Why Lake Superior Is Rising and What That Means for the City of Duluth

Duluth, Minnesota has been identified as a potential refuge for climate migrants who are fleeing from the damaging effects of climate change occurring in their respective hometowns. The city was selected based on qualitative, social criteria that makes it more appealing than other places, but was not deeply examined in terms of environmental impact or in terms of how climate change might be affecting the water level rise of Lake Superior. Ironically, long-term geological processes as well as recent heavy precipitation events linked to climate change, threaten even the most “climate-proof” city in the United States.

Duluth Skyline. (Credit: Evan Kane/Flickr)

The surface of the Great Lakes region is still in the process of bouncing back from the weight of massive glaciers that began retreating near the end of the last ice age 11,000 years ago. These glaciers and ice sheets, which were miles thick, literally pushed the Earth’s crust into its upper mantle. Now, with the glaciers gone, the earth’s surface is rising back upwards, a process known as isostatic rebound. The same way a yoga mat takes some time to return to its original shape after bearing weight––because of the thick consistency of the earth’s mantle––it will take many thousands of years for the land to return to its original equilibrium level.

However, the amount and rate of rise is not uniform across the Great Lakes region; it all depends on the amount of ice that was pushing the land down and how long ago it melted away. For instance, the Hudson Bay area was home to some of the most massive glacial ice sheets, and was the last to see its ice melt away. Thus, the land surface there is rising more than half an inch per year, which sums to over four feet per century.

Isostatic Rebound. (Credit: Brian McNamara/National Oceanic and Atmospheric Administration)

Moreover, rising land in some areas can cause the land to sink elsewhere, creating a sort-of seesaw effect. North America’s Great Lakes lie along the fulcrum of the seesaw: land north of the lakes is bouncing back up from the retreat of Canadian glaciers, causing the land south of the lakes to subside. As a result, residents on the southern shores are seeing water levels rise very slowly over time. 

Lake Superior itself is experiencing rising water levels on its southern shorelines while its northern shorelines are experiencing the opposite. In fact, a paper published by Lee and Southam in 1994, which examined water level limits for Lake Superior for the purposes of hydropower water diversion, stated: “Due to these natural changes, the upper regulation limit is now 0.21 m higher at Duluth, Minnesota, and 0.26 m lower at Michipicoten, Ontario, than in 1902. By 2050, these differences will be as much as 0.34 m higher and 0.43 m lower, respectively.” They concluded that the effects of crustal movement should be considered in long term planning, especially with regard to establishing flood levels along Lake Superior’s southwestern shore.

The contribution of isostatic rebound to water levels in the Great Lakes is just part of the lake level rise story. Andrew Gronewold, a professor in the school for environment and sustainability (SEAS) at the University of Michigan, explained to GlacierHub that while glacial isostatic rebound is indeed occurring over the Great Lakes region, it is not the reason why water levels are so high in Lake Superior right now. “Water levels are driven primarily by rainfall that enters the Lake Superior basin, and by the amount of water that leaves through evaporation,” Gronewold said, and “this increase in precipitation is largely the response to climate change across the region.”

Waves crashing in Lake Superior. (Credit: Tom Ruppe/Flickr)

Gronewold has been researching how changes in precipitation and evaporation lead to both short and long term changes in water levels in the Great Lakes. He mentioned that as recently as five or six years ago, water levels in the lakes were dangerously low. However, as a result of recent heavy precipitation events, Lake Erie and Lake Ontario just broke their all-time record for high water levels, and that goes back over 100 years. Lake Superior rose one meter in just five years. “It’s important to mention that the rate of change due to glacial isostatic rebound is not nearly as fast as the water level rise by precipitation,” said Gronewold. Researchers believe that rapid transitions between extremely high and low water levels could be the new normal as interactions between the global climate and regional hydrological cycles become more variable with climate change.

Not only has there been an increase in the number of precipitation events, but there has also been an increase in the number of heavy rainstorms. This trend is the result of a warming atmosphere, which can hold more moisture, Gronewold explained. Indeed, for every degree (Celsius) of temperature rise, the atmosphere can hold about seven percent more moisture. The Intergovernmental Panel on Climate Change (IPCC) pointed out that eastern North America is one region especially at risk of seeing the largest increases in heavy precipitation as the climate warms.

