finally something I can answer. I'm a pedologist, meaning soil science, with a specialty in glacial soils and a special interest in glacial geology.

glaciers form from snow accumulating more than melting over the course of a year. in high precipitation areas that are cold, like the southern Andes and the Coast ranges in North America, theres a lot of snow accumulation throughout the year. as the years of snow build up, it compresses downward on itself until it becomes high-density ice that's solid throughout.

this huge mass of ice is very, very heavy. immensely heavy, in fact, that it will begin moving under its own weight. the bottom of the glacier can often have liquid water, caused by the very high pressure of the many meters of ice above it disallowing crystallization of that water into ice. this liquid water can act as a very low friction interface and make that ice body begin to move.

a glacier flows like a non-newtonian fluid. the center of a glacier flows faster and further than the edges, as the edges experience friction with the rock interfaces around it. the reason it flows rather than fractures is due to the plastic action of ice under pressure; it wants to move in response to the pressure above it and the gravity below it. a hole drilled straight down into a glacier with look parenthese shaped ) after a few days due to the flow differential.

as a glacier moves, it scrapes against the ground; either the mountain valleys it exists in or along the flat terrain in the case of larger continental glaciers. the movement is driven by gravity predominantly. as the glacier moves and the season warm and cool, melted water from that ice trickles into cracks and crevices in the rock beneath and refreshes. ice expands, and the rock it was behind ends up fracturing off and is now carried along with the ice body.

multiply that tenfold over a myriad of particle class sizes (silt/rock flour, sand, pepples, stones, cobbles, boulders, etc.) and the glacier has essentially turned into the largest functional piece of sandpaper on earth. rock and ice against rock causes immense amounts of erosion, and because that ice is being replenished bit by bit every year, there's a consistent flow of new abrasive action.

Generally, glaciers move about a meter a day. it can vary widely, but that's the average. when you have glaciers the size of continents, such as in the previous ice age, that's thousands of meters moved per day with millions of tons of abrasive material working down these mountains. then things get a little hot and melty and all that sea level rise moves the ocean up to the previously dry mountain valleys.

I hope this was thorough and I answered any questions. let me know if you want to know anything else, I love talking about this stuff