HIAWATHA IMPACT CRATER
by: Charles O’Dale
Data references from: Science Advances 14 Nov 2018:
- Type: Complex
- Age: 2.5ma to 11.7ka (Geological dating)ab
- Diameter: 31 km
- Location: N 79° W 65°
a Formed within the same types of highly metamorphosed 2.5 million year Paleoproterozoic terrain as mapped across most of Inglefield Land. The crater includes ice from the Last Glacial Period (LGP; ~115 to 11.7 ka ago). In radar profiles in the northeast corner of the study area, outside the crater, this unit corresponds to late LGP ice exposed at the surface. To the northeast of and within the structure, this unit sits conformably below the Holocene unit, but within the structure, it does not contain any reflection-rich BøllingAllerød ice (14.7 to 12.8 ka ago), from the period immediately before the Younger Dryas, or the trio of distinct LGP reflections observed throughout the northern Greenland Ice Sheet, the youngest of which is ~38 ka old. (Kurt H. Kjær et al Nov 2018)
b The crater is exceptionally well-preserved, and that is surprising, because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact. But that means the crater must be rather young from a geological perspective. (Natural History Museum of Denmark)
A large impact crater beneath Hiawatha Glacier in northwest Greenland
(Kurt H. Kjær et al Nov 2018)
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.
Image courtesy of: BRIAN T. JACOBS, National Geographic STAFF
This structure is covered by up to 930 m of ice but has a clear circular surface expression. An elevated rim in the bed topography encloses the relatively flat depression with a diameter of 31.1 ±0.3 km and a rim-to-floor depth of 320 ± 70 m. In the center of the structure, the bed is raised up to 50 m above the surrounding topography, with five radar-identified peaks that form a central uplift up to 8 km wide. The overall structure has a depth-to-diameter ratio of 0.010 ± 0.002 and is slightly asymmetric, with a gentler slope toward the southwest and maximum depth in the southeast of the structure. Two winding subglacial channels, up to ~500 m deep and ~5 km wide, intersect the southeast flank of the circular structure. Before entering the structure, the northern channel merges with the southern channel and then spills over a large breach in the structure’s rim upon entering the main depression. These channels do not have a recognizable topographic expression within the structure. On the downstream side of the structure, there is a second smaller breach in the northwestern portion of the structure’s rim. Ice flows through this second breach to form the tongue-shaped terminus of Hiawatha Glacier. The present ice-sheet margin lies ~1 km past this northwestern rim, and it is the circular depression itself that contains the semicircular ice lobe that extends conspicuously beyond the straighter ice-sheet margin farther southwest. (Kurt H. Kjær et al Nov 2018)
In this sample (glaciofluvial sedimen collected from the active floodplain), we found angular quartz grains displaying shock-diagnostic planar deformation features (PDFs). These PDFs are straight, generally penetrative, and spaced down to less than 2 mm. Only a few are decorated by small fluid inclusions, whereas toasting occurs in some grains, i.e., a brown coloration due to intense post-shock hydrothermal alteration of the shock lamellae. The orientations of 37 PDF sets in 10 quartz grains were measured with a five-axis Leitz universal stage. Up to seven different orientations per grain were observed. This distribution is similar to the distribution observed in the central uplifts of large Canadian impact structures, where a threshold shock pressure of >16 GPa was inferred from the presence of PDFs. (Kurt H. Kjær et al Nov 2018)
If this crater could be dated to 12,800 years old, it could certainly be credited as the Younger Dryas instigator, and would end this decades-long debate.
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.
Hitting an ice sheet with a meteorite could cause a number of water-related effects. According to Allen West, retired geophysicist, the impact could vaporize ice, releasing water molecules into the air that would eventually rain back down; it could destabilize the ice such that it slides into the water; it could create icebergs. Any of these, or a combination of them, could have led to a flood of freshwater into the North Atlantic. (Discover 2018)
Kurt H. Kjær, Nicolaj K. Larsen, Tobias Binder, Anders A. Bjørk, Olaf Eisen, Mark A. Fahnestock, Svend Funder, Adam A. Garde, Henning Haack, Veit Helm, Michael Houmark-Nielsen, Kristian K. Kjeldsen, Shfaqat A. Khan, Horst Machguth, Iain McDonald, Mathieu Morlighem, Jérémie Mouginot, John D. Paden, Tod E. Waight, Christian Weikusat, Eske Willerslev, Joseph A. MacGregor. A large impact crater beneath Hiawatha Glacier in northwest Greenland. Science Advances, 2018; 4 (11): eaar8173 DOI: 10.1126/sciadv.aar8173
~12,000 years – YOUNGER DRYAS (YD) EXTINCTION (pre Nov. 2018 data)
