Wednesday – 08 July 2009
Trimlines are the “bathtub rings” left by glaciers retreating. For many glaciers, the maximum observed thickness relates to the Little Ice Age, circa year 1865.
The trimlines are often visible as horizontal changes in rock color or arrangement. Areas of distinct changes in vegetation (lichens, mosses) typically demarcate trim lines.
At Petermann Glacier, trimlines were identified as under-cut gravel [talus aprons from rockfall] roughly 30 meters above the current ice surface level. Given that the lower Petermann Glacier is floating, a 30 meter change in freeboard indicates a ~270 meter [885 foot] change in thickness since circa 1865.
Jason E. Box
Byrd Polar Research Center
guest scientist on Greenpeace ship Arctic Sunrise