Comparing the Spatial Variability of Cosmogenic 10Be Erosion Rates and Channel Steepness to Quaternary Uplift Rates in Northern and Southern Italy

In dynamic equilibrium landscapes rock uplift rates are everywhere balanced by hillslope erosion and river incision rates. Here, we compare the spatial distribution of hillslope erosion rates, inferred from cosmogenic ¹⁰Be concentrations in sediments, and channel steepness, which has been shown to correlate with incision rates, to well-constrained Quaternary uplift rates in the Romagna Apennines and Messina Strait, Italy.

The Romagna Apennines and Messina Strait region have been uplifted since Neogene time in response to subduction zone retreat and slab roll back, respectively. In the north, Pleistocene near shore deposits exposed at the Romagna Apennines mountain front suggest that average uplift rates have been 0.4 ± 0.15 mm/yr since 0.7 Ma. In the Messina Strait region, southern Italy, average uplift rates are 1.02 ± 0.05 (SD) mm/yr, as constrained by a set of ~125 ka marine terraces.

Both channel steepness and hillslope erosion rates increase with increasing uplift rates. Channel steepness is highly variable, up to an order of magnitude in the Messina Strait region, and appears insensitive to increases in uplift rate above 0.8 mm/yr. The average erosion rate inferred from cosmogenic ¹⁰Be concentrations in sediment from 3 catchments in the north is 0.47 ± 0.04 (SD) mm/yr. In the south, the average erosion rate across five catchments is 1.05 ± 0.25 (SD) mm/yr. These average erosion rates are indistinguishable from regional-average uplift rates within one standard deviation.

These data support previous conclusions that distributions of river incision and hillslope erosion rates can be used to infer spatial patterns in uplift rates. However, we suggest that erosion rates inferred from cosmogenic ¹⁰Be may better predict uplift rates in more rapidly uplifting areas. Changes in channel steepness may be limited either by thresholds, or adjustments in channel form and/or incision process that may occur simultaneously with changes in channel steepness.

3-2008-->