Arctic tsunami as an emerging threat for circumpolar coastal landscapes and communities- insight into Karrat Fjord 2017 tsunami wave impacts on Nuugaatsiaq settlement, western Greenland

Abstract:

In the warming Arctic region, landslide-triggered tsunamis become one of the most important geo-hazards with profound effects on the functioning of coastal communities and landscapes. In Greenland, due to the recent climate warming and associated landscape transformation (i.e. retreat of glaciers and permafrost thawing) many mountain slopes were destabilized and released numerous tsunamigenic landslides. For example, in November 2000 a landslide from Paatuut mountain triggered a tsunami (runup ca. 50 m) which destroyed Qullissat town (Disko Island, western Greenland) and destabilized shores along Vaigat Strait even up to 150 km from the landslide location.

Here we report on the largest documented tsunami wave in Greenland to date (runup height ca. 90 m), which resulted from a massive landslide to Karrat Isfjord, western Greenland. On the 17^th of June 2017, a landslide which mobilized 35–58 million m³ of material entered the fjord. It triggered a tsunami wave with a runup height exceeding 90 m close to the landslide, ca. 50 m on the opposite shore of the fjord. The tsunami traveled ca. 32 km along the fjord and reached the settlement of Nuugaatsiaq with ca. 1-1.5 m high waves which flooded the terrain up to 8 m above sea-level. Tsunami waves were powerful enough to destroy the community infrastructure, impact fragile coastal tundra landscape, and unfortunately, injure several inhabitants and cause 4 deaths. Our field survey carried out 25 months after the event results in documentation of the previously unreported scale of damages in the settlement (ca. 48% of infrastructure objects including houses and administration buildings were destroyed by tsunami). We have observed a recognizable difference in the concentration of tsunami deposit accumulations between areas of the settlement overwashed by by the wave and areas of runup and return flow. The key tsunami effects preserved in the coastal landscape were eroded coastal bluffs, gullied and dissected edges of cliffed coast in the harbour and tundra vegetation compressed by boulders or icebergs rafted onshore during the event.

This is a contribution to the NCN project 2018/29/N/ST10/01947: GROZA- Impact of climate-induced geohazards on Greenlandic coastal environments - case study of Disko Bay, W Greenland.