Measurements of water pressure beneath Trapridge Glacier, Yukon Territory, Canada, yield the following generalizations about subglacial conditions in the studied region: (1) Even over short distances the subglacial water system is highly heterogeneous. (2) The subglacial water system consists of at least two distinct components which we refer to as the ''connected'' and ''unconnected'' water systems. (3) Regions of the glacier bed can switch back and forth from being part of the connected or part of the unconnected water system. (4) Large spatial pressure gradients can exist within the unconnected water system, and between the connected and unconnected systems. (5) Rapid pressure variations can occur in the unconnected water system. (6) Pressure variations in the unconnected water system do not match those in the connected system and can, in fact, be strongly anticorrelated with pressure variations in the connected system. If the water pressure variations in the connected system are viewed as a forcing and those in the unconnected system as a response to this forcing, the input--output relation between forcing and response can be efficiently represented as a low-order nonlinear ordinary differential equation. The response of the unconnected system to forcing from the connected system is governed by time constants having approximate magnitudes of ~1.7 hours and ~7.4 hours that we believe are associated with process rates for substrate compression and pore water diffusion, respectively. ¿ American Geophysical Union 1995