DYNAMICS OF THE CURRENT SURGE OF BERING GLACIER, ALASKA

Since reaching its Little Ice Age maximum position at the end of the 19^th century, Bering Glacier has surged at least six times. The first five surges occurred around 1900, around 1920, about 1938–40, 1957–67 (ice displacement in 1957–60 and 1965–67, separated by five years of stagnation), and 1993–95 (ice displacement from April 1993 to Sept. 1994 and May to Sept. 1995). A sixth surge is underway, having begun between May 28, 2008 and October 31, 2008.

Although little is known about the pre-1940 surges, the lsurges of the last half of the 20^th century have been studied using various remote sensing and ground-based methodologies. Each surge resulted in a rapid and sig­nificant terminus advance, accompanied by the transfer of a substantial volume of ice into the expanding terminus area. Both serve as excellent references against which to compare the present surge. Both of these surges had maxi­mum terminus displacements of approximately 10 km, with maximum ice displacement of about 13 km in the first surge. At Tashalich Arm, the westernmost part of the Bering Lobe, the glacier’s terminus retreated rapidly for more than a year prior to the 1993-1995 surge. It then advanced about 3 km.

With the current surge, until July 2009, surface displacements and fracturing were restricted to the glacier area from west of, to northeast of the Grindle Hills. By November 18, 2010, the surge fracturing reached Bering’s terminus. Between November 18, 2010 and January 8, 2011, maximum ice advance exceeded a kilometer. During the six day period between January 8 and 14, 2011, the terminus advanced a maximum of 125 m. Between February 2010 and July 2011, the latest surge has had maximum ice displacements that exceed 3.2 km and similar maximum terminus displacements. Through July 11, 2011, maximum velocities still approached 15 m per day.

At Tashalich Arm, as previously, the glacier’s terminus retreated rapidly before advancing. From February 19, 2010 until November 18, 2010, it retreated 650 m, an average of 2.4 m/day. Since the beginning of 2011, it has advanced more than 3 km. In the 26 days between March 18 and April 15, 2011 it advanced a maximum of 510 m, advancing an average of 19.6 m/day. While, in the 25 day period between April 15 and May 10, 2011 it advanced a maximum of 483 m, advancing an average of 19.3 m/day.