Chunk out of nowhere

Was playing in my survival world and went to get wood, but i have an unfinished bridge above a river... but there is something strange there, something that it was not there the last time i checked the place (March 8th, report was made in 9th)
I really dont know why that happend, never saw something like that before, i just saw that and went to a mountain to check my sorrounding for another chunk, but i just took the picture and quit inmediatly