Rock strength shapes the evolution of Earth's landscapes

Rock formations can appear to be static, silent observers of the passage of time. But under their apparently immovable form, they are in a state of constant change, molded by immense natural forces.

Mountains form over millions of years, as tectonic plates crush into each other. Glaciers, persistent rain, and constant winds, on the other hand, slowly erode the mountains away.

These forces shape the landscapes we observe today, but there is one often-forgotten factor that is important in this process: the rock’s strength.

To learn more about this aspect of landscape evolution, scientists from the University of Toronto Mississauga undertook a detailed investigation of rock strengths and how these affect erosion rates.

Their work, which appeared recently in Science Advances, uncovered a surprising revelation – rock type alone can result in a whopping 20-fold contrast in erosion rates.

This is something that has been underappreciated in past geological models.

The researchers centered on a 200-kilometer section of the southeastern coast of Brazil, an area with a stable climate and little tectonic activity, which made it a perfect natural lab.

By separating rock strength from the other factors, they obtained new knowledge about how landscapes change through time.

Measuring erosion and rock strength

To determine how quickly different types of rock erode, the scientists took a multi-faceted approach, analyzing both erosion rates and the physical properties of the rocks themselves.

They studied river sediments to track landscape changes over time, and provided a clearer picture of long-term geological transformations.

A key part of their research involved measuring the concentration of beryllium-10, a rare radioactive isotope that forms when cosmic rays strike Earth’s surface.

This isotope acts as a natural geological clock – similar to how tree rings reveal a tree’s age – which allows scientists to estimate how long a rock has been exposed to erosion.

The more beryllium-10 present, the longer the rock has remained at the surface.

The team also used a specialized tool called a Schmidt hammer to measure rock strength. This device works by striking the rock with a spring-loaded mass and recording the force of its rebound.

Stronger rocks produce a higher rebound, much like a basketball bouncing higher on a hard court than on soft grass.

Role of rock type in erosion

“The hypothesis is that, if rock strength matters, we ought to see a correlation between rock strength and erosion rates,” explained Lindsay Schoenbohm, a professor of Earth sciences at the University of Toronto Mississauga, and the study’s lead researcher.

“Harder rocks should equal slower erosion rates,” she noted.

The study confirmed this pattern, showing that rock type plays a crucial role in shaping landscapes. Softer rocks erode quickly, influencing the formation of valleys, river systems, and even mountain structures.

Database named “Thor”

To make their findings widely accessible, the researchers compiled their rock strength data into a publicly available database, nicknamed “Thor.”

Launched in December, this resource offers valuable data for scientists studying climate, tectonics, and landscape evolution.

“We created it for people like us, initially – people who are looking at erosion rates in landscapes,” one scientist noted. “But I think the applications could be extremely broad.”

By emphasizing the role of rock strength in shaping landscapes, this research lays the foundation for future studies.

Scientists can now better predict how landscapes will evolve by factoring in not only external forces like climate and tectonics but also the physical properties of the rocks themselves.

Rock strength and land management

Understanding how rock strength influences erosion isn’t just about reconstructing the past – it has real-world implications for the future.

As climate change accelerates weathering processes, areas with softer rocks may undergo more rapid landscape transformations, increasing sediment flow into rivers and coastal ecosystems.

This, in turn, can affect water quality, agriculture, and infrastructure stability.

The findings could also help guide land management and conservation efforts. By identifying regions with highly erodible rock types, policymakers can develop strategies to prevent excessive soil loss and protect ecosystems.

The Thor database offers a valuable tool for scientists and environmental planners to anticipate landscape changes and make informed decisions about land use and conservation.

With these insights, researchers are not only refining our understanding of Earth’s ever-changing landscapes but also offering practical solutions for managing and protecting them.

The full study was published in the journal Science Advances.

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