Wednesday, November 14, 2018

Grey Eagle

Actually, a Black Chested Buzzard Eagle

Nieuport 24, properly decorated

Massive impact crater beneath Greenland ice cap could explain Younger Dryas Ice Age

12,800 years ago, during the Pleistocene, Earth was warming up from its last Ice Age. Temperatures slowly rose while glaciers retreated, that is, until something major happened that triggered a cold snap big enough to leave its mark on the geologic record. Over the course of just decades – the blink of an eye in geological timescales – the planet cooled somewhere between 3 and 11 degrees Fahrenheit (2 to 6 degrees Celsius). The resulting period is known as the Younger Dryas, a mysterious 1000-year blip in history.

Many scientists have suggested – with evidence – that the Younger Dryas was triggered by a meteorite impact. But others have held out, suggesting that volcanic eruptions or, what seems to be the leading favorite, some sort of massive freshwater flood temporarily disrupted climate cycles based out of the North Atlantic. But the main reason scientists have been slow to accept the impact hypothesis is simple: There’s just no crater.

That's changed now.

A team led by Kurt Kjær, professor at the Natural History Museum of Denmark and University of Copenhagen, has discovered a previously overlooked, 19-mile-wide crater that’s been hiding in plain sight under northwest Greenland’s Hiawatha Glacier. In fact, it’s only about 150 miles from Thule Air Base – the U.S.’s northernmost Air Force base and the place where NASA’s IceBridge planes took flight. You can see about a third of the crater’s rounded outline on Google Earth.

Although there's no proof yet that this crater caused a thousand year cooling of the Earth, there are a number of tell-tale signs that a big round hole in the ground was caused by a giant meteor impact.

If this crater could be dated to 12,800 years old, it could certainly be credited as the Younger Dryas instigator.

What’s more, because of the crater’s location on Greenland’s ice sheet, it’s possible that the impact could’ve caused exactly the kind of massive influx of freshwater to the North Atlantic that the Younger Dryas-flood proponents stand behind.

The scientists analysis of the possible ejecta from an impact, and the effect of the angle of impact, is fascinating, and I'm going to repeat it here.

No ejecta layer that might be associated with the Hiawatha impact crater has yet been identified in either Greenland’s rock or ice records. If no ice was present at the time of a high-angle (>45°) impact, then the symmetric ejecta layer would be ~200 m thick at the rim, thinning to less than 20 m at a radial distance of 30 km from the rim (17). However, during most of the Pleistocene, an ice sheet covered the impact area (18). If ice was present and its thickness was comparable to the impactor’s diameter, then a more energetic projectile is required to produce a crater of the observed size, and the fraction of non-ice debris in the ejecta would be smaller than if the impact hit ice-free land (19). Furthermore, regionally extensive ice cover at the time of impact could have resulted in a significant fraction of the ejecta landing on the ice-sheet surface of the Greenland or Innuitian ice sheets, rather than on bare ground. As the crater is situated very close to the present ice margin, the site has almost certainly been ice free during one or several short (~15 ka) interglacial periods during the Pleistocene, such as predicted for the Eemian ~125 ka ago (20). On the basis of present ice-flow speeds (Fig. 1B), most impact ejecta deposited onto the ice sheet would have been transported to the ice margin within ~10 ka. Similarly, based on Holocene vertical strain rates (21), any such ejecta would be less than half of its original thickness within 10 ka.
If the Greenland Ice Sheet was present at the time of impact and a high-angle impact occurred during the late Pleistocene (LGP), then ejecta ought to be present in the four deep ice cores from central and northern Greenland that span the majority of the LGP (fig. S5), but none has yet been identified. At two of the ice cores (GISP2 and GRIP) located farthest (>1000 km) from the crater (fig. S5), the expected initial thickness of a symmetric ejecta layer for a Hiawatha-sized impact on rock is ~0.7 mm with an average particle diameter of ~0.4 mm (17). In the closer ice cores (fig. S5), this thickness increases roughly twofold. If ice were present at the impact site, then a significant fraction of the ejecta would also be ice (19), but the presence of any rock ejecta should be unambiguous in an ice core. A possible complicating factor to interpreting the absence of ejecta in ice cores south of the structure is the presently unknown angle of impact. 
 The Hiawatha impact crater is located farther north (78.72°N) than any other known impact crater, a position that increases the probability of a northward-directed oblique impact given the majority of Earth-crossing asteroids that move in or near the ecliptic plane. Such a scenario might be analogous to the late-Jurassic Mjølnir crater, which is also large (40 km diameter), is high latitude (73.8°N), and produced an asymmetric (northward focused) ejecta layer.

Read the whole thing in all its scientific splendor here.

Much more work remains to be done, but who knows, this previously unknown feature could explain an otherwise mysterious climate fluctuation.

Love this stuff

The guy on the left blends in with the snowy hill pretty nicely, but the guy on the right looks just like a tree!

AFSOC and NSW aboard MC-130H Combat Talon II

The Art of Speed