TY - JOUR

T1 - Effect of ice sheet thickness on formation of the Hiawatha impact crater

AU - Silber, Elizabeth A.

AU - Johnson, Brandon C.

AU - Bjonnes, Evan

AU - MacGregor, Joseph A.

AU - Larsen, Nicolaj K.

AU - Wiggins, Sean E.

N1 - Funding Information: We gratefully acknowledge the developers of iSALE-2D ( www.isale-code.de ), the simulation code used in this work, including Gareth Collins, Kai Wünnermann, Dirk Elbeshausen, Boris Ivanov and Jay Melosh. Some plots in this work were created with the pySALEPlot tool written by Tom Davison. All data associated with this study are listed in tables in the supporting information and shown in figures. The simulations were performed using iSALE-2D, version Dellen r-2114. The simulation inputs and model outputs are available on Harvard Dataverse ( https://doi.org/10.7910/DVN/X6KZJG ). We thank K. H. Kjær (GLOBE Institute, University of Copenhagen) for valuable discussions. NKL thanks the Carlsberg Foundation , Aarhus University Research Foundation 25129 and the Villum Foundation 023440 for supporting this study. EB thanks the Bevan and Mary French Fund for Meteorite Impact Geology for partly supporting this research. The authors also thank Bill McKinnon and the two anonymous reviewers for their comments that helped improve our paper. Publisher Copyright: © 2021 Elsevier B.V.

PY - 2021

Y1 - 2021

N2 - The discovery of a large putative impact crater buried beneath Hiawatha Glacier along the margin of the northwestern Greenland Ice Sheet has reinvigorated interest into the nature of large impacts into thick ice masses. This circular structure is relatively shallow and exhibits a small central uplift, whereas a peak-ring morphology is expected. This discrepancy may be due to long-term and ongoing subglacial erosion but may also be explained by a relatively recent impact through the Greenland Ice Sheet, which is expected to alter the final crater morphology. Here we model crater formation using hydrocode simulations, varying pre-impact ice thickness and impactor composition over crystalline target rock. We find that an ice-sheet thickness of 1.5 or 2 km results in a crater morphology that is consistent with the present morphology of this structure. Further, an ice sheet that thick substantially inhibits ejection of rocky material, which might explain the absence of rocky ejecta in most existing Greenland deep ice cores if the impact occurred during the late Pleistocene. From the present morphology of the putative Hiawatha impact crater alone, we cannot distinguish between an older crater formed by a pre-Pleistocene impact into ice-free bedrock or a younger, Pleistocene impact into locally thick ice, but based on our modeling we conclude that latter scenario is possible.

AB - The discovery of a large putative impact crater buried beneath Hiawatha Glacier along the margin of the northwestern Greenland Ice Sheet has reinvigorated interest into the nature of large impacts into thick ice masses. This circular structure is relatively shallow and exhibits a small central uplift, whereas a peak-ring morphology is expected. This discrepancy may be due to long-term and ongoing subglacial erosion but may also be explained by a relatively recent impact through the Greenland Ice Sheet, which is expected to alter the final crater morphology. Here we model crater formation using hydrocode simulations, varying pre-impact ice thickness and impactor composition over crystalline target rock. We find that an ice-sheet thickness of 1.5 or 2 km results in a crater morphology that is consistent with the present morphology of this structure. Further, an ice sheet that thick substantially inhibits ejection of rocky material, which might explain the absence of rocky ejecta in most existing Greenland deep ice cores if the impact occurred during the late Pleistocene. From the present morphology of the putative Hiawatha impact crater alone, we cannot distinguish between an older crater formed by a pre-Pleistocene impact into ice-free bedrock or a younger, Pleistocene impact into locally thick ice, but based on our modeling we conclude that latter scenario is possible.

KW - craters

KW - ice sheets

KW - impacts

U2 - 10.1016/j.epsl.2021.116972

DO - 10.1016/j.epsl.2021.116972

M3 - Letter

AN - SCOPUS:85105325926

VL - 566

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

M1 - 116972

ER -