The Hazards of Building on a Slope

Before building on a hillside, understand the ways the earth can move.


| September/October 1976



slopes

The view might be magnificent, but make sure the land is not on the move before building on a hillside.


PHOTO: FOTOLIA/MYTHO

Click on the Image Gallery for referenced figures. 

Before you run off, buy a "bargain" piece of hillside, and start constructing the home of your dreams on it, then, you should know how to determine whether or not that slanted acreage is suitable for the use to which you intend to put it.

All Slopes Move, at Least a Little

Any hillside suffers a form of erosion known as mass wasting . This movement can take either the form of a violent landslide (which, obviously, can be catastrophic) or a slow creep (which, over a longer period of time and not so obviously, can be just as catastrophic). You should learn to recognize the evidence left behind by both kinds of land movement and to predict the probability of such movements in the future.

Landslides

Landslides that have already happened come in two varieties: old and fresh. And you should run—not walk—from any real estate agent who shows you either type. Anyone who builds on a known landslide (old or new) is asking for trouble. The added weight of a house and the addition of water (on the lawn, on a garden, in a sewage disposal system, etc.) can reactivate even a long-dormant landslide with disastrous results. And there you'll go to the bottom of the hill, with your new home in splinters around you!

Fig.1 shows a typical landslide and its most recognizable scars. Whether fresh or hundreds of years old, any slide you inspect should exhibit some or all of these characteristics:

[A] SCARP. This is a cut in a hillside where a mass of earth once pulled out of the slope. On a fresh slide, the scarp will have the appearance of a recent excavation. On an older one, the cut may appear to be nothing but an innocent, shallow, rounded depression on the side of the hill. Beware. Such a depression is sometimes not as innocent as it first looks.





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