Are you writing your log to the file system too or just the db? If just the db, then continue to clear it as if it is huge like you mention, it will eventually clean itself up.
You can also clean the event log up using the db directly since there are no other tables which reference the event log primary key. Pretty easy to truncate the table or delete it. I'd suggest doing this when the site has minimal traffic on it.
Lastly you can update your settings so you're not storing so many logs and maybe set custom code to not log specific activities i.e.: mass imports.