Today’s story is the answer to the riddle of March 2024.
Scientists believe about 1 percent of Earth’s 200,000 glaciers are growing. These types of glaciers go through long periods of quiescence and slow ice flow, when excess ice accumulates at higher elevations, followed by periods when the ice flows forward with bursts, in some cases Flows 10 to 100 times faster than normal for periods of months to years.
Surge typically begins when excess meltwater accumulates at the base of the glacier, smoothing the contact area between the glacier and the ground and making it easier for the glacier to move. Although it varies by glacier, surges typically last less than two years and occur every 15 to 100 years.
Changes during surges can be dramatic, especially when glaciers flow into the sea. When this happens, additional water intrudes across the land-ice interface, causing the glacier to move even faster, sometimes by tens of meters per day. When the tides subside and sea-terminated glaciers enter the inactive part of the cycle, waves and tides can push the glaciers back as quickly – or even more quickly – than they had advanced.
This is what has happened in recent decades to Sortebru, a large surge-type glacier in eastern Greenland that flows into a fjord leading to the North Atlantic Ocean. The pair of Landsat images above show how much the glacier has changed in nearly four decades.
The image at left, obtained by the Thematic Mapper on Landsat 5, shows Sortebru and its many tributary glaciers, six years before the surge period in 1986. The main trunk of the glacier and its tributaries flow together in one stream, forming a distinctive shape resembling an icy pie symbol. The image on the right, from OLI (Operational Land Imager) on Landsat 8, shows the same area in 2023, after the tributaries have narrowed their front and retreated, taking a large “bite” from the P.
Note the long brown lines running along the length of Sortebru, which means “black glacier” in Danish. These are lateral and central moraines – mounds of rock and sediment at the edges of the glacier or where tributaries meet. Generally, medial moraine lines follow the path of the glacier; But emerging glaciers flow so fast intermittently that they can create striking bends and kinks called looped, or sometimes raised, moraines.
“Over time, these moraines were pulled under the glacier and formed the teardrop-shaped moraine loops seen in the image,” said glaciologist Hester Giskoot of the University of Lethbridge. Another indication that it was a surge-type glacier, he added, is the cratered “Swiss cheese” surface visible in the 1986 image, which may indicate the filling and drainage of small lakes or glaciers on the surface. There is a cratered pattern formed due to the closing of cracks.
The main branch of Sortebra proceeded between 1992 and 1995. During this period, the glacier front advanced 10 kilometers (6 mi), and its flow speed exceeded a maximum of 20 meters (65 ft) per day. But this progress proved short-lived. When the surge ended, the main trunk began to lose mass and the glacier front rapidly retreated. “Over the past 20 years, Sortebru has lost about 40 square kilometers of ice,” Giskoot said.
Sortebru is part of a wider group of about 130 rising glaciers in this part of eastern Greenland. Glaciologist Harold Lovell said, “Although climate change is having a major impact on the rate of retreat of glaciers in this region, it is completely normal for surge-type glaciers to retreat during their calm phase as they prepare for the next surge.” Let’s make ice for it.” At the University of Portsmouth. “But surge-type glaciers only occur within certain climate parameters, and we think the magnitude of retreat is likely to be increased by climate change.”
A 2023 analysis by Lovell and colleagues reviewed decades of Landsat images and counted a total of 274 growing glaciers in Greenland. While the number of glaciers growing in this part of East Greenland remained roughly the same between 1985 and 2019, the analysis showed that growing activity among glaciers in West Greenland has decreased, possibly due to rising air temperatures in summer.
“In West Greenland, we’re seeing that some of the smaller land-end glaciers that we know grew in the past are unable to grow again,” Lovell said, “possibly because they are too cold in the warmer climate.” Have become more thin.
Do you want more pie in your life? Check out NASA’s Pi Day challenge.
NASA Earth Observatory images by Wanmei Liang, using U.S. Geological Survey Landsat data. Story by Adam Voiland.
