New Research Reveals How Megafloods Shaped Greenland And Iceland

Greenland and Iceland have been periodically reshaped by megafloods over thousands of years, a new paper in the journal Earth-Science Reviews has revealed.

British research duo Jonathan Carrivick and Fiona Tweed have provided the first evidence of gargantuan Greenlandic floods and extensively reviewed the record of comparable events in Iceland. The researchers set out to better understand what constituted a megaflood and find traces of them recorded in the landscapes of these icy islands.

In media stories and even within the scientific literature the authors found that terms like “catastrophic flood,” “cataclysmic flood,” and “super flood” have been used indiscriminately and interchangeably. There are, however, strict definitions associated with each. A “catastrophic flood,” for instance, occurs when peak discharge exceeds 100,000 cubic meters per second — more than 18 times greater than the flow over Niagara Falls. Multiply that by ten (i.e. 1,000,000 cubic meters per second) and you get a sense of what constitutes a true megaflood.

Despite expressly seeking records of megafloods in the landscape and literature, Carrivick and Tweed found that a more practical approach was to identify events with “megaflood attributes.” Scientists have recorded very few true megafloods since those that cascaded off the Laurentide Ice Sheet, which once mantled much of North America in the aftermath of the Last Glacial Maximum. While there have been few recent floods that exceed one million cubic meters per second, there have been several with comparable erosive power and lasting landscape impacts.

Shaped by water

In Greenland, Carrivick and Tweed found 14 sites where huge floods had rampaged down fjords and across expansive “sandur,” or outwash plains. These have typically been outbursts from ice-dammed lakes, which have periodically unleashed inconceivably vast volumes. The glacial lake Iluliallup Tasersua empties every five to seven years and has a capacity of more than six cubic kilometers of water. At its peak, that flow would drown New York City’s Central Park in a column of water deeper than four Empire States Buildings.

Iceland, too, has experienced its fair share of monstrous floods. Many of them have were triggered by volcanic eruptions. Due to the unique setting of Iceland, where the active fire-breathing mountains of the Mid-Atlantic island are blanketed with ice caps and glaciers, erupting magma invariably explodes into the underside of a quenching ice mass. This interaction, more often than not, results in an outburst flood known locally as a “jökulhlaup,” which produces tremendous amounts of power that is capable of reshaping and inundating the island’s plains.

The region surrounding Öræfajökull, one of the most active volcanoes in Iceland, is infamous for having suffered from devastation wrought by both fire and ice.

“After it erupted in 1362, the whole area was renamed as ‘Öræfi,’ which means ‘The Wasteland,” Tweed told GlacierHub. “They renamed the area because it had been inundated by a grey sludge, hyper-concentrated flow deposits and volcanic ash which had eradicated the farmland and rendered it unusable.”

The eruption was the largest in Europe since Vesuvius immortalised the communities of Pompeii and Herculaneum in AD79. The floodwaters rushed out at over 100,000 cubic meters per second — qualifying as a “catastrophic flood.” The torrent was so powerful that it was able to transport rocks weighing 500 metric tons, each equivalent to four and a half blue whales. Despite not strictly meeting the definition of a megaflood, the event certainly bore many of the hallmarks of one.

Vast plumes of sediment flow into the Labrador Sea (Credit: NASA)

But the impacts of such deluges are not limited to their power to remold centuries-old landforms, toss about house-sized chunks of ice, or transport a beach-worth of sediment in a matter of hours.

Outbursts in Greenland can release as much as six billion metric tons of water within a matter of 7-10 days. This rapid draining of a glacier-lake basin radically changes the pressure atop the ice sheets, causing isostatic rebound, which can result in fractured shorelines, as localized sections of coast re-expand.

Water from an outburst flood often passes through a highly pressurized network of conduits within, beneath, and alongside ice. This can trigger a “seismic tremor.” So-called “glacier-derived seismicity” has been measured via seismometers since the early 2000s and experienced by eye-witnesses in the vicinity of Grænalón, one of the most famous jökulhlaup systems in Iceland. The authors note that while these events can be detected and felt, there is negligible impact from them.

Consequences for communities and corporations

Glacier floods also impact the communities living in the shadow of ice. Carrivick and Tweed’s previous work revealed that Iceland has experienced at least 270 glacier outburst floods across 32 sites, killing at least seven people. This makes Iceland among “the most susceptible regions to glacier floods” — and the economic costs that often result.  

