Mudslide Disasters

At least 160 people were killed in the nation of Nepal and more than 400, including dozens of Americans, were listed as missing after flash flooding and mudslides near the border with China. It’s thought that an earthquake may have dislodged part of a glacier and sent massive amounts of muddy water into a populated valley.

It’s been a while since I’ve written about landslides, but I probably should do it more often. We spend time in Gatlinburg, Tennessee, overlooking what Dolly Parton would have called a “holler.”  A holler, or hollow, is a low area nestled between mountains and is often where the population centers are in Appalachia. Pretty much, a similar landscape to the disaster in Nepal.

A mudslide is sometimes called a “debris flow”; it’s basically a landslide with a high-water content. Mudslides act like a river that (if the mud is thick enough) has the consistency of wet concrete. Rocks, trees, and other large objects are carried along and can cause homes to collapse or slide off their foundations. There’s a huge risk of traumatic injury to residents.

While a debris flow may be slow-moving, another type of landslide, called a “mud flow,“ is characterized by a very rapid forceful flow of water and flow. A mud flow is more “liquefied” than a debris flow due, at least partially, to a lot of water added to loosed soil in a short period of time. Looking at videos of the catastrophe, this is probably what happened in Nepal.

Mudslides occur for a variety of reasons: Areas prone to earthquakes, hurricanes, wildfires, and other natural disasters are especially susceptible. Periods of heavy rainfall or snowmelt can saturate the ground and cause instability in sloping areas.

Areas that experience wildfires have hard compacted soil that has difficulty absorbing large amounts of rain, especially if it falls in a short period of time. As such, water that couldn’t get through hard earth quickly forms flash floods that cascade down slopes, picking up soil and debris to become a mudslide.

CAN YOU PREVENT A MUDSLIDE?

Humans contribute to the risk of mudslides by planning poorly: An urge to have a vacation home in a mountain resort may be irresistible, but impractical. Poorly planned roads that are cut into hills and mountains make mudslides even more likely.

The view is great, but the slope is steep

Once you’ve built that home on a hillside, there’s a limited number of preventative measures that can be undertaken. It’s a different story, however, if you’re just now planning out that dream home:

• Beware of steep slopes, natural or man-made runoff conduits, or eroded areas.
• Have the county Geological Survey specialist assess your property for possible mudslide risk.
• Consider flexible pipe fittings (installed by pros) less prone to gas or water leaks.
• Consider building a retaining wall in likely mudslide channels.
• Avoid areas that have experienced mudslides in the past.
• Plan out an evacuation route (or two).
• Have a battery-powered NOAA weather radio.
• Have a medical kit with items to deal with both traumatic injury and water sterilization.

WARNING SIGNS OF A HOME AT RISK

Watch for cracks in paving, walls, foundations, and floors

Sometimes, pressure from unstable earth may give you a hint that trouble is on the way and give you time to evacuate. Mudslide prone areas will begin to show signs of strain:

• Cracks develop in walls, flooring, paving, driveways, or foundations.
• Outside structures (for example, stairs) begin to separate from buildings.
• Doors and windows become difficult to open or close.
• Utility lines start breaking.
• Fences, trees, and utility poles start tilting.
• Water starts accumulating in strange places.
• Roads and embankments along slopes start breaking off at the edges.
• Terrain starts to “bulge” or slant at the base of the slope.

DURING THE EVENT

• Turn on the NOAA radio and listen to warnings as they are reported.
• Warn your neighbors!
• If a mudslide is imminent, get out of Dodge, if at all possible, with the understanding that roads may be washed out.  Heed all weather alerts.

In some mudslides, as in what just occurred in Nepal, things happen very quickly and you might not have time to evacuate:

• If you must stay home, get to the second story if you have one.
• Watch for and avoid downed power lines.
• As the slide passes through, get under a table and curl into a ball, protecting your head.
• If you’re trapped in the mud, survival rates go up if you can form an air pocket around you. As in avalanches, put your arms in front of your face to gain breathing room.
• Always carry a cell phone with you in case you are trapped in the house.

Mudslides can be lethal but are part and parcel of living with Mother Nature. You might not escape a glacier dislodged by an earthquake, but you can plan before you build, know the danger signs, and hit the road as early as possible in the face of an imminent threat.

Joe Alton MD