Report No. : GEO Report No. 357

Report Title : Dating of Colluvium from Natural Hillside Catchments on Lantau Island and Eastern New Territories (2022), 124 p.

Author : R.J. Sewell

Abstract

Understanding the responses of landscape to past climate changes, particularly in terms of landslide magnitude-frequency relations, is helpful for assessing the potential impact of future extreme weather events. Previous dating studies of relict landslides in Hong Kong focused mainly on large deep-seated failures and coastal debris complexes on Lantau (Sewell & Campbell, 2005; Sewell et al, 2006, 2015; Sewell & Tang, 2015). To expand the current landslide age dataset, six new sites (four in eastern New Territories and two on Lantau) under the Landslip Prevention and Mitigation Programme have been investigated and sampled for dating.

Thirty-one new ages of landslide debris have been obtained using radiocarbon and optically stimulated luminescence (OSL) techniques. The latest data are largely consistent with earlier dating results, suggesting that the relict colluvium is 1,000s (with some 10,000s) rather than 100s of years old. Clusters of large, deep-seated landslides occurred between 65,000-45,000 years and at approximately 32,000 years ago. The more frequent pulses of landslide activities during the early to mid-Holocene is considered related probably to climatic amelioration and rising sea levels. The growing landslide age dataset can improve the interpretation of landslide return periods, thereby facilitating the assessment of potential natural terrain landslide hazards under the changing environmental conditions.

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