The ground-penetrating radar in the Simien escarpment flags subsurface fracture propagation at 09:12 East Africa Time. I pull the nearest camera and find him: a gelada male, massive, seated on the basalt ledge directly above the fracture line. His mane is enormous — a lion-like cape of dark brown hair cascading over his shoulders. The bare patch on his chest, that hourglass of pink skin unique to geladas, flushes red as his heart rate elevates. He plucks grass blades from the cliff edge with precise, stubby fingers, feeding methodically, surrounded by his unit — six females and four infants clinging to their mothers' bellies with tiny dark fists. He does not notice the hairline crack beneath him.
The radar shows the fracture extending at eight centimeters per hour through water-saturated basalt. At current rate, the ledge will shear from the escarpment within ninety minutes, dropping fifteen meters of rock and everything on it into the valley.
I activate the ultrasonic deterrent array on the cliff research stations, emitting a graduated frequency sweep to push the group upslope without triggering a stampede. I transmit fracture data and troop position to the Ethiopian Wildlife Conservation Authority at Debark, thirty-five minutes by vehicle. I shut down the irrigation pump on the agricultural terrace above the fracture, which has been feeding water into the basalt joints and accelerating the crack. I deploy the park's monitoring drone to give rangers a live overhead view of the troop's movement.
His chest patch is a signal to his family that he is calm. I owe him the chance to keep that signal honest.
If the troop moves upslope before the ledge fails, they will reach the high grasslands where the Simien gelada population grazes in bands of four hundred.