Icelanders are well acquainted with the natural dangers. Volcanic eruptions, floods, and other geohazards are signature characteristics of their homeland.

Looking to the future, Tweed said: “We can expect to have jökulhlaups for another 200 years, until the ice is gone.”

Such dire flood predictions are unlikely to rattle the stoic Icelanders, who are more liable to fear the prospect of an Iceland bereft of its namesake.

In even less populous Greenland, with people rarely situating themselves in known flood paths, the impacts appear to be less disastrous. That said, Carrivick noted: “When these big outburst floods go into the fjords, and move out of the fjords and up and down the coasts, you get these visible sediment plumes.”

The influx of sediment and freshwater changes the temperature, salinity, and turbidity of the water in a fjord and the nearby ocean, which can drive fish out the region. “It basically shuts down the fishing industry for a couple of days at least,” Carrivick said.

This has potentially massive economic consequences, as 95 percent of Greenland’s exports are fish and fishery products, not to mention that the fishery industry provides employment to approximately 12 percent of the population and puts 87 kilograms of fish on every Greenlander’s table each year.

The Ilulissat Hydroelectric Project, located in Disco Bay, West Greenland, provides energy to 4,500 inhabitants of the town of Ilulissat (Source: Verkís)

Yet longstanding industries are not the only ones exposed to the fickleness of Greenland’s glacier outbursts. As the ice sheet melts, a number of resources are being eyed by extractive industries. Carrivick recounted meeting teams of Swiss experts who had been commissioned by Australian mining companies to set up rigs and conduct mineralogical investigations in deglaciating regions.

He also remarked on the prospects of the hydropower industry, which has taken advantage of booms in other nations, like Nepal. “It might be an exaggeration, but I think it’s goldrush time,” he said. Regulators, he added, might struggle to keep up with monitoring and mitigating environmental impacts.

Whatever the future holds for Iceland and Greenland, Carrivick and Tweed’s research advances significantly scientific knowledge of the history of flooding on these two islands and makes a strong case for remaining attentive to the changes occurring on their diminishing ice masses.

Read more on GlacierHub:

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Iceland’s Öræfajökull Volcano, Buried Under Glacier, Shows Signs of Activity

The Öræfajökull volcano in Iceland is showing signs of activity this month, bringing interest and intrigue to the long dormant volcano whose last known eruption was in 1727-1728. Like many other volcanoes in Iceland, Öræfajökull, the country’s tallest volcano, is mostly buried underneath glacier. The recent activity has caused a large depression in the ice, forming what is referred to as an ice cauldron or subsidence bowl.

The presence of ice could cause an eruption to be phreatomagmatic, which refers to a reaction of magma with ice that causes steam to be released. According to Benjamin Edwards, a volcanologist at Dickinson College in Carlisle, Pennsylvania, “Even a small eruption will likely produce significant melting given the amount of ice in the summit caldera, and in an environment where water can’t leave the area around the volcanic vent rapidly it will probably cause phreatomagmatic eruptions, which are highly explosive.”

It is difficult to know what caused the ice cauldron to form because of limitations in instrumentation, though subglacial eruptions can still be detected through seismic signatures also known as eruption tremors. According to Dave McGarvie, professor at Open University in Milton Keynes, England, the cauldron could be formed due to a small amount of magma that was released or simply from rising heat. He added, “What can be said with certainty is that the presence of a heat source beneath the ice-filled caldera of this volcano is highly unusual. No subsidence bowl in the ice of this caldera has been recorded in the past few centuries.” Cauldrons are found throughout Iceland and have the potential to cause floods. “There are numerous examples of subsidence bowls in Icelandic glaciers that appear to be caused purely by heating– such as those at the ice-covered Katla volcano, and the famous Skaftá cauldrons, which drain periodically and create sizeable glacial outburst floods.”

 

For this reason, scientists believe Öraefajökull has started to wake up. “Whether she’s just rolling over in her sleep, or getting ready to fully waken up– nobody knows. It’s too early to tell,” McGarvie added.

Past eruptions from Öræfajökull have been devastating and helped give the volcano the first part of its Icelandic name, roughly translating to wasteland, wilderness, or desolation, which describes the post-eruption surrounding region (the second half, “jökull” means glacier). M Jackson, a geographer and glaciologist who has done research on Iceland said, “The idea of Öræfajökull erupting is terrifying, especially when you put it the historical context. When Iceland was settled over 1,000 years ago, the area around Öræfajökull was verdant and forested, but in 1362 the volcano underneath the glacier Öræfajökull erupted, triggering catastrophic jökulhlaups [type of glacier lake outburst flood] that flooded and decimated the entire region.”

