Landslides & debris flow
A landslide is a sudden displacement of earth masses, surface weed and rock masses of the ground caused by natural forces or human activity. Landslide sites are natural slopes, valleys’ slopes, water reservoirs, the vicinity of river springs, slopes of excavations and embankments and pits. They may be caused by many factors, including earthquakes, storms, volcanic eruptions, fire and human modification of the land. Over 95% of all landslides in Poland occur in the Carpathian Mountains. It’s also estimated that there’s on average one landslide per 5 km of road and 10 km of railway line in the Carpathians.
During a landslide, masses of rock, earth or rubble move down the slope. Flow of rubble and mud contains rocks, earth and other debris saturated with water. Landslides are developing during heavy rainfall, run-off or rapid snowmelt, turning the earth into a flowing river of mud or “slurry”. They can flow quickly, hitting with little or no warning at avalanche speeds (faster than a man is able to escape). Additionally, they can travel many kilometres from their source, increasing in size as they collect trees, boulders, cars and other materials. Waste streams don’t always stay in the stream channels and can flow sideways or downwards.
When a fire burns a slope, the probability of rubbish flow increases for several years. Although some landslides require long rain and saturated slopes, debris flow can start on a dry slope after just a few minutes of intense rain (about 1 cm of rainfall per hour). In the case of landslides, the precipitation area is more important than the sum of the precipitation over a certain time. Landslides cause various losses: degradation of the area and destruction of all infrastructure (residential buildings, road network, sewage system, telecommunication lines, electricity, gas pipelines, crops, forests).
Before
Here’s what can be done to protect yourself, your family and property from the landslides or a debris flow effects:
• Design a Family emergency plan
• Follow local media’s messages and alerts, obey evacuation warnings
• If you have been instructed to evacuate or you consider it being necessary, do it. Evacuation is often the only way to protect yourself from debris flow or other fast-moving landslides
• You should be prepared for landslides’ appearance by following proper land-use procedures. Avoid building nearby the steep slopes, the mountains’ edges, near a drain or along natural erosion valleys
• Familiarize yourself with the environment. Find out if the landslides had already happened by contacting local officials. Don’t assume that if it took place, the danger for the specific area is bigger. Waste flows can start in places where they never occurred and return to the slopes where they already had been at
• Have your property assessed by a qualified geotechnical expert and follow his recommendations
• Consult with the specialist for advice on appropriate preventive measures for your home or business, such as flexible pipe fittings that can better prevent breakage
• You can’t stop or change the rubble flow path. However, you may be able to protect your property from floodwater or mud with sandbags, retaining walls or rails (barriers)
• In mud and debris flow areas, consider building channels or deflecting walls to direct the flow around buildings. Remember: when the flow is large enough, it goes where it prefers, anyway. Additionally, if you change the flow and it passes through your neighbour’s property, you may be liable for a damage
• If you’re at risk of a landslide, talk to your insurance agent and take out appropriate insurance
Warning signs recognition
Beware of debris flow and other fast-moving landslides that are life-threatening:
• If you’re in the vicinity of a fire, check the alarm notifications and pay attention to the weather forecast for the fire site. The weather nearby the fireplace might be extremely different
• Pay attention and beware of rushing water, mud and unusual sounds
• Abnormal sounds, such as trees crashing or boulders hitting, may indicate an avalanche of stones moving on
• As the landslide approaches, you might hear a silent rumble that will get stronger after time
• Fences, retaining walls, utility pillars, architectural barriers, boulders or trees start to move
• Huge boulders in the landscape may be a sign of the flow of rubble from the past
Beware of slow landslides that are considered as a threat to buildings:
• Changes such as the visible effects of earth movements, small slides and gradually leaning trees are appearing
• Doors or windows jam
• New cracks appear on plaster, tiles, brick or foundations
• External walls, pavements or stairs start to move away from the building
• Slowly expanding, widening cracks appear on the ground or in hardened areas such as streets or driveways
• Underground power lines break down
• A bulging area occurs at the base of the slope
• Water breaks through the earth’s surface in new places
• Fences, retaining walls, utility poles or trees tilt or move
• The earth falls down in one direction and may start to move in that direction underfoot
During
• Follow the local news stations on the radio for warnings
• Comply with all warnings and evacuation notices
• Stay vigilant during a storm that may cause a landslide. There’re many deaths due to landslides, especially at night
• Remember that waiting in order to make sure that the flow of debris is coming can be fatal. It may be too late to escape
• Don’t cross the street with flowing water or mud. Furthermore, don’t cross a bridge if you see a flow approaching. It may grow fast and unable you to escape
• If you get stuck on a landslide, go up the hill as fast as possible
• Avoid river valleys and low-lying areas during times of danger
• If you’re near a stream or canal, pay attention to the sudden increase or decrease in water flow, which changes from clean to muddy. These may be signs that a landslide is coming
After
• Stay away from the landslide gutter. A danger of additional flows may exist
• Listen to local radio or TV stations for the latest information and announcements
• Watch out for floods. They may sometimes follow landslides and rubble flows as the same conditions are a cause of their origination
• Check for injured and trapped people nearby the landslide, without entering the area. Report it to the rescuers
• Notify the damaged power lines, roads and railways to the authorities
• Allow trained specialists to check the foundation of the building, chimney and surrounding area in order to seek the damage
• Restore the ground surface as soon as possible, erosion caused by the loss of ground cover may lead to sudden flooding and additional landslides in the nearest future
• Seek advice from a geotechnical expert to assess the risk of a landslide or develop repair techniques to reduce its risk. The expert will be able to advise on how to prevent or reduce the risk of a landslide without posing a further risk