Abstract:Giant rock avalanche is uncommon globally, but quite devastative, so its recognition is important both for deepening our understanding of regional tectonic background, and for disaster reduction and engineering safety. Based on remote sensing, UAV surveying and filed reconnaissance, a newly recognized Basu giant rock avalanche is reported, with its deposition features characterized, formation and evolution briefly analyzed and volume calculated. Major conclusions are summarized as follow. 1) Basu rock avalanche is developed within the Xiali-Basu rift valley of Bangong-Nujiang suture zone. Bedrocks are mainly marble set of the Paleozoic Jiayuqiao Group and metamorphosed sandstone and mudstone of Jurassic Mali Group. Most of its upper slope is composed of hard rocks dipping down the slope at a steep angle, while the lower slope is mainly of soft rocks dipping steeply into the slope. 2) The avalanche is about 7 200 m long, 4 800 m wide, covering both sides of the Lengqu River, and having an area of 22.5×10⁶ m² and an estimated volume of 3.5×10⁹ m³. Its reserved volume can still reach about 1.4×10⁹ m³, the largest one ever recognized and documented in China. 3) The avalanche is most likely triggered by a historical earthquake, as its debris is highly fractured and can climb up the right bank as high as over 600 m. That is, its sliding speed is quite high. The slide dammed the Lengqu River and the height of its landslide dam is about 185 m. The slide experienced a series of geomorphological process, as dam breaching, secondary Dora Kamiyama sliding, debris accumulation and erosion, and runoff-induced surface erosion, but its geomorphological features are still well reserved. Both the slide and the debris led to the route change of the Lengqu River. 4) Based on the evolution of both the slide and the Lengqu River, it is inferred that the slide occurred during Late Pleistocene, i.e. it is an ancient slide. 5) The recognition of Basu giant avalanche implies that our knowledge on the geological environment of Qinghai-Tibetan plateau is quite limited. For the construction of projects as Sichuan-Tibetan Railway, it is quite necessary to strengthen the investigation of both basic geology and engineering geology, and the evaluation of geo-hazard risk, so as to secure their safety during the construction and operation phases.