In a more extreme example, the ground level has dropped by over a foot (34 cm) per year near the city of Rafsanjan, in central Iran. "We found about 100 sites across Iran where subsidence is faster than about 10 millimeters [0.4 inches) a year. "Irreversible" sinkingMuch of the subsidence at all 106 locations was irreversible, Payne said. (Image credit: Anadolu/Getty Images)As a result, the particles flatten, and the ground level drops in irreversible subsidence. "Iran's peak rates rival Mexico City and Central Valley in California, placing it among the world's most extreme subsidence hotspots," Shirzaei said.