Approximately 13,000 years ago, the earth was emerging from a glacial period, with temperatures approaching modern levels in many areas. In the Younger Dryas (YD) period, suddenly that trend reversed with the planet entering a cooling period lasting 1,300 ± 70 years. During this period the Stone Age Clovis people became extinct along with 35 mammal and 19 bird genera. A thin layer of Black Mat sediment, (YD Boundary – YDB) with a signature of an extraterrestrial impact overlies Clovis-age sites across North America dated ~12.9 ka. Above the YDB containing geology younger than the YD, NO trace of the Clovis people or the extinct 35 mammal and 19 bird genera exist.Black Mat The black organic-rich layer or ‘‘black mat’’ that bridges the Pleistocene-Holocene transition (last deglaciation), is in the form of mollic paleosols, aquolls, diatomites, or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the Younger Dryas cooling episode 10,900 B.P. to 9,800 B.P. (radiocarbon years). This layer or mat covers the Clovis-age landscape or surface on which the last remnants of the terminal Pleistocene megafauna are recorded. Stratigraphically and chronologically the extinction appears to have been catastrophic, seemingly too sudden and extensive for either human predation or climate change to have been the primary cause. This sudden Rancholabrean termination at 10,900 ± 50 B.P. appears to have coincided with the sudden climatic switch from Allerød warming to Younger Dryas cooling (Haynes 2008).Evidence for Impact:A characteristic of the YD boundary is varying peak abundances of:(i) magnetic grains with iridium;(ii) magnetic microspherules;(iii) charcoal;(iv) soot;(v) glass-like carbon containing nanodiamonds: In March 2012, researchers identified a nearly 13,000-year-old layer of thin, dark sediment buried in the floor of Lake Cuitzeo in central Mexico. A family of nanodiamonds, including the impact form of nanodiamonds called lonsdaleite*, Lonsdaleite is unique to cosmic impacts and is conclusively identified within this YD layer.*Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice. In nature, it forms when meteorites containing graphite strike the Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite’s hexagonal crystal lattice. Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with diamond.(vi) carbon spherules: The researchers also found spherules that had collided at high velocities with other spherules during the chaos of impact. Such features could not have formed through anthropogenic, volcanic, or other natural terrestrial processes (Israde-Alcántaraa 2012).
Based on current data, the following is a preliminary model for formation of the YDB. A comet or asteroid, possibly a previously fragmented object that was once greater than several hundred meters in diameter, entered the atmosphere at a relatively shallow angle (>5° and<30°). Thermal radiation from the air shock reaching Earth’s surface was intense enough to pyrolyze biomass and melt silicate minerals below the flight path of the impactor. Pyrolytic products were oxidized, locally depleting the atmosphere of oxygen, and within microseconds, residual free carbon condensed into diamond-like crystal structures, carbon spherules, carbon onions, and aciniform soot. This involved a carbon vapor deposition like process similar to diamond-formation during TNT detonation. In some cases, carbon onions grew around the nanodiamonds and other nanomaterials. At the same time, iron-rich and silicate materials may have melted to form magnetic spherules. Several seconds later, depending on the height of the thermal radiation source, the air shock arrived. Nanodiamonds, magnetic spherules, carbon spherules, and other markers were lofted by the shock-heated air into the upper atmosphere, where prevailing winds distributed them across the Northern and Southern Hemispheres. We suggest that the above model can account for the observed YDB markers (Israde-Alcántaraa et al, 2012).
Grieve R.A.F., Robertson P.B., IMPACT STRUCTURES IN CANADA, the Journal of the Royal Astronomical Society of Canada, February 1975
Kraus et al, Nanosecond formation of diamond and lonsdaleite by shock compression of graphite, Nature Communications 7, Article number: 10970 14 March 2016
Meen V.B., MEREWETHER CRATER – A POSSIBLE METEORITE CRATER,the Proceedings of the Geological Association Canada 1957 pp 49-67. (unless otherwise noted, the Merewether data quoted above is from this paper).
Ian SPOONER, George STEVENS, Jared MORROW, Peir PUFAHL, Richard GRIEVE, Rob RAESIDE, Jean PILON, Cliff STANLEY, Sandra BARR, and David MCMULLIN, Identification of the Bloody Creek structure, a possible impact crater in southwestern Nova Scotia, Canada.Meteoritics & Planetary Science 44, Nr 8, 1193–1202 (2009)
Haynes, C. V., Younger Dryas ‘‘black mats’’ and the Rancholabrean termination in North AmericaDepartments of Anthropology and Geosciences, Arizona, January 23, 2008.
Isabel Israde-Alcántara, James L. Bischoff, Gabriela Domínguez-Vázquez, Hong-Chun Li, Paul S. DeCarli, Ted E. Bunch, James H. Wittke, James C. Weaver, Richard B. Firestone, Allen West, James P. Kennett, Chris Mercer, Sujing Xie, Eric K. Richman, Charles R. Kinzie, and Wendy S. Wolbach, Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis, University of Hawaii, Honolulu, HI, January 31, 2012
Kinzie et al, 2014 Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP.The Journal of Geology, 2014, volume 122.
Nicholas Pintera, Andrew C. Scottb, Tyrone L. Daultonc, Andrew Podolla, Christian Koeberld, R. Scott Andersone, Scott E. Ishmana, The Younger Dryas impact hypothesis: A requiem, Earth-Science Reviews, Volume 106, June 2011
Zamora, A. Solving the Mystery of the Carolina Bays
Younger Dryas Extinction Impact Related? (Bloody Creek @ 29:30).