WinterPromise has a Free unit Study on Volcanoes [1]!! You can download it now and save it to use later. I also saw several more freebies on their site [2]!
If you are unfamiliar with WinterPromise [3] this is a great way to check them out. They have Unit Studies that use a Charlotte Mason approach to learning.
Find more great Free Unit Studies [4] on How to Homeschool for Free!