The Afar Triangle is a triple junction between three tectonic land masses. Within the Afar Triangle are many grabens because the land is being rifted. The site here is an excellent example of where the floor of the valley (where the lake exists) is dropping relative to the blocks on either side. The walls of the valley represent the faults along the valley.
Description
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch or trench. The plural form is variously given as graben or grabens.[2][3]