I haven't been up there for about five months myself, but I can attest to the very small number of people who make the trek, due to the inaccessiblity; thus I too would be dumbfounded at any notion of human cause. Lightening doesn't seem highly likely, but I wonder whether climate change factors are creating ground moisture changes in this region. I have observed other climate change influences in this region that are contributing to surficial dessication, although I have never seen a manifestation of megalith splitting.