Definition

• A glacier forms as an immense body of ice very slowly in terms of human time. The ambient temperature in the area must be below the freezing point of water for a glacier to even maintain its existing size. As a result, most glaciers are above snowlines where solid water in the form of snow or ice can exist permanently rather than seasonally. As ice builds on ice, it becomes more compact in structure, forming larger and larger masses. These masses then move forward as the glacier takes on density.
  
  

Physical Effects

• A glacier's movement occurs very slowly, but in doing so the immense weight and pressure act as a grinder on rock and earth underneath. Flora is smashed flat and then killed as sunlight is cut off. Earth compacts and rock is sheared to smooth surfaces. The process doesn't work in one direction only; glaciers expand and contract, causing a grating effect on the land underneath. Further, glaciers move loose mass, grinding rock against rock as loose boulders are pushed along.
  
  

Method of Change

• Glaciers move in two ways: internal flow and basal sliding. Internal flow happens as the more brittle upper surface of a glacier cracks and breaks. Gravity causes the parts to fall forward into gaps or empty areas. Basal sliding occurs as the underpart of the glacier melts, keeping the ground underneath wet. This moisture softens below material and causes it to warp further.
  
  

Matter Migration

• Being solid ice, glaciers retain significant density and mass. With enough pressure, glaciers can dislodge boulders and parts of rock that would otherwise take significant force to budge. These items are pick up and carried by ice until a glacier stops moving forward and recedes. In doing so, the glacier can move large masses miles away from their origination point, reshaping lands elsewhere with new materials. Earth and smaller material also move and redeposit in new locations, resulting in what is termed "glacial drift."
  
  

Ocean Impacts

• As glaciers break off into oceans, the icebergs add to the ocean's mass. Normally, regular-sized icebergs do not make a significant dent in the ocean's overall density. However, when large shelves and sections of arctic glaciers break off, it can be a different story. Such changes have just recently been occurring in the polar caps with global warming. The effects on the Earth's oceans are unknown as of 2011; however, it is estimated that such additions in large amount could cause sea levels to rise, resulting in storm pattern changes and coastal flooding.