Though ice losses from Antarctica and Greenland make up a greater volume and seem more dramatic, the losses from glaciers on Arctic islands and middle-latitude mountain ranges have been quite significant. A NASA-led research team has recently developed a tool to help researchers investigate more than 30 years of ice velocity data from glaciers, a key variable for detecting how Earth’s ice (the cryosphere) is changing.
Understanding how mountain glaciers change, and how their flow will change in the future, is complicated by the fact that no two glaciers are exactly alike. Malaspina Glacier in southeastern Alaska, for example, may not be moving fast but the motion within the glacier is complex.
The animation above was composed from a sequence of false-color images acquired between 1986 and 2003 by the Landsat 5 and 7 satellites. The moving ice appears in shades of blue. Brown lines are moraines—areas where soil, rock, and other debris have been scraped up by the glacier and deposited at its sides. This debris often gets trapped as internal ribbons of rock where two glaciers merge and become one at a confluence.
Glaciers in this area of Alaska periodically surge, meaning they lurch forward quickly for one to several years. Surging can happen whether a glacier is advancing or retreating. Throughout the animation Malaspina appears to be retreating, and the increased meltwater and retreating ice is causing the lake (bottom-right) to expand. The zigzag pattern of the debris is caused by changes in velocity of the ice.
“Glaciers all have their own personalities, so a detailed study of a single glacier often doesn’t apply to a region as a whole,” said Alex Gardner, a glaciologist at NASA’s Jet Propulsion Laboratory. “To make progress on understanding sea level rise and adapting large-scale water resources, we need to know the fundamental characteristics of glacier flow that apply over entire regions.”
Gardner and colleagues from the University of Alaska and University of Colorado have been working on an initiative known as the Inter-mission Time Series of Land Ice Velocity and Elevation, or ITS_LIVE. The core of the project is the comparison of images acquired with Landsat satellites over the past four decades. The researchers developed a highly efficient “feature tracking algorithm” in which high-performance computers track where the information contained within pixels has moved in the time spanned by two images. This is done millions of times between image pairs, resulting in a data set with many millions of estimated ice velocities.
The second set of images above are examples of the flow velocity maps that Gardner and colleagues can derive from ITS_LIVE data sets. Comparing velocities in 1997 with those of 2017, you can see that velocity changes along Malaspina are more subtle than for the trio of glaciers to the west, which appear to be surging.
Data from ITS_LIVE have already revealed that high-mountain glaciers in Asia are flowing more slowly as they thin and melt. As ice thins, there is less gravitational pull tugging it down the mountainsides. “That might sound intuitive, but it is not necessarily so from glaciological point of view,” Gardner said. “Retreating glaciers have more meltwater reaching their beds; this water can act as a lubricant and cause it to speed up. But our data show that is not case in high mountain Asia.”
Gardner suspects the same will hold true for Alaskan glaciers, but more analysis needs to be done. Can scientists establish a relationship between slowing and thinning ice that holds true for mountain glaciers globally?
ITS_LIVE data were made publicly available through JPL and the National Snow and Ice Data Center web sites in the summer of 2019. “There is so much data, and we can’t explore it all on our own,” Gardner said. “Our hope is that by making the data easily accessible, researchers can access the tools they need to better understand glacier flow around the world.”