Landslide susceptibility and slope instability

The Czech Geological Survey (ČGS) keeps two different things on slope movements. The register of slope instabilities, now also called the register of slope deformations, lists landslides, flows, rockfalls and other slope movements documented in the field and mapped at 1 : 10,000. The landslide susceptibility map divides land into classes by how favourable the conditions for a landslide are.

How to read the data

• Landslides in the register are active, temporarily inactive or inactive. A registered landslide nearby is a concrete finding; what matters is distance, activity and whether it lies above or below the house.
• The susceptibility map has low, medium and high classes. According to ČGS, in the medium class slope instabilities cannot be ruled out, while the high class marks areas with the most favourable conditions for them.
• The susceptibility map is displayed down to a scale of 1 : 25,000, so it is not meant for assessing a single plot.

What to watch out for

For a house on a slope, look for cracks in walls and retaining walls, tilting trees, fences and poles, or waterlogged spots. Before building on a slope, an engineering geologist can assess its stability. Cracks and ground subsidence can also have other causes, such as old mining or faulty foundations.

Frequently asked questions

Is susceptibility the same as a landslide?

No. “Medium landslide susceptibility” is a property of an area on a map, derived from geology and terrain shape, not a problem found at the house. Only a record in the register is a concrete finding.

Where can the maps be found and what else helps?

The register and the susceptibility map are public in the ČGS map services. The slope above and below the house can be estimated from the digital terrain model, and older aerial images show how the slope changed over time.