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Lakes collapse and release meltwater during winter causing inland ice to speed up in Greenland, finds study – Phys.org

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Greenland. Credit: Unsplash/CC0 Public Domain

A team of international researchers has shown for the first time how 18 meltwater lakes in Greenland collapse during winter, which causes the edges of the ice to flow faster. The new knowledge is essential for understanding how climate change influences the flow of ice masses in the Arctic.

In the middle of in 2018, an almost 50-year-old meltwater lake disappeared from the ice sheet in western Greenland. The lake was covered by snow and ice when it collapsed but stored inside. The water disappeared into newly formed cracks and drifted down through the approximately 2 km thick layer of ice. The water hit the rock bed under the ice and flowed out from under the ice sheet toward the sea.

This meltwater acted as lubrication between the rock bed and the thick ice on top. As a result, the large mass of ice could slide faster toward the coast, accelerating an unusually large region of inland ice. The drainage of this lake caused several other lakes in the adjacent area to collapse too. In total, the collapsed lakes have released approximately 180 million tons of meltwater that has ended up in the world’s oceans.

This activity is shown by new international research based on and led by the French Université Grenoble Alpes with contributions from DTU Space at The Technical University of Denmark (DTU). The study has just been published in Geophysical Research Letters.

“The meltwater lakes on the ice sheet form in the summer when the ice on the surface melts. It is well known that these lakes can collapse and drain during summer. But, surprisingly, this takes place in the winter too. This is the first time that it has been shown that these specific lake drainages cause large ice accelerations during winter when temperatures are very low,” says postdoc and researcher Nathan Maier, lead author of the article.

As a researcher at the Université Grenoble Alpes in France, he led the extensive international research collaboration behind the discovery. He is now a researcher at Los Alamos National Laboratory in the U.S.

“In total, the lakes drained in connection with this incident have resulted in 180 million tons of water flowing into the sea. This is roughly equivalent to the contents of 80,000 Olympic swimming pools measuring 50 by 25 by 2 meters,” states Nathan Maier.

The 50-year-old lake, which was the first to drain, was located approximately 160 km inland, high on the ice sheet. The lake consisted of melted water and had a frozen ice lid because of the cold winter temperatures. When it collapsed, and the water flowed underneath the ice toward the coast of western Greenland, it started a cascade of events that caused other lakes to be drained of their water too. Among other things, the pressure from the water that ran under the ice from the 50-year-old lake probably helped to form further cracks in the ice above, making these lakes leak as well.

18 lakes drained in an area about three times the size of greater London

A total of 18 lakes collapsed accelerating a 5,200 square kilometers area of the ice sheet, corresponding to more than three times the size of greater London. The researchers note that it happened across a month in the winter of 2018 when air temperatures were below freezing.

“We have only investigated a limited area, but we have good reason to assume that similar events take place in many more places in Greenland. If this applies to larger parts of the ice sheet, it could be quite large amounts of meltwater that disappear in this way and cause the ice sheet to slide faster towards the sea,” says Jonas Kvist Andersen, a postdoctoral researcher at DTU Space in Denmark and co-author of the article.

The investigated area primarily includes the large Jakobshavn Isbræ, which flows into the sea in western Greenland and is the fastest flowing glacier in the world, as well as a smaller glacier south of it that ends on land.

Unknown if winter drainages will become more prevalent

It seems obvious to conclude that the lakes have started to collapse in winter due to global warming. Especially when an almost 50-year-old lake is suddenly drained in the middle of winter and the meltwater ends up in the sea and contributes to sea level rise. But that is not a given, according to the researchers.

“It is still unknown if drainages like these will become more prevalent in a warmer future and then contribute further to ice sheet mass loss. More research is needed to get a better understanding of the mechanisms, or triggers, that cause the lakes to drain,” says Nathan Maier.

