GLACIATION OF WRANGELL MOUNTAINS 39 



their upper end they appear as a broad plain into which the rivers 

 have cut considerable valleys. 



Extent of earlier glaciers. — In the Copper River Valley, as in all 

 the valleys of these mountains, the ice has formerly been much more 

 extensive than at present. The mountain just below the glacier was 

 once surrounded, and perhaps entirely covered by the ice. Men- 

 denhall advanced the opinion that the entire Copper River basin 

 was probably at one time occupied by ice. 



NABESNA VALLEY 



Nahesna Glacier. — The Nabesna Glacier is the great body of ice 

 which occupies the head of the valley of the same name. , It receives 

 the ice from a great portion of the north slopes of the Wrangell 

 Mountains, its feeding-ground extending from Mount Wrangell in 

 an east-southeast direction to Mount Regal, a distance of 43 miles. 

 The outlines of the glacier form a complicated dendritic pattern, as 

 about 40 cirques contribute their ice to it. At a point 20 miles 

 northeast of Mount Blackburn the ice is confined within a single 

 valley and forms a lobe a little more than two miles wide. Below 

 this point the glacier is of nearly uniform width, and receives but a 

 single important tributary. It moves from this point northeast and 

 then north to its terminus, a distance of 20 miles. The total length 

 of the glacier, from Mount Wrangell to its lower end is about 55 

 miles, and its area approximately 400 square miles. 



As viewed from the mountain-side, below Nikonda Creek (Fig. 2), 

 the main lobe of the glacier shows a fairly smooth surface and a 

 uniform slope as far as the eye can see. There are no cascades or 

 steep pitches on the surface, although the great branch which comes 

 in from the direction of Mount Regal descends steeply into the main 

 valley. The surface slope of the main lobe is about 50 feet per mile. 



Moraines. — ^A prominent medial moraine follows the center of 

 the glacier for many miles above its lower end. It is flanked closely 

 on either side for a part of its length by narrower parallel moraines. 

 The debris showing on the surface becomes more prominent to the 

 northward, and near the terminus the band-like ridges become so 

 frequent that at its north edge the ice is entirely covered by rock 

 debris, arid grades imperceptibly into the terminal moraine. 



