Intresting videos on deep sandbeds

[SteveZ15]

Im new and learning about different methods used in a reef system,I found these vids informative on what goes on in a sand bed. Hopefully this will answer some questions on this topic.
http://www.youtube.com/watch?v=d0mN3W_CZ9Y
http://www.youtube.com/watch?v=wDMkGDtD0dw