Decades of space data used to reconstruct glacial surge

Between 1992 and 2007, Canada’s Mittie Glacier experienced a surge event in which its flow rapidly accelerated and its front edge advanced. Until recently the mechanisms behind this surge remained poorly understood, but scientists have now delivered fresh insight into the event using a decades-long timeseries of satellite observations.

The research – published in the Annals of Glaciology – drew on data from a succession of missions, including the European Space Agency’s trailblazing European Remote Sensing satellites (ERS-1 and ERS-2), which are cornerstone ESA Heritage Missions.

Historic glacial surge

One of the largest glaciers on Ellesmere Island in the Canadian Arctic, Mittie Glacier flows north from the Manson Icefield, draining into Smith Bay off the island’s southeast coast.

Luke Copland, Professor at the University of Ottawa and study lead author, said: “It has long been known that Mittie and other glaciers on Ellesmere are prone to surges – as shown by the dramatic surge reported from 1992 to 2007 – but understanding of the details of such events has previously been limited due to a lack of long-term analyses covering the entire surge cycle. Our research aimed to address this knowledge gap.”

The research team pieced together a timeseries spanning from 1972 to 2018 that was used to track key changes to Mittie Glacier.

In addition to Synthetic Aperture Radar (SAR) data from the ERS satellites, the timeseries included further SAR data from the Japanese Earth Resources Satellite (JERS-1) and the Advanced Land Observing Satellite (ALOS-1), as well as optical imagery from several Landsat missions. JERS-1, ALOS-1 and the Landsat missions used in the study are also part of ESA’s Heritage Missions programme.

What is a Heritage Mission?

Heritage Missions are Earth observation satellites that have completed operations and whose data are safely archived at ESA. They include ESA satellites, such as the ERS satellites and Envisat, as well as some missions that were operated by international partners. As part of the Heritage Space programme, ESA preserves, continuously improves, and disseminates data from these missions to the scientific community, enabling cutting-edge research into the long-term changes impacting the planet.

Back to the beginning

Luke continued: “Data from ERS-1 and JERS-1 were crucial for our reconstruction of the timing and extent of the surge's initiation. Increased ice flow causes the formation of new fissures and crevasses on the glacier surface. In SAR imagery, we can identify these changes in roughness by identifying brighter areas of imagery with increased backscatter.”

ERS-1 imagery acquired in 1994 shows that the glacier had a relatively smooth surface at this time. However, in early 1995, JERS-1 revealed the first signs of the surge by detecting increased backscatter due to new crevassing over the lowermost 5 km of the glacier. A year later, ERS showed that this surface roughness and crevassing had extended a further 5 km up the glacier.

Over the next decade, SAR observations and optical imagery indicated that the surge event grew to impact the lower 30 km of the glacier. These data revealed a huge 3 km-wide crevasse that opened in 1997 before gradually starting to close after 2007.

The combination of SAR and optical data was also used to track the position of the glacier’s front edge, known as the terminus, as well as glacier flow speeds. The terminus advanced by around 7.4 km between 1994 and 1999, with flow velocity increasing from 100 metres per year in 1994 to a maximum of 4,800 metres per year in 1996, the highest ever reported for a glacier in the Canadian Arctic.

Flow rates started to slow in the late 2000s, marking the beginning of the end of the surge.

Uncovering the cause

Having completed a detailed analysis of the surge, the scientists were able to propose a potential event that triggered it.

The team reported that several factors – including the initiation at the terminus, the spread of the surge upstream, and a large part of the glacier being grounded below sea level – strongly suggest that the surge was triggered by the terminus becoming buoyant and lifting off the sea floor.

Luke concluded: “Historical data from Heritage missions were invaluable in helping us to reconstruct the surge of Mittie Glacier. In particular, SAR data from ERS and JERS-1 enabled us to observe the onset of the event, which occurred in winter when there was little daylight and heavy snow cover.”