THE CATSKILL GEOLOGISTS: Climate Change in Columbia County, Part 7: What’s the risk to your house?

WE STARTED OUT with a series of columns about climate change in Columbia County, but this has evolved into a series about landslides. That actually does make sense; we see increasing rainfall as soaking the ground thus leading to the landslides. If you have been reading our columns, then your most immediate concern may be not so much the climate as it is what chances are there that your home will slide downhill. Let’s deal with this in our final column in the series.

We need to alert you to what to look for. And to do that we need to introduce you to the nature of what is called a rotational landslide. That’s the type of slide we are afraid of. Take a look at our first illustration. The main part of the slide consists of those curved surfaces. The earth gives way and curved fractures open up. Masses of cohesive silt and clay slide downhill in a rotating fashion (see arrows). Downhill, the shove pushes all the sediment before it. That sediment crumples and that is the “foot” of the slide (on right). Uphill what is left behind is a steep slope, almost a cliff. That is the “head” of the slide (on left). It’s not unusual for the head to be curved. See our second illustration.

Do you live in a house atop a steep slope? Are you worried about possible landslides? First get a barbeque skewer and drive it into the ground. If it slips into the earth easily then you are probably living on those old lake silts. That’s bad. Next, look around and see if there are any fractures in the ground. That, too, is bad. Next, check out the trees. Are there any uphill ones leaning backwards? Is the slope curved. See our second illustration again. That’s, of course, also bad. Are there downhill trees leaning forward? That’s, we think, very bad. Are there fractures in the basement walls? Well, you can guess what that is.

Is the house old? That, at last, is good. The older the house, the more stable the ground is likely to be.

Notice the trees that are tilting toward the uphill slope. Photo contributed

This drawing shows the direction of a rotational landslide. Image contributed

But, in the end, don’t panic. Your house might slide someday but don’t lose sleep over it. Houses are washed away by floods; they are blown away in storms; they burn down. You don’t let those threats worry you, do you?

‘The older the house, the more stable the ground is likely to be.’

There are soil engineers who can improve the ground’s drainage. That can mitigate the threat. But we have not yet found one in Columbia County.

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