Seismic Evidence of Impact Breccia and Unlithified Sediments under
Hiawatha Glacier
Abstract
Hiawatha Crater in northwest Greenland is one of only two confirmed
impact craters under an ice sheet. Hiawatha therefore offers a rare
proxy for understanding the interactions between active glacial dynamics
and impact craters on other planetary bodies. Here we characterize
Hiawatha’s subglacial environment, presenting the results of two
active-source seismic experiments and interpreting them in concert with
previous radar sounding analysis. Seismic reflectivities at a site with
a single basal radar reflector are consistent with a substrate of impact
melt-bearing breccia. At a site where radar sounding revealed a
porewater reflector 10–15 m below the base of the ice sheet, our
seismic results are consistent with a substrate of unlithified
sediments. We propose a model where supraglacial water supplies heat for
basal melting, leading to rain–out of unconsolidated sediment from
dirty basal ice (fringe) and permitting a permeable porewater-bearing
basal layer to persist without consolidating.