Mass movements in cave sediments: investigation of a ~40,000-year-old guano mudflow inside the entrance of the Great Cave of Niah, Sarawak, Borneo |
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Authors: | A P Dykes |
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Institution: | (1) School of Earth Sciences & Geography, Kingston University, Penrhyn Road, Kingston-upon-Thames, Surrey, KT1 2EE, UK |
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Abstract: | The West Mouth of the Great Cave at Niah in Sarawak, northwest Borneo and the North Passage that leads to the West Mouth contain
large deposits of guano. The main deposit, several metres thick in places, forms the sloping floor of the entire North Passage.
A mass movement deposit identified in the West Mouth, having a volume of 600 m3, originated as a guano mudflow up the North Passage in the order of 40,000 years ago. This failure of the guano slope was
investigated to determine whether particular conditions or events could be identified as the most likely causes. The physical,
hydrological and geotechnical properties of samples of the material were determined so that the stability of the slope could
be assessed. Stability analyses showed that shearing failure of the slope would require inputs of water to the slope in quantities
for which no feasible explanation can be suggested. However, the properties of the guano are similar to those of loess, indicating
a high susceptibility to ‘hydrocollapse’. Very shallow failure of the slope, possibly as several smaller mudflows, could therefore
have occurred due to additional water in quantities that could realistically be supplied as rainwater spray, possibly with
a seismic trigger. The climate must therefore have been wetter than it is at present. These findings have implications for
the interpretation of sediment deposits in other relict caves. |
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Keywords: | Biogenic cave sediments Guano Mass movement Geotechnical properties Metastable sediments Sarawak Niah cave |
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