COSMOGENIC NUCLIDE DATING OF LANDSLIDES/ROCK AVALANCHES IN NE PAMIR, CHINA

Large-scale landslides/rock avalanches exceeding >10⁶ m³ in volume are significant events that result in erosional degradation of mountains, change orogenic mass balance, and imperil human populations and their infrastructure. Determining the distribution of landslides through time is key to assess hazards and for understanding trigger mechanisms, such as climatic change, phases of enhanced earthquake frequency, or post-glacial stress relaxation.

Four large landslides were identified and mapped in the NE Chinese Pamir, a tectonically active orogen. The Bulunkou landslide is the smallest of the four landslides with a volume of ~ 16×10⁶ m³. The dip of the bedrock foliation is the same as the movement direction of the landslide. The landslide is offset 5.4m vertically by the Kongur normal fault. Four exposure dating samples were collected and are being processed. The Muztagh landslide is located on the southwest side of the Muztagh Ata peak with a volume of ~2138×10⁶ m³. The toe of this landslide climbs up to ~120m on opposite hill. Holocene earthquake surface ruptures are found to the north and the south of the landslide along the foot of Muztagh Ata. Averaged ¹⁰Be ages of 7 large surface boulder samples from the Muztagh landslide are 14.4±2.0ka. The Taheman landslide is located on south side of Muztagh Ata just to the north of the 1895 Tashkurgan earthquake (M7) surface rupture. The dip of bedrock foliation is the same as the direction of mass movement. The average age of 6 large surface boulder samples is 6.8±0.9ka. The Yimake landslide is on the frontal margin of the Pamir and has a volume ~1450×10⁶m³. There is no active fault across the landslide. The dip direction of the bedrock in the source area is southwest, but the direction of mass movement is northeast. Four TCN samples are collected and still in processing.

Given the tectonically active nature of this area and the presence of nearby faults, these four landslides might have been triggered by earthquakes. However, we need to do more work to rule out other causes including glacial debuttressing, long-term increased precipitation, geologic structure etc.