describe the terrain of the Yukon

From the text:

"...there seemed to be an indescribable darkness over the face of things. That was because the sun was absent from the sky."

"The Yukon lay a mile wide and hidden under three feet of ice. On top of this ice were as many feet of snow. It was all pure white. North and south, as far as his eye could see, it was unbroken white. The one thing that relieved the whiteness was a thin dark line that curved from the pine-covered island to the south."