THE YUKON DELTA
Delta ID # 41.
Contributed by Huh et al, 2004.
Yukon River Delta, USA, North America
LOCATION LAT. 62°51’N, LONG. 164°35’W
LANDMASS DRAINED NORTH AMERICA(USA).
BASIN OF DEPOSITION BERING SEA
CLIMATE SUB ARCTIC(Dcf),
AIR TEMP RANGE–18°C TO 9°C,
TIDAL AMPLITUDE1.2 M
DISCHARGE WATER51000 M3/S,
DRAINAGE BASIN AREA9.32X105 KM2
ID 7079016000027650, PATH 79 ROW 16
IMAGE ACQUIRED OCTOBER 2, 2000
Contributed by Professor James Coleman, LSU. From: Coleman and Huh, 2004.
The Yukon River rises in Precambrian, Paleozoic, and Carboniferous sediments of Alaska and Canada. The drainage basin covers some 829,700 sq km and the river flows some 3,219 km west and empties into the Bering Sea. The average basin elevation is 740 m, with a maximum of 2,797 m and a minimum of 50 m. The basin is frozen for nearly one-half of the year, and little or no flow is experienced in the channel. Average annual rainfall is 502 mm, with a maximum of 2,041 mm and a minimum of 77 mm. Drainage density of the tributaries is quite dense (Figure 88).
The alluvial valley of the river is well defined and controlled primarily by the structural grain of the region. Although some meandering is displayed by the main channel within the alluvial valley, it is braided most of its distance. The average annual discharge is 6,115 cu m/sec with a maximum of 12,988 cu m/sec and a minimum of 895 cu m/sec. Discharge peaks in May/June, following thawing in the basin and declines over the next few months until November when the basin again freezes. During the winter months, discharge averages less than a 1,000 cu m/sec.
The delta has an area of 5,280 sq km and protrudes into the Bearing Sea. Much of the delta plain is inactive and active deposition takes place mostly at the three active river mouths (Plate 40). Much of the interdistributary region consists of small lakes and contains channel scars of former active distributaries. Much of the delta plain is covered by these small lakes. Pleistocene terrace remnants (light colored areas in Plate 40) are found just north and south of the active delta. Along the shoreline are ice-pushed beach ridges that contain a large volume of woody debris in the form of large logs. For some 180 days, the entire delta plain is frozen solid and permafrost occurs almost throughout the delta.
Since there is very little agricultural or industrial use in this remote delta only changes in open water were calculated. In addition, this was one of the few arctic deltas in which geo-registered images were available for analysis and since no industrial use is present in the delta plain, any changes in open water would be solely caused by natural processes. The delta area analyzed is shown in Plate 40A and the delta plain area is 4,747 sq km (1,173,009 acres). Satellite images were obtained for 1985 and 2001 and comparisons were determined by analysis in ArcView. The 1985 image contained 299,852 acres of open water or roughly 26 percent of the delta plain consists of lakes and open water channels. Some seven years later, in 1992, the open water in the delta plain was calculated to be 649,565 acres or an increase in new open water of 349,713 acres or an increase of nearly 54 percent of new open water (Plate 40A). Note that a small percentage of this loss resulted from shoreline erosion (Plate 40A. During this same interval of time, some 78,176 acres of new wetlands were formed at the mouths of the rivers and by infilling of some of the open water lakes. Thus in this seven year period, there was a net loss of delta plain wetlands of 271,537 acres or the annual rate of wetland loss is 38,791 acres/year. As there is virtually no influence by man in the delta plain, this significant loss is solely the result of natural processes. Since a high percentage of the loss is along the shoreline of the lakes that exist on the delta plain and in the creation of numerous small new lakes, it is interesting to speculate that the global warming trend might be the most significant contribution to this wetland loss.