The Landsat mission, a joint effort between the National Aeronautics and Space Administration (NASA) and the U.S. Geological Survey (USGS), has been collecting data on Earth’s physical features via satellite since the 1970s. “The Landsat data record — humanity’s longest continuous record of our planet from space — has been an invaluable tool for scientists and decision-makers in many fields, from natural resources to agricultural productivity and climate change.”* Now, the Landsat mission has joined with Google Earth Engine to release historical images of Earth compiled into interactive time-lapse videos. The animations are free to the public and represent an archive of continuous global land observations that help paint a more complete vision of our shared planet.
One of the time-lapse Earth images featured is the massive retreat of Alaska’s Columbia Glacier. Columbia is a tidewater glacier, meaning it terminates in the sea. It crouches in the Chugach Mountains of southeastern Alaska, accumulating new snow that slowly compresses into ice. Over time the glacial mass of ice ‘flows’ downhill, eventually pressing into the waters of Prince William Sound. There pieces of the glacier break off, calving large chunks of ice into the ocean which form icebergs.
Over the last 20 years Columbia Glacier has been on the move: the terminus (end) of the glacier has retreated 16 kilometers (nearly 10 miles). While the glacial tongue was previously grounded on an underwater terminal moraine, a large underwater mass of stone deposited over time by the glacier’s movement, swift melting likely caused by heightened temperatures melted the ice away from the moraine. No longer bookended by solid shore and a solid underwater base, the length of glacier extending through water is more vulnerable to the ocean’s motion and more likely to swiftly lose length through calving. By roughly 2020, the glacier is expected to retreat 15 more kilometers (9.3 miles) until its mass rests solely on solid ground above sea level.
Columbia Glacier is not the only glacier on the move. According to the World Glacier Monitoring Service, many of the world’s glaciers will disappear by the end of the century. Of the 2,000 glaciers observed in Alaska, 99% are retreating. Glaciers die when the snow they accumulate is less than the water they lose due to melting which occurs during warmer months. Glacier mass balance is a measure of the net gain or loss of snow/ice over the course of each year, and the long-term balance of glaciers measured around the world shows that glaciers are losing mass.
A tidewater glacier like Columbia is not directly forced by climate; we cannot blame rising temperatures alone for its retreat. Complex mechanical rules (like the movement of currents and tides in the water below the glacier encouraging or discouraging calving) govern glacial advance and retreat. However, climate does appear to force rapid retreat because it triggers glacial thinning. At the present location of Columbia Glacier’s terminus, the ice is 1,600 feet thinner than it was 20 years ago. Glacial melting is significant to our society because it can cause sea level rise – threatening low lying coastal areas, and the populations who make their homes there. Disappearing glaciers also mean loss of steady water supplies for people who use glacier-fed rivers for reliable irrigation and drinking water. A study funded by the National Science Foundation projected 0.8 to 2 meters (about 3 to 6 feet) of sea level rise by 2100.
Knowing more about glaciers informs us about the way the Earth has changed in the past, and helps us map out and model how our planet will change in the future.
Laura Nielsen 2013
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- ‘New Public Application of Landsat Images Released’ National Aeronautics and Space Administration (NASA) http://www.nasa.gov/mission_pages/landsat/news/google-engine.html
- ‘Climate Change Indicators in the United States | Glaciers’ United States Environmental Protection Agency (EPA)
- ‘Glacier Movement Limits How Fast Sea Level Can Rise’ National Science Foundation (NSF)
- ‘Glaciers and Ice Sheets: Climate Change Impacts from the BBC Weather Centre’ British Broadcasting Corporation
- ‘Monte Carlo ice ﬂow modeling projects a new stable conﬁguration for Columbia Glacier, Alaska, c. 2020’ The Cryosphere
- ‘World of Change: Columbia Glacier, Alaska’ NASA Earth Observatory