Gumushane is a small city located on highway connecting the harbour city Trabzon in the Black Sea Region of Turkey to the Eastern Anatolia. Following an excavation to create an area for housing on the northeast side of this highway, a large and rapid planar failure inclined to the southwest occurred. A large amount of fractured and weathered granitic material moved downward over this planar failure. After the failure, the highway was closed to traffic for 1 week, and more than ten houses on top of this failure were collapsed completely. The present study aims to investigate the mechanism of this failure. The study was performed using kinematical, limit equilibrium and numerical analyses for both post- and pre-failure conditions. Based on the detailed field observations, the failure mode was determined to be planar, and the slide mechanism was determined to be controlled by three fault planes. As a result of these analyses, it can be concluded that the slope before failure had critical conditions and that the excavation and uncontrolled blasting triggered and accelerated the slope failure.