Transient Water Flow in Subglacial Channels

Abstract

Abstract A hydraulic mechanism is postulated as the source of certain low-frequency (1-5 Hz) seismic signals that are recorded in the vicinity of temperate glaciers. To illustrate that the mechanism is a plausible seismic source, the equations of motion and continuity for transient flow in a subglacial conduit are developed. The solution to these equations is obtained for the case of the flow of water being terminated in a glacial conduit. Using reasonable values of physical parameters taken from the literature, the displacement of the conduit walls is determined as a function of time and distance along the tunnel. The spectral character of the proposed source and the period of time over which it operates is compared with seismic records of typical type II signals. The agreement in terms of these parameters is good. To further examine the validity of the proposed seismic source a preliminary energy calculation is made which demonstrates that the proposed mechanism is energetically reasonable. Evidence of hydraulically generated seismic waves from a dam site is introduced to support the theory of a hydraulic source. Based on the evidence presented, it is suggested that the flow of water from glaciers is modulated by an internal flow regime that is intermittent in time and space. The substance of this paper is included in a report by the present authors entitled “Hydraulic transients: a seismic source in volcanoes and glaciers”, published in Science, Vol. 203, No. 4381, 1979, p. 654–56.