Depending on when it was formed, the size and speed it is moving it could be either an Avalanche or Glacier.
If it is an incredibly old, slow moving, large, ice mass it is likely a Glacier; however if it is a quickly moving, small (relatively), ice mass it is an Avalanche.
Known as an ice floe
icebergs
glacier
A glacier (slowly) An avalanche (fast)
a mass of snow, ice, and rocks falling rapidly down a mountain side
Cap Polar ice cap Mountain ice cap
An Alpine Glacier.
Known as an ice floe
glacier
icebergs
a mass of snow, ice, and rocks falling rapidly down a mountain side
A glacier (slowly) An avalanche (fast)
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AVALANCHE!
It's an avalanche.
a mass of snow, ice, and rocks falling rapidly down a mountain side
The answer to the question is a glacier is a mass of ice.