Fragility of a dark gray shale in northeastern Jamaica: effects and implications of landslip exposure

Abstract

Rapid weathering of strong, hitherto un-weathered shale rocks was fast enough to have been measurable weekly (>4 mm depth per week). Regular early morning rain showers followed by hot, dry afternoons caused frequent wet/dry cycles which facilitated rapid slaking of the shale. Other landslips occurred concurrently on the south bank of the Wild Cane River, where the rock beds dip towards lower ground. Resistance to impacts in the rock fabric was equally low after decades, or weeks of exposure. It was concluded that the combination of high frequency wet/dry cycles on steeply dipping shale beds, and rock attitude caused very rapid weathering. Rapid slaking of the illitic shales could cause high turbidity levels in contiguous aquatic environments. Building foundations and roads could be rapidly de-stabilized even on such freshly exposed, apparently consolidated sites.