Kobuk

Course

It is commonly assumed that the Kobuk River issues from Walker Lake, but the headwaters of the river are actually to the east of Walker Lake in the Endicott Mountains within Gates of the Arctic National Park and Preserve, just north of the Arctic Circle. The river flows briefly south, descending from the mountains through two spectacular canyons (Upper and Lower Kobuk Canyon), then generally west along the southern flank of the western Brooks Range in a broad wetlands valley. In the valley it passes a connected community of inland native villages, including Kobuk, Shungnak, and Ambler, where it receives the Ambler River.

Surface water and hydrology

The Kobuk River is ice-covered for an average of six months of the year and in general, late October to late May is a period of relatively low flow. Annually, the hydrograph reflects two flood peaks: the first is associated with spring break-up and the second, a lesser peak, is associated with late summer precipitation. As the snowpack begins to melt toward the end of May, flow in the Kobuk River increases with most of the runoff occurring during June. Flow during the summer (July through September) is dominated by variable precipitation events.

Most of the major tributaries of the Kobuk River flow from the north, draining the mountains in the southern Brooks Range.

History

The Kobuk's Inuit name, Kuuvak, means "great river". It was first transcribed by John Simpson in 1850 as "Kowuk". The river was explored by Lt. G. M. Stoney, USN, in 1883–1886, who wrote the name "Ku-buck" but proposed that it be called "Putnam" in honor of Master Charles Putnam, USN, an officer of the Rodgers, who was carried to sea on the ice and lost in 1882. Lt. J. C. Cantwell, USRCS, also explored the river in 1884 and 1885 and spelled the name "Koowak" on his map and "Kowak" in his text. Ivan Petroff spelled the river name "Kooak" in 1880, and W. H. Dall spelled it "Kowk" in 1870. Lt. H. T. Allen, US Army, transcribed the Koyukon Indian name for the river in 1885, which he spelled "Holooatna" and "Holoatna."

Geology and soils

Permafrost regions along the Kobuk River are shown in the accompanying figure.

The Kobuk River is a periglacial river, fed by a remnant glacial lake (Walker Lake) and mountain snowmelt in the Brooks Range. It cuts a channel through a landscape otherwise dominated by permafrost. The Kobuk's current form and structure is a direct result of several stages of erosion and channel formation following the last glacial retreat.

As the glacier first retreated and melted, large amounts of highly erodible, fine-grained sediment dropped out in relatively high mountain valleys. The availability of this fine-grained, loose sediment combined with a high gradient to turn a newly forming Kobuk River into a fast-working sediment transport system.