The Greenland Hiawatha glacier conceals an enormous impact crater beneath the Ice Sheet. The asteroid, regardless of its age, had significant environmental effects in the Northern Hemisphere. It also likely had global consequences with billions of tons ice that was vaporized in a matter of seconds.
GREENLAND
Greenland is the largest island in the world and is mostly covered by the biggest mass of ice on the planet, after the Antarctic Ice Sheet. The Greenland Ice Sheet has the longest mass of glacier ice in northern hemisphere. It extends 2500km from north to south, and up to 1000km from east to west.
With an area of 1,736,000 square kilometers and a volume of 2,600,000 cubic kilometers, it contains 10 percent of the Earth’s total freshwater. This is approximately equivalent to 6.5 metres of sea-level equivalent.
Image above the Greenland glacier from NOAA climate
If spread uniformly across the world’s oceans due to a complete melting, it will raise sea level by about 6.5 meters. The interior of Greenland Ice Sheet is composed of a northern and southern dome with elevations of 3200m and 2850m, respectively. These two domes are linked by a saddle that reaches 2500 meters in elevation.
Radar signals from satellites or aircraft are the most common method of measuring ice thickness. Radar signals travel through ice until they reflect off boundaries such as the top of the bedrock. The electrical properties of bedrock and water are key to the signal reflection.
Greenland is the 12th largest country and the largest island in the world. Because of its small size and low population, Greenland is the least populated country in the world with an estimated 0,026 people per square mile.
Even though Greenland is big, it is dwarfed by even the smallest continent, Australia, which is significantly larger than Greenland covering about 6 % of the world’s land area. Greenland is only 1,45 percent.
It is quite surprising that we tend to think Greenland is huge on the maps. However, it is actually much smaller than we think. Take a look at the image below to see its true size.
Credits to the image above that shows the true size continents
The Greenland Ice Sheet outlet glaciers are extremely variable in terms size, flow speed, and ice release. There is a fundamental distinction between land-terminating outlets glaciers, such the Russel Glacier located in southwest Greenland. These glaciers are capable of moving at speeds of several tens to thousands of meters per annum. Tidewater glaciers however, have speeds that range from hundreds to thousands of metres per year.
The largest outlet glaciers end in tidewater. These include Jakobshavns Isbrae to the west, Helheim Glacier to the southeast, and Kangerdlugssuaq to the southeast.
Sentinel-1 Landsat data provides the Glacier front position for Jakobshavn Isbrae. The inset shows Jakoshavn Island in Greenland. Source: The Cryosphere Copernicus
Jakobshavns Isbrae is west Greenland’s largest outlet glacier (image above). Also known as Sermek Kujalleq, it is also known by its Greenlandic Greenlandic name. This glacier drains approximately 6 percent of the entire ice sheet’s catchment area, or 110,000 km2.
In fact, it was believed that Greenland’s inland glacier flow was unlikely to change in short timescales. The thick, cold ice was a barrier that prevented surface-to-bed drainage. Zwally, a famous scientist from the ice sheet, made a profound shift in perspective by presenting clear evidence of seasonal velocity fluctuations such as Swiss Camp at beginning of 2000s.
Velocity flow over Greenland Source NASA Scientific Visualization Studio
Climatic data are available for Greenland for a number surface weather stations. Satellite observations provide coverage for many other variables.
Greenland’s climate exhibits high interannual variability in terms of temperature and precipitation. A large portion of the temperature variability can be attributed to shifts in relative strengths of Azores High and Icelandic Low, also known as the North Atlantic Oscillation or NAO.
The NAO’s positive phase is indicative of a deeper Icelandic Low (i.e. More frequent traveling depressions are seen over the north Atlantic. There is also a stronger high pressure region over the subtropical Atlantic. These conditions correspond with colder winters in Greenland.
Averaged 2m Kelvin temperature, sea ice extent and year (a) over (b) and (c) JJA. Source Copernicus, Ettema et.al. 2010
The negative phase of the NAO, however, is marked by a weaker Azores High and Icelandic Low, which corresponds with milder winters for Greenland. It is less clear how the NAO and precipitation variability in Greenland relate.
