Subglacial Processes and Subglacial Hydrology

Abstract

The hydrology of glaciers is known to have a significant influence on glacier dynamics. Rapid variations in dynamics can occur due to changes in the glacial and subglacial hydrology. However, our understanding of the subglacial drainage system is based on few direct and usually short-term observations. In this thesis, two decades of pressure measurements at the glacier bed are investigated. The measurements were carried out at the Svartisen Subglacial Laboratory in Northern Norway where load cells installed at the ice-rock interface under =200 m of glacier ice record normal stress. A statistical study of the records for the period 1992-2014 demon- strates that the glacier bed response depends strongly on surface melt and the routing of subglacial water. Changes in subglacial hydrology cause several types of mechanical response at the glacier base. Water increases basal connectivity in summer whereas local processes, such as local ice flow, dominate the pressure signal in winter. The comparison of two summers with high, but contrasting connectivity (correlated vs anti-correlated pressure signal) demonstrates that fluctuations in meltwater input force a load transfer from the connected hydrological system to the unconnected part of the drainage system. Modelling of load transfer near a pressurised channel simulates the observed anti-correlated response in normal stress at the glacier bed. Daily pressure events are also investigated and characterise the response in pressure of the unconnected system, which differs from daily fluctuations in water pressure as measured in boreholes. The peak and decay in pressure that comprise these events are inferred to be a result of the stress bridging effect that occurs during the contraction of the drainage system. The peak in pressure is reproduced with an experiment where an artificial cavity contracts over the load cell and with a stress bridging model that incorporates shear stress transfer near a subglacial cavity. Observations from load cells and boreholes are not contradictory; instead they com- plement each other and help us characterise the mechanical and hydrological dynamics occurring at the glacier bed.

Subglasial hydrologi og subglasiale prosesser