Brief communication: The Khurdopin glacier surge revisited – extreme flow velocities and formation of a dammed lake in 2017

Abstract

Abstract. Glacier surges occur regularly in the Karakoram, but the driving mechanisms, their frequency and its relation to a changing climate remain unclear. In this study, we use digital elevation models and Landsat imagery in combination with high-resolution imagery from the Planet satellite constellation to quantify surface elevation changes and flow velocities during a glacier surge of the Khurdopin Glacier in 2017. Results reveal that an accumulation of ice volume above a clearly defined steep section of the glacier tongue since the last surge in 1999 eventually led to a rapid surge in May 2017 peaking with velocities above 5000 m a −1 , which were among the fastest rates globally for a mountain glacier. Our data reveal that velocities on the lower tongue increase steadily during a 4-year build-up phase prior to the actual surge only to then rapidly peak and decrease again within a few months, which confirms earlier observations with a higher frequency of available velocity data. The surge return period between the reported surges remains relatively constant at ca. 20 years. We show the potential of a combination of repeat Planet and ASTER imagery to (a) capture peak surge velocities that are easily missed by less frequent Landsat imagery, (b) observe surface changes that indicate potential drivers of a surge and (c) monitor hazards associated with a surge. At Khurdopin specifically, we observe that the surging glacier blocks the river in the valley and causes a lake to form, which may grow in subsequent years and could pose threats to downstream settlements and infrastructure in the case of a sudden breach.

Glacial and geomorphic effects of a supraglacial lake drainage and outburst event, Everest region, Nepal Himalaya

“…Pond observations during the monsoon are intermittent at best (Watson et al, 2016;Miles et al, 2017a) and thus we recommend the adoption of highfrequency repeat optical imagery (as in this study) and syn-thetic aperture radar data products (e.g. Strozzi et al, 2012) for improved monsoon monitoring of glacier hydrology.…”

“…Benn et al, 2017;Rounce et al, 2017), subglacially (e.g. Walder and Driedger, 1995;Wadham et al, 2001;Garambois et al, 2016), or adjacent to ice margins (Huss et al, 2007;Steiner et al, 2018). These storage components are interlinked: water retained at the surface can reach englacial and subglacial systems through hydrofracture or exploitation of zones of permeabil-E. S. Miles et al: Geomorphic effects of Himalayan supraglacial lake outburst ity (e.g.…”

The State of Remote Sensing Capabilities of Cascading Hazards Over High Mountain Asia

“…Given the plethora of imagery being generated, new innovative methods such as algorithms using Google Earth Engine (e.g., Kraaijenbrink et al, 2017) are being developed to automatically analyze these large datasets. For more detailed studies, higher resolution (0.3-3 m) satellite imagery with improved temporal resolution (e.g., PlanetScope, WorldView) enable near real-time monitoring of the filling and potentially catastrophic drainage of supraglacial (e.g., , moraine-dammed (e.g., Byers et al, 2018), icedammed (e.g., Steiner et al, 2018), and landslide-dammed lakes (e.g., Kargel et al, 2016). Additionally, SAR images, which rely on the backscattering intensity to delineate glacial lakes (e.g., Strozzi et al, 2012), provide reliable, repeat images of glacial lakes that are unobstructed by clouds.…”

“…New products such as the Global Land Ice Velocity Extraction from Landsat 8 (GoLIVE) provide velocity estimates for any Landsat 8 image pair. High-resolution optical imagery with short revisit times such as PlanetScope (e.g., Steiner et al, 2018) or reliable SAR images (e.g., Round et al, 2017) are also enabling detailed investigation of seasonal surface velocities.…”

“…A similar study on Khurdopin Glacier used a high-resolution DEM with optical imagery from Planet and Landsat, which provided enough clear-sky images to monitor the speed-up of the glacier and the subsequent growth and drainage of an icedammed glacial lake (Steiner et al, 2018) (Figure 5). Khurdopin Glacier also has a long history of GLOFs, which led local villages to develop an early warning system that uses bonfires at night or gunfire during the day to alert subsequent posts down valley of the flood (Iturrizaga, 2005).…”