Long ago the Great Race learned how to master the subspace. They used it for travel and communication, but also for more mundane purposes, like storage. If you are lucky enough to uncover one of the Great Race's storage rifts, many of your storage needs will be covered.
A ravine is formed during movements of the planet's plates. It is too hot down there so it can only act as a natural waste sequestration well, which can store up to 100,000 waste at its first level.