Massive study provides first detailed look at how Greenland’s ice is vanishing

The surface of the Greenland Ice Sheet. A new study uses NASA data to provide the first detailed reconstruction of how the ice sheet and its many glaciers are changing. The research was led by University at Buffalo geologist Beata Csatho. -  Beata Csatho
The surface of the Greenland Ice Sheet. A new study uses NASA data to provide the first detailed reconstruction of how the ice sheet and its many glaciers are changing. The research was led by University at Buffalo geologist Beata Csatho. – Beata Csatho

The Greenland Ice Sheet is the second-largest body of ice on Earth. It covers an area about five times the size of New York State and Kansas combined, and if it melts completely, oceans could rise by 20 feet. Coastal communities from Florida to Bangladesh would suffer extensive damage.

Now, a new study is revealing just how little we understand this northern behemoth.

Led by geophysicist Beata Csatho, PhD, an associate professor of geology at the University at Buffalo, the research provides what the authors think is the first comprehensive picture of how Greenland’s ice is vanishing. It suggests that current ice sheet modeling studies are too simplistic to accurately predict the future contributions of the entire Greenland Ice Sheet to sea level rise, and that Greenland may lose ice more rapidly in the near future than previously thought.

“The great importance of our data is that for the first time, we have a comprehensive picture of how all of Greenland’s glaciers have changed over the past decade,” Csatho says.

“This information is crucial for developing and validating numerical models that predict how the ice sheet may change and contribute to global sea level over the next few hundred years,” says Cornelis J. van der Veen, PhD, professor in the Department of Geography at the University of Kansas, who played a key role in interpreting glaciological changes.

The project was a massive undertaking, using satellite and aerial data from NASA’s ICESat spacecraft and Operation IceBridge field campaign to reconstruct how the height of the Greenland Ice Sheet changed at nearly 100,000 locations from 1993 to 2012.

Ice loss takes place in a complex manner, with the ice sheet both melting and calving ice into the ocean.
The study had two major findings:

  • First, the scientists were able to provide new estimates of annual ice loss at high spatial resolution (see below).

  • Second, the research revealed that current models fail to accurately capture how the entire Greenland Ice Sheet is changing and contributing to rising oceans.

The second point is crucial to climate change modelers.

Today’s simulations use the activity of four well-studied glaciers — Jakobshavn, Helheim, Kangerlussuaq and Petermann — to forecast how the entire ice sheet will dump ice into the oceans.

But the new research shows that activity at these four locations may not be representative of what is happening with glaciers across the ice sheet. In fact, glaciers undergo patterns of thinning and thickening that current climate change simulations fail to address, Csatho says.

“There are 242 outlet glaciers wider than 1.5 km on the Greenland Ice Sheet, and what we see is that their behavior is complex in space and time,” Csatho says. “The local climate and geological conditions, the local hydrology — all of these factors have an effect. The current models do not address this complexity.”

The team identified areas of rapid shrinkage in southeast Greenland that today’s models don’t acknowledge. This leads Csatho to believe that the ice sheet could lose ice faster in the future than today’s simulations would suggest.

The results will be published on Dec. 15 in the Proceedings of the National Academy of Sciences, and the study and all information in this press release are embargoed until 3 p.m. Eastern Time that day.

Photos, data visualizations and video are available by contacting Charlotte Hsu at the University at Buffalo at chsu22@buffalo.edu.

How much ice is the Greenland Ice Sheet losing?

To analyze how the height of the ice sheet was changing, Csatho and UB research professor and photogrammetrist Anton Schenk, PhD, developed a computational technique called Surface Elevation Reconstruction And Change detection to fuse together data from NASA satellite and aerial missions.

The analysis found that the Greenland Ice Sheet lost about 243 metric gigatons of ice annually — equivalent to about 277 cubic kilometers of ice per year — from 2003-09, the period for which the team had the most comprehensive data. This loss is estimated to have added about 0.68 millimeters of water to the oceans annually.

The figures are averages, and ice loss varied from year to year, and from region to region.

Why are today’s projections of sea level rise flawed, and how can we fix them?

Glaciers don’t just gradually lose mass when the temperature rises. That’s one reason it’s difficult to predict their response to global warming.

In the study, scientists found that some of Greenland’s glaciers thickened even when the temperature rose. Others exhibited accelerated thinning. Some displayed both thinning and thickening, with sudden reversals.

As a step toward building better models of sea level rise, the research team divided Greenland’s 242 glaciers into 7 major groups based on their behavior from 2003-09.

“Understanding the groupings will help us pick out examples of glaciers that are representative of the whole,” Csatho says. “We can then use data from these representative glaciers in models to provide a more complete picture of what is happening.”

In a new project, she and colleagues are investigating why different glaciers respond differently to warming. Factors could include the temperature of the surrounding ocean; the level of friction between a glacier and the bedrock below; the amount of water under a glacier; and the geometry of the fjord.

“The physics of these processes are not well understood,” Csatho says.

