Extended Data Fig. 1: Relic crevasses in Henry Ice Rise.
From: Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene
a, Radargram, aligned perpendicular to the divide ridge (inset shows the location). One undulating isochrone is delineated with colours showing normalized elevation. b, c, Close-up views of the boxed regions indicated in a. In both close-up panels, diffractors (hyperbolic reflectors) are interpreted as expressions of relic crevasses (data are unmigrated). The red vertical dashed line is the present-day grounding line31. d–f, Radargrams aligned approximately perpendicular to northern relic crevasses (d and e show migrated data). In c (6 km ≤ x ≤ 8 km) and f (0.3 km ≤ x ≤ 1.4 km) isochrones intercepting the bed are evident. g, Three relic crevasses mapped across several radar lines over a Radarsat Antarctic Mapping Project (RAMP) image94. The inset is an oblique, three-dimensional view of the features over an interpolated surface, showing the bed elevation zb (see Methods). Crevasse spacing in these areas ranges between approximately 200 m and 600 m. The arrow indicates the view direction of the oblique view.
