Holistic quantification of transient landscape response to rock uplift changes in the Fiumara Allaro catchment, Calabria, Italy

It is well understood that landscapes do not immediately adjust to changes in tectonic boundary conditions but instead undergo transient adjustments over time. Few studies have documented this transient adjustment by collectively examining fluvial, hillslope, erosional, and chemical weathering responses to tectonic perturbations. Here, we address this knowledge gap by investigating the Fiumara Allaro drainage basin, a ~98 km² catchment located in the Serre Massif of Calabria, Italy. The Fiumara Allaro is well-suited for such a study because it is predominantly underlain by granitic rock, has experienced a well-constrained order-of-magnitude increase in rock uplift rate at ~1.5 Ma, and benefits from high-resolution digital topographic data. Using a nested sampling approach, we collected data on channel width and grain size, and measured major element water chemistry as well as ¹⁰Be cosmogenic radionuclide concentrations along a transect from the steep lower reaches of the Fiumara Allaro to its high-elevation, low-relief upland. These data, combined with detailed topographic analysis, provide a holistic understanding of the landscape’s response to a step change in rock uplift rate. Geomorphic metric analysis reveals distinct contrasts between relict topography and actively incising regions, highlighting the transient nature of the landscape. Knickpoints are consistently observed at elevations between ~800 and ~1,000 m, separating the relict landscape from actively incising domains. Above the knickpoints, in the relict landscape, lower normalized steepness index (k_sn) values (~10–30 m⁰.⁸) reflect slow fluvial incision and a limited response to tectonic forcing. In contrast, the actively incising landscape below the knickpoints shows elevated k_sn values (~50–70 m⁰.⁸), indicating rapid incision and dynamic adjustment to increased uplift rates. Estimates of channel width, cast as the normalized wideness index, drop by more than a factor of 2 below the knickpoints, indicating channel narrowing after accounting for downstream increases in drainage area. Erosion rates in the relict landscape remain low, ~0.06–0.27 m/Myr, while rates downstream increase significantly to ~0.40–0.50 m/Myr, reflecting active incision driven by uplift. Grain size distributions further corroborate these trends: coarse material (D₈₄ ~731 mm) is concentrated in actively incising zones, while finer material (D₈₄ ~43–64 mm) dominates the relict landscape upstream. Preliminary water chemistry data indicate that cation concentrations generally increase below the knickpoints before declining further downstream, suggesting a potential coupling between physical and chemical weathering processes. Hillslope curvature analysis indicates that hilltops sharpen in response to active incision, reflecting ongoing transient adjustment to increased uplift rates. The Fiumara Allaro basin clearly exhibits geomorphic evidence of transient adjustment to uplift, with knickpoints and marked differences in erosion rates, k_sn values, grain size distributions, and water chemistry trends between relict and incising domains, highlighting a delayed response to tectonic forcing. More detailed findings, along with an assessment of fluvial and hillslope response times and a discussion of the implications for physical and chemical weathering in transient landscapes, will be presented at the meeting.