Counties in South Dakota where landslides pose the greatest threat

In South Dakota, over half of the land is susceptible to landslides in 6 counties.

A landslide occurs when rock, debris, or earth moves down a slope. Inclines like hills and bluffs are a critical element of slides, meaning mountainous regions are at higher risk. Typically, landslides are triggered by forces like heavy rainfall, snowmelt, earthquakes, volcanic activity, human activities, or some combination of factors. Often, they're impossible to predict.

According to the Geological Survey, places where weak or fractured earth sit on steep slopes are likely to experience landslides—for example, areas with a history of strip mining. In Appalachia, about 1,400 square miles of land are scarred by strip mining within the Ohio River basin, according to an Inside Climate News analysis of satellite imagery. Together, the "waste rock" left behind, increasing stream flows, and heavy rainfalls brought on by climate change create a deadly recipe for landslides. This part of Appalachia is also near the Gulf of Mexico, where fast-warming waters stir up exceptionally fast-growing storms, as was the case with Hurricane Helene.

Combined, these elements create the highest vulnerability to landslides in the region. Much of West Virginia, in particular, is at risk: In 47 of the state's 55 counties, more than 90% of the land is susceptible to slides. Parts of Virginia, Kentucky, Ohio, Tennessee, and North Carolina are also exceedingly vulnerable.

Parts of California's coastline have also been plagued by major landslides. Earlier this year, a rockslide destroyed a part of Highway 1 along the state's famed Big Sur. The earth below the highway isn't sturdy, and wetter storms are further weakening it, contributing to more frequent and severe landslides. The majestic Big Sur stretch is an iconic road trip and tourism destination, where the highway winds along cliffs above the Pacific Ocean. However, it was forced to close to most traffic, and still offers just one lane at some points.

Other landslide risk factors include population growth, rapid land use changes, urbanization, heavy logging and deforestation, and inappropriate use of lands—slopes in particular. Wildfires also generate landslide hazards, leaving behind excess debris that can be dragged down during floods, as was the case in Big Sur.

The heightened frequency and severity of landslides are a direct consequence of logging, mining, and climate change, with massive repercussions for safety and critical infrastructure in the U.S. and around the world.

Hazard maps like those from the Geological Survey are a tool that federal, state, and local governments can use to identify landslide vulnerabilities and prepare for them. Preparation and mitigation efforts might include landslide drills, evacuation plans, improved drainage systems, and slope stabilization. Governments in susceptible areas can adopt disaster-resilient building codes and standards, as well as restrictions on mining and logging.

In some cases, such as Highway 1, there are no obvious solutions to fully protect against landslides. Still, with increased awareness and response plans, people can make more informed decisions on where to live (or safely visit) and can prepare themselves for landslides and their aftermath.

Read on to see where in South Dakota is most vulnerable to the growing landslide threat.

- Percent susceptible area: 8.1%
- Total susceptible area: 34 square miles

- Percent susceptible area: 8.3%
- Total susceptible area: 48 square miles

- Percent susceptible area: 8.4%
- Total susceptible area: 73 square miles

- Percent susceptible area: 8.5%
- Total susceptible area: 37 square miles

- Percent susceptible area: 8.5%
- Total susceptible area: 49 square miles

- Percent susceptible area: 9.0%
- Total susceptible area: 71 square miles

- Percent susceptible area: 9.0%
- Total susceptible area: 91 square miles

- Percent susceptible area: 9.1%
- Total susceptible area: 85 square miles

- Percent susceptible area: 9.3%
- Total susceptible area: 64 square miles

- Percent susceptible area: 9.3%
- Total susceptible area: 107 square miles

- Percent susceptible area: 10.0%
- Total susceptible area: 81 square miles

- Percent susceptible area: 11.0%
- Total susceptible area: 95 square miles

- Percent susceptible area: 11.7%
- Total susceptible area: 95 square miles

- Percent susceptible area: 13.0%
- Total susceptible area: 105 square miles

- Percent susceptible area: 13.2%
- Total susceptible area: 70 square miles

- Percent susceptible area: 14.0%
- Total susceptible area: 78 square miles

- Percent susceptible area: 15.6%
- Total susceptible area: 107 square miles

- Percent susceptible area: 15.7%
- Total susceptible area: 164 square miles

- Percent susceptible area: 15.8%
- Total susceptible area: 173 square miles

- Percent susceptible area: 16.2%
- Total susceptible area: 101 square miles

- Percent susceptible area: 16.7%
- Total susceptible area: 118 square miles

- Percent susceptible area: 18.2%
- Total susceptible area: 134 square miles

- Percent susceptible area: 18.4%
- Total susceptible area: 136 square miles

- Percent susceptible area: 18.5%
- Total susceptible area: 85 square miles

- Percent susceptible area: 19.1%
- Total susceptible area: 99 square miles

- Percent susceptible area: 20.0%
- Total susceptible area: 220 square miles

- Percent susceptible area: 21.5%
- Total susceptible area: 186 square miles

- Percent susceptible area: 24.6%
- Total susceptible area: 554 square miles

- Percent susceptible area: 26.0%
- Total susceptible area: 122 square miles

- Percent susceptible area: 26.4%
- Total susceptible area: 427 square miles

- Percent susceptible area: 32.2%
- Total susceptible area: 928 square miles

- Percent susceptible area: 32.8%
- Total susceptible area: 879 square miles

- Percent susceptible area: 34.6%
- Total susceptible area: 481 square miles

- Percent susceptible area: 35.8%
- Total susceptible area: 887 square miles

- Percent susceptible area: 36.9%
- Total susceptible area: 435 square miles

- Percent susceptible area: 37.5%
- Total susceptible area: 616 square miles

- Percent susceptible area: 38.5%
- Total susceptible area: 1,339 square miles

- Percent susceptible area: 42.4%
- Total susceptible area: 739 square miles

- Percent susceptible area: 42.7%
- Total susceptible area: 779 square miles

- Percent susceptible area: 43.9%
- Total susceptible area: 863 square miles

- Percent susceptible area: 44.8%
- Total susceptible area: 435 square miles

- Percent susceptible area: 46.0%
- Total susceptible area: 861 square miles

- Percent susceptible area: 49.1%
- Total susceptible area: 711 square miles

- Percent susceptible area: 49.1%
- Total susceptible area: 1,139 square miles

- Percent susceptible area: 50.1%
- Total susceptible area: 657 square miles

- Percent susceptible area: 50.7%
- Total susceptible area: 516 square miles

- Percent susceptible area: 56.5%
- Total susceptible area: 1,571 square miles

- Percent susceptible area: 60.4%
- Total susceptible area: 1,265 square miles

- Percent susceptible area: 69.7%
- Total susceptible area: 1,086 square miles

- Percent susceptible area: 76.8%
- Total susceptible area: 614 square miles

This story features data reporting and writing by Paxtyn Merten and is part of a series utilizing data automation across 50 states.