Fig. 5: Conceptual model for the formation of ribs by tidally modulated grounding-line migration.
From: Rapid retreat of Thwaites Glacier in the pre-satellite era
a, Grounding at low water forms a rib by settling and sediment bulging/extrusion at the grounding line ahead of an ice plain. b, Subsequent grounding-line migration occurs during high water with the ice-shelf base displaced upwards and landwards by the tide, allowing contact with warm ocean water. Basal melting is enhanced by tidal mixing in the narrow cavity. c, Grounding line settles at new position on the next low water, creating a second rib in series. The amplitude and spacing of ribs is a function of tidal amplitude, which modulates the distance of retreat from ridge to ridge. Bottom: plot depicting typical diurnal tide cycle for a 48 h period at Thwaites Glacier. Intervals on x-axis correspond to 0.2 days (4.8 hours). a–c relate to positions on the tidal cycle. Triangles denote successive grounding-line positions. Note exaggerated vertical scale in all images; the true sea-floor expression of the ridges is subtle, with sea bed and ice bottom slopes only fractions of a degree.