The NASA missions: A colossal undertaking

The study combined data from various NASA missions, including:

  • NASA’s Ice, Cloud and Land Elevation Satellite (ICESat), which measured the ice sheet’s elevation multiple times a year at each of the nearly 100,000 locations from 2003-09.

  • NASA’s, massive aerial survey that employs highly specialized research aircrafts to collect data at less frequent intervals than ICESat. These missions began measuring the Greenland Ice Sheet’s elevation in 1993. Operation IceBridge was started in 2009 to bridge the time between ICESat-1 and ICESat-2, and will continue until at least 2017, when NASA’s next generation ICESat-2 satellite is expected to come online.

Csatho says the new study shows why careful monitoring is critical: Given the complex nature of glacier behavior, good data is crucial to building better models.

Collaborators

Besides Csatho, Schenk and van der Veen, the project included additional researchers from the University at Buffalo, Utrecht University in The Netherlands, the Technical University of Denmark and Florida Atlantic University.

Massive study provides first detailed look at how Greenland’s ice is vanishing

The surface of the Greenland Ice Sheet. A new study uses NASA data to provide the first detailed reconstruction of how the ice sheet and its many glaciers are changing. The research was led by University at Buffalo geologist Beata Csatho. -  Beata Csatho
The surface of the Greenland Ice Sheet. A new study uses NASA data to provide the first detailed reconstruction of how the ice sheet and its many glaciers are changing. The research was led by University at Buffalo geologist Beata Csatho. – Beata Csatho

The Greenland Ice Sheet is the second-largest body of ice on Earth. It covers an area about five times the size of New York State and Kansas combined, and if it melts completely, oceans could rise by 20 feet. Coastal communities from Florida to Bangladesh would suffer extensive damage.

Now, a new study is revealing just how little we understand this northern behemoth.

Led by geophysicist Beata Csatho, PhD, an associate professor of geology at the University at Buffalo, the research provides what the authors think is the first comprehensive picture of how Greenland’s ice is vanishing. It suggests that current ice sheet modeling studies are too simplistic to accurately predict the future contributions of the entire Greenland Ice Sheet to sea level rise, and that Greenland may lose ice more rapidly in the near future than previously thought.

“The great importance of our data is that for the first time, we have a comprehensive picture of how all of Greenland’s glaciers have changed over the past decade,” Csatho says.

“This information is crucial for developing and validating numerical models that predict how the ice sheet may change and contribute to global sea level over the next few hundred years,” says Cornelis J. van der Veen, PhD, professor in the Department of Geography at the University of Kansas, who played a key role in interpreting glaciological changes.

The project was a massive undertaking, using satellite and aerial data from NASA’s ICESat spacecraft and Operation IceBridge field campaign to reconstruct how the height of the Greenland Ice Sheet changed at nearly 100,000 locations from 1993 to 2012.

Ice loss takes place in a complex manner, with the ice sheet both melting and calving ice into the ocean.
The study had two major findings:

  • First, the scientists were able to provide new estimates of annual ice loss at high spatial resolution (see below).

  • Second, the research revealed that current models fail to accurately capture how the entire Greenland Ice Sheet is changing and contributing to rising oceans.

The second point is crucial to climate change modelers.

Today’s simulations use the activity of four well-studied glaciers — Jakobshavn, Helheim, Kangerlussuaq and Petermann — to forecast how the entire ice sheet will dump ice into the oceans.

But the new research shows that activity at these four locations may not be representative of what is happening with glaciers across the ice sheet. In fact, glaciers undergo patterns of thinning and thickening that current climate change simulations fail to address, Csatho says.

“There are 242 outlet glaciers wider than 1.5 km on the Greenland Ice Sheet, and what we see is that their behavior is complex in space and time,” Csatho says. “The local climate and geological conditions, the local hydrology — all of these factors have an effect. The current models do not address this complexity.”

The team identified areas of rapid shrinkage in southeast Greenland that today’s models don’t acknowledge. This leads Csatho to believe that the ice sheet could lose ice faster in the future than today’s simulations would suggest.

The results will be published on Dec. 15 in the Proceedings of the National Academy of Sciences, and the study and all information in this press release are embargoed until 3 p.m. Eastern Time that day.

Photos, data visualizations and video are available by contacting Charlotte Hsu at the University at Buffalo at chsu22@buffalo.edu.

How much ice is the Greenland Ice Sheet losing?

To analyze how the height of the ice sheet was changing, Csatho and UB research professor and photogrammetrist Anton Schenk, PhD, developed a computational technique called Surface Elevation Reconstruction And Change detection to fuse together data from NASA satellite and aerial missions.

The analysis found that the Greenland Ice Sheet lost about 243 metric gigatons of ice annually — equivalent to about 277 cubic kilometers of ice per year — from 2003-09, the period for which the team had the most comprehensive data. This loss is estimated to have added about 0.68 millimeters of water to the oceans annually.

The figures are averages, and ice loss varied from year to year, and from region to region.

Why are today’s projections of sea level rise flawed, and how can we fix them?

Glaciers don’t just gradually lose mass when the temperature rises. That’s one reason it’s difficult to predict their response to global warming.

