In my inexpert experience, two things seem relevant;

1. Ice, especially ice broken and loosened by movement and shifting pressure, tends to generally fall apart in chunks and clumps when melting.

2. Murphy's Law always applies, especially when you aren't ready for it.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort