Abstract
AbstractThe importance of glacier sliding has motivated a rich literature describing the thermomechanical interactions between ice, liquid water and bed materials. Early recognition of the gradient in melting temperature across small bed obstacles led to focused studies of regelation. An appreciation for the limits on ice deformation rates downstream of larger obstacles highlighted a role for cavitation, which has subsequently gained prominence in descriptions of subglacial drainage. Here, we show that the changes in melting temperature that accompany changes in normal stress along a sliding ice interface near cavities and other macroscopic drainage elements cause appreciable supercooling and basal mass exchange. This provides the basis of a novel formation mechanism for widely observed laminated debris-rich basal ice layers.
Highlights
At an ice–liquid interface, the dependence of melting temperature on normal stress drives ice regelation (e.g. Bottomley, 1872; Telford and Turner, 1963; Nye, 1967; Drake and Shreve, 1973; Gilpin, 1979; Rempel and Meyer, 2019)
Cavity formation is associated with heterogeneity in the normal stress exerted on the basal ice interface, since the liquid pressure is typically lower than the ice overburden pressure (e.g. Iken and Bindschadler, 1986) and higher stresses elsewhere must support the remaining glacier weight
We focus on the freezing that is induced as ice slides from regions of elevated normal stress, supported in part by ice–mineral interactions, onto regions of reduced normal stress balanced solely by the liquid pressure
Summary
At an ice–liquid interface, the dependence of melting temperature on normal stress drives ice regelation (e.g. Bottomley, 1872; Telford and Turner, 1963; Nye, 1967; Drake and Shreve, 1973; Gilpin, 1979; Rempel and Meyer, 2019). We focus on the freezing that is induced as ice slides from regions of elevated normal stress, supported in part by ice–mineral interactions, onto regions of reduced normal stress balanced solely by the liquid pressure. Such transitions are expected as slip transports ice over macroscopic drainage elements (e.g. cavities), and as macroscopic drainage elements incised upwards into the ice (e.g. R-channels) are dragged across newly unloaded mineral exposures. This is noteworthy because the properties of basal ice, including the presence and concentration of entrained debris, can influence sliding behavior and erosion (e.g. Thompson and others, 2020)
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