In the study, scientists found that some of Greenland’s glaciers thickened even when the temperature rose. Others exhibited accelerated thinning. Some displayed both thinning and thickening, with sudden reversals.

As a step toward building better models of sea level rise, the research team divided Greenland’s 242 glaciers into 7 major groups based on their behavior from 2003-09.

“Understanding the groupings will help us pick out examples of glaciers that are representative of the whole,” Csatho says. “We can then use data from these representative glaciers in models to provide a more complete picture of what is happening.”

In a new project, she and colleagues are investigating why different glaciers respond differently to warming. Factors could include the temperature of the surrounding ocean; the level of friction between a glacier and the bedrock below; the amount of water under a glacier; and the geometry of the fjord.

“The physics of these processes are not well understood,” Csatho says.

The NASA missions: A colossal undertaking

The study combined data from various NASA missions, including:

  • NASA’s Ice, Cloud and Land Elevation Satellite (ICESat), which measured the ice sheet’s elevation multiple times a year at each of the nearly 100,000 locations from 2003-09.

  • NASA’s, massive aerial survey that employs highly specialized research aircrafts to collect data at less frequent intervals than ICESat. These missions began measuring the Greenland Ice Sheet’s elevation in 1993. Operation IceBridge was started in 2009 to bridge the time between ICESat-1 and ICESat-2, and will continue until at least 2017, when NASA’s next generation ICESat-2 satellite is expected to come online.

Csatho says the new study shows why careful monitoring is critical: Given the complex nature of glacier behavior, good data is crucial to building better models.

Collaborators

Besides Csatho, Schenk and van der Veen, the project included additional researchers from the University at Buffalo, Utrecht University in The Netherlands, the Technical University of Denmark and Florida Atlantic University.

Himalaya tectonic dam with a discharge

The Himalaya features some of the most impressive gorges on Earth that have been formed by rivers. The geologic history of the famous Tsangpo Gorge, in the eastern Himalaya, now needs to be rewritten.

A team of German, Chinese, and American geoscientists have namely discovered a canyon, filled with more than 500 m of sediments beneath the bed of the present-day Yarlung Tsangpo River upstream from the gorge. Using drill cores, the scientists were able to reconstruct the former valley floor of this river, which allowed them to reconstruct the geological history of the Tsangpo Gorge (Science, 21.11.2014). They discovered that the gorge obtained its steep form in response to rapid tectonic uplift in the Himalaya, two to three million years ago. “Because of its high gradient, the river incises its bed very rapidly”, explains Dirk Scherler from the GFZ German Research Centre for Geosciences. “The rocks here are eroded at annual rates of up to one centimeter per year which is matched by tectonic uplift of the same rate.” The collision of India with the Eurasian continent has created a tectonic dam here.

This barrier caused a lower flow velocity of the Yarlung Tsangpoupstream. Previously, the river had deeply incised into the Tibetan Plateau. Due to the reduced flow rate the sediments which the Yarlung Tsangpo River and its tributaries eroded from the highlands were deposited in the river bed along hundreds of kilometers.

The scientists estimated that these deposits are up to 1000 m thick. “Five drillings have been conducted over a distance of 300 km upstream of the gorge”, says Dirk Scherler. “One of the drillings encountered bedrock after 540 meters of sediments. From the drill cores, we were able to infer the reduction in stream flow velocity and date the initiation of sedimentation using cosmogenic nuclides. These are rare isotopes that are produced by cosmic rays near the Earth’s surface. Three Million years ago, the river was still incising into Himalayan bedrock.” But today the once huge canyon is buried by sediments.

The Yarlung Tsangpo is the largest high mountain river on Earth. It flows along a distance of 1700 km across the Tibetan Plateau, at an elevation of around 4000 meters and follows the boundary between India and Eurasia. In the eastern Himalaya, the river leaves the high plateau and breaks through the world famous, horseshoe-shaped Tsangpo Gorge for the plains of India.

The new findings show that rapid incision of the Yarlung Tsangpo and the development of the Tsangpo Gorge occurred in response to tectonic uplift, and not, as previously thought, the other way round. In addition, these observations refute existing hypotheses that relate the origin of the Tsangpo Gorge to river capture of the Yarlung Tsangpo by the Brahmaputra River.

Geologists discover ancient buried canyon in South Tibet

This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge -- the new discoveries falsify this hypothesis. -  Ping Wang
This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge — the new discoveries falsify this hypothesis. – Ping Wang

A team of researchers from Caltech and the China Earthquake Administration has discovered an ancient, deep canyon buried along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The geologists say that the ancient canyon–thousands of feet deep in places–effectively rules out a popular model used to explain how the massive and picturesque gorges of the Himalayas became so steep, so fast.

“I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet,” says Jean-Philippe Avouac, the Earle C. Anthony Professor of Geology at Caltech. “When I first saw the data, I said, ‘Wow!’ It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today. That was a big discovery, in my opinion.”

