The North Korean mountain used for the underground testing of nuclear weapons might be suffering from “tired mountain syndrome,” according to experts studying satellite photos of the test site. “Tired mountain syndrome” is the name for increased fractures and permeability in the surrounding rock, caused by multiple underground nuclear tests. Mount Mantap is a 7,200-foot-high peak in the north of the country, which scientists say “visibly shifted” during North Korea’s most recent detonation on Sept.