Surge-type glaciers typically undergo cyclical flow instability due to mass accumulation; however, some recent glacier surges have caused irreversible ice loss in a short period. At Vavilov Ice Cap, Russia, surge-like behavior initiated in 2013 and by spring 2019 the ice cap had lost 9.5 Gt of ice (11% mass of the entire basin). Using time series of surface elevation and glacier velocity derived from satellite optical and synthetic-aperture radar imagery, we identify a shift of flow pattern starting in 2017 when shear margins formed within the grounded marine piedmont fan. Multiple summer speedups correlate with warmer summers during 2015–2019 and suggest that surface melt may access the subglacial environment. Force balance analysis and examination of the Péclet number show that glacier thinning propagated upstream in 2016–2017, and diffusion became a significant dynamic response to thinning perturbations. Our results suggest that the glacier has entered a new ice stream-like regime.