Geologists like Avouac and his colleagues, who are interested in tectonics–the study of the earth’s surface and the way it changes–can use tools such as GPS and seismology to study crustal deformation that is taking place today. But if they are interested in studying changes that occurred millions of years ago, such tools are not useful because the activity has already happened. In those cases, rivers become a main source of information because they leave behind geomorphic signatures that geologists can interrogate to learn about the way those rivers once interacted with the land–helping them to pin down when the land changed and by how much, for example.

“In tectonics, we are always trying to use rivers to say something about uplift,” Avouac says. “In this case, we used a paleocanyon that was carved by a river. It’s a nice example where by recovering the geometry of the bottom of the canyon, we were able to say how much the range has moved up and when it started moving.”

The team reports its findings in the current issue of Science.

Last year, civil engineers from the China Earthquake Administration collected cores by drilling into the valley floor at five locations along the Yarlung Tsangpo River. Shortly after, former Caltech graduate student Jing Liu-Zeng, who now works for that administration, returned to Caltech as a visiting associate and shared the core data with Avouac and Dirk Scherler, then a postdoc in Avouac’s group. Scherler had previously worked in the far western Himalayas, where the Indus River has cut deeply into the Tibetan Plateau, and immediately recognized that the new data suggested the presence of a paleocanyon.

Liu-Zeng and Scherler analyzed the core data and found that at several locations there were sedimentary conglomerates, rounded gravel and larger rocks cemented together, that are associated with flowing rivers, until a depth of 800 meters or so, at which point the record clearly indicated bedrock. This suggested that the river once carved deeply into the plateau.

To establish when the river switched from incising bedrock to depositing sediments, they measured two isotopes, beryllium-10 and aluminum-26, in the lowest sediment layer. The isotopes are produced when rocks and sediment are exposed to cosmic rays at the surface and decay at different rates once buried, and so allowed the geologists to determine that the paleocanyon started to fill with sediment about 2.5 million years ago.

The researchers’ reconstruction of the former valley floor showed that the slope of the river once increased gradually from the Gangetic Plain to the Tibetan Plateau, with no sudden changes, or knickpoints. Today, the river, like most others in the area, has a steep knickpoint where it meets the Himalayas, at a place known as the Namche Barwa massif. There, the uplift of the mountains is extremely rapid (on the order of 1 centimeter per year, whereas in other areas 5 millimeters per year is more typical) and the river drops by 2 kilometers in elevation as it flows through the famous Tsangpo Gorge, known by some as the Yarlung Tsangpo Grand Canyon because it is so deep and long.

Combining the depth and age of the paleocanyon with the geometry of the valley, the geologists surmised that the river existed in this location prior to about 3 million years ago, but at that time, it was not affected by the Himalayas. However, as the Indian and Eurasian plates continued to collide and the mountain range pushed northward, it began impinging on the river. Suddenly, about 2.5 million years ago, a rapidly uplifting section of the mountain range got in the river’s way, damming it, and the canyon subsequently filled with sediment.

“This is the time when the Namche Barwa massif started to rise, and the gorge developed,” says Scherler, one of two lead authors on the paper and now at the GFZ German Research Center for Geosciences in Potsdam, Germany.

That picture of the river and the Tibetan Plateau, which involves the river incising deeply into the plateau millions of years ago, differs quite a bit from the typically accepted geologic vision. Typically, geologists believe that when rivers start to incise into a plateau, they eat at the edges, slowly making their way into the plateau over time. However, the rivers flowing across the Himalayas all have strong knickpoints and have not incised much at all into the Tibetan Plateau. Therefore, the thought has been that the rapid uplift of the Himalayas has pushed the rivers back, effectively pinning them, so that they have not been able to make their way into the plateau. But that explanation does not work with the newly discovered paleocanyon.

The team’s new hypothesis also rules out a model that has been around for about 15 years, called tectonic aneurysm, which suggests that the rapid uplift seen at the Namche Barwa massif was triggered by intense river incision. In tectonic aneurysm, a river cuts down through the earth’s crust so fast that it causes the crust to heat up, making a nearby mountain range weaker and facilitating uplift.

The model is popular among geologists, and indeed Avouac himself published a modeling paper in 1996 that showed the viability of the mechanism. “But now we have discovered that the river was able to cut into the plateau way before the uplift happened,” Avouac says, “and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision.”

###

The other lead author on the paper, “Tectonic control of the Yarlung Tsangpo Gorge, revealed by a 2.5 Myr old buried canyon in Southern Tibet,” is Ping Wang of the State Key Laboratory of Earthquake Dynamics, in Beijing, China. Additional authors include Jürgen Mey, of the University of Potsdam, in Germany; and Yunda Zhang and Dingguo Shi of the Chengdu Engineering Corporation, in China. The work was supported by the National Natural Science Foundation of China, the State Key Laboratory for Earthquake Dynamics, and the Alexander von Humboldt Foundation.

Himalaya tectonic dam with a discharge

The Himalaya features some of the most impressive gorges on Earth that have been formed by rivers. The geologic history of the famous Tsangpo Gorge, in the eastern Himalaya, now needs to be rewritten.

