New research finds possible second impact crater hiding under Greenland ice

WASHINGTON — Scientists have discovered a possible second impact crater buried under more than a mile of ice in northwest Greenland.

This follows the finding, announced in November 2018, of a 19-mile-wide crater beneath Hiawatha Glacier – the first meteorite impact crater ever discovered under Earth’s ice sheets. Though the newly found impact sites in northwest Greenland are only 114 miles apart, at present they do not appear to have formed at the same time according to the new study, published in AGU’s journal Geophysical Research Letters.

If the second crater, which has a width of over 22 miles, is ultimately confirmed as the result of a meteorite impact, it will be the 22nd largest impact crater found on Earth.

“We’ve surveyed the Earth in many different ways, from land, air and space – it’s exciting that discoveries like these are still possible,” said Joe MacGregor, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who participated in both findings.

Before the discovery of the Hiawatha impact crater, scientists generally assumed that most evidence of past impacts in Greenland and Antarctica would have been wiped away by unrelenting erosion by the overlying ice. Following the finding of that first crater, MacGregor checked topographic maps of the rock beneath Greenland’s ice for signs of other craters. Using imagery of the ice surface from the Moderate Resolution Imaging Spectroradiometer instruments aboard NASA’s Terra and Aqua satellites, he soon noticed a circular pattern some 114 miles to the southeast of Hiawatha Glacier. The same circular pattern also showed up in ArcticDEM, a high-resolution digital elevation model of the entire Arctic derived from commercial satellite imagery.

“I began asking myself ‘Is this another impact crater? Do the underlying data support that idea?’,” MacGregor said. “Helping identify one large impact crater beneath the ice was already very exciting, but now it looked like there could be two of them.”

To confirm his suspicion about the possible presence of a second impact crater, MacGregor studied the raw radar images that are used to map the topography of the bedrock beneath the ice, including those collected by NASA’s Operation IceBridge. What he saw under the ice were several distinctive features of a complex impact crater: a flat, bowl-shaped depression in the bedrock that was surrounded by an elevated rim and centrally located peaks, which form when the crater floor equilibrates post-impact. Though the structure isn’t as clearly circular as the Hiawatha crater, MacGregor estimated the second crater’s diameter at 22.7 miles. Measurements from Operation IceBridge also revealed a negative gravity anomaly over the area, which is characteristic of impact craters.

“The only other circular structure that might approach this size would be a collapsed volcanic caldera,” MacGregor said. “But the areas of known volcanic activity in Greenland are several hundred miles away. Also, a volcano should have a clear positive magnetic anomaly, and we don’t see that at all.”

Although the newly found impact craters in northwest Greenland are only 114 miles apart, they do not appear to have been formed at the same time. From the same radar data and ice cores that had been collected nearby, MacGregor and his colleagues determined that the ice in the area was at least 79,000 years old. The layers of ice were smooth, suggesting the ice hadn’t been strongly disturbed during that time. This meant that either the impact happened more than 79,000 years ago or – if it took place more recently– any impact-disturbed ice had long ago flowed out of the area and been replaced by ice from farther inland.

The researchers then looked at rates of erosion: they calculated that a crater of that size would have initially been more half a mile deep between its rim and floor, which is an order of magnitude greater than its present depth. Taking into account a range of plausible erosion rates, they calculated that it would have taken anywhere between roughly a hundred thousand years and a hundred million years for the ice to erode the crater to its current shape – the faster the erosion rate, the younger the crater would be within the plausible range, and vice versa.

“The ice layers above this second crater are unambiguously older than those above Hiawatha, and the second crater is about twice as eroded,” MacGregor said. “If the two did form at the same time, then likely thicker ice above the second crater would have equilibrated with the crater much faster than for Hiawatha.”

To calculate the statistical likelihood that the two craters were created by unrelated impact events, MacGregor’s team used recently published estimates that leverage lunar impact rates to better understand Earth’s harder-to-detect impact record. By employing computer models that can track the production of large craters on Earth, they found that the abundance of said craters that should naturally form close to one another, without the need for a twin impact, was consistent with Earth’s cratering record.

“This does not rule out the possibility that the two new Greenland craters were made in a single event, such as the impact of a well separated binary asteroid, but we cannot make a case for it either,” said William Bottke, a planetary scientist with the Southwest Research Institute in Boulder, Colorado, and co-author of both MacGregor’s paper and the new lunar impact record study.

Indeed, two pairs of unrelated but geographically close craters have already been found in Ukraine and Canada, but the ages of the craters in the pairs are different from one another.

“The existence of a third pair of unrelated craters is modestly surprising but we don’t consider it unlikely,” MacGregor said. “On the whole, the evidence we’ve assembled indicates that this new structure is very likely an impact crater, but presently it looks unlikely to be a twin with Hiawatha.”

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This paper is freely available for 30 days. You can download a PDF copy of the article by clicking on this link: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078126

Source: AGU Newsroom

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25 thoughts on “New research finds possible second impact crater hiding under Greenland ice

  1. Two nearby astroblemes could certainly be explained by a comet having calved shortly prior to impact. It would be fascinating to discover if they were approximately contemporaneous.

  2. Interesting article, whatever it turns out to be. Consider the comment “Also, a volcano should have a clear positive magnetic anomaly, and we don’t see that at all.” Not so fast, a volcano’s magnetic signature depends on several factors, like composition, where mafic volcanos have more minerals contributing to induced magnetization, and the biggee, whether the earths magnetic field was positive or reversed when the volcanic rocks cooled below the Curie Point. Reversed polarized volcanics have the remnant subtracted from the induced and can be quite difficult to interpret.

