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Photo June 14, 2002 |
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Photo June 20, 2002 |
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Photo June 23, 2002 |
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Photo June 28, 2002 by National Park Service. |
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Photo July 3, 2002 by National Park Service. |
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Photo July 16, 2002 by US Forest Service. |
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Photo July 21, 2002 by US
Forest Service. |
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Photo August 10, 2002 by National Park Service. |
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Photo August 14, 2002 by National Park Service. |
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Photo August 15, 2002 by National Park Service. |
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Photo May 20, 2002 |
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.
Photographs made by the U.S. Geological Survey, the U.S. Forest Service, Yakutat
Range District, and the U.S. National Park Service, Yakutat Ranger Station. Click on any photo for enlargement
of the entire series (about 750 KB.
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