Large, low-latitude volcanic eruptions can also have a significant influence on the climate over Greenland. These include particularly cool years after eruptions of Mount Pinatubo in the Philippines (1992), El Chicon (1982), and Agung (Bali (1963).
Since the 1980s, there has been an overall trend towards higher temperatures in Greenland. The temperature rise over Greenland is strongly related to, but greater than, the temperature trend for the entire northern hemisphere. This suggests that it may reflect anthropogenic gas concentrations rather than regional climate variability.
Although there is a lot more variability between years, warmer summers and longer melt periods have led to higher ice surface temperatures. The Greenland Ice Sheet has an average snow accumulation rate that exceeds the average melt rate. This means that the surface mass balance in the area is positive. Data from snowpits and climatic modeling indicate that total accumulation averages 299 ± 23 kilograms per cubic meter per year, although with significant interannual variations.
There has been a notable increase in accumulation over Greenland in recent years, which is largely offset by the trend towards increasing abolition.
Above: Rate of elevation change for the Greenland Ice Sheet 1992-2018. Source Nature, IMBIE Team (2019).
Conventionally, the ice sheet is assumed to have been in equilibrium during 1961-1990, which is defined as the so-called “reference period”. Many evidences today suggest that the Greenland Ice Sheets are currently thinning at elevations below 2000 meters and thickening above 2000 meters.
There are many methods that can be used to estimate the current rate at which mass is being lost from the Greenland Ice Sheet. The three main methods for measuring the current ice sheet mass balance include (1) snowfall input minus Iceberg output, (2) changes of elevation using satellite altimetry, (3) changes in gravity using Satellite Gravimetry.
Image from NASA Scientific Visualization Studio.
All of these methods agree that Greenland Ice Sheet is losing approximately 250 Gigatons each year since 2005. That’s equivalent to 8000 tonnes of ice per minute.
The latest measurements in Greenland pretty much confirm researchers’ worst fears: Greenland is not only continuing to lose ice, but the loss is accelerating even more. However, we are probably still far from the maximum Greenland Ice Sheet decrease.
Scientists analyzing a Greenland ice core from the Eemian interglacial concluded that during this geological period, more or less 130,000–115,000 years ago, the Greenland Ice Sheet was about 8 degrees Celsius warmer than today. This caused a thickness reduction of the northwest Greenland Ice Sheet by about 400 ± 250 meters, reaching surface elevations 122,000 years ago of 130 ± 300 meters lower than at present.
Scientists believe that clouds could increase Greenland Ice Sheet melting. A study published in Nature Communications in 2016 indicates that clouds overall enhance Greenland Ice Sheet’s meltwater runoff by more than 30% owing to decreased meltwater refreezing in the firn layer during the night.
Above: A modeled configuration for the Greenland Ice Sheet in today’s (left) as well as during the last Eemianinterglacial. Source Alley et al. Quaternary Science Journal, 2019.
The extremely famous scientist Michael Mann and Stefan Rahmstorf warn that the observed cold blob in the North Atlantic during years of temperature records is a sign that the Atlantic Ocean’s Meridional overturning circulation (AMOC) may be weakening by melting Greenland. They discussed their findings in several scientific papers and concluded that the AMOC circulation has shown a remarkable slowdown over the past century.
A GRACE satellite data-based study from 2016 found that freshwater runoff from Greenland Ice Sheet was increasing and could lead to a disruption in AMOC, which could affect Europe and North America.
Image above, source NASA/NOAA
This situation is presently described by many climatologists, oceanographers, and glaciologists as being past the “point of no return” mainly because of two factors: the increased meltwater runoff and the ablation of the marine-terminating glaciers, which is defined as ice discharge.
Researchers informed the Greenland Ice Sheet that it lost 532 billion metric tonnes of ice in 2019, as per the 20 August 2020 report. This is more than the previous record of 464 million metric tons set in 2012.
