Land ice velocity

Over the past 25 years, satellite observations have revolutionised our understanding of how fast ice flows, and how quickly changes in ice speed can occur. Historically, the expression ‘changing at a glacial pace’ would be used to conjure up an image of something changing extremely slowly, over decades or centuries. However, satellite observations from European missions such as ERS-1 and 2 show that this is not true, and that many glaciers flow extremely quickly at speeds of more than 1 kilometre a year.

One of the fastest flowing glaciers in the world is Jakobshavn Isbrae, on the West Greenland ice sheet. Satellite observations have shown that this colossal ice stream flows at up to 10 kilometres a year during the winter, nearly doubling in speed in the summer as warmer air temperatures and increased melt water lubricate the ice.

Giant icebergs in the Jakobshavn Isbrae fjord.  Credit:Hogg/CPOM

Giant icebergs in the Jakobshavn Isbrae fjord. Credit:Hogg/CPOM

At CPOM we also use satellite datasets to measure long term changes in ice speed. For example, although little seasonal change has been observed, during the last 25 years ice velocity increases of over 42% have been measured on Pine Island Glacier on the West Antarctic Ice Sheet. In Antarctica, areas of ice velocity speed up are dynamically unstable and comprise the largest component of ice sheet sea level rise contribution.

Despite a long term trend for increasing ice velocity in many regions such as the Amundsen Sea Sector and the Antarctic Peninsula, speed up has not been constant through time and multiple years with no significant change have also been observed. However, present day measurements of ice velocity provide an independent means of measuring ice mass loss from the most rapidly changing ice sheet regions.

Ice velocity map of Pine Island Glacier from Sentinel-1.  Credit:Hogg/CPOM

Ice velocity map of Pine Island Glacier from Sentinel-1. Credit:Hogg/CPOM

The CPOM Near Real Time (NRT) ice velocity data portal provides up to date measurements of the ice speed of major ice streams in Antarctica and Greenland. The ice velocity maps are produced by tracking moving features in synthetic aperture radar data acquired by ESA’s Sentinel-1 satellite. This data is made freely available to the scientific community and allows us to rapidly monitor changes in ice speed, such as the seasonal speed up.