Radar‐Sounding Characterization of the Subglacial Groundwater Table Beneath Hiawatha Glacier, Greenland

Abstract

Recent airborne radar-sounding surveys revealed a 31 km-wide impact crater beneath Hiawatha Glacier, part of the northwestern Greenland Ice Sheet (Kjaer et al., 2018). These radar data were collected with a new ultrawideband (UWB) radar sounder that revealed the glacier's bed topography and internal structure in unprecedented detail (Wang et al., 2016;Yan et al., 2017). Within these data, Kjaer et al. ( 2018) also identified a distinct reflection beneath the ice-bed interface that was unusually flat and specular, which they hypothesized to be the groundwater table. However, this observation has yet to be confirmed by radiometric or hydrologic analyses, and the intervening material sandwiched between the glacier and this reflection was not characterized.The unique geologic setting of a subglacial complex impact crater could be partly responsible for this reflection. While the deglaciated region immediately adjacent to Hiawatha Glacier (Inglefield Land) is composed of highly metamorphosed Paleoproterozoic rock (Kjaer et al., 2018), unconsolidated impact breccias are expected to be widespread within the crater floor surrounding the central uplift (Osinski & Pierazzo, 2013). Debris-rich ice is observed outcropping along the base of ice cliffs along the western margin of Hiawatha Glacier, and Kjaer et al. (2018) hypothesized that basal material is being actively entrained within Hiawatha Glacier, based on the UWB radar sounding data. A possible second large subglacial impact crater has also

A Late Paleocene age for Greenland’s Hiawatha impact structure

“…1B ). Water could accumulate there subglacially—as occurs presently in the sediment ~10 m beneath the ice ( 29 )—and then outburst catastrophically, which would consequently disrupt ice flow into the structure. However, this scenario would require an unusually large volume of subglacial water to have accumulated there, which is not clearly supplied by apparent basal melting farther upstream ( 30 ).…”

Impact melt rocks from the Late Paleocene Hiawatha impact structure, northwest Greenland

“…Modeling of subglacial drainage channels around the structure indicates local transportation of material out of the structure through a main drainage channel on its northwestern side, running beneath the terminus of the narrow Hiawatha Glacier, an outlet glacier protruding from the Greenland Ice Sheet (Figure 1a; Bessette et al., 2021; Kjær et al., 2018). Three glaciofluvial sand samples (HW12‐2016, HW13‐2016 and HW21‐2016) were collected from the foreland adjacent to the Hiawatha structure in 2016 (Kjær et al., 2018); the first two were collected 4 km downstream from the terminus of Hiawatha Glacier and the latter at the tip of the glacier (Figure 1).…”