Coastal gullies formed by piping on a permafrost marine terrace near Iqaluktuuttiaq (Cambridge Bay), Nunavut, Canada

Piping is the formation of subsurface tunnels (pipes) due to sediment removal by groundwater flow, which can lead to surface collapse and gully formation, thus transitioning from subsurface to surface erosion. While piping occurs across various climates, its formation in periglacial environments and its impact on these landscapes remain poorly documented. This study examines the morphology and environmental conditions of gullies that formed on a permafrost marine terrace near Iqaluktuuttiaq (Cambridge Bay), Nunavut (Canada), and provides the first conceptual model linking piping to gully formation in a periglacial environment. Nineteen gullies were surveyed along a 430-m coastline with a 2–4 m high bluff experiencing accelerated coastal erosion. Field observations, remotely piloted aircraft system (RPAS) surveys, and permafrost cryostratigraphy confirmed that the gullies did not form from ice-wedge degradation, but rather from lateral groundwater flow causing piping. Piping was confined to the top sand layer of the terrace, where the thaw front and underlying layer of silt loam acted as impermeable barriers (aquitards). Piping likely peaked during snowmelt when the sand layer became saturated. Gullies predominantly formed within the last 4–5 m of the terrace where the steep bluff and collocated seepage face, deeper thaw front, and terrace subsidence likely increased the lateral hydraulic gradient. This study improves understanding of piping in periglacial environments and highlights its interactions with surface, thermal, and coastal erosion in shaping Arctic coastal landscapes. • 19 gullies were surveyed on a permafrost marine terrace near Iqaluktuuttiaq, Canada • Gullies formed due to piping and pipe collapse in the top sand layer of the terrace • Piping was confined to the sand layer due to the underlying sediment and thaw front • Piping and gully evolution were likely also influenced by coastal erosion • This study is the first to link piping to gully formation in continuous permafrost