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Comment by ternaryoperator | Hacker News Reader

Is a 50-ton boulder rare or super-rare?

In chicagoland, yes. For someone who moved there from California, it was strange that rocks hardly larger than a human warranted school field trips and plaques. Perhaps it is geologically cool, but I was unimpressed as a 6th grader. https://live.staticflickr.com/65535/53236492797_60069bde90_b...

In an area that was covered by a glacier in the last 20k years, yes.

Chicago was covered by ice during the most recent glaciation, which means that boulder is probably a glacial erratic covered by till leftover from the movement of the glacier.

It's not just the fact that the area was covered by ice. The local geology is also a factor.

Glacial erratics are everywhere in Scandinavia, which also obviously was covered by the ice. Small ones, like in the article, are scattered all over. Large ones weigh thousands of tons and may often be mistaken for bedrock.

I suspect there are other areas in North America where that's also true.

There are no mountains in Ontario or Saskatchewan and that is where the glaciers came from, there’s only the exposed bedrock of the Canadian Shield.

Glacial erratic https://en.wikipedia.org/wiki/Glacial_erratic

I thought the same thing. My back yard is full of huge rocks. Nothing quite that large, maybe 1/3 of that size. A few doors down there is a boulder twice as big as the O'Hare one.

I'm speaking in volume. I'm not sure of the mass of these boulders.

Medium-rare I would guess

Well-done, I must say.

Dunno, but I haven't ever come across one on my property.

Not from the look of it.

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