Diagram from the study.
This illustration shows how diorite and monzogranite bedrock differ in shaping landscapes. The differences in rock type influence plant growth, soil characteristics, and water infiltration into the ground, leading to significant differences in runoff and erosion between landscapes underlain by these different rock types. Credit: Lodes et al. [2024], Figure 13
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Earth Surface

Drainage density, or the total length of rivers and streams within a landscape, influences how water and sediment move across Earth’s surface, making it a key factor for understanding landscape evolution. Rock type may be an important factor in setting drainage density, but its specific role in landscape evolution has been debated. Hard, erosion-resistant rocks typically produce fewer streams, while softer rocks promote dense river networks. However, variations in chemical weathering, vegetation, and soil formation can muddle simple relationships between rock type and drainage patterns.

Lodes et al. [2024] address this knowledge gap through a detailed analysis of topography and erosion in a slowly-eroding stream basin in semi-arid Central Chile. The authors find that landscapes underlain by monzogranite bedrock have higher stream density than those underlain by diorite bedrock. The nutrient-poor composition of monzogranite supports less vegetation, which leads to drier soils and increased surface runoff, ultimately producing denser stream networks. The monzogranite bedrock is also more weathered and breaks into smaller grains, making it easier for streams to carve through than the diorite.

These findings show that rock type can directly shape the patterns of stream networks, illuminating our understanding of the role of rock type in shaping hydrological systems. These results have important implications for predicting how landscapes may respond to climate change over geological time scales.

Citation: Lodes, E., Scherler, D., Wittmann, H., Schleicher, A. M., Stammeier, J. A., Loyola Lafuente, M. A., & Grigusova, P. (2024). Influence of lithology and biota on stream erosivity and drainage density in a semi-arid landscape, Central Chile. Journal of Geophysical Research: Earth Surface, 129, e2024JF007684. https://doi.org/10.1029/2024JF007684

  —Marisa Repasch, Associate Editor, JGR: Earth Surface

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