Mountain landscapes have dynamic climates that, together with tectonic processes, influence their topographic evolution. Spatial and temporal variations in rainfall are ubiquitous in these settings as orographic precipitation patterns evolve with climate change and topography. Despite important implications such changes have for river incision, their influence is understudied. Here, we investigate how changes in rainfall pattern should affect both the steady state form and transient evolution of river profiles at the catchment scale using the stream power model. We find that spatially varied rainfall patterns can complicate steady state relationships between mean rainfall, channel steepness and fluvial relief, depending on where rainfall is concentrated in catchments, and lead to unexpected transient behavior if they are neglected. Specifically, changes in rainfall pattern cause multi‐stage transient responses that differ from responses to uniform changes in rainfall. Disparate responses by rivers that experience different rainfall conditions, particularly trunk and tributary rivers, are also an important factor in understanding catchment‐wide responses to climate change. Accounting for such disparities in sampling strategies and topographic analyses may, therefore, be vital for detecting and quantifying climate's role in landscape evolution. Lastly, we show how explicitly accounting for rainfall patterns in channel steepness indices, and thus spatial variations in erosional efficiency, may advance understanding of landscape sensitivity to climate. These results have important implications for detecting transient responses to changes in rainfall pattern (and more broadly climate), interpretation of morphometrics in steady state and transient landscapes, and quantifying the sensitivity of landscapes and erosion rates to climate.
Unraveling the relative impacts of climate, tectonics, and lithology on landscape evolution is complicated by the temporal and spatial scale over which observations are made. We use soil and desert pavement classification, longitudinal river profiles,10Be‐derived catchment mean modern and paleo‐erosion rates, and vertical incision rates to test whether, if we restrict our analyses to a spatial scale over which climate is relatively invariant, tectonic and lithologic factors will dominate the late Quaternary landscape evolution of the Calchaquí River Catchment, NW Argentina. We find that the spatial distribution of erosion rates, normalized channel steepness indices, and concavity indices reflect active tectonics and lithologic resistance. Knickpoints are spatially coincident with tectonic and/or lithologic discontinuities, indicating local base‐level control by faulting. Catchment mean erosion rates, ranging from 22.5 ± 2.6 to 121.9 ± 13.7 mm/kyr, and paleo‐erosion rates, ranging from 56+43/‐19to 105+60/‐33mm/kyr, are similar, possibly suggesting that Quaternary climate changes have not had a strong enough influence on erosion rates to be detected using cosmogenic10Be. However, punctuated abandonment of pediment and strath terraces at 43.6+15.0/‐11.6, 91.2+54.2/‐22.2, and 151+92.7/‐34.1ka and disparities between vertical incision rates and catchment mean erosion rates could suggest periods of landscape transience, possibly reflecting climate cyclicity. Our results emphasize the role of tectonic uplift and lithologic contrasts in shaping long‐term erosion rates and channel morphology at the relatively local scale of the Calchaqui River Catchment, in contrast to regional‐scale studies which find precipitation to exert the dominant control.
more » « less- NSF-PAR ID:
- 10459576
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 124
- Issue:
- 8
- ISSN:
- 2169-9003
- Page Range / eLocation ID:
- p. 2265-2287
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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