In the United States, landslides occur in every single state and territory.
However, they are most common in the coastal and mountainous regions of California, Oregon, and Washington.
Alaska and Hawaii also experience landslides more often than other states.
If you’re in an at-risk location, here’s how you can prevent landslides.
1. What is a landslide?
The term landslide describes a wide range of ground movements such as rockfalls, deep failure of slopes, and shallow debris flows.
The main reason for a landslide is gravity acting on an over-steepened slope.
With that, however, there are other contributing factors.
These include:
Erosion by rivers, glaciers, or ocean waves that create over-steepened slopes
Rock and soil slopes that are weakened through saturation by snowmelt or heavy rains
Earthquakes that create stresses that make weak slopes fail
Earthquakes that are a magnitude 4.0 and greater
Volcanic eruptions that produce loose ash deposits, heavy rain, and debris flows
Excess weight from the accumulation of rain or snow, stockpiling of rock or ore, waste piles, or man-made structures that stress weak slopes to failure and other structures
When slope material becomes saturated with water, it may develop a debris flow or mud flow.
This slurry of rock and mud can pick up trees, houses, and cars and block bridges or tributaries, which causes flooding along its path.
2. Where do landslides occur?
As noted above, landslides occur in every single state and U.S. territory.
In fact, the Appalachian Mountains, the Rocky Mountains, and the Pacific Coastal Ranges as well as some parts of Alaska and Hawaii have severe landslide problems.
If you’re located in an area composed of very weak or fractured materials resting on a steep slope, then you’re at risk of experiencing landslides.
3. How can you prevent landslides?
The physical causes of landslides cannot be removed.
However, geologic investigations, good engineering practices, and effective enforcement of land-use management regulations can help to reduce landslide hazards.
So, if you live in an area that’s naturally prone to landslides, you’ll want to follow these steps to protect your property.
Keep material and structures away from slopes
1. Remove loose or heavy material from the top of the slope
Rocks, fallen trees, and other debris — primarily at the top of a hill — can put your property at risk for a landslide.
Clear off your property’s slopes and remove any material that may come loose to minimize landslide risk.
To do this, you may need to hire a professional with heavy equipment.
We recommend consulting a contractor.
When removing material, be sure to relocate it all together.
DO NOT move it to a place where it could slide onto your neighbor’s property.
2. Avoid piling junk at the top of a hill
If you pile all your junk at the top of the hill, it can come loose and slide down the hill.
“Junk” includes scrap wood, lawn cuttings, spare parts, etc.
Pile all debris at least 10 feet away from the edge.
You should also avoid dumping water at the top of the slope as this can cause it to gradually erode the soil and make it looser.
3. Build sheds and other structures away from an edge
If you’re planning to put a new structure on your property, make sure it’s far from the edge of a slope.
We recommend consulting an engineer before building to ensure it’s a safe distance.
While there isn’t a hard rule on how far it should, you can follow their advice before you start building.
The distance will depend on the soil, drainage, slope, and how prone the area is to landslides.
Control the water on your property
1. Fix any leaks in your pipes or drainage system
When you have leaks in your water system, they can gradually erode the soil under your property.
Hire a professional to check all your pipes and ensure there are no leaks.
If you do find leaks, then you should fix them right away.
A couple of signs that leaks exist include an unusually high water bill, a musty smell, or puddles on your property when it hasn’t rained.
You should check both indoor and outdoor lines, including your pool.
Leaky pools are a common cause of gradual soil erosion.
2. Install flexible fittings to prevent your pipes from breaking
Using flexible fittings prevents leaks because they won’t crack.
You can install these yourself or have a plumber do it for you.
They’re useful in areas prone to landslides because they won’t break if there’s a shift in the ground.
3. Make sure your drainage system leads directly to the base of the incline
If you have a downspout, it must carry water all the way to the bottom of the slope.
This stops the water from either pooling or running down the slope and loosening the ground in the process.
If the base is further than your property goes, then make sure your system flows to the nearest storm drain or natural runoff area.
Your system should also drain far away from your neighbors as well because you don’t want your water draining onto their property.
4. Avoid building sprinkler systems on a slope
Sprinklers on a slope can loosen and erode soil, which makes it unstable.
To prevent this, locate your sprinkler system a safe distance away from the slope.
Have a professional install any irrigation system you put on your land so that it complies with local codes about how far it must be from a slope.
Strengthen the ground
1. Remove loose soil and replace it with more dense material
Remember, soil erosion is a huge factor in landslides.
Consider speaking with a contractor about replacing your topsoil with denser, tightly packed sandy soil.
This can help make your property more stable.
However, as with all the items on this list, you must hire a professional for this job because it requires machinery and equipment.
Additionally, to prevent increased landslide risk, you cannot push any old material back up the slope or toward the edge.
Finally, with this step, you must take other landslide prevention steps.
Otherwise, this soil will erode as well and become landslide-prone.
2. Build a retaining wall at the base of a slope to protect your home
If you live at the base of a slope, then your best chance for protection is a heavy brick retaining wall.
It should extend the entire length of your property.
We recommend using mortar to connect the bricks instead of dry-stacking them as dry-stacked walls don’t provide much protection from a landslide.
If you want to go the extra mile, reinforce your retaining wall with metal spikes drilled into the ground rock.
Invest in a professional who is experienced in building these types of walls, especially in an area prone to strong landslides.
3. Plant trees and shrubs on hills to keep the soil packed and protected
Vegetation is one of the best ways to keep soil from eroding, which helps prevent landslides.
