The bumps are caused by hard braking – is that right? if so, there are some in weird places that you shouldn’t be braking in/on.
The main problem seems to be people trying to go fast and then shitting it and grabbing a handful of rear brake (surely it should be fornt for more control) and locking up the wheel?
The 4×4 comment was a pisstake and in no way meant to be serious – still happened and was funny to watch though :)