Researchers studying southern Alaska's Variegated Glacier believe they have found an explanation for why the 24-km-long ice mass, like other "surging" glaciers, periodically speeds up in its movement down valley. The surges, they propose, have to do with increases in water pressure beneath the glacier— the result of inhibited drainage at the base of the ice—that cause it to become more slippery and to flow faster.
The Variegated Glacier, located northwest of Juneau near the village of Yakutat, is small among surging glaciers, but it has been one of the most extensively studied in this century. Every 18–20 years, it begins to accelerate its flow rate. The last time such a surge began was in January 1982. The glacier reached a peak velocity of 9 m per day by summertime, then returned to near normal flow rates of 1–2 m per day by early fall. It started up again in November 1982, however, and by the next spring was speeding along at 54 m per day. Then, in early July 1983, the surge stopped abruptly when large amounts of water drained out of the glacier.