If the soil on your property is bare, try planting some plants with thick, deep-rooted systems.
We recommend trees, shrubs, and tall grasses.
If your slope already has plants on it, protect them.
Don’t cut them down or pull up shrubs without replacing them.
If you must remove vegetation for some reason, get new plants in place as soon as possible.
Preventing erosion is key to preventing landslides.
If the slope is primarily on your neighbor’s property, then talk to them about growing plants there.
If necessary, offer to help pay for it.
This could be the factor that helps protect your property.
4. Dig a ditch to divert landslides away from your home
Landslides can still happen, and if you live in a landslide-prone area, then there’s a good chance that they still will.
So, you should protect your home with a ditch surrounding your property.
This ditch will help to capture or divert the debris to another location and thus protect your home from any potential damage.
Before you get started on this job, make sure you consult a contractor.
A proper ditch requires a lot of technical knowledge and equipment.
It’s not as simple as just digging a hole in the ground.
Make sure the debris is redirected to a vacant area.
You never want your ditch to redirect debris to a neighbor’s property.
This could harm them or their property, and you could be liable for damages.
4. Should you live in a landslide-prone area?
That’s a great question!
The best way to prevent landslides is to abandon the areas of greatest geohazard.
When possible, evacuate from areas that are prone to landslides or limit the use of lands where slope stability is questionable.
There should also be early warning systems based on the monitoring of ground conditions, like slope displacement and groundwater levels.
5. Why study landslides?
Landslides are a geologic hazard that occurs in every state in the U.S.
Because they affect every area, they’re worth studying to understand how they can be prevented as well as how their damages can be mitigated.
In the U.S. alone, landslides are estimated to cause over $1 billion in damages.
They also cause anywhere from 25 to 50 deaths per year.
You can’t address these issues without understanding them.
6. What is a debris flow?
When discussing landslides, you’ll often hear the phrase “debris flow” used.
Mudslides, mudflows, lahars, or debris avalanches can all be referred to as debris flows.
They’re all common types of fast-moving landslides that generally occur during periods of intense rainfall or rapid snowmelt.
These flows typically start on steep hillsides or shallow landslides.
They will liquefy and accelerate to speeds that are about 10 mph.
That said, they can exceed 35 mph.
The consistency of debris flows ranges from watery mud to thick, rocky mud.
The flow can carry large items, including boulders, trees, and cars.
They are among the most dangerous types of landslides in the world due to their high speeds and sheer destructive force.
7. Are debris flows or floods more dangerous?
Debris flows are more dangerous and destructive than floods for the following reasons:
10 to 50 times greater peak discharge
Flow height up to 5 times greater
Flow velocity same or greater
Greater than 50 percent sediment content
Coarse-grained surge fronts
8. What should you do before a landslide?
If you know you’re in a landslide-prone area, you should take the following actions to stay safe.
Adhere to local land-use regulations. Your home should always follow local building codes to make sure your house is as safe as it can be in a given area.
Put property protections in place. Use the tips above to protect your property with retaining walls, vegetation, nets, sandbags, etc.
Add sandbags in exposed areas. This can help you divert water from pathways or places where a retaining wall or vegetation has given out.
Avoid building your home in places that may be in a path of a landslide. If possible, don’t build your home near a slope that’s at risk of a landslide.
Do your search. Check the FEMA Flood Map Service Center to understand flood zones and land slippages in your area.
Look for new cracks in your home. You may find them in your door, window jambs, walls, foundation, etc.
This can be an indication of a previous landslide and demonstrate the risk of a future landslide as well.
9. How do you stay safe during a landslide?
If a landslide is occurring in your area, here’s what you do.
You must act quickly!
Get to higher ground. If you’re not able to evacuate because the landslide is already upon you, get to an upper level of your home and listen to the radio/TV for updates.
Watch for flowing water. If you’re in your vehicle, watch for any flowing water as this could be an indication a landslide will occur.
Listen for boulders knocking together or trees crackling. This is important especially if you’re hiking.
You want to listen for any sounds that could indicate a slope so you can move to higher ground if needed.
You’re generally safer away from slopes.
10. What do you do after a landslide?
The aftermath of a landslide can be scary.
Here are the steps we recommend.
Avoid the area where the landslide occurred. Even if you think the landslide is over, it might not be.
Take extra precautions.
Call for help if you were immediately affected. If you’re trapped, then you want rescue missions to be able to hear and reach you as fast as possible.
Check for damage on your property. Once local authorities clear you to return to the area, check your property for any damages and report it.
Listen to your water company. After a landslide occurs, your water may be contaminated.
Pay attention to any boil advisories or communications from your local water utility company.
Final Thoughts
Landslides are scary, and most people don’t realize how commonly they occur.
If you live in an affected area, make sure you read up on local recommendations and take the proper precautions.
You don’t want to put yourself or your house at risk accidentally.
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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.
Prior to starting Gokce Capital, Erika received a Bachelor of Architecture from the University of Southern California and a graduate degree in Urban Policy from Columbia University. She worked as both an architectural designer and engineer in New York before joining the New York City Department of Housing Preservation and Development.
Erika currently lives in the New York Metropolitan area with her spouse, daughter and cat. She is originally from Chicago and still considers herself a midwesterner at heart.
Erika also loves to read, write and travel (fun fact, she has visited all 50 states and more than 30 countries!). Her new book, Land Investing Mistakes: 11 True Stories You Need To Know Before Buying Land, is now available on Amazon.