|Gilkey glacier ogives, rimmed by medial moraines|
(58° 49.280'N 134° 21.481'W)
So what are these patterns on the surface of valley glaciers, and how do they form? Ogives are curved bands across the surface of a glacier, with convexity facing downhill. The bands are characterized by alternating dark and light groupings. The darker bands are devoid of ice-bubbles, are formed from melting & refreezing of ice in the summertime, and contain sediment accumulated at icefalls where open crevasses become a pit of deposition. The lighter bands are filled with snow & air bubbles from the non-summer months when precipitation is greatest, and a fresh snowpack acts as a layer of protection against weathering. Thus ogives are a seasonally created phenomenon. The crescent shape is due to velocity/friction differences between the lateral edges of a glacier where velocity is low & friction is high, and the center of a glacier where velocity is high & friction is low.
|glacial flow lines relative to surrounding bedrock|
|During summer, the glacier's surface melts and crevasses collect windblown particles, creating the dark band|
During winter, the surface is covered with snow, protecting it from weathering and creating the light band
|A valley glacier replete with ogive banding, stemming from near Mont Blanc in the Graian Alps|