Water-Scrum-Fall is essentially when agile/scrum development processes are only applied to the development team's work(usually the implementation step in waterfall), and most of the previous project management 'waterfall' system remains in place. Those articles are primarily listing it as the reality for most shops where the development team does not have full control of the process, so agile cannot be used across the entire project. I don't believe either one is really trying to say it should be adopted, but it is somewhat common. The second article is more focused on the benefits/drawbacks so companies that find themselves in this model can improve what they have without massive process redesign.
Avalanche is best described as a faulty implementation of scrum where each 'sprint' is most of a waterfall. Each stage/department iterates rapidly on its own subset of work and has to communicate the results of those steps to the other departments. The result is often that each phase of the 'waterfall' is happening at the same time for the entire product. It is also characterized by extreme breakdowns in communication. Features are often being redesigned while being implemented or tested by departments that can't keep track of what stage each feature is at. The result is mass chaos and confusion, extremely difficult to manage projects, and poor morale as work is regularly(read: very frequently) invalidated by changing requirements/design.
The key difference between the two is that Water-Scrum-Fall is scrum in waterfall, which doesn't fundamentally break either model. Avalanche is waterfall in scrum, which is a slow motion catastrophe.