When Hurricane Helene battered the Southeastern U.S. in September 2024, it lasted only a few days but its impacts are far from over. The storm’s immediate destruction was followed by a chain of slower, subtler changes to the landscape, many of which are only beginning to reveal their consequences. In the wake of Helene, landslides buried roads river channels shifted, and forests were torn apart leaving behind unstable terrain and sediment-laden rivers that now pose long-term risks of flooding and erosion.
These are not just aftershocks they are part of a complex phenomenon scientists call cascading hazards.
A Chain Reaction of Destruction
Cascading hazards occur when one natural event sets off a domino effect of future dangers. A landslide triggered by a storm may block a river, only for that river to later flood when it can no longer flow freely. A wildfire can burn away vegetation and alter the soil, turning hillsides into high-risk zones for debris flows during the next rainfall. These changes don’t follow a predictable script and they don’t stop when the skies clear.
Geomorphologist and lead author of a new Science journal study, who worked with a team of researchers from 18 universities and the U.S. Geological Survey, says that understanding these linked disasters requires rethinking how we predict and prepare for natural hazards. Traditional models, which often rely on past events to forecast future ones, fall short in a world where the land itself is constantly reshaping in response to climate and geological shifts.
The Earth, in a sense holds onto the memory of disasters. Sediment disturbed by an earthquake or storm can continue to move and change the land for decades. One notable case is the 1950 Assam earthquake in India, which triggered thousands of landslides. The sediment from those landslides slowly moved through the Brahmaputra river system, eventually causing flooding and altering river courses in Bangladesh nearly 20 years later.
Similarly after the 2008 Sichuan earthquake China experienced an uptick in debris flows long after the shaking stopped. These delayed consequences show that the full impact of disasters can take years or even decades to unfold.
A Worsening Threat in a Warming World
While cascading hazards have always existed, their intensity and frequency are increasing. Climate change is amplifying the conditions that create these domino effects: stronger storms, more intense wildfires heavier rainfall. Meanwhile, urban development continues to encroach on fragile ecosystems, placing more people and infrastructure directly in harm’s way.
In California for example repeated cycles of wildfire followed by mudslides have made it increasingly difficult for residents to insure their homes. Some insurers have pulled out of the state altogether, citing unsustainable risks.
But it’s not just climate change that fuels these evolving threats. Earth own geological processes earthquakes, volcanic eruptions can also set off long-lasting hazards. The eruption of Mount St. Helens in 1980 continues to pose challenges to this day. The U.S. Army Corps of Engineers still manages ash and sediment to prevent downstream flooding more than 40 years later.
Rethinking Risk and Forecasting the Future
The traditional approach to estimating risk looking backward no longer suffices in a world of cascading hazards. What’s needed now are dynamic models that evolve in real-time, much like weather forecasting systems. Thanks to advances in remote sensing, including satellites, drones, and lidar (a laser-based mapping system), scientists can now track changes in terrain, river flow, and vegetation with remarkable precision.
These observations are fed into geomorphic models that simulate how sediment moves through landscapes. Researchers are already using such models to anticipate post-wildfire debris flows, and to predict how sediment pulses will impact river systems.
The goal is clear: turn the Earth’s memory into foresight. By understanding how one disaster sets the stage for the next, these models can help decision-makers implement better building codes, reinforce infrastructure, plan emergency responses, and revise insurance pricing to reflect true risk.
Living With an Evolving Landscape
The broader lesson from Hurricane Helene and other cascading events is that we must shift our mindset. Disasters aren’t isolated episodes they are part of an ongoing, interconnected system of change. Earth’s surface is not a static backdrop but a living, evolving system, shaped as much by yesterday’s storms as by today’s weather.
Understanding this dynamic is critical for resilience. It challenges communities, insurers, and planners to move beyond short-term recovery and embrace long-term adaptation. The transformations may be slow and quiet, but they are real and they are building toward the next crisis.
If we fail to track and prepare for these hidden hazards, we risk being caught off guard again. But with smarter forecasting, better data, and a deeper appreciation of nature’s complexity, we can build systems and societies capable of weathering what lies ahead.