A team of German, Chinese, and American geoscientists have namely discovered a canyon, filled with more than 500 m of sediments beneath the bed of the present-day Yarlung Tsangpo River upstream from the gorge. Using drill cores, the scientists were able to reconstruct the former valley floor of this river, which allowed them to reconstruct the geological history of the Tsangpo Gorge (Science, 21.11.2014). They discovered that the gorge obtained its steep form in response to rapid tectonic uplift in the Himalaya, two to three million years ago. “Because of its high gradient, the river incises its bed very rapidly”, explains Dirk Scherler from the GFZ German Research Centre for Geosciences. “The rocks here are eroded at annual rates of up to one centimeter per year which is matched by tectonic uplift of the same rate.” The collision of India with the Eurasian continent has created a tectonic dam here.

This barrier caused a lower flow velocity of the Yarlung Tsangpoupstream. Previously, the river had deeply incised into the Tibetan Plateau. Due to the reduced flow rate the sediments which the Yarlung Tsangpo River and its tributaries eroded from the highlands were deposited in the river bed along hundreds of kilometers.

The scientists estimated that these deposits are up to 1000 m thick. “Five drillings have been conducted over a distance of 300 km upstream of the gorge”, says Dirk Scherler. “One of the drillings encountered bedrock after 540 meters of sediments. From the drill cores, we were able to infer the reduction in stream flow velocity and date the initiation of sedimentation using cosmogenic nuclides. These are rare isotopes that are produced by cosmic rays near the Earth’s surface. Three Million years ago, the river was still incising into Himalayan bedrock.” But today the once huge canyon is buried by sediments.

The Yarlung Tsangpo is the largest high mountain river on Earth. It flows along a distance of 1700 km across the Tibetan Plateau, at an elevation of around 4000 meters and follows the boundary between India and Eurasia. In the eastern Himalaya, the river leaves the high plateau and breaks through the world famous, horseshoe-shaped Tsangpo Gorge for the plains of India.

The new findings show that rapid incision of the Yarlung Tsangpo and the development of the Tsangpo Gorge occurred in response to tectonic uplift, and not, as previously thought, the other way round. In addition, these observations refute existing hypotheses that relate the origin of the Tsangpo Gorge to river capture of the Yarlung Tsangpo by the Brahmaputra River.

Geologists discover ancient buried canyon in South Tibet

This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge -- the new discoveries falsify this hypothesis. -  Ping Wang
This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge — the new discoveries falsify this hypothesis. – Ping Wang

A team of researchers from Caltech and the China Earthquake Administration has discovered an ancient, deep canyon buried along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The geologists say that the ancient canyon–thousands of feet deep in places–effectively rules out a popular model used to explain how the massive and picturesque gorges of the Himalayas became so steep, so fast.

“I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet,” says Jean-Philippe Avouac, the Earle C. Anthony Professor of Geology at Caltech. “When I first saw the data, I said, ‘Wow!’ It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today. That was a big discovery, in my opinion.”

Geologists like Avouac and his colleagues, who are interested in tectonics–the study of the earth’s surface and the way it changes–can use tools such as GPS and seismology to study crustal deformation that is taking place today. But if they are interested in studying changes that occurred millions of years ago, such tools are not useful because the activity has already happened. In those cases, rivers become a main source of information because they leave behind geomorphic signatures that geologists can interrogate to learn about the way those rivers once interacted with the land–helping them to pin down when the land changed and by how much, for example.

“In tectonics, we are always trying to use rivers to say something about uplift,” Avouac says. “In this case, we used a paleocanyon that was carved by a river. It’s a nice example where by recovering the geometry of the bottom of the canyon, we were able to say how much the range has moved up and when it started moving.”

The team reports its findings in the current issue of Science.

Last year, civil engineers from the China Earthquake Administration collected cores by drilling into the valley floor at five locations along the Yarlung Tsangpo River. Shortly after, former Caltech graduate student Jing Liu-Zeng, who now works for that administration, returned to Caltech as a visiting associate and shared the core data with Avouac and Dirk Scherler, then a postdoc in Avouac’s group. Scherler had previously worked in the far western Himalayas, where the Indus River has cut deeply into the Tibetan Plateau, and immediately recognized that the new data suggested the presence of a paleocanyon.

Liu-Zeng and Scherler analyzed the core data and found that at several locations there were sedimentary conglomerates, rounded gravel and larger rocks cemented together, that are associated with flowing rivers, until a depth of 800 meters or so, at which point the record clearly indicated bedrock. This suggested that the river once carved deeply into the plateau.

To establish when the river switched from incising bedrock to depositing sediments, they measured two isotopes, beryllium-10 and aluminum-26, in the lowest sediment layer. The isotopes are produced when rocks and sediment are exposed to cosmic rays at the surface and decay at different rates once buried, and so allowed the geologists to determine that the paleocanyon started to fill with sediment about 2.5 million years ago.

