Catastrophe & Climate · Beneath Hiawatha Glacier, north-west Greenland

Hiawatha Crater

A 31-kilometre crater hidden under a kilometre of ice — briefly the great hope of Younger Dryas impact theorists, until the zircons spoke.

Mainstream: c. 58 million years ago (Late Palaeocene; Kenny et al. 2022)Alternative: Initially speculated to be under 100,000 — possibly under 13,000 — years old, feeding Younger Dryas impact theories78.72°, -66.27°

Catastrophe

At a glance

Hiawatha Crater — Photo: NASA · Public domain

In 2018 a Danish-led team announced something remarkable: airborne radar had revealed a 31-kilometre-wide circular depression in the bedrock beneath Hiawatha Glacier at the north-western edge of the Greenland Ice Sheet — the first impact crater ever found under a continental ice sheet, and among the largest 25 known on Earth. Sand flushed from beneath the glacier contained shocked quartz and impact melt, and geochemistry pointed to a fractionated iron asteroid perhaps 1.5 kilometres across. The crater looked surprisingly fresh, and because parts of it seemed to disturb ice from the last glacial period, speculation erupted that the impact might be shockingly recent — perhaps even the trigger of the Younger Dryas cold snap 12,800 years ago. Four years later, laboratory dating delivered a very different answer.

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The mainstream view

What archaeology says

The discovery paper by Kurt Kjaer of the Natural History Museum of Denmark, with NASA glaciologist Joseph MacGregor and colleagues, was careful about age: the crater post-dated the Palaeoproterozoic bedrock and its sharp morphology was consistent with anything from three million years old to — provocatively — the end of the last ice age. That window overlapped the Younger Dryas, and the authors acknowledged the possibility, igniting headlines. But radiometric dating settled the matter. In 2022, Gavin Kenny of the Swedish Museum of Natural History and colleagues published in Science Advances two independent clocks run in two different laboratories: uranium-lead dating of shocked zircon in Stockholm and argon-argon dating of impact-melt sand in Copenhagen (under geochronologist Michael Storey). Both converged on 57.99 plus or minus 0.54 million years — the Late Palaeocene, roughly eight million years after the dinosaur-killing Chicxulub impact.

At 58 million years old, Hiawatha struck a Greenland that was ice-free temperate rainforest, and any climatic effects must be sought in Palaeocene records, not the Pleistocene. Researchers now investigate whether it relates to carbon-cycle wobbles near the Palaeocene-Eocene boundary. The crater's youthful appearance turned out to be a lesson in how slowly landscapes erode under certain conditions, and how deceptive 'freshness' can be. For the mainstream, Hiawatha is also a methodological parable: a bold hypothesis was aired, tested against hard isotopic evidence, and revised without rancour — precisely how science is supposed to work.

Key evidence cited

Uranium-lead dating of shocked zircons giving c. 58 million years (Kenny et al., Science Advances 2022)
Independent argon-argon dating of impact-melt sand converging on the same Late Palaeocene age
Shocked quartz and melt-rock clasts in glaciofluvial sediment confirming a genuine impact origin
Geochemistry indicating a fractionated iron asteroid over a kilometre across
Reinterpretation of the 'disturbed' basal ice as ordinary glacial deformation, not impact damage

The alternative view

What the skeptics propose

Between 2018 and 2022, Hiawatha was the most tantalising piece of physical evidence ever offered to the Younger Dryas impact hypothesis — which had long been mocked for lacking a crater. Graham Hancock featured it prominently in America Before (2019) as the possible smoking gun of the cataclysm he argues destroyed an advanced Ice Age civilisation, noting the discovery team themselves had left a Younger Dryas age on the table. The radar data showed genuinely puzzling features: disturbed, debris-rich basal ice of apparent last-glacial age above the crater, and a subglacial drainage pattern that seemed too crisp for a deeply ancient structure. A second possible crater (the 36-kilometre 'Paterson' structure) spotted by MacGregor nearby in 2019 added to the sense that north-west Greenland might record geologically recent bombardment.

Most impact-hypothesis proponents have accepted the 58-million-year date — the two-method, two-laboratory agreement is difficult to dispute — and shifted their argument: the Younger Dryas event, they now stress, was likely an airburst swarm from a fragmenting comet (as at Tunguska, which left no crater), so no crater should be expected at all. Some continue to note the unresolved oddities of the overlying ice, which Kjaer's team attributed to normal glaciological processes. Hiawatha remains a touchstone in alternative-history circles less as evidence than as narrative: proof that enormous geological surprises can still hide under the ice, and that mainstream science took a 'crazy' possibility seriously enough to test it.

Key evidence cited

The crater's remarkably fresh morphology, initially judged consistent with a very young age
Debris-rich, deformed basal ice above the structure that appeared to date from the last glacial period
The discovery paper itself (Kjaer et al. 2018) explicitly allowing an age as young as the Pleistocene
A possible second large crater (Paterson) 183 km away, briefly suggesting a recent double impact
Proponents' argument that a fragmenting-comet airburst scenario for the Younger Dryas never required a crater

Genuinely open questions

Did the Hiawatha impact perturb the Palaeocene climate, and can its ejecta be found in marine sediment cores?
Is the nearby Paterson structure a genuine impact crater, and if so, what is its age?
How did such a large crater retain sharp relief for 58 million years beneath moving ice?

Worth knowing

When the asteroid struck, Greenland had no ice at all — the crater now buried under a kilometre-thick glacier was punched into a warm rainforest inhabited by early primates' relatives.