Abstract The Alani-Paty landslide has damaged streets, utilities, and homes built on a debris apron in Honolulu, Oahu, Hawaii. Failure of weathered, crudely stratified, highly plastic, debris-apron deposits has created several similar landslides in southeastern Oahu. The Alani-Paty landslide affects about 60 residential lots. It is about 300 m long, 160 m wide, 7-10 m thick, and consists of two main kinematic elements that are separated by a right-lateral shear zone. One element has moved about 4 m, mainly by translation, down a slope of about 12°, and the adjacent element has moved about 3 m down a slope of 9°. Longitudinal stretching in the upslope third and shortening in the downslope two-thirds characterize deformation in each element; landslides in Ohio, Utah, and Colorado have deformed similarly. Smectite-rich clay layers within the deposits are medium to stiff, and measured angles of residual friction range from 6° to 11° with cohesion intercepts less than 12.5 kPa. Saturated hydraulic conductivity within the landslide decreases with depth; below the slip surface, the hydraulic conductivity increases. Rainfall infiltrates at the ground surface, percolates downward and perches on the zone of low hydraulic conductivity near the slip surface, keeping the slide mostly saturated year round. The main body of the landslide moves during rainy periods, when the ten-day average rainfall exceeds 25 mm/day and the pore-water pressures in the upslope quarter of the landslide increase 10-30 kPa. Pore pressure increases within the landslide occur 1-2 days following the onset of rainfall and result from infiltration of rainfall and runoff; after materials above the perennial water table become saturated, downward propagating pressure waves triggered by bursts of intense rainfall produce further, short-lived increases in pore pressure. This elevated pore pressure at the slip surface triggers movement. The ground-water response in the upslope quarter of the landslide is relatively rapid compared to responses in other landslides described in the literature.

Orographic precipitation on the southern flank of the southeastern Koolau Mountains produces a pronounced precipitation gradient. The corresponding gradient in the intensity of the chemical weathering environment provides an opportunity to address the effects of varying chemical weathering intensity on the composition of clay-size weathering products in soils developed on basalt. In addition, little-modified remnants of the constructional surface of the Koolau Volcano, isolated by stream dissection, remain as facets on the southern ends of the parallel ridges of the study area. By comparing clay mineralogy of soils developed on these older geomorphic surfaces with those developed on the younger sharp-crested ridges and steep side slopes, the effects of weathering duration on clay mineralogy can also be addressed. Soil clays in this part of the Koolau Mountains are mineralogically complex; principal phases include smectite, kaolinite, and halloysite, but pure end member phases are uncommon. Rather, most phases contain some amount of mixed layering. Smectite may contain small (<5%) amounts of randomly interstratified halloysite. Similarly, kaolinite commonly contains a small proportion of halloysite interlayers. A complex halloysitic phase shows evidence of interstratification with both smectite and kaolinite. Nonphyllosilicates found in the clay fraction include gibbsite, goethite, rare quartz, and perhaps cristobalite. The gradient in precipitation is reflected in soil clay mineralogy by varying proportions of dominantly smectitic, kaolinitic, and halloysitic phases. In regions of relatively low precipitation (<2,000 mm/yr), soils are dominated by the smectitic and halloysitic phases. With increased precipitation (as much as ∼4,000 mm/yr), kaolinitic and halloysitic phases become the dominant clay minerals, and goethite and gibbsite become increasingly abundant. Older soils developed on geomorphic surfaces representing the original constructional surface of Koolau Volcano are markedly more leached than those from younger landscapes in the same precipitation regime. Although smectite may be present, kaolinite is the dominant phase, and accumulations of Fe and Ti occur in the uppermost soil levels. Enrichment of Zr and Ti in these soils, as compared to concentrations in the original basaltic parent material, indicates that as much as 75% of the parent material has been lost. Thus weathering duration may affect soil clay composition in the same way as weathering intensity. Because smectite and halloysite are expandable clay minerals, their presence in soils may decrease slope stability and influence the nature of slope processes. Soil avalanches occur on steep slopes throughout the study area, whereas slow-moving landslides appear to be restricted to gentler slopes in drier parts of the study area where smectite is abundant. The clay mineralogy of soils thus appears to influence the nature of slope processes in the southeastern Koolau Mountains.

Abstract Based on a conference of the same title, there are 126 papers published, in whole or in part, in this volume. The principal objective of the conference was to provide a forum for presenting and discussing papers on the potential energy and mineral resources of the Circum-Pacific region emphasizing the exploration and development of energy and mineral resources in a manner compatible with the environment. The papers contained in this volume include subjects in geology and geophysical research; exploration and development of oil, gas, and coal and of geothermal, solar, and nuclear energy; exploration and development of ferrous and nonferrous metallic minerals and nonmetallic minerals; and the pertinent economic and environmental problems. These consist of 17 general papers, 7 papers on coal, 15 papers on geothermal energy, 28 papers on hydrocarbons, 13 papers on hydrogeology, and 46 papers on minerals. This volume should prove to be an indispensable reference for scientific, technical, and economic development among all Pacific nations.