Landslides risk in South Dakota

Landslides in South Dakota: what causes them here

South Dakota is not a landslide hotspot the way California, Oregon or West Virginia are, and the state's overall landslide risk is rated low. That said, slope failures and related ground movement do happen here — and they tend to catch homeowners off guard, because they often occur on slopes that have looked stable for decades.

Three broad settings produce most of the state's slope movement:

• The Black Hills and surrounding foothills. Steep forested hillsides, canyon walls and road cuts in Lawrence, Pennington, Custer and Meade counties are the state's most landslide-prone terrain. Heavy rain on burned or cleared slopes can send debris flows and rockfall onto roads and into homes below.
• The Missouri River bluffs and valley walls. The steep bluffs that line the Missouri River trench — near Pierre, Fort Pierre, Chamberlain, Yankton and Vermillion — are made up of layered glacial deposits and shales that slump and slide when saturated.
• Pierre Shale and badlands terrain. Much of central and south-central South Dakota is underlain by the Pierre Shale, which contains bentonite clays that swell when wet and lose strength as they absorb water. The White River badlands in the southwest are the same story at a much faster pace, where soft rock erodes and collapses continuously.

Timing matters as much as location. The highest-risk windows are late winter and early spring, when snowmelt and spring rain soak into slopes, and the freeze-thaw cycles of that season repeatedly expand and weaken soil and rock. Summer thunderstorms can also trigger rapid failures, especially in the Black Hills. Long droughts can prime a slope for later failure: as clay-rich soils dry, they crack, and when rain finally arrives, water moves quickly into those cracks. Human activity is a major factor too — cut slopes for roads and driveways, added fill at the top of a hill, leaking water lines, septic drain fields and lawn irrigation all add water or remove support from slopes.

How it affects homes

Most landslide damage to South Dakota homes is slow rather than dramatic. A creeping slope or expansive clay soil can move a foundation by inches over years, producing cracks that are easy to dismiss as normal settling. Common signs and damage include:

• Cracks in foundations, basement walls, driveways, patios and interior drywall, especially cracks that widen over time.
• Doors and windows that begin to stick, or floors that feel uneven.
• Bowing or leaning basement and retaining walls as soil pressure increases.
• Soil pulling away from the foundation, or a visible bulge or slump at the toe of a slope.
• Broken water, sewer or septic lines, ruptured irrigation lines and damaged well casings as the ground shifts.
• In faster failures, rockfall, debris flows or a sudden slump that undermines a deck, garage or the home itself.

Insurance is the part many homeowners miss. Standard homeowners policies typically exclude earth movement, which includes landslides, mudslides, sinkholes and most soil settlement. Federal flood insurance through the National Flood Insurance Program generally does not cover landslide either, although its definition of "flood" does include mudflow. Some carriers offer a difference in conditions (DIC) or specialized earth-movement endorsement that can add back limited coverage; availability and terms vary widely, so it is worth asking your agent directly. Keep dated photos, repair receipts and any engineering reports — documentation helps if you ever file a claim or sell the home.

How to prepare your home

Because landslides cannot be prevented outright, preparation focuses on reducing water on slopes, recognizing warning signs early and avoiding changes that weaken ground under and around your house.

1. Learn your slope. Check county planning or zoning records and state geologic maps for known landslides or unstable soils near your property, and ask whether previous slope failures have been recorded in your area.
2. Move water away from the house and slope. Keep gutters clean, extend downspouts so they discharge several feet from the foundation, and grade the ground so it drains away from the home rather than toward the top of a hill.
3. Fix every leak. Repair dripping outdoor faucets, broken irrigation heads, leaking water or sewer lines and failing septic systems. Water is the most common trigger for slope movement.
4. Keep deep-rooted vegetation on slopes. Trees and shrubs with deep roots help hold soil. Avoid clearing entire hillsides, and do not over-water landscaping on or above a slope.
5. Do not cut into the toe of a slope or add fill at the top without advice from a licensed geotechnical or civil engineer. The same applies to new retaining walls, room additions, pools and driveways.
6. Inspect regularly. Watch for new cracks, tilted fence posts or utility poles, springs or seeps appearing on a slope, or soil separating from the foundation. Photograph anything suspicious with a date reference so you can tell whether it is changing.
7. Make a plan. Follow Ready.gov landslide guidance: if the ground starts moving, get out and away from the slide path rather than staying to watch, and warn neighbors. Alert local officials so roads and utilities can be checked.
8. Review your coverage. Talk with your insurance agent about what your policy does and does not cover, and document the condition of your home now.

Frequently asked questions

Does South Dakota actually have landslides?

Yes, though they are far less frequent and less destructive than in mountainous western states. The USGS Landslide Hazards Program documents landslide and debris-flow activity in the Black Hills, along steep river bluffs and in the state's shale and badlands terrain. Most events are small and slow-moving, but they can still cause serious property damage.

Is landslide damage covered by homeowners insurance in South Dakota?

Usually not. Most standard homeowners policies exclude earth movement, including landslides, mudslides and settlement. Federal flood insurance covers mudflow as part of its flood definition but does not cover landslide. Ask your agent whether a difference in conditions (DIC) policy or an earth-movement endorsement is available for your property, and read the exclusions carefully before you rely on any coverage.

Which parts of South Dakota are most at risk from landslides?

The steep slopes of the Black Hills and their foothills, the bluffs and valley walls along the Missouri River, and the clay-rich Pierre Shale and badlands areas of central and western South Dakota. Within those regions, risk is highest on cut slopes, on hillsides that receive concentrated runoff, and on properties where irrigation, septic systems or utility leaks add water to the ground.

Official resources

• South Dakota Office of Emergency Management — state preparedness, response and hazard information.
• USGS Landslide Hazards Program — science, maps and research on landslides and debris flows.
• Ready.gov – Landslides and Debris Flow — federal guidance on warning signs, evacuation and safety.