What are the signs of landslide development? What do I do if a landslide occurs?

By Landslide Hazards Program

Landslides are dangerous and very difficult to predict. Some landslides may provide clues that they are about to happen; others may happen suddenly without any warning signs.

Signs of a moving landslide include:

Sounds of cracking or breaking wood, knocking boulders, groaning of the ground, or other unusual sounds - especially if the sound increases.
Rapidly moving landslides are said to generate a loud rumble and ground vibrations, like the sensation of a passing freight train.
If you are near a stream, a sudden change in stream water levels, especially during or right after an intense or prolonged storm event.

Geologists assess damage after debris-flow event

Sources/Usage: Public Domain. View Media Details

Heavy rainfall on the afternoon of August 3, 2022 triggered a debris flow in the Hermits Peak-Calf Canyon burn area. A USGS monitoring station installed in the drainage basin captured video footage of the flow. This clip of the video shows the flow from 13:43:00 MDT to 13:45:32 MDT.

Image: 2005 Landslide in La Conchita, CA — On January 10, 2005, a landslide struck the community of La Conchita in Ventura County, California, destroying or seriously damaging 36 houses and killing 10 people. For a USGS rerpot on this event, please see USGS Open-file report, "Landslide Hazards at La Conchita, California."

If you notice these signs or observe a landslide in progress:

Leave the area immediately, but only if it is safe to do so! Landslides are dangerous, very difficult to predict, and can occur rapidly. A landslide can instantaneously destroy a car or house.
If you are in a building being hit by a landslide, it is best to not evacuate and either go to the highest floor or climb onto a countertop until the landslide passes. If you evacuate in an active landslide, the landslide can carry you away. Note that landslides may occur in pulses, so the first landslide may not be the last landslide.
Report the landslide immediately to your local authorities.

Geologists assess debris flow — USGS geologists deployed to Santa Barbara County to support a geohazard assessment of the Montecito area

Signs of a potential landslide:

New cracks, bulges, or other deformation in the ground, roadways, or other surfaces.
The appearance of flowing water on a slope or water ponding where this has never occurred before.
Sagging or taut utility lines caused by leaning utility poles, deformed fences, or tilting of trees on a hillside.
Sticking windows or doors; new cracks in walls, ceilings, or foundations.
Broken or leaking utilities, such as water, septic, or sewer lines.
Separation of structures from their foundation or soil pulling away from the foundation.
Abnormal changes in water well levels.

Home with large crack in foundation — Building damage caused by a slow landslide in Boyd County, Kentucky. Previous repairs reveal that the landslide has moved in the past.

large crack in residential yard — Large cracks formed in this yard after a large landslide occurred downslope of a home. Though the home wasn't directly impacted by the landslide, the cracks in the yard are indicators of potential additional movement and increased landslide risk.

crack in home due to slow landslide movement — Building damage caused by a slow landslide in Boyd County, Kentucky, 2017

If you observe some of these warning signs it should be reported to your local authorities so that the area can be properly evaluated. You may need to hire a professional geologist or engineer with landslide experience to assess your property.