The roles of channelization and parameter sensitivity on feedbacks between subglacial hydrology and glacier dynamics

On most glaciers and ice sheet outlets the majority of motion is due to basal sliding, but the importance of feedbacks between subglacial and hydrology and glacier dynamics are poorly understood. Using a coupled subglacial hydrology and glacier dynamics model, we investigate parameter sensitivity of feedbacks between the two systems by simulating a meltwater-induced speedup event on an idealized mountain glacier, both with and without allowing channelization of subglacial drainage. When channelized drainage is absent, we find that net feedbacks are strongly negative over a wide range of the hydrology model and sliding law parameter space, indicating that the sliding-opening of subglacial cavities is the dominant feedback between the water and ice systems. Net positive feedbacks, which do occasionally occur in our parameter space, are rare and brief. Parameter combinations that favor feedback strength at initial vs. later times differ due to the role of drainage system evolution in the coupled system. When channelization is allowed, feedbacks between subglacial hydrology and ice dynamics can still control a substantial fraction of the magnitude and duration of the response to a speedup event prior to channelization. However, our modeling also argues that subglacial channelization is required to terminate surface meltwater induced speedup events over timescales that are commensurate with observations of late summer slowdown. Feedbacks between subglacial hydrology and ice dynamics appear to be insignificant once channelized drainage becomes efficient because evolution of distributed drainage is thereafter dominated by the influence of the channel.