Tortum Waterfall is a 48-metre drop in eastern Turkey that exists because a mountain came down. About three centuries ago a limestone flank of Kemerli Mountain slid into the valley, sealed the Tortum stream and drowned eight kilometres of it. The lake and the waterfall were made in the same instant: the fall is where the lake gets out, across a hard lip about twenty metres wide. Nobody knows the year. Turkish sources put it anywhere from the late 1600s to a precise 1748, and none rests on a dating study. Eleven kilometres from Uzundere the road passes a glass floor cantilevered 143 metres above the lake, with the whole dammed valley under your shoes. At the falls a long stone stairway with an iron railing drops to the plunge pool. The spray has your sleeves wet before the last step, and keeps the stone slick even in high summer.
The rainbow has a rule of its own. It appears only once the sun has cleared the gorge rim and strikes the mist head-on, so an early visit leaves the spray grey. And there are days when nothing falls at all. A hydroelectric plant takes the lake's water into a channel above the lip, so for most of the year the drop carries only what the plant has to release. In May and June the snowmelt arrives faster than it can be diverted, the water goes over at full width, and you hear it from the road before you see it; by a dry September the same wall carries a thread. In the Erzurum winter it freezes into pale pillars, and ice climbers come for them. By law it must never stop: the Council of State fixed the flow in 2010 at 3.5 cubic metres a second, ankle-deep across that twenty-metre lip, and a court ordered it kept running in 2011. It has not always. When the company closed the channels for repairs in February 2022, the provincial governor's office had to force the water back. For nine days before that, a forty-eight-metre wall of rock stood completely dry.