The surface features and internal structure of an integrated open system pingo in the source area of the Yangtze River on the Qinghai-Tibet Plateau

Abstract

The Qinghai-Tibet Plateau was traditionally deemed unsuitable for large-scale perennial frost mound developing due to climatic and geological constraints. A mound-like geomorphological feature was found in the source area of the Yangtze River in 2020. We conducted a comprehensive investigation to explore its surface features and internal structure, with photogrammetry, drilling, geophysical survey, and ground temperature measurement, and then it was identified as an open system pingo. The pingo was situated at 4860 m above sea level, and was characterized by an irregular conical shape with a 9.5-meter height, a basal diameter of 110 m, and a slope angle of less than 30°. Frost cracks were developed on the top of the mound, indicating extensive surface deformation there. A 10.5 m-thick ice core just beneath the active layer, and a 6.3 m-thick water lens below were found during the drilling of the borehole. The underlying artesian aquifers were considered to play a pivotal role in the geomorphological formation, providing both water source and uplift pressure through bottom-up injection of groundwater. Further analysis suggested that the presence of suitable hydrogeological conditions for the emergence of similar large-scale frost mounds in this region, with potential for multiple pingos or pingo scars in the vicinity. The finding offers novel insights into the research on permafrost and periglacial geomorphology in the Qinghai-Tibet Plateau, enhancing understanding of the formation mechanism of perennial frost mounds and the way of deep groundwater storage and migration under the unique periglacial environment of the plateau, and also provides a terrestrial parallel for exploration of pingo-like features and relevant water activities on other planets like Mars.