SQL Server 2008 R2: From a SQL Server Log file, how do I find out what is causing an event Problem:

The attached image is a screen shot of the SQL Server log showing an event that happens every Tuesday at around 1:20 AM. This event is causing the transaction log backup chain to break and all subsequent transaction log backups to fail.

Question:

How can I find out what is causing/doing this?
For the purpose of not leaving this question open and in hopes that it helps someone in the future, I wanted to detail the steps I followed to solve my problem. 
In following the advice given about running a trace around the time the Recovery model is changed, I found that there was indeed a task that was shrinking the log.



Summary

Using SQL Server Profiler trace allowed me to find out what was causing the problem.