| Summary: | Despite the ubiquity of tunnel channels and valleys within formerly glaciated areas, their origin remains enigmatic. Few modern analogues exist for event-related subglacial erosion. This paper presents evidence of subglacial meltwater erosion and tunnel channel formation during the November 1996 jökulhlaup, Skeiðarárjökull, Iceland. The jökulhlaup reached a peak discharge of 45,000 – 50,000 m 3 s -1 , with flood outbursts emanating from multiple outlets across the entire 23 km wide glacier snout. Subsequent retreat of the south-eastern margin of Skeiðarárjökull has revealed a tunnel channel excavated into the surrounding moraine sediment and ascending 11.5 m over a distance of 160 m from a larger trough to join the apex of an ice-contact fan formed in November 1996. The tunnel channel formed via hydro- mechanical erosion of 14,000 m 3 - 24,000 m 3 of unconsolidated glacier substrate, evidenced by copious rip-up clasts within the ice-contact fan. Flow reconstruction provides peak discharge estimates of 683 m 3 s -1. The tunnel channel orientation, oblique to local ice flow direction nd within a col, suggests that local jökulhlaup routing was controlled by (a) subglacial topography and (b)the presence of a nearby proglacial lake. We describe the first modern example of tunnel channel formation and illustrate the importance of pressurised subglacial jökulhlaup flow for tunnel channel formation.
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