The researchers’ reconstruction of the former valley floor showed that the slope of the river once increased gradually from the Gangetic Plain to the Tibetan Plateau, with no sudden changes, or knickpoints. Today, the river, like most others in the area, has a steep knickpoint where it meets the Himalayas, at a place known as the Namche Barwa massif. There, the uplift of the mountains is extremely rapid (on the order of 1 centimeter per year, whereas in other areas 5 millimeters per year is more typical) and the river drops by 2 kilometers in elevation as it flows through the famous Tsangpo Gorge, known by some as the Yarlung Tsangpo Grand Canyon because it is so deep and long.

Combining the depth and age of the paleocanyon with the geometry of the valley, the geologists surmised that the river existed in this location prior to about 3 million years ago, but at that time, it was not affected by the Himalayas. However, as the Indian and Eurasian plates continued to collide and the mountain range pushed northward, it began impinging on the river. Suddenly, about 2.5 million years ago, a rapidly uplifting section of the mountain range got in the river’s way, damming it, and the canyon subsequently filled with sediment.

“This is the time when the Namche Barwa massif started to rise, and the gorge developed,” says Scherler, one of two lead authors on the paper and now at the GFZ German Research Center for Geosciences in Potsdam, Germany.

That picture of the river and the Tibetan Plateau, which involves the river incising deeply into the plateau millions of years ago, differs quite a bit from the typically accepted geologic vision. Typically, geologists believe that when rivers start to incise into a plateau, they eat at the edges, slowly making their way into the plateau over time. However, the rivers flowing across the Himalayas all have strong knickpoints and have not incised much at all into the Tibetan Plateau. Therefore, the thought has been that the rapid uplift of the Himalayas has pushed the rivers back, effectively pinning them, so that they have not been able to make their way into the plateau. But that explanation does not work with the newly discovered paleocanyon.

The team’s new hypothesis also rules out a model that has been around for about 15 years, called tectonic aneurysm, which suggests that the rapid uplift seen at the Namche Barwa massif was triggered by intense river incision. In tectonic aneurysm, a river cuts down through the earth’s crust so fast that it causes the crust to heat up, making a nearby mountain range weaker and facilitating uplift.

The model is popular among geologists, and indeed Avouac himself published a modeling paper in 1996 that showed the viability of the mechanism. “But now we have discovered that the river was able to cut into the plateau way before the uplift happened,” Avouac says, “and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision.”

###

The other lead author on the paper, “Tectonic control of the Yarlung Tsangpo Gorge, revealed by a 2.5 Myr old buried canyon in Southern Tibet,” is Ping Wang of the State Key Laboratory of Earthquake Dynamics, in Beijing, China. Additional authors include Jürgen Mey, of the University of Potsdam, in Germany; and Yunda Zhang and Dingguo Shi of the Chengdu Engineering Corporation, in China. The work was supported by the National Natural Science Foundation of China, the State Key Laboratory for Earthquake Dynamics, and the Alexander von Humboldt Foundation.

Fountain of youth underlies Antarctic Mountains

Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. -  Tim Creyts
Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. – Tim Creyts

Time ravages mountains, as it does people. Sharp features soften, and bodies grow shorter and rounder. But under the right conditions, some mountains refuse to age. In a new study, scientists explain why the ice-covered Gamburtsev Mountains in the middle of Antarctica looks as young as they do.

The Gamburtsevs were discovered in the 1950s, but remained unexplored until scientists flew ice-penetrating instruments over the mountains 60 years later. As this ancient hidden landscape came into focus, scientists were stunned to see the saw-toothed and towering crags of much younger mountains. Though the Gamburtsevs are contemporaries of the largely worn-down Appalachians, they looked more like the Rockies, which are nearly 200 million years younger.

More surprising still, the scientists discovered a vast network of lakes and rivers at the mountains’ base. Though water usually speeds erosion, here it seems to have kept erosion at bay. The reason, researchers now say, has to do with the thick ice that has entombed the Gamburtsevs since Antarctica went into a deep freeze 35 million years ago.

“The ice sheet acts like an anti-aging cream,” said the study’s lead author, Timothy Creyts, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. “It triggers a series of thermodynamic processes that have almost perfectly preserved the Gamburtsevs since ice began spreading across the continent.”

The study, which appears in the latest issue of the journal Geophysical Research Letters, explains how the blanket of ice covering the Gamburtsevs has preserved its rugged ridgelines.

Snow falling at the surface of the ice sheet draws colder temperatures down, closer to protruding peaks in a process called divergent cooling. At the same time, heat radiating from bedrock beneath the ice sheet melts ice in the deep valleys to form rivers and lakes. As rivers course along the base of the ice sheet, high pressures from the overlying ice sheet push water up valleys in reverse. This uphill flow refreezes as it meets colder temperature from above. Thus, ridgelines are cryogenically preserved.

The oldest rocks in the Gamburtsevs formed more than a billion years ago, in the collision of several continents. Though these prototype mountains eroded away, a lingering crustal root became reactivated when the supercontinent Gondwana ripped apart, starting about 200 million years ago. Tectonic forces pushed the land up again to form the modern Gamburtsevs, which range across an area the size of the Alps. Erosion again chewed away at the mountains until earth entered a cooling phase 35 million years ago. Expanding outward from the Gamburtsevs, a growing layer of ice joined several other nucleation points to cover the entire continent in ice.