    • Ron, also collapsed caldera are a prominent feature of highly explosive
      rhyolitic types- highly aluminous and silicious with comparatively low iron – so no magnetic high. A volcano of this size may well have been able to blast through a fairly thick ice sheet, although its location near the extension of the Mid-Atlantic Ridge suggests it would be mafic lava if it were volcanuc. This more quiescent type forms inverted wash basin shaped volcanoes melted into the overlying ice (called a Tuya). They are common in Iceland and in NW Britush Columbia and I’m sure down below the ice in still active West Antarctica.

    • Volcanoes bring “fresh”, mixed material through the earth coat.

      over geological times, the earth’s crust is “normalized” by seismic events.

      Whereby heavy metals sink and lighter material “floats up”.
      _____________________________________________________

      the younger the volcanic activity the higher the metal content the stronger the magnetic deviation.

    • Cheers Bill. Hope you are staying warm with the latest Polar cold.
      Or did you jet on down to Aruba for Valentine’s with BFF Al Gore?

  3. they calculated that it would have taken anywhere between roughly a hundred thousand years and a hundred million years for the ice to erode the crater to its current shape…”

    Well somewhere between 10^5 to 10^8 years ago. So…. 3 orders of magnitude… that pretty well nails it down between the start of the last Ice Age and the mid-Cretaceous.

  4. Most be a lot of crater “twins, pairs” around the globe but most in the oceans / see beds.

    Unlikely to get detected in foreseeable times.

  5. Most be a lot of crater “twins, pairs” around the globe but most in the oceans / sea beds.

    Unlikely to get detected in foreseeable times.

    • Large submarine craters are likely to be detected, but there will be a lot fewer than on land, for three reasons:

      Minor impacts in deep water will not even leave a crater. Example: the Pliocene Eltanin impact in the south Pacific.

      The deep ocean floor is quickly “reprocessed” and subducted. There is no deep ocean floor older than 200 million years. Only very occasionally will the remains of an ocean impact end up on land and recognized (there is one in Nevada though).

      Impacts on continental shelves will often be fairly quicly buried by sediments and difficult to find. There are probably some Chesapeake-type buried craters that haven’t been found yet.

      Impact craters are typically found in stable Precambrian shield areas, with shallow or no sediment cover and very low erosion rates. Especially if recent glaciation has scraped off the sediment cover.

      • How can you possibly say that definitively David? No “likely” or “imho” needed!? I know on good authority the Hiawatha paper had to endure ~27 reviews – who stripped out every last reference to the YDB. Such a terrible, terrible shame you and Anthony are closed minded about a well published and supported hypothesis which severely undermines your very own antogonists at WUWT. I answer soon based on substance as wells

    • Our examination of the HW21-2016 glaciofluvial sediment sample allows us to conclude three things about its source. First, the shocked quartz grains with multiple PDF orientations very likely originate from a large impact crater upstream from the sampling site. Second, the glassy particles, microbreccias, carbonaceous materials associated with shocked quartz and microbreccias, and grains that are likely ejecta that require a rapidly cooled surficial environment can only be derived from an intact or largely intact crater. Third, the PGE anomalies suggest that these metals derive from a highly fractionated iron asteroid.

      The sum of these tentative age constraints suggests that the Hiawatha impact crater formed during the Pleistocene, as this age is most consistent with inferences from presently available data. An impact before the Pleistocene cannot clearly explain the combination of the relative freshness of the crater’s morphology and the ice sheet’s apparently ongoing equilibration with the presence of the crater. We emphasize that even this broad age estimate remains uncertain and that further investigation of the age of the Hiawatha impact crater is necessary. Regardless of its exact age, based on the size of the Hiawatha impact crater, this impact very likely had significant environmental consequences in the Northern Hemisphere and possibly globally (35).

      Kjær et al., 2018

      The impact most likely occurred during the Pleistocene (2.6 Ma to 12 ka). The crater was the result of an iron or iron-nickel asteroid or large meteor. If such an impact occurred at the Younger Dryas or anytime in the Late Pleistocene, this wouldn’t be possible:

      Nor would this be possible…

      https://en.m.wikiversity.org/wiki/Geochronology/Ice_cores

      Camp Century is practically right next door to Hiawatha, DYE-3 is on the other side of the ice sheet and Bird Station is at the other end of the world. The Younger Dryas impact supposedly destabilized the Laurentide Ice Sheet (about the same size as the East Antarctic Ice Sheet). Hiawatha didn’t even leave a mark on the much smaller Greenland Ice Sheet.


      A massive impact 13-14 ka that close to Camp Century would have left a very clear mark in the Late Pleistocene…

      Greenland Ice Sheet Stratigraphy: “This image shows the layers from radargram data that were collected by an Operation Ice Bridge flight over the Greenland ice sheet on May 2, 2011. An overlay of colored lines traced along layers indicates the age of individual layers across the ice sheet. The age layers are colored by the period colour, with Holocene layers shown in green and those from the last ice age shown in blue. Labels indicate the age of various layers. The 1966 Camp Century ice core is shown on the left.”

  6. I grew up in Sudbury, Canada home to the third-largest known impact crater or astrobleme on Earth. They have lots of nickel mining there.

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