|
 Three
million years ago the Yukon River once flowed
south and east, instead of north and west as it does today. Argilite was in the sedimentary mountains to the north,
on the other side of the Tintina Trench. A paleo-Yukon
River had once carried
this rock south and had also formed series of high terraces.
Fifteen Miles Northwest of Dawson
City is where the
headwaters of this ancient river formed until sometime between 2.9 and 2.6
million years ago when the Cordilleran ice sheet blocked its flow to the
south and east, and the river changed its course.
The Yukon River eventually cut a new channel, flowing northwest to the Bering Sea. Its headwaters are now far to the south among
the glaciers of the coastal mountains in northwestern British Columbia.
Ice flowing north and west from the Cordilleran ice sheets joined with local
valley glaciers flowing south out of the Ogilvie Mountains. When the ice intermingled,
it filled the Tintina Trench.
Glacial ice was known to have blocked the northward flow of the Porcupine
River, sending it west toward the Yukon River.
The Laurentide ice also dammed the Peel River and
most of its tributaries to form glacial Lake
Hughes in the middle Peel Valley.
This lake drained into the Eagle River, which flowed on to another huge glacial lake
in the Old Crow Basin
area. Glacial Lake
Old Crow drained south and west, capturing the Porcupine River, and
eventually joining the Yukon River.
The most recent glaciation occurred towards the end
of the Pleistocene Epoch, and lasted from about 30,000 to 10,000 years ago. A
more extensive glaciation, called the Reid,
occurred about 200,000 years ago.
For additional information on the Geological History of The Yukon River: Alejandra
Duk Rodkin
|
