Making Rocks Sleep

I have fractured rocks in my Level Design level. they slide down a hill with the player and land at the bottom. 90% of the time they settle in a perfectly position, but there are times when the chunks of rock block off the path, preventing the player from advancing. Usually, the player can awkwardly climb over them, but more than once that hasn't been an option. 

I learned how to make the fractured objects "sleep" upon resting. So, when the rocks come to rest, there is a brief pause, then they shrink down and eventually disappear.  You can adjust the timing so the rocks disappear after a longer pause and adjust how long they take to shrink once they start to disappear.