In March 2014, a neighborhood in Oso, Washington experienced the deadliest landslide in the country's history. Researchers from the University of Washington (UW) found that in the past 2,000 years, the same area, which is located on the North Fork of the Stillaguamish River, experiences a landslide at least every 140 years.

Doctoral student and lead author Sean LaHusen wrote that the study's main takeaway is that the area is a "very dynamic landscape," adding that it is highly unlikely that the region's recurring landslides will stop. The research was published in the journal Geology.

LaHusen's team analyzed the aftermath of the massive 2014 landslide that left 43 people dead. Using a laser-scanning technique called lidar that clears away area vegetation, the team created maps to analyze evidence of past landslide events. The team also scoured the rivers and nearby slopes in search of slide fragments that can be used for radiocarbon dating.

The team discovered a huge landslide called Rowan which occurred approximately 500 years ago. LaHusen's team found that 15,000 years ago when the glaciers retreated, the river valley area had become a landslide hot spot. The glaciers' departure left clay, sand, till and lake sediments that became a slide-prone, unstable mix.

"We know that the ingredients are there for unstable hill slopes, regardless of what we do. But knowing this place is so unstable, we ought to take a careful look at our land-use practices," added UW geologist and co-author Alison Duvall.

Landslide Safety Tips

A landslide refers to a downhill movement of mud, rocks, soil, and other debris. It can be slow and capable of causing gradual damage or fast and capable of quickly destroying anything in its path. A majority of landslides are caused by heavy rains, earthquake, snowmelt and other natural forces.

Landslides tend to occur in the same area. During rainstorms, a sudden or gradual flow of debris onto roads is common. Areas that become highly saturated with water have higher chances of debris and mud flows.

It is important to know what to do to stay safe before, during and after a landslide occurs, espcially if you live in a landslide-prone area. Below are some landslide safety tips from the American Red Cross.

Living In High-Risk Landslide Areas

• Landslide-prone areas should have an emergency response team and evacuation plans. Participate in local emergency response groups to learn where to proceed should landslides strike.
• Be aware of your region's highest landslide risk areas.
• Investigate storm water drainage patterns, particularly on the slopes nearest your house.
• Devise an emergency landslide evacuation plan with your household. Conduct practice evacuation drills to ensure each member knows what to do and where to go.
• Prepare and maintain an emergency kit for your entire household.

Things To Pack In Landslide Emergency Kits

• Seven-day supply of medicine and a first aid kit
• Flashlight and extra batteries
• Battery-powered radio
• Three-day water supply, one gallon per person daily
• Three-day supply of easy-to-prepare food that stores well such as canned meat, beef jerky, powdered milk, canned vegetables and fruits, peanut butter and hard candy
• Personal hygiene items
• Handy tool kit
• Contact information of family and emergency departments
• Mobile phones with extra chargers
• Copies of important documents such as birth certificates, passports, insurance policies, proof of address and the lease or deed to your home
• Cash

Signs Of Danger And Immediate Action

• Tune in to the local news and monitor updates on evacuation notices.
• Evacuate immediately if you suspect that a landslide will occur. Inform neighbors who might be at risk.
• Moving debris often make cracking sounds due to breaking trees and knocking boulders. Listen for unusual sounds.
• Residents near bodies of water should watch out for changes in water flow and appearance. Muddy waters could indicate moving debris, mud and fallen rocks.
• Many landslide deaths occur while people are sleeping. It is vital that you stay awake and monitor changes in your surroundings during severe storms.

Post-Landslide Actions

• Landslide areas are prone to additional slides. It is best to steer clear of these areas until officials announce it is safe to go back.
• Look for trapped and injured individuals. Extend a hand to neighbors who require help like the elderly, persons with disabilities and families with infants.
• Report any damaged utility lines to authorities, as well as potential hazards that could do cause harm.
• When assessing the safety of an area, look for damage in the area's foundation and chimney.
• Get help from geotechnical experts to evaluate the hazards of landslide areas. Experts can help in employing techniques to reduce landslide risks.

Photo: U.S. Geological Survey | Flickr

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