To add to this,
Akainu also commented on the feeling of "haki".
Unless the huge thing in question was coated with haki, I doubt it would crush the person's human form. Depending on the element, the person should be able to escape as there form is ethereal enough to get through the tiniest of cracks. Teach is the only one who wouldn't be able to do anything about it. Possibly Caribou and Crocodile as well.
Smoker should be fine as his smoke should disperse enough to get him through the cracks. Same with Ace, Ceasar, and potentially Monet.
Eneru and Kizaru would be fast enough to escape, and even then, I can't even really imagine catching light or lightning under anything.
Kuzan has demonstrated the ability to "
phase" through things so he should be fine as well. Akainu should be able to melt his way through as well.
Keep in mind though, the huge thing I thought of for the scenario was just a large poneglyph looking block that was bigger than Issho's meteors.