Abstract
AbstractTo understand the mechanism of simultaneous drainage event related to supraglacial lakes on a debris-covered glacier, we investigated water-level variations of supraglacial lakes on the southern Inylchek Glacier in Kyrgyzstan. To examine these variations, we used daily aerial images for 2017–2019 from an uncrewed aerial vehicle that were converted to 15 cm-digital surface models and ortho-images. Our main results are as follows: (1) When one lake drained, the water levels of other lakes simultaneously increased, indicating that drainage water is shared with several lakes through a main englacial conduit. In one drainage event, a branched off englacial conduit clearly connected to a main englacial conduit. (2) Sometimes several lakes discharged simultaneously, indicating that several lakes had connected to a main englacial conduit that had opened. Such cases can cause larger-scale drainage than that from the opening of a branched off englacial conduit. (3) Simultaneous drainage occurred twice in the same year, each time through a different conduit, indicating that the main englacial conduit can be abandoned and reused. (4) In some lakes, the water level on the hydraulic gradient line increased gradually with nearly the same increase rate just before drainage. Such an increase may be an indicator of a possible simultaneous drainage event.
Highlights
In Asian mountain regions, large-volume drainage events occur from supraglacial lakes on debris-covered glaciers
We investigated daily water-level variations of the lakes in the summers of 2017, 2018 and 2019, primarily using digital surface models (DSMs) and ortho-images derived from an uncrewed aerial vehicle (UAV)
We used DSMs and ortho-images derived from an uncrewed aerial vehicle (UAV) to investigate daily water-level variations of supraglacial lakes on a debris-covered glacier in 2017, 2018 and 2019
Summary
In Asian mountain regions, large-volume drainage events occur from supraglacial lakes on debris-covered glaciers. On 29 April 2009, in the Lunana region of northwestern Bhutan, a sudden large discharge event occurred through englacial or subglacial conduits at the Tshojo Glacier, forcing the evacuation of the people of Punakha Town, located 70 km downstream (Komori and others, 2012). After this event, Yamanokuchi and others (2011) observed a large outlet of an englacial conduit through which drainage water flowed at the glacier terminus. From April to July 2017, a supraglacial lake with an area of 180 000 m2 rapidly formed on a tributary of the Khumbu Glacier, completely discharged in mid-July (Miles and others, 2018a) These recent studies show that large-scale drainage events are coupled with supraglacial and englacial water-storage dynamics
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