Deep beneath the slopes of the Oregon Coast Range, soil nearly 5 meters thick harbors far more carbon than scientists have realized—twice as much, according to new research that rewrites our understanding of how mountains store planet-warming greenhouse gases. The finding, led by researchers at the University of Oregon and published in Science Advances, suggests that hilly and mountainous landscapes have long been underestimated as powerful natural carbon reservoirs, opening new pathways for fighting climate change.
The discovery emerged from an unexpected place: nearly 10,000 landslides scattered across the Oregon Coast Range, some dating back 480,000 years. Brooke Hunter, then a doctoral student in the lab of earth scientist Josh Roering, and her team cored deep into six representative landslides to measure how much carbon they held. What they uncovered challenged a fundamental assumption in climate science. Previous global models estimated soil depths of about 30 centimeters in mountainous terrain. The Oregon researchers found something radically different: landslide deposits often contained soil more than 5 meters—16 feet—deep, packed with organic carbon accumulated over millennia of weathering.
Why had mountains been overlooked for so long? Partly because they are difficult to study. Mountainous terrain is hard to traverse, and measuring soil depth and composition across steep slopes requires painstaking fieldwork. Scientists studying carbon storage had instead focused on flat agricultural regions, where soil deposition and erosion patterns are more predictable and easier to model. Mountains were assumed to be poor carbon stores because they erode so rapidly that soil doesn't linger long enough to accumulate carbon. "There was a misconception that mountainous areas would not hold much carbon because they're so rapidly eroding and there's not much soil," Roering explained. "What we're saying is, it's actually the opposite."
The thick, fine-grained soils that accumulate in landslide zones proved especially good at trapping carbon. The finer the soil particles, the greater the surface area available to chemically bind carbon molecules—a process that unfolds over thousands of years as rock slowly weathers into soil. The older and more weathered these zones become, the more carbon they accumulate. When the researchers extrapolated their findings across the entire study area, the results were striking: carbon stocks in deep-settled landslides are roughly twice as large as predicted by previous global models.
This matters because soil holds more carbon than all vegetation and the atmosphere combined, as Hunter noted. Accurate carbon budgeting—knowing where carbon is stored and in what quantities—is essential for designing effective climate solutions. Scientists are increasingly exploring natural approaches like enhancing rock weathering by spreading minerals on landscapes or seeding soils to help them sequester more carbon. But these interventions work best when informed by precise maps and models that account for actual soil depth and composition.
The Oregon research underscores a crucial insight: there is no single climate fix. Instead, better geomorphic understanding of how landscapes shape soil storage can help scientists tailor solutions to specific sites. By integrating field observations with models that account for how terrain evolves over time, researchers can now identify mountainous regions likely to respond well to natural climate solutions. For landscapes already storing twice as much carbon as we thought, protecting that carbon—through forest cover that prevents erosion, for instance—becomes an even more urgent priority.