NASA's Operation IceBridge radar and laser surveys in 2015 revealed a bowl-shaped depression in the bedrock beneath Greenland's Hiawatha Glacier.
Notes on verification
Confirmed by NASA press release, peer-reviewed Science Advances paper (Kjær et al. 2018), ScienceNews, and Wikipedia. Minor nuance: radar was the primary instrument, laser altimetry supplemented topographic mapping. [cascade flags: wikipedia_dropped_other_sources_exist | tier=silver indep_score=0.983 clusters=3 claim_tier=notable]
Sources
- City-size impact crater found under Greenland ice (seed:history_and_archaeology)
- https://www.nasa.gov/news-release/international-team-nasa-make-unexpected-discovery-under-greenland-ice (corroboration)
- https://www.sciencenews.org/article/hiawatha-crater-greenland-age-younger-dryas (corroboration)
- https://www.science.org/doi/10.1126/sciadv.aar8173 (corroboration)