Declines in Arctic sea ice are now well documented, with record September minima markedly decreasing over the last 15 years. At the same time, coastal erosion rates exceeding 30 meters per year have recently been documented along Alaska’s Beaufort Sea coastline, and a number of studies suggest that these erosion rates have accelerated over the last half-century. While these observations suggest a causal relationship between sea ice decline and coastal change, a lack of direct observational evidence has limited our progress in understanding the processes driving coastal erosion in this region. This project for the first time documented the relative roles of thermal and wave energy. Our team showed from time lapse photography, meteorological monitoring, and laboratory analysis of coastal bluff materials, that erosion along a segment of Alaska’s Beaufort Sea coastline is driven largely by thermal processes. Thawing of the ice-rich permafrost coastline by relatively warm seawater in the late summer undermines coastal bluffs, leading to topple failures of discrete blocks defined by ice-wedge polygons. Coastal erosion rates in this setting are likely to increase with continued Arctic warming, and this has important implications for local settlements and possible future infrastructure.