“Right now, our understanding of how surface melting will affect mass loss from Greenland in the future is based entirely on the assumption that melting only affects the speed of the ice flow during summer. Our discovery, that large accelerations in the ice flow caused by stored meltwater that drains during winter, significantly changes how we understand ice sheet hydrology over annual time scales.”

The researchers have arrived at the new results by analyzing large amounts of radar data and satellite optical images.

Winter meltwater drain should be included in new climate models

It is not only the oldest lakes that collapse after existing for decades. There are several types of cycles, according to the scientists. Some lakes form and collapse within a year; for others, it happens every few years.

The collapsed lakes affect the ice sheet, or glacier, melting in Greenland in several ways. The water from the lakes ends up in the sea. The water lubricates the ice sheets from beneath causing them to slide faster towards the coast exposing them to additional melting. In addition, the structure of the enormous ice masses changes. There could be other mechanisms at play as well.

“It is essential to describe what happens when the melting process takes place in winter so that this knowledge can be included in future models for ,” states Jonas Kvist Andersen.

Draining lakes and waterflow found with radar data and satellite optical images

The researchers have used Synthetic Aperture Radar (SAR) interferometry based on data from the Sentinel-1 satellites from the European Space Agency (ESA) to map how the 18 lakes on the ice sheet in western Greenland have been drained, and how the water from them has subsequently flowed downwards and out to sea.

Visual and optical photos have been retrieved from other European and US satellites. They have been used to identify the lakes and their change over a few months in the winter of 2018. The radar images have been supplemented with photos from older satellites. In this way, it was possible for the scientists to follow the development of the lakes over several decades, including establishing when they were drained.

The Sentinel-1 satellites, which cover the Arctic from an orbit just under 700 km above Earth, have a SAR unit, which sends radar signals obliquely down towards the surface of the , from where they are returned to the satellite.

By analyzing differences and displacements in the radar signal phase, it is possible to measure the movement of the ice surface relative to the satellite. When several measurements are compared, a distinction can be made between horizontal movement (when the ice flow is accelerated) and vertical movement (when the meltwater pushes the overlying ice upwards).

This way, information is obtained about the movement of the meltwater and the ice after the water has drained from the bottom of the .

More information:
Nathan Maier et al, Wintertime supraglacial lake drainage cascade triggers large‐scale ice flow response in Greenland, Geophysical Research Letters (2023). DOI: 10.1029/2022GL102251

Citation:
Lakes collapse and release meltwater during winter causing inland ice to speed up in Greenland, finds study (2023, February 21)
retrieved 21 February 2023
from https://phys.org/news/2023-02-lakes-collapse-meltwater-winter-inland.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
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Here’s how Helene and other storms dumped a whopping 40 trillion gallons of rain on the South

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More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.

That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.

“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”

The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.

Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.

Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.

Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.

Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.

Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.

“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”

The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.

North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.

Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”

Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.

Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.

For Dello, the “fingerprints of climate change” were clear.

“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”

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‘Big Sam’: Paleontologists unearth giant skull of Pachyrhinosaurus in Alberta

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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.

On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.

They call it “Big Sam.”

The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.

It didn’t die alone.

“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.

She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”

“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.

The head alone, she said, is about the size of a baby elephant.

The discovery was a long time coming.

The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.

“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.

When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”

“It contains about 100 to 300 bones per square metre,” she said.

Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.

About a year ago, they found the second adult: Big Sam.

Bamforth said both dinosaurs are believed to have been the elders in the herd.

“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.

“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”

The genders of the two adults are unknown.

Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.

The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.

She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.

“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.

“It’s pretty exciting.”

This report by The Canadian Press was first published Sept. 25, 2024.

The Canadian Press. All rights reserved.

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The ancient jar smashed by a 4-year-old is back on display at an Israeli museum after repair

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TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.

Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.

Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.

The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.

The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.

It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.

Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.

Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.

Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.

Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.

Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.

The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”

The Canadian Press. All rights reserved.

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