Re-evaluation of the origins of Late Quaternary ramparted depressions in Wales

This thesis describes the results of sedimentological and near-surface geophysical investigations of the internal structure of late Pleistocene permafrost and glacial ice-related 4 ramparted depressions' in Wales. These data were used to evaluate the possible origins of these landforms, which have previously been interpreted as the remains of open system pingos or lithalsas (mineral palsas). Six sites were investigated: i) Hirwaun valley ii) Llanio Fawr iii) Crychell Moor iv) Cledlyn valley v) Cletwr valley and vi) Llanpumsaint. Each site investigation is presented as an individual case study. The precise origins of these landforms remain uncertain. The density of landforms at all sites however is inconsistent with their interpretation as relict open system pingos. Some sites (Hirwaun valley and Llanio Fawr) are unequivocally glacial in origin, whilst others (e.g. Llanpumsaint) are most probably a type of relict periglacial ground-ice mound, although formation via the grounding of icebergs in a proglacial lake cannot be ruled out. Conversely, the ramparted depressions of the Cledlyn and Cletwr valleys probably formed as a result of the meltout of stagnating glacier ice, although permafrost-related origins are also possible. The investigations of relict landforms are complemented by geophysical investigations (ground penetrating radar and electrical resistivity) of active open system pingos from Svalbard. Data from both the relict and active landforms suggests that groundwater seepage through geological discontinuities is important for ground-ice mound formation, and that there is a continuum of ground-ice mounds, from features cored with lenses of segregation ice (e.g. palsas and lithalsas) to others cored with massive, injection ice (pingos). Transitional forms between these two extremes will contain a mixture of ground-ice types