The Hidden Peril: Slow-Moving Landslides Threaten Global Communities

Landslides are often associated with sudden, catastrophic events that sweep away everything in their path. However, a new study reveals the insidious danger of slow-moving landslides, which can creep at a pace as slow as one millimeter per year, yet still pose significant risks to human settlements. These gradual movements are frequently overlooked in risk assessments, leading to a false sense of security among communities residing on steep slopes in mountainous regions. As cities expand and populations grow, more people are forced to settle in these precarious areas, increasing their vulnerability to landslides that could accelerate abruptly, causing severe damage and even fatalities.

The study, published in the journal Earth’s Future, is the first global assessment of exposure to slow-moving landslides. It estimates that approximately 1.3 billion people currently live in mountainous regions, with hundreds of thousands residing on land susceptible to these creeping disasters. Joaquin Vicente Ferrer, the lead author, warns that this rapidly growing population is at considerable risk. The research highlights that about 7% of documented landslides are inhabited by large populations, with the most densely populated areas located in South America and Africa. Major settlements in Central Asia, Northeast Africa, and the Tibetan Plateau are also identified as being particularly vulnerable.

Urban growth is a significant factor contributing to increased exposure to slow-moving landslides. As cities expand into mountainous areas, the pressure for land forces populations to settle on unstable slopes, sometimes years after the initial landslide activity. This phenomenon is exacerbated by limited housing options, especially for poorer communities who have no choice but to inhabit these risky zones. The strength of the relationship between urban expansion and landslide exposure varies by region, with Western North America and Southeast Africa showing the strongest links between flooding and slow landslides.

The need for comprehensive mapping and monitoring of slow-moving landslides is urgent. The study emphasizes the importance of detailed risk assessments to better protect communities at risk. Enhanced mapping efforts would provide valuable information for urban planners, engineers, and emergency managers, enabling them to make informed decisions about land use and hazard preparedness. Such efforts are particularly crucial in regions with known risks but insufficient data, as more accurate maps could significantly reduce the impact of future landslides.

In the United States, a new study by the US Geological Survey (USGS) has produced a nationwide landslide susceptibility map, revealing that almost half of the country has potential landslide zones. This detailed assessment aims to support risk-reduction efforts and inform land-use planning. The map utilizes advanced data analysis and high-resolution elevation data, showing that 44% of the US could experience landslides, meaning millions of Americans may be living in more vulnerable areas than previously thought. The regions most susceptible include Appalachia, the Rocky Mountains, the California coast, and Southeast Alaska.

The USGS map was created by analyzing an inventory of nearly one million previous landslides and using high-resolution elevation data. This approach has provided a comprehensive picture of landslide risk, covering areas with known high risks and regions where the potential for landslides was not well understood. The map does not predict specific events or their timing but offers a probability-based assessment of areas more prone to landslides. This information is vital for homeowners and communities in high-risk areas, providing insights into preparedness and highlighting regions where further research and mapping are needed.

Climate change is exacerbating landslide risks, as heavy rainfall events – the primary trigger for landslides – are becoming more common and intense. The USGS recommends several precautionary measures for individuals living in high-risk regions, such as staying informed about local geology and monitoring warning signs like large cracks in the soil, leaning trees, and burned watersheds. In some cases, property owners may need to consult engineering geologists for evaluations. These proactive steps can help mitigate the impact of landslides and protect lives and property.

A recent USGS study found that 85 million people in the US sleep in areas with a high risk of landslides, while 75 million live in landslide-prone regions during the day. California has the highest number of people at risk, but West Virginia and Puerto Rico have the highest proportion of people in danger. The new map extends the range of areas at risk and includes regions beyond those with the highest threat. The level of detail provided by the map can be useful for urban planners, engineers, emergency managers, and homeowners, helping to create a more hazard-ready nation.

The new map uses color-coding to indicate areas with higher or lower susceptibility to landslides, with red being the most vulnerable, yellow being less so, and white having negligible risk. Landslides are defined as the movement of a mass of rock, debris, or earth downhill, and can be triggered by various factors including rainfall, snowmelt, changes in water level, stream erosion, earthquakes, volcanic activity, and human activities. Underwater landslides can also occur, causing tsunamis that can damage coastal areas. The detailed map helps individuals and communities be better prepared for these hazards.

Landslides pose a serious threat to communities in the Rocky Mountains and Sierra Nevada Mountains, as well as other regions highlighted by the USGS interactive map. Warning signs of a landslide include large cracks in the soil, leaning trees and telephone poles, and burned watersheds. The top trigger of landslides is extreme rainfall events, which are increasing due to human-caused climate change. Other triggers include earthquakes and human development. The map, created by analyzing nearly one million previous landslides, serves as a valuable tool for understanding landslide susceptibility in the US.

Research from the UK shows that landslides are not just a problem in the US. There have been over 400 landslides globally this year alone, resulting in over 3,600 deaths. This global scale of the issue underscores the importance of sharing information and raising awareness about natural hazards. The collaboration between different public media stations and the support of organizations like the Corporation for Public Broadcasting highlight the need for proactive measures to protect communities from landslides. The release of the USGS map brings attention to the ongoing threat and the necessity for increased efforts in mapping and monitoring slow-moving landslides.

Overall, the hidden peril of slow-moving landslides requires urgent attention and action. As urban growth continues and climate change intensifies, the risks associated with these creeping disasters will only increase. Comprehensive mapping, monitoring, and risk assessments are essential to safeguard vulnerable populations and reduce the impact of future landslides. By staying informed and taking proactive measures, communities can better prepare for and mitigate the effects of these insidious threats. The new studies and maps provide valuable resources for understanding and addressing the complex challenges posed by slow-moving landslides, ultimately contributing to a safer and more resilient world.