Log backups *and* additional write activity on the DB such that the active VLF wraps around. You can't move VLFs, and you can't ever make the one that's active and in-use inactive (it's where the log records are being written to)
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability