err, really? do you have a module installed that could be creating these? there is nothing in the default installation that I know of that would create these and if I saw them i would be thinking i had been hacked.
What is it that's being dumped? The files are 80MB+.
I've checked error logs and there's nothing there for that period except a few 'memory exhausted' errors in relation to sapphire/core/Object.php - which seem to have been fixed by up'ing memory limit using php.ini method.
Appreciate any help to avoid this happening again.