Glaciation is the observation and study of massive geological processes dealing with the transformation, movement and effects of ice sheets or glaciers on the environment. Through many annual snowfalls accumulation exceeding that of the Earth's ability to melt it begins to happen, compaction then literally forces the air out from between the individual snowflakes. Layers upon layers of snow build-up and eventually turn into glacial ice as the snow recrystallizes, increasing its grain-size and eventually density increases to the point that it turns into a solid block of ice. It can be seen to give off a blue appearance due to its properties that absorb all other light colors except blue which it transmits instead.
The zone of accumulation is the point at which ablation or loss of snow and/or glacial ice is of little consequence. The zone of ablation is the point of the glacier that accumulation does not exceed ablation. Ablation can include the effects of wind, the Sun melting the snow, or evaporation. Thus the firn or equilibrium line as it is called is between the zone of accumulation and the zone of ablation. For example mountains have a zone of accumulation at high altitudes near the peak as temperatures do not allow full summertime melt. 
Weight as a Movement Factor
Once accumulation of enough glacial ice occurs giving it a thickness of about 66 feet its own weight forces it to move. This movement is accomplished by two factors; internal deformation and basal slip. The movement has lubrication through melt water at the bottom, due to internal deformation a hard plastic type of flow is achieved hurling the top of the glacier faster than the bottom. So fast that glaciers have been observed to move 1,000 feet in a year, usually 10 inches a day.
Most of the erosion and topography of North America was accomplished by glaciation which consequently caused high mountainous regions to form. There have been many periods of glacial ice build-up in Earth's past, the latest of which, according to current secular geological thinking, ended only 10,000 years ago. 
- Glaciation Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
- Glaciers and Glaciation Prof. Stephen A. Nelson. Tulane University.
- Glaciation Internet Geography
- Landforms of Glaciation Dr. Michael Pidwirny, University of British Columbia Okanagan
- What is Glaciation? What Causes it? NOAA Paleoclimatology