurring slope lineae have been observed on its central-peak slopes, as have relatively youthful gully-like landforms; the latter are observed adjacent to or in the midst of the former, as well as on all of the rim-material slopes. Three of the gullied slopes on the northern-rim materials exhibit landscape features that, on Earth, are synonymous with wet periglaciation, i.e. landscape modification by the freeze–thaw cycling of water. These features include: (1) gelifluction-like lobes; (2) patches of surface polygonization, possibly underlain by ice wedges and formed by thermal-contraction cracking; and (3) shallow, rimless and polygonized basins morphologically akin to terrestrial alases. Here, we use the spatial association of the gully-like landforms together with the putatively wet periglacial assemblages or complexes to deduce and ascribe, albeit indirectly, a wet origin to the former.

Abstract Periglacial environments are characterized by cold-climate non-glacial conditions and ground freezing. The coldest periglacial environments in Pleistocene Britain were underlain by permafrost (ground that remains at or below 0°C for two years or more), while many glaciated areas experienced paraglacial modification as the landscape adjusted to non-glacial conditions. The growth and melt of ground ice, supplemented by temperature-induced ground deformation, leads to periglacial disturbance and drives the periglacial debris system. Ice segregation can fracture porous bedrock and sediment, and produce an ice-rich brecciated layer in the upper metres of permafrost. This layer is vulnerable to melting and thaw consolidation, which can release debris into the active layer and, in undrained conditions, result in elevated porewater pressures and sediment deformation. Thus, an important difference arises between ground that is frost-susceptible, and hence prone to ice segregation, and ground that is not. Mass-movement, fluvial and aeolian processes operating under periglacial conditions have also contributed to reworking sediment under cold-climate conditions and the evolution of periglacial landscapes. A fundamental distinction exists between lowland landscapes, which have evolved under periglacial conditions throughout much of the Quaternary, and upland periglacial landscapes, which have largely evolved over the past c. 19 ka following retreat and downwastage of the last British–Irish Ice Sheet. Periglacial landsystems provide a conceptual framework to interpret the imprint of periglacial processes on the British landscape, and to predict the engineering properties of the ground. Landsystems are distinguished according to topography, relief and the presence or absence of a sediment mantle. Four landsystems characterize both lowland and upland periglacial terrains: plateau landsystems, sediment-mantled hillslope landsystems, rock-slope landsystems, and slope-foot landsystems. Two additional landsystems are also identified in lowland terrains, where thick sequences of periglacial deposits are common: valley landsystems and buried landsystems. Finally, submerged landsystems (which may contain more than one of the above) exist on the continental shelf offshore of Great Britain. Individual landsystems contain a rich variety of periglacial, permafrost and paraglacial landforms, sediments and sedimentary structures. Key periglacial lowland landsystems are summarized using ground models for limestone plateau-clay-vale terrain and caprock-mudstone valley terrain. Upland periglacial landsystems are synthesized through ground models of relict and active periglacial landforms, supplemented by maps of upland periglacial features developed on bedrock of differing lithology.

Abstract In engineering terms, all materials deposited as a result of glacial and periglacial processes are transported soils. Many of these deposits have engineering characteristics that differ from those of water-lain sediments. In the UK, the most extensive glacial and periglacial deposits are tills. Previously, engineering geologists have classified them geotechnically as lodgement, melt-out, flow and deformation tills, or as variants of these. However, in this book tills have been reclassified as: subglacial traction till, glaciotectonite and supraglacial mass-flow diamicton/glaciogenic debris-flow deposits (see Chapter 4 , Sections 4.1 – 4.3 ). Because this classification is new, it is not possible to relate geotechnical properties and characteristics to the subdivisions of the new classification. Consequently, the domain/stratigraphic classification, recently developed by the British Geological Survey and others, has been used and their geotechnical properties and characteristics are discussed on this basis. The geotechnical properties and characteristics of the other main glacial and periglacial deposits are also discussed. For some of these (e.g. glaciolacustrine deposits, quick clays and loess), geohazards relating to the lithology and/or fabric of the deposit are discussed along with their properties. Other geohazards that do not relate to lithology and/or fabric are discussed separately as either local or regional geohazards. In some cases (e.g. glaciofluvial sands and gravels), the geotechnical properties and behaviour are similar to sediments deposited under different climatic conditions; these deposits are therefore not discussed at length. Similarly, some of the local geohazards that are found associated with glacial and periglacial deposits relate to current climatic conditions and are not discussed here. Examples include land-sliding and highly compressible organic soils (peats).