Giant mid-Holocene landslide-generated tsunamis recorded in lake sediments from Saqqaq, West Greenland

Abstract. The Vaigat strait (Sullorsuaq) in central West Greenland is well known for its susceptibility to landslides and historical landslide-generated tsunamis. Recent mapping of the seabed in the Vaigat Strait has revealed several prehistoric giga-scale tsunamigenic landslides; however, their ages are unknown. Here, we report sedimentological evidence from six coastal lakes at 19 to 134 m above sea level (a.s.l.) on the Saqqaq foreland located at the eastern end of Vaigat. Using optical, X-ray fluorescence (XRF), and magnetic susceptibility core scanning in our sedimentological analysis along with a screening for marine diatoms and radiocarbon dating, we find evidence of at least two tsunami events occurring at 7.6 and 7.3 cal. ka BP. Using a previously published, recalibrated relative sea level curve from Arveprinsen Ejland (Alluttoq), located 40 km southeast of Saqqaq, we infer wave run-up heights of 41–66 and 45–70 m respectively for the two tsunamis. These run-up heights from prehistoric tsunamis are several orders of magnitude larger than the historic landslide-tsunami run-up heights at Saqqaq which only reached an elevation of c. 3 m in November 2000. While two giant tsunamis can be found in the lake sediment records, landforms from at least nine giga-scale landslides are present on the seafloor of Vaigat, we infer that the older giant tsunamis must have happened between the last deglaciation and the oldest sediment in the lakes (c. 10 to 8.5 cal. ka BP).