Weathering profile of non-welded ignimbrite and the water infiltration behavior within it in relation to the generation of shallow landslides

The mechanism underlying rain-induced shallow landslides of non-welded ignimbrite is found to be a special type of weathering profile and the behavior of water infiltrating through that profile, according to our study of Ito ignimbrite in southern Kyushu, Japan. Rhyolitic volcanic glass, the primary...

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Bibliographic Details
Published in:Engineering geology 2005-05, Vol.78 (3), p.187-207
Main Authors: Chigira, Masahiro, Yokoyama, Osamu
Format: Article
Language:English
Subjects:
Applied sciences
Buildings. Public works
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Geotechnics
Ignimbrite
Landslide
Natural hazards: prediction, damages, etc
Soil mechanics. Rocks mechanics
Soil moisture
Weathering
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Summary:The mechanism underlying rain-induced shallow landslides of non-welded ignimbrite is found to be a special type of weathering profile and the behavior of water infiltrating through that profile, according to our study of Ito ignimbrite in southern Kyushu, Japan. Rhyolitic volcanic glass, the primary component of ignimbrite, is first hydrated and dissolved, forming halloysite. Halloysite near ground surface is then transported through the ignimbrite by infiltrating water and becomes clogged in interstices to form clay bands. Suction monitoring across a weathering profile indicated that downward infiltration of water is disrupted once by a zone of less-permeable clay bands and again at the weathering front. This disruption at the front is caused by a capillary barrier effect caused by the structure where finer, weathered material overlies coarser, fresh material. This results in a well-defined weathering front, particularly beneath a slope where water flux is parallel to the front, whereas the front is transitional beneath a ridge top where the front is nearly horizontal and the water flux is normal to the front. Infiltrating water from rain increases the weight of weathered material and decreases the suction within the material, which is the final trigger of a shallow landslide of non-welded ignimbrite; long-term weathering, which proceeds on the order of years, provides slide material.
ISSN:0013-7952
1872-6917
DOI:10.1016/j.enggeo.2004.12.008