Understanding Landslides, Mudslides, and Staying Safe: Expert Guidance by Joe Alton MD

Intense and prolonged heavy rainfall has wreaked havoc across the state of California, triggering a series of landslides. One particularly dramatic incident in San Clemente saw several homes precariously perched on the edge of a cliffside due to the erosion caused by these landslides. The Golden State has experienced an unusual volume of rain in specific regions, leading to widespread destruction and road blockages.

Landslides, which involve the sudden movement of large masses of soil, rocks, and debris down a slope, are typically induced by disturbances that disrupt the natural stability of the terrain. These disturbances can result from events like wildfires or poorly planned land development, making slopes more susceptible to landslides, especially during and after periods of heavy rainfall.

It's important to note that landslides are not confined to California alone. In regions like the Great Smoky Mountains, scars on the landscape serve as a testament to past landslide occurrences.

It's worth distinguishing between landslides, avalanches, and mudslides. While avalanches primarily consist of snow and ice cascading down mountainsides, often carrying rocks and trees with them, they are most commonly observed in the Northern Hemisphere from December to April. On the other hand, landslides can occur at any time and result in the fragmentation of larger sections of the mountainside itself. Mudslides, also known as debris flows, are a specific type of landslide characterized by a high water content. They behave like a powerful, fast-moving river, particularly when the mud is thick, resembling wet concrete. Mudslides can have devastating consequences, including the collapse of homes and the risk of severe injury to residents.

An event characterized by an exceptionally rapid flow of water and debris, often resulting from heavy rainfall or rapid snowmelt, is sometimes referred to as a "mud flow." Mud flows are distinct due to their high water content compared to other types of landslides.

Human activities can contribute to the vulnerability of an area to landslides. For instance, constructing roads into hills and mountains can increase the likelihood of mudslides. Similarly, riverside properties situated at the base of a hill or mountain are at higher risk. Homeowners living on slopes should consider several precautions:

1. Seek an assessment from a geological survey specialist to evaluate potential risks.
2. Use flexible pipe fittings to reduce the risk of gas or water leaks.
3. Construct retaining or deflection walls to redirect potential mudslide channels around buildings.
4. Avoid building in areas with a history of mudslides.
5. Plan at least two evacuation routes.
6. Ensure you have a battery-powered NOAA weather radio.
7. Maintain a well-equipped medical kit for dealing with traumatic injuries.

Although the exact timing of a landslide is unpredictable, there are warning signs that indicate potential trouble:

• Cracks in walls, flooring, paving, driveways, or foundations.
• Separation of outside structures, like stairs or pavers, from buildings.
• Jammed doors and windows.
• Broken utility lines.
• Tilted fences, trees, and utility poles.
• Accumulation of water in unexpected areas.
• Erosion and breaking of roads and embankments along slopes.
• Bulging or slanting of flat terrain at the base of slopes.
• Sudden changes in water levels in nearby creeks.
• Small flows of mud may precede larger ones.
• Some reports suggest that approaching mudslides emit a deep rumbling sound.

Landslides can be particularly lethal at night, so residents in at-risk areas should remain vigilant during nighttime storms. Being alert and awake can significantly increase the chances of survival, as people who are asleep may be less responsive during a landslide event.

When a landslide is imminent, quick action is crucial. If you have time, warn your neighbors before evacuating the area. The safest course of action is to move away from the path of the slide and head to higher ground. If you choose to stay put, seek shelter on the second story of your home if available. Watch out for downed power lines. During the slide, take cover under a table and curl into a protective ball to shield your head. If trapped in mud, forming an air pocket around you can increase your chances of survival, and you can attempt to create this space by holding your arm in front of your face.

In emergency situations, having a means of communication, such as a cell phone or a loud whistle, is vital. Remember that you can survive without water for up to three days and without food for a longer period. Always stay prepared and equipped.

After a landslide event:

• Avoid the slide area, as additional slides may occur.
• Stay tuned to emergency information.
• Be cautious of potential flooding following landslides.
• Look out for injured or trapped individuals near the slide. In normal conditions, avoid the main slide area and direct professional rescuers to potential locations.
• Report broken utility lines and damaged roads promptly.
• Consider replanting damaged terrain with trees to restore the land, as the loss of ground cover can lead to future landslides.
• If your property has been affected, consult trained professionals for a comprehensive inspection to assess the need for further action.

These measures can help reduce the risks associated with landslides and improve the safety of residents in landslide-prone areas.

Joe Alton MD