Coarse Sediment Transport in a Near‐Terminus Subglacial Channel

Abstract We present the first large‐sample, spatially resolved measurements of coarse sediment transport within a subglacial meltwater channel. We released 324 radio‐tagged pebbles into a near‐terminus channel of Glacier d’Otemma, Switzerland, and monitored their positions through 10–50 m of ice during the mid to late melt season. Concurrently, proglacial discharge and bedload flux were monitored at the terminus. Particles moved infrequently: more than half never moved, most remained near their release location, and only 25% were exported to the proglacial river. Particle export was more consistently related to recent movement history than to proglacial discharge or bedload export, whereas virtual velocity showed no consistent relationship with these predictors. These observations indicate substantial coarse sediment retention within an active near‐terminus subglacial channel, potentially weakening short‐term correspondence between coarse subglacial transport and proglacial sediment export.