A great deal has been learned about water flow through glaciers in the past three decades. Much of the progress has been theoretical, as experimental techniques for studying the englacial and subglacial hydraulic systems are few and not yet fully exploited, and observational evidence is difficult to obtain for obvious reasons. An added benefit of the recent progress is that we have gained a much better understanding of glacial erosional processes and of the origin of certain glacial landforms that owe their existence to the interaction between water and ice.

We begin this chapter with a discussion of the development and geometry of englacial water conduits in temperate glaciers. Then, the subglacial part of the system is examined. Finally, we consider geomorphic implications of some of the recent research.

The upper part of the englacial hydraulic system

Veins and the initial development of passages

Nye and Frank (1973) argued that veins should be present along boundaries where three ice crystals meet, and that at four-grain intersections these veins should join to form a network of capillary-sized tubes through which water can move. They thus concluded that temperate ice should be permeable.

Such capillary passages have been observed in ice cores obtained from depths of up to 60 m on Blue Glacier, Washington (Figure 8.1a) (Raymond and Harrison, 1975). The veins are triangular in shape (Figure 8.1b) and roughly 25 μm across.

Estimates of the permeability of glacier ice resulting from this vein system vary widely.