The researchers say that the mechanism that stalled aging of the Gamburtsevs at higher elevations may explain why some ridgelines in the Torngat Mountains on Canada’s Labrador Peninsula and the Scandinavian Mountains running through Norway, Sweden and Finland appear strikingly untouched. Massive ice sheets covered both landscapes during the last ice age, which peaked about 20,000 years ago, but many high-altitude features bear little trace of this event.

“The authors identify a mechanism whereby larger parts of mountains ranges in glaciated regions–not just Antarctica–could be spared from erosion,” said Stewart Jamieson, a glaciologist at Durham University who was not involved in the study. “This is important because these uplands are nucleation centers for ice sheets. If they were to gradually erode during glacial cycles, they would become less effective as nucleation points during later ice ages.”

Ice sheet behavior, then, may influence climate change in ways that scientists and computer models have yet to appreciate. As study coauthor Fausto Ferraccioli, head of the British Antarctic Survey’s airborne geophysics group, put it: “If these mountains in interior East Antarctica had been more significantly eroded then the ice sheet itself
may have had a different history.”

Other Authors


Hugh Carr and Tom Jordan of the British Antarctic Survey; Robin Bell, Michael Wolovick and Nicholas Frearson of Lamont-Doherty; Kathryn Rose of University of Bristol; Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources; David Braaten of Kansas University; and Carol Finn of the U.S. Geological Survey.

Copies of the paper, “Freezing of ridges and water networks preserves the Gamburtsev Subglacial Mountains for millions of years,” are available from the authors.

Scientist Contact


Tim Creyts

845-365-8368

tcreyts@ldeo.columbia.edu

Fountain of youth underlies Antarctic Mountains

Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. -  Tim Creyts
Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. – Tim Creyts

Time ravages mountains, as it does people. Sharp features soften, and bodies grow shorter and rounder. But under the right conditions, some mountains refuse to age. In a new study, scientists explain why the ice-covered Gamburtsev Mountains in the middle of Antarctica looks as young as they do.

The Gamburtsevs were discovered in the 1950s, but remained unexplored until scientists flew ice-penetrating instruments over the mountains 60 years later. As this ancient hidden landscape came into focus, scientists were stunned to see the saw-toothed and towering crags of much younger mountains. Though the Gamburtsevs are contemporaries of the largely worn-down Appalachians, they looked more like the Rockies, which are nearly 200 million years younger.

More surprising still, the scientists discovered a vast network of lakes and rivers at the mountains’ base. Though water usually speeds erosion, here it seems to have kept erosion at bay. The reason, researchers now say, has to do with the thick ice that has entombed the Gamburtsevs since Antarctica went into a deep freeze 35 million years ago.

“The ice sheet acts like an anti-aging cream,” said the study’s lead author, Timothy Creyts, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. “It triggers a series of thermodynamic processes that have almost perfectly preserved the Gamburtsevs since ice began spreading across the continent.”

The study, which appears in the latest issue of the journal Geophysical Research Letters, explains how the blanket of ice covering the Gamburtsevs has preserved its rugged ridgelines.

Snow falling at the surface of the ice sheet draws colder temperatures down, closer to protruding peaks in a process called divergent cooling. At the same time, heat radiating from bedrock beneath the ice sheet melts ice in the deep valleys to form rivers and lakes. As rivers course along the base of the ice sheet, high pressures from the overlying ice sheet push water up valleys in reverse. This uphill flow refreezes as it meets colder temperature from above. Thus, ridgelines are cryogenically preserved.

The oldest rocks in the Gamburtsevs formed more than a billion years ago, in the collision of several continents. Though these prototype mountains eroded away, a lingering crustal root became reactivated when the supercontinent Gondwana ripped apart, starting about 200 million years ago. Tectonic forces pushed the land up again to form the modern Gamburtsevs, which range across an area the size of the Alps. Erosion again chewed away at the mountains until earth entered a cooling phase 35 million years ago. Expanding outward from the Gamburtsevs, a growing layer of ice joined several other nucleation points to cover the entire continent in ice.

The researchers say that the mechanism that stalled aging of the Gamburtsevs at higher elevations may explain why some ridgelines in the Torngat Mountains on Canada’s Labrador Peninsula and the Scandinavian Mountains running through Norway, Sweden and Finland appear strikingly untouched. Massive ice sheets covered both landscapes during the last ice age, which peaked about 20,000 years ago, but many high-altitude features bear little trace of this event.

“The authors identify a mechanism whereby larger parts of mountains ranges in glaciated regions–not just Antarctica–could be spared from erosion,” said Stewart Jamieson, a glaciologist at Durham University who was not involved in the study. “This is important because these uplands are nucleation centers for ice sheets. If they were to gradually erode during glacial cycles, they would become less effective as nucleation points during later ice ages.”

Ice sheet behavior, then, may influence climate change in ways that scientists and computer models have yet to appreciate. As study coauthor Fausto Ferraccioli, head of the British Antarctic Survey’s airborne geophysics group, put it: “If these mountains in interior East Antarctica had been more significantly eroded then the ice sheet itself
may have had a different history.”

