TY - JOUR T1 - A large impact crater beneath Hiawatha Glacier in northwest Greenland JF - Science Advances Y1 - 2018 A1 - Kjær, Kurt H. A1 - Larsen, Nicolaj K A1 - Binder, Tobias A1 - Bjørk, Anders A A1 - Eisen, Olaf A1 - Fahnestock, Mark A A1 - Funder, Svend A1 - Garde, Adam A A1 - Haack, Henning A1 - Helm, Veit A1 - Houmark-Nielsen, Michael A1 - Kjeldsen, Kristian K A1 - Khan, Shfaqat A A1 - Machguth, Horst A1 - McDonald, Iain A1 - Morlighem, Mathieu A1 - Mouginot, Jérémie A1 - Paden, John D A1 - Waight, Tod E A1 - Weikusat, Christian A1 - Willerslev, Eske A1 - MacGregor, Joseph A. AB - We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact-related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron asteroid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet. VL - 4 UR - http://advances.sciencemag.org/ http://advances.sciencemag.org/lookup/doi/10.1126/sciadv.aar8173 ER - TY - JOUR T1 - Radar attenuation and temperature within the Greenland Ice Sheet JF - Journal of Geophysical Research: Earth Surface Y1 - 2015 A1 - MacGregor, Joseph A. A1 - Li, Jilu A1 - Paden, John D A1 - Catania, Ginny a A1 - Clow, Gary D A1 - Fahnestock, Mark A A1 - Gogineni, S Prasad A1 - Grimm, Robert E A1 - Morlighem, Mathieu A1 - Nandi, Soumyaroop A1 - Seroussi, Helene A1 - Stillman, David E VL - 120 UR - http://doi.wiley.com/10.1002/2014JF003418 ER - TY - JOUR T1 - Radiostratigraphy and age structure of the Greenland Ice Sheet JF - Journal of Geophysical Research: Earth Surface Y1 - 2015 A1 - MacGregor, Joseph A. A1 - Fahnestock, Mark A. A1 - Catania, Ginny A. A1 - Paden, John D A1 - Prasad Gogineni, S. A1 - Young, S Keith A1 - Rybarski, Susan C A1 - Mabrey, Alexandria N A1 - Wagman, Benjamin M A1 - Morlighem, Mathieu KW - 10.1002/2014JF003215 and Greenland Ice Sheet KW - ice core KW - ice-penetrating dynamics KW - ice-sheet dynamics VL - 120 UR - http://doi.wiley.com/10.1002/2014JF003215 ER -