Hubbard Glacier, Alaska
Hubbard Glacier is the largest tidewater glacier on the North American continent. It has been thickening and advancing toward the Gulf of Alaska since it was first mapped by the International Boundary Commission in 1895 (Davidson, 1903). This is in stark contrast with most glaciers, which have thinned and retreated during the last century. This atypical behavior is an important example of the calving glacier cycle in which glacier advance and retreat is controlled more by the mechanics of terminus calving than by climate fluctuations. If Hubbard Glacier continues to advance, it will close the seaward entrance of Russell Fiord and create the largest glacier-dammed lake on the North American continent in historic times as it has done in 1986 and 2002. The Slow Advance of a Calving Glacier: Hubbard Glacier, AK is a summary of growth and advance measurements of Hubbard Glacier as presented at the International Glaciological Society symposium on Fast Glacier Flow held in Yakutat, Alaska, June 10-14, 2002. Hubbard Glacier remains an ongoing study of calving glacier dynamics for the scientific community.
Hubbard Glacier creates dam on Russell Fiord
In 2002 the advancing terminus of Hubbard Glacier created a glacier lake dam which turned Russell Fiord in to a lake for about two and a half months. Rising water in the newly formed lake altered local hydrology and was a threat to nearby communities. During the two and a half months that the channel was dammed, Russell Lake rose 61 feet. In 1986 a similar scenario resulted when the glacier caused dam raised the lake level 84 feet over the course of five months. Erosion from water eventually carved a new outlet channel and restored the fiord to its previous elevation in both cases. In 2002 the rising level of Russell Lake was recorded by a stage recorder installed on June 23, 2002 at Marble Point in Russell Lake (about 4.5 miles south east from the near-closure site). Output from USGS station #15130000 shows the 2002 lake rise and outburst. Photos of Hubbard Glacier advancing show the advancement of the glacier and eventual closure of the seaward entrance to Russell Fiord.
These photographs show an eastward-looking view of a small section of the Hubbard Glacier terminus and the evolution of the "squeeze-push" moraine in front of Gilbert Point that blocked the tidal exchange between Disenchantment Bay (bottom of photos) and Russell Fiord (top of photos), creating Russell Lake which rose to 18.6 meters (61 feet) above sea level over 2½ months before it finally outburst on August 14, 2002 creating the second largest glacial lake outburst worldwide in historical times.
Had the blockage held, Russell Lake would have eventually overflowed into the Situk River when its level reached about 40 meters (130 feet) above sea level.
In late May or early June, 2002, Hubbard Glacier pushed a moraine plug across the seaward entrance to Russell Fiord and began to restrict the tidal exchange between Disenchantment Bay and Russell Fiord. By early June, as the moraine continued to grow, the tidal exchange was blocked. From then on, a delicate balancing act was played out between the slow advance and growth of the moraine dam from glacier movement and its erosion by water overflowing the dam. Early in the blockage, small amounts of water leaked from Russell Lake over the moraine dam into Disenchantment Bay. Despite this small leak, the dam held and lake level rose at an average rate of more than 0.24 meters per day (0.8 feet per day) because of the large amount of runoff and glacial melt in the basin. By late July, the dam completely sealed off the lake.
August 10 photographs showed that the water was again flowing over the dam. On August 11 and 12 heavy rains fell in the area (nearly 4 inches alone on Aug. 12). This may have tipped the balance in favor of the dam's erosion though other factors such as possible slow down of the glacier's movement or reduced growth of the moraine may also have played a role.
At about 3 a.m., Aug. 14, real-time USGS water gage data revealed that the water level in the Lake had peaked at about 18.6 meters (61 feet) above sea level and had begun to drop.
The outflow increased throughout the day due to rapid erosion of the lake outlet channel. Water discharge peaked at about midnight on Aug. 14 with a one-hour average rate of 54,000 cubic meters per second (1.9 million cubic feet per second) at a lake level of 11 meters (36 feet), which meant a water-level drop of nearly 0.9 meter per hour (3 feet/hour). By 10 a.m. on Aug. 15, the lake level had dropped below the USGS water gage sensor level of 4.9 meters (16 feet) above sea level, with the discharge still at about 14,000 cubic meters per second (500,000 cubic feet per second). The lake level returned to its more normal sea level by early afternoon on Aug. 15, ending the outburst event about 36 hours after it started, and returning the lake to its former status as a fiord. The recent episode carved out a new 200 meter-wide (600 feet) entrance into Russell Fiord and the entire moraine dam is now gone. A total of 3.86 cubic kilometers of stored water (0.9 cubic miles) were discharged in the outburst event.
A one-hour peak discharge of 54,000 cubic meters of water per second (1.9 million cubic feet per second) is the second largest measured glacial lake outburst worldwide in historical times, exceeded only by the 1986 outburst from Russell Lake, which was about 105,000 cubic meters per second (3.7 million cubic feet per second). In comparison, the August 14 peak discharge was about 30 percent greater than the peak historic flow on the Mississippi River at Baton Rouge, La.
Photos courtesy of the U.S. Geological Survey, the U.S. Forest Service Yakutat Range District, and the U.S. National Park Service Yakutat Ranger Station.