With dry bureaucratic precision, the daily incident reports from Rikers Island chronicle a surge of violence and disorder churning within the vast New York City jail complex.

Since New Year’s Eve, according to the internal reports, at least 12 inmates have been slashed or stabbed, eight of them in the face or neck. Inmates and correction officers suffered lacerations, concussions, punctured eardrums, and fractures to noses, eye sockets, jaws and hips. In one recent brawl, a chunk of an inmate’s ear was bitten off, according to the confidential reports, which were obtained by The New York Times.

Not since the gang riots of the 1980s and early 1990s has violence at Rikers Island so alarmed oversight officials, union leaders and inmate advocates. Over the past decade, the use of force by correction officers has jumped nearly 240 percent, even as the daily population has declined by almost 15 percent over the same period, according to data from the city’s Correction Department obtained under the Freedom of Information Law.

The mayhem inside city jails is especially striking given the historic declines in rates of homicide and other violent crimes outside of them. At the heart of the rising violence is an inmate population that has changed significantly in recent years and has in many ways grown more volatile.