Extended Data Fig. 5: Temporal evolution of fracture propagation and ice accretion.

This is the same as Fig. 3, except that diurnal changes in channel water level are included. The lower edge of the shading shows the fracture depth, and the water level is shown by the grey solid line. Shading indicates the thickness of ice accretion on to the fracture walls (Eq. (9)), with stippling and hatching indicating where total ice accretion is sufficient to close fractures of width 1 or 3 cm, respectively, before they reach the bed. These examples used L_f = 250 m, r_c = 1.0 m based on observations in SW Greenland¹³, and the measured borehole temperature profiles shown in Fig. 1. Note that propagation rate is independent of fracture width w_f (see Methods). The main changes from Fig. 3 are the longer propagation times, which allow thicker ice accretion and a more restricted range of conditions for full-depth hydrofracture.