From the site:

This website is an educational resource that describes the science behind volcanoes and volcanic processes. The site is sponsored by NASA under the auspices of Project ALERT (Augmented Learning Environment and Renewable Teaching). It is intended for the education of university students of geology and volcanology and teachers of earth science. Each section in the menu builds upon previous sections. For users who lack fundamental knowledge of volcanological principles and terms, it is best to proceed through the website in a progressive manner. More advanced users will find each section self-contained and can navigate through the website as their interest dictates.