Debris Avalanching in the Southern Appalachians: An Influence on Forest Soil Formation

Abstract

Abstract In early November 1977, a storm system that formed in the Gulf of Mexico moved northeast into the Appalachian Mountains of North Carolina. It produced intense (30–120 mm h −1 ), heavy rainfall (200–320 mm), which triggered debris avalanching in steep terrain of the Pisgah National Forest. Soil material displaced by the mass wasting was in the order of 2 to 3 × 10 3 ha −1 along avalanche tracks, which exceeded 1 km in length. Peak stormflows had recurrence intervals ranging from 20 to >100 yr. Factors prominent in development of the storm were evaluated using infrared satellite imagery and rain gauge data. Most debris avalanches on one well‐documented basin originated in shallow Umbric and Typic Dystrochrepts soils on upper slopes and ran out onto Typic Haplumbrepts, Typic Hapludults, and Typic Fluvaquentic Dystrochrepts soils in lower gradient deposition zones. Although debris avalanching in the Appalachian Mountains is a rare phenomenon in human history (100–1000+ yr return period), it is a major and frequent geomorphic process influencing soil formation.