This is an incredible photo depicting the wake vorticies generated by aircraft. The two counter rotating vortices are clearly visible in the cloud as it spins around.
Vorticies generated by smaller aircraft are almost negligible, however, vorticies generated by larger, heavier aircraft can be extremely dangerous. The aircraft’s weight, speed and shape (configuration) govern the strength of the vorticies it creates.
The U.S. Federal Aviation Administration (FAA) states that between 1983 and 2000, there were 130 aircraft accidents and 60 aircraft incidents in the U.S. that resulted from probable encounters with wake turbulence. 14 of these accidents were fatal (11%). Eighty-seven of the accidents (67%) and forty-seven of the incidents (87%) occurred at or below 200 feet above ground level.