According to the IPCC, Earth’s surface warmed an average of approximately one degree C above pre-industrial levels by 2017. This rise might seem small, but the amount of energy that is required to heat the entire surface of the earth by one degree is extremely large. We are already seeing intense sea level rise along the Eastern Coast of the US, worsening wildfires in California, an immense decline in fishery productivity, and the exposure of hundreds of millions of people to climate related risk and poverty. This is forcing millions, especially those in coastal communities, to migrate places that are more climate safe.    

Time series plot of Lake Superior water levels: When working for NOAA, Gronewold helped develop the Great Lakes Water Level Dashboard as a tool to look at long term water level data in the Great Lakes. Notice the recent rising trend. The red line represents the average water level for the period of record while the blue dots represent the average water level in a given month. (Credit: Andrew Gronewold/NOAA).

Duluth, a major port city on Lake Superior, was identified among several other cities in the Upper Midwest as a potential climate refuge for those escaping the damaging effects of climate change in their own hometowns. Jesse M. Keenan, a lecturer in architecture at Harvard University, served as the principal investigator in the “Duluth Climigration” (climate migration) project. “We are seeing the northerly migration of flora and fauna, and the idea is that people will follow,” said Keenan.

“No city can be ‘climate proof,’ no one is immune from climate change,” Keenan explained in his lecture to Duluthians this past April, but there are places that are better insulated than others. Right next to Lake Superior, Duluth the “air-conditioned” city, makes a good case for being quite climate proof. Moreover, recent research out of the University of Maryland suggests Duluth may see a similar climate as Toledo, Ohio, a city 550 miles southeast of Duluth, by 2080.

The video above is a lecture given by Dr. Jesse M. Keenan in April of this year, and is geared towards informing Duluthians about why their city would make an outstanding “climigration” refuge.

“What do people look for when they move?,” Keenan proposed to GlacierHub. Duluth boasts urban affordability, a strong health care system, strong primary and higher education systems, and it also displays core infrastructure that would capture mid- and upper-income consumer preferences. Furthermore, the city has excess capacity for new housing and businesses because it is a residual of the rust belt which saw industrial decline and gradual depopulation starting around 1980. “It has been in a long, long population decline, so any measure of additional population resonates,” Keenan explained. Within the past decade, the entire town gained just 56 people. Though his team did not take into account the environmental impact component of migration in their decision, Keenan affirmed, “I do not discount the associated challenges of water management in terms of stormwater management and managed lake levels, but Duluth itself, has qualitative aspects that make it a good ‘refuge.’” 

Downtown Duluth on the shore of Lake Superior (Credit: Jacob Norlund/Flickr)

Keenan argued that if refugees were to move there, they should settle in high density housing downtown, rather than expand suburbanization, as it provides an opportunity to revive mass transit and build sustainably. “I think this is the most interesting part of the project, actually, because when people move, land becomes very inundated, and this is a chance to move away from the suburban high carbon footprint and build sustainable high-density housing,” Keenan remarked, “and it could easily be like the brownstones of Brooklyn – very nice and beautiful.” 

The important thing to figure out is who will be on the move, which market and demographics they will represent, and what this will mean for the housing lifecycle, tax base, and development. Many Floridians currently imperiled by intense storms and sea level rise may choose to relocate here because Lake Superior resembles the ocean. There have been people who have actually relocated to Duluth as a result of Keenan’s research – “They’ve read these papers and have said ‘That’s it, we’re moving to Duluth!’ Keenan said, and “I want to meet these people.”


The massive glacial ice sheets that carved the Great Lakes make Duluth a deepwater port. Ocean-going ships can reach it, even though it is situated far inland. (Credit: Sharon Mollerus/Flickr)

When asked whether Duluth might make a good climate refuge, Gronewold explained: “As a citizen of the region, I can say that Duluth is an amazing city and the Upper Midwest is a great place to live, but it’s really hard to untangle all the impacts that climate change might have, not only on water and temperature, but also on the economy.” Duluth’s location on Lake Superior provides a cool climate, fresh potable water, and a stable, deepwater shipping hub favorable for climate migration. But now the Great Lakes, to which Duluth owes so much, are changing as a result of slow geological processes as well as much more rapid climate change.

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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.

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