Iceland has plans in place if Öræfajökull erupts including partially closing the ring road which encircles the country and links all the major settlements. Gísli Pálsson, a professor of anthropology at the University of Iceland, explained that if an eruption does occur, an immediate alert will be sent to nearby communities with requests for evacuation of farming communities and possibly the town of Höfn and the village of Kirkjubæjarklaustur. ”The worst scenario would be heavy floods and massive clouds and layers of ash,” he said.

The Icelandic government and community is well-prepared in case an eruption does occur. “Volcanic activity in Iceland is ongoing, and embedded in the social fabric of Icelandic society,” said Jackson. “Volcanic activity is reported in the news regularly, and people are vigilant. The government monitors all activity intensely, and the system is highly functional. When I lived in Iceland, I was impressed how often I received alerts for any activity, such as earthquakes, gas leaks, and floods.”

The interaction between melting glaciers and erupting volcanoes can be causal as well. Pálsson said it seems likely that with the thinning of the glacier, a circular pattern is established and eruptions will be more frequent than before, resulting in further thinning of the glacier. “An interesting and possibly devastating spinoff from global warming,” he said.

According to Jackson, Iceland’s largest icecap, Vatnajökull, is located above a hotspot, with many volcanoes buried underneath glaciers. In the last eight hundred years, Vatnajökull has experienced over eighty subglacial volcanic eruptions alone, she said. Many scientists speculate that as Vatnajökull increasingly melts, the rate of volcanic eruptions and earthquakes will increase. “The material products of increased volcanic activity are likely to have long lasting effects on Icelandic society,” she said.

In 2010, Iceland’s Eyjafjallajökull volcano eruption released ash clouds that disrupted air travel in and throughout Europe for an entire week. Öræfajökull could erupt a similar ash cloud, as could other volcanoes in Iceland. With climate change potentially increasing the frequency of eruptions, the world has one more important reason to quickly mitigate the effects of climate change.

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Photo Friday: Ice Cauldron Forms on Iceland’s Highest Volcano

Iceland’s highest volcano, Öræfajökull, recently showed signs of life with the Icelandic Meteorological Office (IMO) reporting the formation of a new ice cauldron. Ice cauldrons form when ice is melted from below during times of increased volcanic activity. The volcano last erupted in 1727 and also erupted in 1362, the largest eruption in recorded Icelandic history. The IMO has increased its monitoring of the volcano and issued a yellow aviation warning, signaling an increase in volcanic activity above background levels. Back in 2010, Iceland’s Eyjafjallajokull volcano erupted, grounding thousands of flights. However, there are currently no signs of an impending eruption of Öræfajökull. Check out images of Öræfajökull below.

Photo of satellite view of cauldron
Satellite view of a cauldron forming on the summit of ÖRÆFAJÖKULL (Source: @Vedurstofan/Twitter).

 

Photo of ÖRÆFAJÖKULL and cauldron forming
Another satellite view of ÖRÆFAJÖKULL and the cauldron forming (Source: Antti Lipponen/Creative Commons).

 

Photo of ÖRÆFAJÖKULL from the ground
ÖRÆFAJÖKULL from the ground (Source: Theo Crazzolara/Creative Commons).

 

Photo of ÖRÆFAJÖKULL from the ground showing its extensive glacial coverage.
ÖRÆFAJÖKULL from the ground again showing its extensive glacial coverage (Source: Aarne Granlund/Twitter).

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Icelandic Zombie Glacier Survives by Shedding Dead Bits

Falljökull glacier. Photo: © Matt Malone
Falljökull glacier. Photo: © Matt Malone

It’s alive! British scientists recently discovered that a glacier named Falljökull in Iceland, considered dead, is in fact partially “alive.” Using 3D imaging of the interior and surface of the glacier, they found that its long top section, which extends in a steep ice fall from the ice cap Öraefajökull to a plateau below, has at least temporarily saved itself by severing ties with a lower stagnant, dead piece. It brings to mind that lone hiker pinned under a rock who hacked off his arm a few years ago to escape certain demise in the wild.

Perched as it is between dead and undead, Falljökull has earned the nickname zombie glacier in the popular press. But it’s not clear whether this unusual glacier behavior of sloughing off dead ice–behavior that had never before been reported–will keep this patient alive over the long run. Today, the glacier’s active, or living, length is about 700 meters shorter than it was five years ago.

