Winone is quite right. Fissures are a consequence of differential velocity through the ice column that is a result of friction with the substrate or obstacles. With the increase in pressure at depth, ice becomes plastic. At the contact area, friction and pressure contribute to the formation of a thin layer of liquid water below a glacier. Additionally, geothermal heat can account for liquid water below a glacier.
Thanks Stormer....and thanks for putting it better than I could ever!...lol
2. fissures and cracks are created in the brittle upper surface of glaciers as they pass over/around subsurface features, they do form a passage way for surface melt water to reach the base of glacers.
I forgot differential rates of movement account for them as well, however these are commonly associated with subsurface features as well but they are not a melt water feature as claimed by winnie.
Melt water sources - pressure and or geothermal - not friction. Water will reduce friction but is not caused by it that is the point of it all.