The volcanic top layer of ground is obviously very porous, allowing water to drain down until it reaches a harder layer it can't penetrate -- so it flows sideways until it reaches this fast-moving river.
The walking path leads around and over the river and along volcanic landscapes. This is a very nice place to spend about 30 minutes and take some great pictures. The smell of french fries makes me notice the small restaurant on site.
Tip: <F11> for full-screen viewing . . . . Page 24 of 64