A ten-year record of supraglacial lake evolution and rapid drainage in West Greenland using an automated processing algorithm for multispectral imagery

摘要

The rapid drainage of supraglacial lakes introduces large pulses ofmeltwater to the subglacial environment and creates moulins, surface-to-bedconduits for future melt. Introduction of water to the subglacial system hasbeen shown to affect ice flow, and modeling suggests that variability inwater supply and delivery to the subsurface play an important role in thedevelopment of the subglacial hydrologic system and its ability to enhanceor mitigate ice flow. We developed a fully automated method for trackingmeltwater and rapid drainages in large (> 0.125 km2)perennial lakes and applied it to a 10 yr time series of ETM+ and MODISimagery of an outlet glacier flow band in West Greenland. Results indicateinterannual variability in maximum coverage and spatial evolution of totallake area. We identify 238 rapid drainage events, occurring most often atlow (< 900 m) and middle (900–1200 m) elevations during periods ofnet filling or peak lake coverage. We observe a general progression of bothlake filling and draining from lower to higher elevations but note that thetiming of filling onset, peak coverage, and dissipation are also variable.Lake coverage is sensitive to air temperature, and warm years exhibitgreater variability in both coverage evolution and rapid drainage. Mid-elevationdrainages in 2011 coincide with large surface velocity increasesat nearby GPS sites, though the relationships between ice-shed-scale dynamicsand meltwater input are still unclear.