Landslide

Background & Extent

What Triggers Landslides?

Often landslides are triggered from a combination of activities including:

Intense rainfall: Soil and rock material on slopes may have high moisture levels, increasing pore-water pressure, which destabilizes the slope and causes slides. Subsequently, surface-water erosion may also cause landslides.

Earthquakes: Ground shaking during earthquakes can cause landslides in many different topographic and geologic settings.

Water-level change: Rapid lowering of groundwater against a slope can trigger landslides, especially along dams, coastlines, reservoirs, and rivers. The pore pressure in soil or rock material may not be able to adjust to a sudden drawdown of water causing slope instability.

Human activities: Many destabilizing activities may trigger landslides. These include vegetation removal, surface and underground mining, excavation of toe slopes, loading on a slope, and leakage from pipes.

Geology: Easily weathered rock types and soils, especially on steep slopes, combined with the triggers listed above are susceptible to landslides.

How Do Landslides Move?

Landslide is a general term for a wide variety of down slope movements of earth materials that result in the perceptible downward and outward movement of soil, rock, and vegetation under the influence of gravity. In areas where a landslide is prone to happen, the event itself usually must be triggered by some other phenomena such as an earthquake or heavy rainfall. Slope failures are major natural hazards throughout the world. A slope failure is classified based on how it moves and the type of material being moved.

There are four identified types of major slope failures:

• Slide: A slide is the downward displacement of material along one or more failure surfaces. The material can be soil, rock, etc., and may be broken into a number of pieces or remain a single, intact mass.
• Flow: A flow is similar to a slide in the fact that downward displace of materials occur. However, the distinguishing characteristic is the high water content involved in a flow. The combination of loose soils, rocks, organic matter, air, and water form a mass with the appearance of a viscous fluid.
• Lateral Spred: A lateral spread refers to the displacement of gently sloping ground as a result of pore pressure build-up or liquefaction in a shallow, underlying layer of material. The movement rates are typically very slow but can occur spontaneously.
• Falls: A fall occurs when masses of roc or other material detach and descend down a steep slope or cliff. Falls usually result from an earthquake or common erosion and gravity. The movement rate of a fall is extremely rapid and damage can be critical.

Location, Past Events, & Impact

The following map displays landslide locations in the BRADD region from the Kentucky Geological Survey. KGS determined possible landslide locations through local reports, LiDAR-derived digital elevation models, and aerial photos. A complete data breakdown can be found here.

Please note that the landslides shown on the map do not have the same confidence ranking. Confidence ranking indicates how likely it is that the landslide occurred, and it can range from 1, possible landslide to 8, definite landslide. 

How to use the map: 

1. Select your county to just see its landslide locations.
2. Hover your mouse  over the dots to find more information about the landslide location – such as geologic formation, confidence level, etc. 
3. Hover your mouse over the map to zoom in and out and search for a location. 

Probability

Occurrence

Since 1991, KGS has recorded 43 possible landslides in the BRADD region. Please note that the map in the previous section includes all landslides within the KGS database, and therefore it shows 3 more events that occurred before 1991. 

• Allen County:  0 events/30 years = 0 landslide events per year or 0% chance of a landslide event happening annually.
• Barren County: 3 events/30 years = .1 landslide events per  year or 10% chance of a landslide event happening annually. 
• Butler County: 18 events/30 years = .6 landslide events per year or 60% chance of a landslide event happening annually
• Edmonson County: 5 events/30 years =.17 landslide events per year or 17% chance of a landslide event happening annually.
• Hart County: 6 events/30 years = .2 landslide events per year or 20% chance of a landslide event happening annually.
• Logan County: 2 events/30 years = .06 landslide events per year or 6% chance of a landslide event happening annually. 
• Metcalfe County: 2 events/30 years = .06 landslide events per year or 6% chance of a landslide event happening annually. 
• Monroe County: 3 events/30 years = .1 landslide events per year or 10% chance of a landslide event happening annually. 
• Simpson County: 0 events/30 years = 0 landslide events per year or 0% chance of a landslide event happening annually. 
• Warren County: 5 events/30 years = .17 landslide events per year or 17% chance of a landslide event happening annually. 

Landslide Susceptibility

During Kentucky’s 2018 Hazard Mitigation Plan update, Kentucky Geological Survey (KGS) developed a landslide susceptibility map for the state in order to show which areas have greater landslide risk due to slope and geology. Using the KGS data, BRADD staff created a landslide susceptibility dashboard for our 10-counties. Click on the button below to access the BRADD Landslide Dashboard.

Overall Probability

Overall, the BRADD HMP ranks the probability of a landslide occurrence as low to medium because of past events, climate change, and landslide susceptibility. This was determined using the classification definitions outlined by FEMA (click here for more information).

Vulnerability & Impact

There is little warning time prior to the beginning of landslide. As such, landslides have the following potential impacts:

Hazard Vulnerability Summary Analysis

Overall, the BRADD region has a low to moderate vulnerability to landslide events. For a break down by county, please use the accordion below.