Force perspective for sure! The very top of the peak that the Miss Tilly sits on is only 80'-90' feet high. Same thing for Summit Plummet. The actual 'mountain' only goes 90' feet up...then up 30 feet of stairs to the top.Here's an aerial pic. They actually use extreme forced perspective at this park as you'll notice. The Volcano is very small, but up high so it looks big from below. The wooded structure in the center forefront (by the lazy river) is what I was referring to. That's where the wave generator is.
Krakatau is going to be more than double the height of both Disney waterpark 'mountains'.