Glacial sediment
Glaciers are made up of more than just ice and snow. They contain water 
, rocks 
and sediments . This can make the ice look very dirty.
Meltwater at the bottom of the glacier can refreeze onto bedrock. As the glacier advances, bits of bedrock are pulled from the surface and carried with the ice. Loose rocks and debris are also incorporated into the ice at the bottom of the glacier.
Rock and debris falling from mountains lands on the glacier surface. This material is carried along like it was on a giant conveyer belt.
During the summer, ice and snow begin to melt. The meltwater flows in streams on top of the glacier. Meltwater flows to the bottom of the glacier through cracks and vertical drainage shafts called moulins.
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