By default Journal entries are autoarchived after a period of 6 months under Outlook 2010, but this can be changed:
- Click on File > Option > Note and Journal
- In the Right pane > Click on the "Journal Options" button
- In the small dialog that opens click on the "AutoArchive Journal" Entries button.
- Check the "Archive this folder using these settings"
- An there you are, configure the frequency (Weeks, month...)for auto archive settings
- Validate with the Apply button.