Abstract
Landscapes and soils evolve in non‐linear ways over millennia. Current knowledge is incomplete as only average denudation (or erosion) rates are normally estimated, neglecting the temporal discontinuities of these processes. The determination of regressive and progressive phases of soil evolution is important to our understanding of how soils and landscapes respond to environmental changes. The Sila Massif (Italy) provides a well‐defined geomorphological and geological setting to unravel temporal variations in soil redistribution rates. We used a combination of in situ cosmogenic radionuclide measurements (10Be) along tor (residual rock) height profiles, coupled with fallout radionuclides (239+240Pu) in soils, to model soil denudation rates over the last 100 ka. We measured rates prior to the Last Glacial Maximum (LGM) of ≤30 t km−2 yr−1 (~0.036 mm yr−1). Following the LGM, during the transition from the Pleistocene to the Holocene, these rates increased to ~150–200 t km−2 yr−1 and appeared to be above soil production rates, causing regressive soil evolution. For the last ~50 years, we even describe erosion rates of ≥1,000 t km−2 yr−1 (~1.23 mm yr−1) and consider human impact as the decisive factor for this development. Consequently, the natural soil production rates cannot cope with the current erosion rates. Thus, a distinct regressive phase of soil formation exists, which will give rise to shallowing of soils over time. Overall, our multimethod approach traced denudation and erosion histories over geologic and human timescales and made a new archive to soil science and geomorphology accessible.
Raab, Gerald