You might be asking yourself, montmorillonite? I don’t even know how to pronounce it, but it is commonly known as Yazoo clay in central Mississippi. And central Mississippi rests on a formation of the stuff, as shown here:
Yazoo clay has remarkably expansive properties. As Landris T. Lee, Jr., notes in a 2012 U.S. Army Engineer Research and Development Center (ERDC) study sponsored by the Mississippi Department of Transportation, “Yazoo clay is the most active shrink-swell (expansive or high volume change) clay found in the state of Mississippi, and is the largest contiguous near-surface expansive clay deposit east of the Mississippi River.”
Put simply, when Yazoo clay becomes wet, it expaaaaaaaaaaaaaands–by as much as 240% as shown in this figure. When it becomes dry, it contracts.
Source: Landris T. Lee Jr., P.E. U.S. Army Engineer Research and Development Center, GS-E Geotechnical and Structures Laboratory. State Study 151 and 236: Yazoo Clay Investigation. Available at: http://mdot.ms.gov
As you can imagine, this stuff is challenging for home construction and maintenance. And as a relative newcomer to Jackson, how do you deal with it? You can hire foundation experts every 7 or 8 years to come in and make needed foundation repairs. Expensive. Or you can just get used to the cracks (my preferred method).
At first, the size of the cracks on my walls freaked me out. They seemed to grow longer and wider with each successive rainstorm. I’ve since come to regard the cracks as Belhaven features. My property (constructed in 1940) wouldn’t be a Belhaven bungalow without the darn cracks, I mean features.