udump pdump cleanup?

 I'm running Oracle 10g R2 on SUSE10 on the z platform.

I've noticed that my udump and bdump areas are using lots of space.  For example the udump area is using about 60 MB for the trc files.  These files have dates from today to back in August when I installed Oracle.

Do these areas automatically cleanup?  Perhaps after a certain length of time, or number of files, or total size of directory?  Or is this something that needs to be looked at, and ocassionally cleaned up manually?

If it needs to be cleaned up manually, is there some documentation on manual clean up practices that need to be done on a periodic basis?  i.e. What else do I need to do to keep a healthy database?