Cracked soil

Question: Why do some soils develop huge cracks when they dry and others don’t? What is it about the soil that causes this?

vertisol

Vertisol showing large cracks during a dry period. Note the pocket knife for scale. Photo: Soil Science Society of America Marbut slide collection.

Answer: Some soils have a high content of clay minerals known as smectites. When smectite clays get wet, water moves into a space between the structural units that make up the clay mineral. The presence of the water molecules pushes the structural units apart, causing the clay mineral to expand, or swell.

When these clays dry out, the water molecules are removed from the inter-structural spaces and the clays shrink. When this shrinking takes place in millions of clay structural units in a volume of soil, the shrinking can be enough to create large cracks in the soil. Soils with a high shrink-swell clay content are known as Vertisols.

Vertisols are found in several places in the United States, including the Gulf Coastal Plain of Texas, the Mississippi River Valley from Illinois to the Gulf Coast, central Montana, western South Dakota, and the Red River Valley of North Dakota and Minnesota. Other major Vertisol regions in the world include central India, eastern Australia, and eastern Sudan and South Sudan.

–Answered by Eric Brevik, Dickinson State University

Have a question for Soils Matter? Post it as a comment below, or email us at soils-matter@soils.org.

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4 responses to “Cracked soil

  1. First of all I would like to say wonderful blog! I had a quick question that I’d like to ask if you don’t mind.
    I was interested to know how you center yourself and clear your
    mind prior to writing. I’ve had a tough time clearing my thoughts in getting my thoughts out.
    I do enjoy writing however it just seems like the first 10
    to 15 minutes tend to be wasted just trying to figure out how to begin. Any recommendations or tips?
    Appreciate it!

    • In my experience, that first 10 to 15 minutes (or 30 minutes or hour!) is not “wasted” time, but a necessary part of the writing process. Maybe some writers can plop down at the computer and start typing away, but I always seem to need a fair amount of time to think–or just stare at a blank screen–when I’m starting to write something new. So my biggest tip is not to judge how your writing process is going, but just let it happen as it happens. That should help ensure that you’ll continue to enjoy it and not find it a chore.

      Anyway, I don’t know if that’s helpful or not. Maybe some other bloggers would like to weigh in? Thanks for writing.

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