Modelling Subglacial Erosion and Englacial Sediment Transport of the North American Ice Sheets

The glacial geology of North America is a rich resource upon which reconstructions of ice sheets are made Numerical modelling of ice sheets based on ice physics is an alternate avenue for cryospheric reconstruction However such algorithms are unable to draw from the full wealth of geomorphic data because a largescale forward model of basal processes necessary to link the ice and the bed is not available I develop a processbased model of sediment production entrainment deposition and transport to ll this conspicuous gap Subglacial abrasion is modelled following Hallet and a quarrying model dependent on subcritical crack growth is constructed Entrainment proceeds predominantly by intrusion into the sediment Iverson and Semmens and when basal melt exceeds the rate of entrainment englacial sediment is deposited Both vertical redistribution of englacial sediment within an ice column and lateral transport of debris is considered Ice entrains loose debris from the bed transports it downstream and deposits an allochthonous debris train observable on the modern landscape This can be modelled when an accurate geo logic representation of the bed is used allowing the exploitation of distinct lithologies as natural tracers of ice motion Also incorporation of the dierences in physical properties between various lithologies is possible with such a lithologically realistic description of the bed Several processes are functions of bed topography and a description of smallscale topography within a largescale grid is required a downscaling method is therefore developed Basalice processes must be coupled to both ice sheet conditions and subglacial hydrology The MarshallClarke thermomechanical ice sheet model Marshall Marshall and Clarke ab Marshall et a