All contemporary images showed that the loch is divided in two halfs, by two finger-like peninsulas protruding from either side. The fingers almost touch each other, leaving a ankle-keep, a few metres wide channel in between - the infamous Valve. Here the Valve in December 2019. The southern half is further subdivided by another finger, the peninsula. This is not the mystery.
The mystery was an old image I found on Geograph, which seemed to show that the eastern finger of the Valve was broader in summer 2005. I concluded that the loch must be a dynamically changing landscape, and decided to monitor it. Further research, conducted from the warm confines of my living room, revealed the banal truth. The image from 2005 was taken when the loch was still and the sun was out. The combination of mirror images of mountains and shadows of mountains make the finger look broader. There is no real change, just shadows and reflections. No real mystery either, just a normal puzzle. The field advances incrementally. The project is concluded.
Six years I have been chasing shadows and reflections. But the loch was really different that day in 2015, there is no denying that. Shadows and reflections are just as real as a landslide. They just follow other laws. And as transient events they can only be scientifically confirmed when, by some coincidence, the circumstances conspire to create the same conditions again. Here is the mirror image of Carn nan Gabhar touching the tip of the Peninsula, creating a second valve.