More than half of Iceland's numerous ice caps and glaciers exist near or directly over volcanoes, meaning that sometimes, fire and ice unite. For example, Mýrdalsjökull—Iceland's fourth largest ice cap located at the country's southern tip—covers the Katla volcano. Katla erupts about twice per century, with the last confirmed eruption in 1918.
"Katla has been 'due' for a while now," said Throstur Thorsteinsson of the University of Iceland. "There have been episodes of seismic activity, but still no big eruption." Signs of small glacial outburst floods, called jökulhlaups, could be an indication that small events are occurring below the ice cap, he said, "but nothing has been well confirmed."
Despite the volcano's current quiet period, the Mýrdalsjökull ice cap has undergone changes that show up in satellite imagery acquired 28 years apart. The Operational Land Imager on the Landsat 8 satellite acquired the top image on September 20, 2014. The Thematic Mapper (TM) sensor on the Landsat 5 satellite acquired the bottom image on September 16, 1986.
In the top image, the southwest-central part of Mýrdalsjökull has dimple-like features that are actually ice cauldrons—depressions caused by geothermal heat from the volcano below. Along the northern part of the ice cap, ablation has exposed brown bands of ash that were deposited by past eruptions. A few of the bands are likely from Hekla, a stratovolcano with relatively frequent eruption events. Across the middle of the ice cap, the dark surface can likely be attributed to more recent volcanic episodes.
Not all of the differences between the images, however, are associated with volcanic activity. In 1890, Iceland's glacier coverage peaked for the first time since the end of the Ice Age. Since the peak, however, rising temperatures led many of the region's glaciers to begin retreating. A cooler climate in the 1940s allowed some glaciers to briefly advance again, but since the 1990s, most of the monitored glaciers have been in retreat.
A notable example is Sólheimajökull, the long outlet glacier on the southwest side of the ice cap, which has been retreating as much as 50 meters (164 feet) per year. This particular glacier is easily accessible, as the parking lot is moved almost annually to accommodate tourists.
References and Further Reading
- Iceland Glaciological Society (2014) Glacier variations. Accessed November 12, 2014.
- Iceland Glaciological Society, About terminus variations. Accessed November 12, 2014.
- NASA Earth Observatory (2004, February 4) Iceland. Accessed November 12, 2014.
- USGS Science Features (2013, October 16) Surveying Ice and Fire: Mapping Iceland’s Glaciers and Subglacier Volcanic Calderas. Accessed November 12, 2014.
NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey. Caption by Kathryn Hansen.
- Instrument(s):
- Landsat 5 - TM
- Landsat 8 - OLI
