Soil-gas radon and ground radioactivity surveys across a portion of the Great Valley of West Virginia indicate that residuum and soils formed above some carbonate rocks have sufficient levels of radon gas to cause high indoor radon values. Data indicate no correlation of soil-gas radon concentration with faults, cleavage, joints, or calcite veins. Instead, soil-gas radon distribution appears to be controlled by the solution of carbonate bedrock and the subsequent development of thick, red, clay-rich residuum, which may contain as much as 4 times the concentration of radium, 10 times the concentration of uranium, and 5 times the concentration of thorium as the underlying bedrock. Such residuum and associated soil develops over some parts of the Elbrook, Conococheague, and Beekmantown Formations, and can have concentrations of radon in soil-gas exceeding 4,000 pCi/L. In areas of the Great Valley underlain by siltstone, fine-grained sandstone, and shale of the Martinsburg Formation, soil-gas radon values can exceed 4,000 pCi/L. In these areas, bedrock alone appears to have sufficient thorium, radium and uranium concentrations to generate the soil-gas radon measured. Previous work by others and our own preliminary evaluations indicate that soil-gas radon levels are high enough to cause indoor air in homes to exceed 4 pCi/L, the U.S. Environmental Protection Agency’s (EPA) action level for radon. Aeroradiometric maps and National Uranium Resource Evaluation (NURE) Program data do indicate anomalously high radioactivity in some areas where radon soil-gas concentrations were high. These data, used with available geologic maps, soil maps, and maps showing thickness of residuum, are useful in predicting areas of radon soil-gas hazards.

Study of slope movements triggered by the storm of November 3–5, 1985, in the central Appalachian Mountains, U.S.A., has helped to define the meteorologic conditions leading to slope movements and the relative importance of land cover, bedrock, surficial geology, and geomorphology in slope movement location. This long-duration rainfall at moderate intensities triggered more than 1,000 slope movements in a 1,040-km 2 study area. Most were shallow slips and slip-flows in thin colluvium and residuum on shale slopes. Locations of these failures were sensitive to land cover and slope aspect but were relatively insensitive to topographic setting. A few shallow slope movements were triggered by the same rainfall on interbedded limestone, shale, and sandstone. Several large debris slide-avalanches were triggered in sandstone regolith high on ridges in areas of the highest measured rainfall. Most of these sites were on slopes that dip 30 to 35° and lie parallel to bedding planes, presumably the sites of least stability.

Of the many types of landslides common to Puerto Rico, debris flows—the mobilization and flow of rock and soil down steep slopes—are the most abundant in many areas. On October 5–8, 1985, a tropical storm produced extreme rainfalls and consequent widespread debris flows along the south-central coast of Puerto Rico. Locally, 24-hr rainfall exceeded 560 mm, 4-day rainfall exceeded 750 mm, and intensities reached 70 mm/hr. Most of the flows occurred in an area where Tertiary limestone and detrital sediments form 20° to 40° slopes covered by less than 2 m of colluvium or residuum. Many areas received more rainfall and had steeper slopes but contained far fewer flows. The distribution of flows probably was caused by a small cell of very intense rainfall or by localized engineering properties of the colluvium that rendered it more susceptible to failure in the area of concentration. Most of the flows resulted from storm-induced buildup of pore pressure at the colluvium/bedrock contact. The debris generally failed in disk-shaped slabs as much as 15 m across and 0.5 to 1.5 m thick. All the colluvium in the source areas mobilized and exposed bedrock surfaces parallel to the original ground surface. The flowing debris scoured surficial soil down to bedrock and destabilized preexisting gully walls, which triggered additional thin debris slides into the channel. Material contributed by channel scouring and side-slope debris sliding commonly made up 90 to 95 percent of the debris deposit. Debris flows are recurrent phenomena in southern Puerto Rico. Several flows incised channels into older debris-flow deposits, and in some areas, as many as three successively older debris deposits were exposed. Preliminary dating of debris-flow deposits suggests that recurrence intervals for flows at a given site could range from several decades to several hundred years.