block retaining wall cracking

A lot of the work I'm doing on my property is rejuvenating. I've got some trees that have had quite "interesting" pruning work, lots of iris bulbs, many of which have reverted back to their original purple or white. I have lots and lots of white ones. Last year I cut out a lot of dead wood in the fruit trees scattered around the place. This year I'm seeing a problem with the retainging walls begginning to crack! What can I do? I have a picture. But, there are some places that are much worse. The picture shows two of the four levels that lead up to my house; they are all shored up by these retaining walls. Any ideas, thoughts, comments or exclamations are welcome!
Cathy