The title explains it all. Do objects suspended in ice sink over time? You may remember the story of World War 2 planes that were found 260 ft under the ice which would be anachronistic with seasonal ice layering alone. I'm trying to establish other possible mechanisms. I know that ice flows up and down in glaciers, but will an object actually sink in ice over time?
Also, in what way would they sink? Would heavier parts sink faster than the lighter. Does buoyancy play a role.
If the article you are referring to is this one, then the planes didn't sink into the ice but were buried by blizzards.
Ice does exhibit ductile flow at stress of around 1 to 10MPa, but this pressure is equivalent to around 100 to 1000 tons per square metre and this is far above the stresses normally produced by objects resting on ice. Glaciers flow because the stress is concentrated at the interface between the ice and the rock, and this can produce the enormous stresses required.
So the answer to your question is that no, objects don't sink into ice under their own weight (unless your object is made from neutronium). However freeze thaw cycles can give this impression.
I say yes, things can sink in ice. Here's why: there's a thin layer of liquid on the surface of ice that is why ice is slippery. When you put a body on the surface of ice, it'll keep displacing the layer of liquid, getting deeper and deeper, and will eventually sink completely,
I think that just measuring the number of feet of ice above the plane wouldn't be a very accurate way to determine whether the planes had sunk or not, which they likely did. What would also need to be measured would be the thickness of the ice below the planes at the time of landing and the time of recovery. So far, I haven't found any data on that. But, hypothetically, if the depth of the glacier were 3000 feet when the planes landed and the depth below the planes was only 2800 feet when they were recovered, then one could suspect that the planes did actually sink, but with the added accumulation of 60 feet of ice for a total depth of 3060 feet.
And since a significant amount of glacial melting occurs underneath glaciers, which can also affect the rate of of glacial travel, the entire glacier itself is likely sinking down, wearing away and melting from the bottom as more snow and ice accumulate on top. So that would have to be factored in too. Several feet of snow can also compress down to just a few inches of ice with added weight on top. So there are many variables at play here.
What would be cool would be to use several metal objects of substantial mass with GPS devices inside and place them in a vertical line at various depths in the ice, including both extremes--one on the surface of the ice sheet and one on the bedrock below--for a few seasons to see how far they move vertically and laterally. The bedrock itself also moves according the weight on top, including variations in atmospheric pressure. Those data would paint a more vivid picture of what happens to non-ice objects on top of glaciers over time.
