Articles | Volume 17, issue 3
Research article
08 Mar 2017
Research article |  | 08 Mar 2017

Meteorological factors driving glacial till variation and the associated periglacial debris flows in Tianmo Valley, south-eastern Tibetan Plateau

Mingfeng Deng, Ningsheng Chen, and Mei Liu

Abstract. Meteorological studies have indicated that high alpine environments are strongly affected by climate warming, and periglacial debris flows are frequent in deglaciated regions. The combination of rainfall and air temperature controls the initiation of periglacial debris flows, and the addition of meltwater due to higher air temperatures enhances the complexity of the triggering mechanism compared to that of storm-induced debris flows. On the south-eastern Tibetan Plateau, where temperate glaciers are widely distributed, numerous periglacial debris flows have occurred over the past 100 years, but none occurred in the Tianmo watershed until 2007. In 2007 and 2010, three large-scale debris flows occurred in the Tianmo Valley. In this study, these three debris flow events were chosen to analyse the impacts of the annual meteorological conditions, including the antecedent air temperature and meteorological triggers. The remote sensing images and field measurements of the adjacent glacier suggested that sharp glacier retreats occurred in the 1 to 2 years preceding the events, which coincided with spikes in the mean annual air temperature. Glacial till changes providing enough active sediment driven by a prolonged increase in the air temperature are a prerequisite of periglacial debris flows. Different factors can trigger periglacial debris flows, and they may include high-intensity rainfall, as in the first and third debris flows, or continuous, long-term increases in air temperature, as in the second debris flow event.

Short summary
Annual air temperature spiked and glacier retreated shortly before the three periglacial debris flows in Tianmo valley. However, they did not occur when glacier retreat was sharpest, resulting from the frozen bared glacial till as the melting of internal ice lags behind glacial retreat. The activity of the glacial till can be enhanced by prolonged high air temperature. Finally, either rainfall or continuous percolation of ice ablation water flows can generate debris flow.
Final-revised paper