THE BEDROCK BELOW THE FIRE SHEET
The bedrock that lies below the Ice Sheet’s central portion is fairly flat and close enough to sea level. However the periphery is almost completely covered by coastal mountains, which drain the interior.
The Precambrian Shield crystals dominate Greenland’s geology. The Precambrian Shield, which is the oldest known bedrock in Greenland, is located around Nuuk, Greenlandic capital.
Additionally, the Isua Greenstone Belt is located in southwest Greenland and contains some of Earth’s oldest bedrock, at around 3,800 million years.
Image above, Greenland’s bed-rock elevation from Bamber et al. (2003) Digital elevation model based remotely sensed surveys from the 1970ies/90s, gridded at a 5 km resolution
In the 1970s, the first airborne radar surveys of Greenland Ice Sheet were made. Over the past two decades, more comprehensive soundings of the ice sheets have been possible. In the mid-1990s extensive airborne radar sounding revealed the underbelly of the Greenland Ice Sheet, and clarified many processes and events that have resulted in its current topography.
Borehole drilling through the ice has made it possible for researchers to explore features beneath the ice. Data from radar surveys reveal the history of the ice sheet’s late Pleistocene, and Holocene periods through internal stratigraphy.
Image above, cross-section from radar data showing the age of Greenland Ice Sheet. Credit: NASA’s Scientific Visualization Studio and MacGregor et al., 2015.
A HUGE CRATER INSIDE NORTHWESTERN GREENLAND’S ICE SHEET
A strange circular shape in the Greenland ice sheet’s northwest edge led scientists from Denmark to examine the radar data collected by NASA. First examinations of radar data for the Arctic Regional Climate Assessment, and Operation IceBridge project revealed a troubling structure in the underlying rock.
Their thoughts were confirmed by additional airborne radar. Scientists discovered a large circular depression in Greenland Ice Sheet’s bed topography. The structure covered by up to 930 m of ice presents 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 ± 70m.
The answer was simple! It is located about a kilometer below ice and measures 31 km in circumference, with a depth of 300m. This is first Greenland’s meteorite crater ever discovered.
Image above, source NASA Scientific Visualization Studi
On the downstream side of the structure, there is a second smaller breach in the northwestern portion of the structure’s rim. The second breach is where ice flows through to form the tongue-shaped terminus for Hiawatha Glacier. Hiawatha Glacier ends in a large river, which eventually discharges into Nares Strait. This river is the most sediment-rich and discharging from a land-terminating glacier northwestern Greenland.
The Greenland Ice Sheet margin at the moment is located approximately one kilometer from this rim. The circular depression contains the semicircular Ice Lobe that extends beyond the ice sheet margin farther southwest.
Above, the geomorphological as well as glaciological setting of Hiawatha Glacier. A regional view, C Hillshade topography; B Digital Elevation Model. Source ScienceAdvances, Kiaer et al. (2018)
WHY ARE SCIENTISTS CONVINCED THAT THIS IS AN IMPACT CREATER?
Scientists examined the mineralogy as well as the geochemistry of foreland glaciofluvial soils that were released by the Hiawatha Glacier’s terminus. They discovered angular quartz grains that had emerged from the ice, and they also exhibited shock-diagnostic planar features.
These features, which are only visible in microscope views, are evidence of high-pressure stress. They also found a wide variety of shock-metamorphosed glassy grains, ranging in size from 0.1 to 2 mils.
These glassy grains can be interpreted as a result of the impact melting of individual components in the metasedimentary composition.
Image above, source NASA
The researchers were able to determine many things about the source of the quartz grains by conducting an in-depth analysis of all glaciofluvial samples. The quartz grains most likely come from a large impact pit upstream of the sampling site.
Additionally, the quartz’s glassy particles, carbonaceous material and carbonaceous matter, which are likely ejecta, can only be extracted from an intact or largely intact Crater. They found clear evidence of iron meteorite.
Scientists concluded that Hiawatha Glacier was underlain by a meteorite-impact crater. This is the result of a bolide approximately 1 kilometer in size. It is the first known impact crater beneath an ice sheet.
