## 3 Results
### Engineering geology
#### 3.3.2 Analysis of Intensity and Hazard-Formation Processes  
Based on field survey data and hazard scale classifications, landslides, collapses, and debris flows (CLD) on the Qinghai-Tibet Plateau are predominantly small- to medium-scale events, with large-scale disasters occurring less frequently. Additionally, 2858 hazard sites lack scale annotations. Statistical analysis (Figure 9, Table 3) shows that debris flowsrepresent a disproportionately high share of medium-, large-, and exceptionally large-scale events, accounting for 18.74%, 5.58%, and 0.51%, respectively, indicating their greater destructive potential. In contrast, collapses and landslides are primarily small-scale events, comprising 15.78% and 8.73% of all hazards, although a notable proportion of large-scale occurrences are still recorded (collapses: 1.88%, landslides: 3.86%), demonstrating that some collapses and landslides also have significant impacts. Overall, debris flows are more likely than collapses and landslides to generate medium- and high-intensity disasters. A total of 1319 large and exceptionally large-scale disasters have been documented across the Plateau, predominantly concentrated in Comprehensive Zone II (48.67%), followed by Zone I (28.96%) and Zone III (17.06%), while Zones IV-VIII together account for only 5.3%. This spatial distribution is primarily controlled by geomorphological and tectonic conditions. Zones IV-VIII are situated in the central and northwestern regions of the Plateau, characterized by broad basins and relatively gentle terrain, which are generally unfavorable for the development of large-scale hazards. Conversely, Zones I-III, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Scale**} & \multicolumn{3}{c}{**Disaster Type and Proportion of/\%**} \\ \cline{2-4}  & **Collapse** & **Landslides** & **Debris Flows** \\ \hline Extra-large & 0.10 & 0.08 & 0.51 \\ Large & 1.88 & 3.86 & 5.58 \\ Medium & 4.41 & 8.91 & 18.74 \\ Small & 15.78 & 8.73 & 31.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistics on the scale of geological hazards on the Qinghai–Tibet Plateau where collapses, landslides and debris flows (CLD) have occurred. Figure 9: Graded statistics of CLD hazard scales in each comprehensive subzone. Subzones: I, Alpine Valley Freeze–Thaw Tectonic Zone; II, Alpine Canyon Tectonic–Erosional Zone; III, Alpine Freeze–Thaw Tectonically Active Zone; IV, Fauulted Basin Weathered Fragmentation Zone; V, Permafrost–Weathered Rock Belt; VI, Permafrost–Nival Erosion Zone; VII, Alpine Hard Rock Freeze–Thaw Debris Zone; VIII, Alpine Lake Basin Saline Soft Rock Zone. located within the Himalayas, Hengduan Mountains, and Qilian Mountains, feature steep topography and active tectonics, providing favorable conditions for the occurrence of large-scale disasters. Consequently, 94.69% of all large- and exceptionally large-scale events are concentrated in these three zones. Although large-scale disasters result from the combined influence of endogenic and exogenic geological processes, they comprise only 12.01% of the total. Small- to medium-scale disasters dominate the region, with 9655 recorded events, accounting for 87.99%. These smaller-scale hazards are triggered by the interaction of tectonic structures, meteorological factors, and engineering geological conditions. The differences in hazard-inducing environmental factors across the eight comprehensive zones lead to varied and complex hazard formation mechanisms, summarized as follows: Zone I (Yarlung Tsangpo River Valley and Adjacent Highlands): Tectonically fractured lithology (30.884%) provides the material basis, precipitation (26.482%) promotes erosion, and anthropogenic disturbances amplify instability, forming a \"tectonic fracturing-engineering disturbance-precipitation erosion\" mechanism. Subsurface thermal gradients and seasonal heating may further exacerbate slope instability [61].