Rapidin situconversion of late-stage volcanic materials to halloysite implicated in catastrophic dam failure, Hawaii

Abstract

Ka Loko Dam, in Kauai, Hawaii, failed suddenly and catastrophically on March 14, 2006. The resulting breachwas marked by three topographic benches, the lowest of which exposed native volcanic deposits once resident in the dam foundation. These deposits were found to contain outcrops of a waxy, gel-like material that appeared to result from in situ weathering processes. This unusual material was found to be highly enriched in halloysite. Gravel-size pieces in the hydraulic fill of the embankment derived from these materials also exhibited significant in situ weathering and significant halloysite content. Engineers and geologists generally recognize that bedrock materials weather progressively into soil constituents over ‘geological time’, and that this process is accelerated in tropical environments. Still, the strength, stiffness and durability of bedrock, earth and embankment materials are not expected to vary significantly over the geologically short life of a dam. In the case of Ka Loko Dam, however, the volcaniclastic sediments that comprise the local bedrock experienced substantial in situ weathering over its geologically brief 115-year operational lifetime. Prolonged exposure to seepage of anoxic water weathered the sediments completely to saprolite, including weak, sensitive, fine, spherical halloysite.

The rise and rise of halloysite

“…The final two papers of the special issue have a focus on spherical halloysite and particularly its geotechnical importance. Shaller et al (2016) describe an investigation into the sudden and catastrophic failure of a dam holding water for crops on the island of Kauai, Hawaii. Seepage of deoxygenated waters through the 115-yearold dam appears to have altered the volcanic basaltic rocks and pyroclastic deposits rapidly (in a geological sense) to spherical halloysite, and has also removed Fe oxides.…”