Frost Cracked Rock - Svalbard - 1

This rock is about 30-40cm high (12-16") and quite clearly split three times where it sits. It's the sort of thing you can read about in physical geographic and geological texts but is quite striking when you actually see it in situ.

What I don't know about such things is whether the crack progresses slowly or quickly. Does it shoot through the rock with a sound? I'd like to imagine a resounding crack. Or is it a case of a slow (minutes/hours/days/weeks?) progression and then gentle easing of pressure?