Till Genesis and Hydrogeological Properties

Hydrogeological properties of tills are highly dependent upon factors as grain-size distribution, compaction, orientation of particles, presence of fractures and occurrence of sorted sediments. These factors are again dependent upon the till forming processes. Lodgement tills formed under active, temperate sliding glaciers are usually compact, rather homogeneous and in many cases they are fractured. Melt-out tills deposited in connection with stagnant ice are in most cases less dense, have a lower content of fine-grained particles and a higher abundance of sorted sediment lenses. Flow tills which are mainly formed by a secondary flow of supraglacial debris are commonly very variable, they may have a low content of fine-grained components, a low degree of compaction and they are often closely connected with sorted glaciofluvial sediments. Till genesis is in many cases difficult to interpret, and an objective description of all main characteristics of the till is important in hydrogeological studies. The lodgement till has a lower effective porosity than the melt-out and flow tills due to its finer grain-sizes and higher compactness. The saturated hydraulic conductivity is lower, and dependent upon the fracture pattern. In melt-out tills and flow tills the occurrence of well sorted sediments will in many cases control the hydraulic conductivity. In all till types the structural properties are most important for the saturated water flow.