Image above, Hiawatha glacier terminus. Source ESA-Sentinel-2
The characteristic complex crater structure beneath the ice, which includes a subdued central elevation, provides clear evidence. This crater may be one of 25 largest impact structures on Earth. It is the only one with significant remnants of its original topographic expression.
The radar data suggests that fragments from the Greenland Ice Sheet’s groundrock have been incorporated into the Greenland Ice Sheet’s ice base. This indicates that the impact was quite recent.
Image from NASA Scientific Visualization Studio.
The preliminary estimates of the impact’s energy are astounding. A 31-kilometer-wide impact crater in crystalline rock needs roughly 3×1021 Joule of Energy to be formed. If we assume that the meteorite striking the Hiawatha Crater had a velocity of 20 kilometers per second, and was made of iron with a density at 8,000 kilograms per cubic meter (which is about 1.5 kilometers), then it would have an impactor diameter around 1.5 kilometers.
The impact dynamics would have been amazing. The meteorite created a bowl-shaped depression that was approximately 7 km deep and 20km in diameter. This structure collapsed in less than a minute and formed a complex crater measuring 800m deep and 31 km in diameter.
About 20 cubic kilometers worth of rock would have been vaporized and melted within seconds. Half of it would have remained inside the crater, forming a melt sheet up to 50 meters deep.
However, scientists are unsure if the Greenland Ice Sheet was present at the time the impact occurred.
WHAT IS THE AGE DE LA CRATER
Now, here’s the big question: How old is the crater? Radiometric decay systems are used to date impacts craters. The Hiawatha Impact Crater has no evidence that can be used to establish an absolute age.
Geomorphological evidence was used by scientists to infer the possible age at the crater’s origin in the first attempts. The crater is certainly younger than the Paleoproterozoic rock outcropping in the nearby foreland. The Paleoproterozoic Era spanned the time period of 2,500 to 1,600,000,000 years ago.
When analyzing the erosion rates, they estimated that it would take at least 5,000 years to erode the central uplift and crater floor and partially fill the space to form the present morphology. This assumption assumes that the crater has been covered in ice for most of its existence. This results in a maximum erosion time of 50 million year, when you consider the lower-end rate.
Radar evidence of active subglacial eroding at present and active sediment deposition at glacier terminus point towards a faster subglacial erosion rate, and therefore a younger age. More, HiawathaGlacier’s radio stratigraphy is highly anomalous compared to the rest of the Greenland Ice Sheet. The ice is not uniform or complete across the entire crater.
The layer of last-ice-age glacier ice is quite thin and disturbed. However, the Holocenic layer of ice is perfectly preserved. Radar reflections from volcanic rock grit trapped inside the ice can also be linked to dated cores drilled elsewhere. These reflections cease at 11.700 years ago, which marks the beginning of Holocene. Below that, the glaciers are disturbed. The crater’s bed is rough, not yet smoothed down. This indicates that the crater is less than 100,000 years old and is actively eroding.
Despite its age, the Hiawatha Impact Crater’s size indicates that the asteroid likely had significant impacts on the Northern Hemisphere as well as global environmental consequences. The impact of the asteroid hitting faraway areas would have been felt.
The region would have been interested in the hurricane-force wind and objects up to 100 kilometers away would have been leveled. If the impact happened when Greenland was covered in ice, which is most of the past 2 million years, billions of tons of ice would vaporize within an instant leading to an influx of fresh water into the world’s oceans.
It is possible that such an influx occurred about 12800 years ago. This helped to create the Younger Dryas, a thousand year glacial period. The evidence for such a flow is not yet conclusive.
Next, we need to determine exactly when this massive asteroid arrived so that the search can start.
We will keep this page updated with any new information. Also, if you have seen this article in the Google App (Discover) feed or social media, click the like button (♥) to see more of our forecasts and our latest articles on weather and nature in general.
SEE ALSO
Arctic Sea Ice Extent 2nd Highest in 18 years at the end 2021, Now Closer to 13,000,000 square kilometers, while Hudson Bay Finally Froze within the Last 2 Weeks
Source: Severe Weather
