That's a veeeeerrrrrrrrry elaborate answer.Veeeeeerrrrrrrrry sloooowwwwllllllyyyy...Explain how glaciers move.
[spoiler]I believe that you are looking for this, though: Glaciers flow downhill because of gravity and the internal deformation of the ice.[/spoiler]
If I'm right, someone can go in my place. I will be at Summer Camp Sunday to Saturday.
I'm gonna guess: the ice melts, which makes water. The water wets the surface the glacier is on, causing it to slip and slide at a pretty slow pace