The hidden life of ancient landscapes: Insights from Brazil

Sometimes, you look at a vast, flat landscape—like the Araripe Plateau in northeastern Brazil—and it feels eternal, immovable. But that calm surface hides a dynamic, slowly unfolding story. Despite its apparent stability for nearly 90 million years, Araripe is anything but static. Beneath the quiet lies a tale of erosion, buried sediments, and the delicate balance between geology and time.

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This plateau isn’t just scenic; it plays a key role in dividing major river basins—the Jaguaribe, the São Francisco, and the Parnaíba—and offers a window into how dryland landscapes evolve over geological timescales. At the heart of this research are two powerful tools: cosmogenic nuclide analysis and geomorphic metrics. The first involves measuring isotopes like beryllium-10 and aluminum-26—natural cosmic “clocks” formed when rocks are exposed to cosmic particles. These reveal how long a surface has been exposed and how fast it is eroding. The second includes analysing river steepness and features like knickpoints to interpret erosion dynamics.

What do these tools tell us?

The Araripe Plateau is eroding at a snail’s pace—less than 20 meters per million years. That’s slower than the thickness of a sheet of paper per century. Yet, this slow erosion isn’t uniform. Regions underlain by softer Paleozoic rocks erode faster than areas capped by resistant Cretaceous sandstones and conglomerates. Rock type—lithology—emerges as the dominant force in long-term landscape evolution.

And the sediment? It’s not just freshly eroded material. In some river systems, up to 84% of sediment comes from previously buried deposits—floodplains storing, then releasing, ancient particles. This mixing complicates the interpretation of erosion rates and tells us that river systems are far from simple conveyors of material—they are archives of complex histories.

Geomorphic metrics add more layers. High stream steepness values and numerous knickpoints in the north and northwest suggest more active incision. In contrast, gentler slopes in the São Francisco basin may reflect longer periods of erosional smoothing. Perhaps even more fascinating: the rivers are stealing territory from each other. Drainage divides are not fixed; over time, the Parnaíba basin is encroaching on its neighbors in a slow-motion hydrological tug-of-war.

Comparisons with other Brazilian landscapes deepen the picture. In the Vermelho Watershed, fluviokarst and steep escarpments show much faster erosion. In the Paraná region, complex rock types and slope variations lead to spatially variable denudation. In both regions, just like Araripe, the evidence points to buried and reworked sediments—meaning apparent erosion rates can be misleading without careful interpretation.

Across all three regions, the conclusion is clear: erosion is slow, lithology matters, and sediment histories are complex. Understanding these ancient rhythms of change not only enriches our view of Earth’s past but also helps us frame the challenges of today. Human activities—deforestation, urbanization, mining—can drastically accelerate these slow natural processes. How we alter sediment flows and disrupt long-term stability raises profound questions about our impact on landscapes shaped over millions of years.

In the end, even the most ancient landforms are in motion. We just need the right tools—and the patience—to read their stories.

The Araripe Plateau, on the Cearense side shot in August 2019 during the fieldwork that will yield the results published in Oliveira et al. (2025) - Shot on Minolta XG9 and Kodak Proimage 100.

References: 

Oliveira, J. G., Siame, L. L., Santos, L. J. C., Leanni, L., Ribeiro, S. C., de Holanda Bastos, F., & Aster Team. (2025). Relief inversion and denudation dynamics in a semi-arid landscape (Araripe Plateau, NE Brazil): Insights from cosmogenic nuclides and geomorphic surfaces. Evolving Earth, 3, 100064.

Uagoda, R., Siame, L. L., Garnier, J., Leanni, L., Caldeira, D., Braucher, R., ... & Aster Team. (2025). Decoding surface processes from escarpment to watershed: Insights from karst landscapes using cosmogenic nuclides and geochemical data. Geomorphology, 109794.

Bortolini, W., Siame, L. L., da Silveira, C. T., Leanni, L., Santos, L. J. C., & ASTER Team. (2025). Denudation asymmetries and drainage divide migration: Insights into the evolution of the Devonian Escarpment in Paraná, Brazil. Geomorphology, 109813.