Late Quaternary paraglacial and periglacial deposits in the high mountains of Taiwan

During the last Pleistocene glacial cycle, Taiwan's high mountain ranges were glaciated in the uppermost altitudinal zone with a calculated lowering of the equilibrium line altitude (ELA) of ca. 1500 m down to 2800 m (Hebenstreit et al. 2025). Glacial erosion of the upper valley reaches formed trough-valleys. Lateral and terminal moraines as well as outwash deposits were deposited at or near the ice margins, respectively, at different stages of the glaciation. Subsequently, slope processes and fluvial activity have been reworking those sediments and reshaping those landforms during and after the glaciation to adjust the relief gradually to its present shape. These processes are called paraglacial processes (Ballantyne 2002).

 

In the Hsueh Shan range, we mapped a sequence of terraces composed of cobbles and boulders at the confluence of the Taoshan river and the Chijiawan river at an altitude of ca. 1900 m, which corresponds with the assumed lowest altitude of the last-glacial glacier termini. Surface exposure dating with paired in-situ produced terrestrial cosmogenic nuclides (TCN) of meter-sized boulders on the terrace surfaces gives evidence of enhanced glacio-fluvial activity, presumably reworking glacial deposits during the last phase of the glaciation at the Pleistocene-Holocene transition. 

 

Lowering of the altitudinal zones and consequently of surface processes during glacial times entails periglacial processes on slopes not affected by glacial or fluvial processes (Böse 2006). This includes frost weathering and solifluction. The periglacial zone is presently restricted to altitudes above 3500 m in Taiwan.

 

A sediment profile at ca. 2050 m on the slope above the glacio-fluvial terraces shows a stratification typical for cover beds in mountainous periglacial environments (Kleber & Terhorst 2024): Above debris of local underlying bedrock follow layers enriched by aeolian dust. The sediment has been partly reworked and mixed by solifluction. Optically stimulated luminescence (OSL) ages of the silty matrix confirm its formation during the last glacial cycle; and a lowering of the periglacial altitudinal zone of 1500 m can be inferred.

 

References

Ballantyne, C. K., 2002: Paraglacial geomorphology. Quaternary Science Reviews

21 (18–19), 1935-2017.

 

Böse, M., 2006: Geomorphic altitudinal zonation of the high mountains of Taiwan. Quaternary International 147 (1), 55-61.

 

Hebenstreit, R., Hardt, J., Böse, M., 2025: The lowermost last‐glacial equilibrium line altitude in the Taiwanese Central Mountain Range and its implications for the palaeoclimate and the tropospheric moisture transport in East Asia. Journal of Quaternary Science 40 (5), 831-846.

 

Kleber, A., Terhorst, B. (eds.) 2024: Mid-Latitude Slope Deposits (Cover Beds)

2nd Edition. Elsevier Science