Other Authors


Hugh Carr and Tom Jordan of the British Antarctic Survey; Robin Bell, Michael Wolovick and Nicholas Frearson of Lamont-Doherty; Kathryn Rose of University of Bristol; Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources; David Braaten of Kansas University; and Carol Finn of the U.S. Geological Survey.

Copies of the paper, “Freezing of ridges and water networks preserves the Gamburtsev Subglacial Mountains for millions of years,” are available from the authors.

Scientist Contact


Tim Creyts

845-365-8368

tcreyts@ldeo.columbia.edu

Fracture-controlled erodibility, great rock climbing

Tuolumne Meadows in Yosemite National Park is an iconic American landscape: It is a sub-alpine meadow surrounded by glacially sculpted granitic outcrops in the Sierra Nevada Mountains. Because of its accessibility and aesthetic appeal, it is a focal point for both vacationers (up to 4,200 people per day) and geoscientists. It also has historical significance: The idea for a Yosemite National Park came to John Muir and Robert Underwood Johnson over a campfire there.

As the largest sub-alpine meadow in the Sierra Nevada, Tuolumne Meadows is also a geomorphic anomaly: The presence of broad and open topography is commonly associated with bedrock erodibility. In contrast, the nearby vertical rock walls — including Cathedral Peak, Matthes Crest, and Lembert Dome — suggest bedrock durability. Despite these geomorphic differences, the entire region is underlain by the same lithology, the Cathedral Peak Granodiorite.

In this new study published in the November 2014 issue of GSA Today, authors Richard A. Becker, Basil Tikoff, Paul R. Riley, and Neal R. Iverson present evidence that this anomalous landscape is the result of preferential glacial erosion of highly fractured bedrock. In particular, tabular fracture clusters (TFCs) are common in the Cathedral Peak Granodiorite in the Tuolumne Meadows area. TFCs are dense networks of sub-parallel opening-mode fractures that are clustered into discrete, tabular (book-like) zones.

The authors conclude that Tuolumne Meadows resulted from ice flowing perpendicularly to high TFC concentrations. In contrast, ice flowing parallel to variable TFC concentrations formed the vertical rock walls. Thus, the exceptional rock climbing around Tuolumne Meadows is a direct result of fracture-controlled variations in erodibility — on the 10 meter to 100 meter scale — within a single lithology. This finding supports the contention that landscape evolution is strongly controlled by bedrock fracturing and that tectonic processes that result in fracturing may generally exert a fundamental and underappreciated role in geomorphology.

ARTICLE

Preexisting fractures and the formation of an iconic American landscape: Tuolumne Meadows, Yosemite National Park, USA

Richard A. Becker et al., Dept. of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA, USA, Pages 4–10; doi: 10.1130/GSATG203A.1.

Fracture-controlled erodibility, great rock climbing

Tuolumne Meadows in Yosemite National Park is an iconic American landscape: It is a sub-alpine meadow surrounded by glacially sculpted granitic outcrops in the Sierra Nevada Mountains. Because of its accessibility and aesthetic appeal, it is a focal point for both vacationers (up to 4,200 people per day) and geoscientists. It also has historical significance: The idea for a Yosemite National Park came to John Muir and Robert Underwood Johnson over a campfire there.

As the largest sub-alpine meadow in the Sierra Nevada, Tuolumne Meadows is also a geomorphic anomaly: The presence of broad and open topography is commonly associated with bedrock erodibility. In contrast, the nearby vertical rock walls — including Cathedral Peak, Matthes Crest, and Lembert Dome — suggest bedrock durability. Despite these geomorphic differences, the entire region is underlain by the same lithology, the Cathedral Peak Granodiorite.

In this new study published in the November 2014 issue of GSA Today, authors Richard A. Becker, Basil Tikoff, Paul R. Riley, and Neal R. Iverson present evidence that this anomalous landscape is the result of preferential glacial erosion of highly fractured bedrock. In particular, tabular fracture clusters (TFCs) are common in the Cathedral Peak Granodiorite in the Tuolumne Meadows area. TFCs are dense networks of sub-parallel opening-mode fractures that are clustered into discrete, tabular (book-like) zones.

The authors conclude that Tuolumne Meadows resulted from ice flowing perpendicularly to high TFC concentrations. In contrast, ice flowing parallel to variable TFC concentrations formed the vertical rock walls. Thus, the exceptional rock climbing around Tuolumne Meadows is a direct result of fracture-controlled variations in erodibility — on the 10 meter to 100 meter scale — within a single lithology. This finding supports the contention that landscape evolution is strongly controlled by bedrock fracturing and that tectonic processes that result in fracturing may generally exert a fundamental and underappreciated role in geomorphology.

ARTICLE

Preexisting fractures and the formation of an iconic American landscape: Tuolumne Meadows, Yosemite National Park, USA

Richard A. Becker et al., Dept. of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA, USA, Pages 4–10; doi: 10.1130/GSATG203A.1.