(covers information from several alternate timelines)
A Kerr loop was a temporal phenomenon which could be created through the interactions of high-energy discharges.
In 2344, a temporal rift which was the formation of a Kerr loop from superstring material, was created through the intense weapons fire in a battle between the USS Enterprise -C and four Romulan Warbirds at the Klingon outpost at Narendra III. The Enterprise-C was inadvertantly responsible for the creation of an alternate timeline when it drifted into the rift and traveled through time. (TNG: "Yesterday's Enterprise")