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For various magical reasons, a particular area of my world spent roughly 100 years under an average of 10m of ice (3 - 15m of compacted snow). Unlike a conventional glacier, this was stationary. Snow fell effectively uniformly (or close enough for this question) and just did not melt. The average temperature (year round) hovered slightly below freezing. Roughly 100 years later, the magical source was removed and a reverse effect caused it to melt off. This question doesn't care about the effects of the melting--that's already handled.

Before this happened, the area had been inhabited by a group of people who built in (reinforced) stone and other cold-weather-adapted styles, with buildings mostly 1-2 stories but occasionally as much as 4. Due to magic, their buildings had roughly equivalent physical strength/durability to modern reinforced concrete, but with much less use of glass and steel. For the purposes of the question, you can consider them to be effectively concrete. The people themselves left the area as the endless winter substantially set in, with time to do what they could with tools at hand to "winterize" the structures.

How much damage would have those structures and their contents have sustained? Total destruction (collapse)? Destruction of fragile materials (glass windows, contents susceptible to water damage, etc) but generally intact? Something else entirely?

I expect that underground things like cellars and underground vaults would be basically fine as long as they weren't exposed to the cold and moisture, while there wouldn't be tons left of the contents of surface buildings unless those were relatively durable (so statues maybe, books no). I'm less comfortable about making predictions about the structures themselves.

Notes: The magic used to reinforce the materials can be treated as simply a durability enhancement to reach roughly modern standards. Natural weathering other than the ice itself would be nice to know, but is secondary. Weathering from other sources (such as creatures) can be ignored.

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  • $\begingroup$ "The average temperature (year round) hovered slightly below freezing" - this means that the area goes through many, many freeze/thaw cycles. Not good for buildings. $\endgroup$
    – Alexander
    Apr 6, 2022 at 0:45
  • $\begingroup$ It is really hard to make ice be stationary. It is heavy and gravity moves it. Even mountains sag under gravity. Once it starts moving, you have to deal with the erosive effect of both the ice and anything in the ice (such as rocks that have been picked up). $\endgroup$
    – David R
    Apr 6, 2022 at 14:32
  • $\begingroup$ @DavidR In this case due to topography (the area being effectively a bowl, enclosed on all sides), I'm considering those effects as being second (or further) order and wanted to ignore them to focus on the "what about the ice just sitting there" first-order effects. $\endgroup$ Apr 6, 2022 at 22:54

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How much does 10m of ice weigh?

1 cubic meter of ice = 900 kg

An ice cube 10m high = 10 x 900 = 9000 kg/square meter load on the roof.

Googling around I found that Lufthansa cargo planes cap weight at 2000 kg/m2. These floors are structures meant to carry heavy things.

A building roof is not meant to carry weight like this. Snow is usually what puts weight on roofs and in places with heavy snow, the roofs are angled to shed it.

It is of course possible to make a floor that will support 9000 kg/m2. It will be a seriously robust floor. To keep the roof from falling thru and pancaking down through interior floors, your people will need to make a bridgelike exterior structure around the building using pillars or girders, and then over the existing roof a platform substantial enough to protect the roof of the building underneath.

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  • $\begingroup$ But not all of the ice is on the roofs--that's 10m above ground level, assumed flat, so if the building is ~3m tall, it only has 7m of ice on it and if it's taller than 10m it has no ice on it (or at least not substantial amounts. And the area was already cold-weather, so we can assume slanted roofs. Does that change the answer? $\endgroup$ Apr 5, 2022 at 22:08
  • $\begingroup$ @BenjaminTHall a load of 6,300 kg/m² is still a serious load. $\endgroup$ Apr 5, 2022 at 22:13
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    $\begingroup$ @BenjaminTHall: No roof in this world is made to hold six or nine tonnes per square meter, and very few floors, basically only floors which were purpose built to hold such loads. The roofs will collapse. The attic will collapse. The floors will collapse. $\endgroup$
    – AlexP
    Apr 5, 2022 at 22:23
  • $\begingroup$ Understood. Then squashed buildings it is. Whatever remains will be underground or seriously magically protected (well outside the norm). $\endgroup$ Apr 5, 2022 at 22:27
  • $\begingroup$ I understood this was just 10m of magic ice on the roof so that was the number. If this falls as snow and the roofs can shed snow then there might be minimal on top, as you say. That is ok! That is Buffalo NY. $\endgroup$
    – Willk
    Apr 5, 2022 at 22:40

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