Re: What causes blue ice when its thickness does not exceed 200 feet?

Hi Cindy,

The earlier post and answer you refer to discussed the formation of glacier 
ice from snow. The same process takes place in ice caps in Greenland and 
Antartica, where the weight of accumulated snow squeezes the air out of the 
ice and makes it clear. When we look through a large piece of it (tens to 
hundreds of metres optical path length), it looks blue due to atomic 
absorption effects.

Ice can also look blue due to it reflecting the blue of the sky, but if you 
have seen glaciers or large icebergs you will be aware that it is a 
different blue - an eerie electric blue with a hint of green, so that isn't 
the cause of most of the blue, but it helps.

The question you seem to be asking is "If the ice needs to be squeezed by 
200 ft of snowpack before it goes clear/blue, how can we see bits of it 
exposed?"

The answer is simple. Glaciers and icecaps flow downhill and outwards away 
from their sources to areas where they melt, or break up into icebergs. We 
see exposed faces of the interior ice in icebergs, or areas where the 
overlying snow has melted away.

Also, ice forms in other circumstances. Thick multi-year sea ice is also 
blue, since it formed as solid ice with much less trapped air and the 
multi-year freeze-thaw cycle purges it of what little air it has. Polar 
Bears often walk beside and on blue-tinted sea ice.

Nick