Formation and Drainage of Glacier Dammed Dań Zhùr (Donjek) Lake, Yukon

Abstract

Dań Zhùr (Donjek) Glacier, located in the St. Elias Mountains, Yukon, is a surge-type glacier that undergoes cyclical periods of rapid advance over a period of ~1-2 years, followed by retreat for a period of ~10 years (Kochtitzky et al., 2019). Dań Zhùr Chù’ (Donjek River) runs perpendicular to the terminus of the glacier and past surges have, at times, caused the terminus to advance enough to block the river, leading to the formation of an ice-dammed lake (Kochtitzky et al., 2020). The glacier most recently surged between 2012 and 2014, and since then Dań Zhùr Lake has drained three times: in 2017, 2018 and 2019. When a glacier dam fails, the drainage of the lake can be catastrophic and cause flooding downstream. In the case of Dań Zhùr Lake, the most recent drainage event occurred on July 13th, 2019, when the ~2.45 km2 lake drained in less than 36 hours and created an ice canyon through the glacier terminus. Time-lapse cameras and pressure sensors were used to capture the drainage event, and air photos taken during the melt season (June and September) were used to construct digital elevation models (DEMs) of the glacier terminus, lake, and lake basin. The method of drainage for the 2019 event was determined to be flotation of the terminus, leading to rapid subglacial drainage of the lake. There were also noticeable changes in water extent downstream during the 2019 event, meaning that there is a potential risk to downstream recreational users. Because of the formation of a large ice canyon after the 2019 drainage, it is very unlikely that that the lake will reform until the next surge, which is anticipated to occur around 2024. Following that surge, the size of Dań Zhùr Lake is expected to increase during the next quiescent phase, as the continued glacier recession will expose a larger basin for the lake to form in, and flotation will continue to be a likely mechanism for drainage. However, in the long term it is unlikely that ice-dammed lakes will continue to form at Dań Zhùr Glacier, as there is a trend of the maximum terminus extent during each surge being smaller than the previous one, meaning that the glacier will no longer block the flow of Dań Zhùr Chù’.