Soil formation in kettle holes from high altitudes in central Apennines, Italy

Kettle holes are relatively common features of glaciated landscapes and have been widely reported in the literature. The work reported here documents the presence of kettle holes at high altitude and low latitude in the Central Apennines (Italy) and describes the geomorphic and pedogenic processes that originated the soils infilling these depressions. The areas selected for this study were located on three of the main massifs of the Central Apennines (Italy): Gran Sasso, Majella, and Sibillini. The kettle holes on these massifs formed at the end of the Würm glaciation, appear smaller and shallower than those reported from elsewhere in the northern hemisphere, are roughly circular in form and do not contain bogs or lakes. In each area the dimensions of 40 kettle holes were measured and three kettle holes were excavated to examine the soils developed inside them. The size of the kettle holes was highest in the Sibillini massif, where the glaciers reached altitudes as low as 1700. m in the very narrow, low-lying valleys. It is hypothesised that at lower elevations the glacier receded more rapidly generating larger blocks of ice and consequently larger kettle holes. Once formed, the kettle hole depressions were very effective as sediment traps and acted as sink for materials washed in from the surrounding slopes or from more distant wind-blown sources. In the kettle holes from Gran Sasso and Majella massifs, small fragments of woody charcoal were found. The material filling the kettle holes accumulated inside them in the form of layers. Soils formed inside the kettle holes showed horizons whose thickness and properties appeared mostly inherited from the amassed layers. The only pedogenic process common to the kettle holes of the three massifs was the incorporation of organic matter that, as expected from the rather cold climatic conditions, was subjected to slow dynamics. In the kettle holes of the Majella massif, the horizons developed from layers rich of materials of volcanic origin, and the formation of short-range order minerals occurred. We conclude that the soils inside the kettle holes are a repository of geomorphic, pedogenic and, in reference to the source of the charcoal, paleo-environmental information.