“It would be nice to think that the behaviour we have described at Falljökull could represent a type of ‘survival mechanism’ whereby steep mountain (Alpine) glaciers can quickly adapt to warming summer temperatures and decreasing snow fall during the winter months,” wrote Emrys Phillips, British Geological Survey research scientist and lead-author of the paper, in an email. But its survival ultimately depends on whether it remains “attached” to the Öraefajökull ice cap, its source, he said. And predicting how the glacier will behave in the future is tricky.

Consider snow and ice, and you may conjure barren, unforgiving landscapes that don’t sustain much life. But most glaciers are in some sense “alive,” an idea first proposed by legendary naturalist John Muir in the late 1800s. This means that the vast sheets, bulging tongues and glittering blue crowns of ice that constitute a glacier are mobile. They flow and advance in ice-rivers and ice-falls in winter and retreat in summer, according to seasonal patterns in snowfall and melt and given the pull of gravity that results when giant hunks of packed and frozen H2O are pitched at an alpine angle.

Of course, many glaciers are melting faster than they can accumulate new ice from snowfall, wind-blown snow, avalanches and frozen rain in the winter—mostly attributed to rising temperatures and increasing soot and dust in the atmosphere around the globe. This means the seasonal balance between advancing and retreating is thrown off, which can result in such a severe decline in glacier mass that the glacier is declared “dead.” A dead glacier stops moving and simply melts in place, like a giant ice cube in an empty glass on a hot day in summer.

The fault line where the living and dead pieces of the Falljökull glacier meet. "You can see the highly crevassed ice fall which feeds ice to Falljökull and then below that a ‘bulge’ in the glacier surface which is fractured and pocked marked by hollows – this area represents the living active part of the glacier. The thrust faults which are formed as the ice moves forward can be seen in the lower part of the glacier (the curved fractures cutting across the ice)," says British Geological Survey scientist Emrys Phillips. Photo Credit: British Geological Survey.
The fault line where the living and dead pieces of the Falljökull glacier meet. “You can see the highly crevassed ice fall which feeds ice to Falljökull and then below that a ‘bulge’ in the glacier surface which is fractured and pocked marked by hollows – this area represents the living active part of the glacier. The thrust faults which are formed as the ice moves forward can be seen in the lower part of the glacier (the curved fractures cutting across the ice),” says British Geological Survey scientist Emrys Phillips.
Photo Credit: British Geological Survey.

At Falljökull, the team of scientists, who published their research in the AGU Journal of Geogphysical Research in October, found that a new ice front has formed between living and dead pieces of the Falljökull glacier, with the living section actually surging up over the dead section into a bulge at a giant fault line. The scientists note that retreat of the original ice front has accelerated since 2007 and is moving at a faster rate than in any 5-year period since annual measurements began in 1932. Meanwhile, the upper part of Falljökull is still flowing forward at between 164 to 230 feet per year.

“Although the margin of Falljökull has ceased moving and is now undergoing stagnation, field and photographic evidences clearly show that the icefall remains active, feeding ice from the accumulation zone on Öraefajökull to the lower reaches of the glacier,” the scientists write in the paper. “To accommodate this continued forward motion, the upper section of the glacier below the icefall is undergoing intense deformation (folding and thrusting) and, as a result, is being thrust over the lower, immobile section of Falljökull.”

The group expects Falljökull is not the only glacier behaving in this manner, but finding out for sure will require more research. “As far as we know, this is the first time that this type of structural adjustment in active glacier length has been reported, so we cannot be certain that other mountain glaciers respond in the same way as Falljökull,” wrote Phillips. “But that said, from informal comments made by colleagues working in North America, Svalbard and elsewhere in Iceland, plus reading the published literature, we think that it is possible that a number of other Alpine-type glaciers are potentially behaving in a similar way.” In particular, they expect it may be found in places such as the Himalayas, Andes, Alps and Cascades.

The team of scientists was able to detect this zombie glacier behavior using Ground Penetrating Radar to map the ice’s internal structure; terrestrial Laser scanning (LiDAR) to create a 3D model of the surface of the glacier and surrounding landforms; four Global Navigation Satellite System stations on the glacier’s surface to record its velocity, and digital mapping and measuring of the glaciers surface structures, such as fractures, crevasses and faults.

 

Andrew Finlayson setting up the ground penetrating radar. Photo Credit: British Geological Survey.
Andrew Finlayson setting up the ground penetrating radar. Photo Credit: British Geological Survey.

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