Tread chunking when driving on gravel is completely normal. I grew up on a gravel road and we never had tires that looked new after the first trip home. If there are cuts between the tread blocks, that's a different story, but if it's just little pieces missing out of the tread blocks themselves it's nothing to worry about.
2012 Silver Sport S, Silver, 6 speed, soft top, 3.73s, LSD, PCG, Infiniti, deep tint windows, Pro Comp 1028 wheels, 33" Duratracs, Smittybilt bumpers and steps, KC fog lights, Mopar slush mats and fuel door.
Happiness is a belt fed weapon.