August 17, 2004
This waterfall enters the plunge pool from the bottom! Most of the McKenzie River in Oregon has been diverted to a reservoir about 2 miles (3.2 km) upstream, bypassing the original course of the river. Only when the water in the river is very high does part of it flow in its original course. It then falls into the "Blue Hole" from the cliff at the far side of the pool and is called Tamolitch Falls.
For most of the year, a portion of the river flow escapes the diversion and travels through the porous lava rock and enters the pool from the bottom. It has been estimated that as much as half of the McKenzie river flow follows this route. The outflow from the pool (not shown) is quite impressive.
The water in the pool is extremely clear (travelling through several kms of lava acts to filter it). Clear water is inherently blue if sufficiently deep -- a 2-3 m depth is required. The Blue Hole is easily 10 m deep. Water more readily absorbs the red end of the visible light spectrum so that only the shorter wavelength colors (blues and greens) are scattered back toward the viewer. This is why a swimming pool appears blue even if it has white tiles. A bathtub is not deep enough to detect this phenomenon.