In southeast Florida, how deep do you have to dig to get out of sand? What do you hit after sand?

Great question!

Normally, soil is referred to as the “skin” of the earth. And, the amount of soil in any location is dynamic – there can be erosion, or weathering, or many processes that lead to soil deposition and loss.

Beach with fence and grass

Although Florida has 663 miles of beaches, it’s a state with a variety of soils. Source: Morguefile

Florida is a unique state. It has the reputation of being made of sand, but that is not always the case. Along the 832 miles from Pensacola to Key West, the soil varies. The soils of our nearly 47,600 farms support the culture of over 300 agriculture products with an economics value of over $148 billion. That is impressive given that much of the state is covered by a sand cap that can be over 100 feet deep in places. However, we also have soils with high water tables, and other soils that are made not of sand, silt and clay, but of organic matter.  Parts of the Everglades are a good example. Southeast Florida, south of Palm Beach County, is one of those places in Florida where the sand cap, when present, can be shallow. How do we know this?

The Natural Resources Conservation Service (NRCS) develops what soil scientists refer to as “soil surveys.” The survey of the Dade County Area can be found at http://www.nrcs.usda.gov/Internet/FSE_MANUSCRIPTS/florida/FL686/0/Dade.pdf. Soil surveys describe the types of soils found in each state, and other information needed to determine if land is suitable for building, agriculture, or other uses.

How deep is the sand in southeast Florida, when there is sand? According to the Florida soil survey, the sand is not as deep as you might think. It is only about 3 to 4 feet. Below the sand (or organic material) is limestone. The survey refers to the limestone as part of the Biscayne aquifer, and it specifies the limestone as “Miami Limestone.” The depth to limestone can be inches with rock outcropping in places. A good example of this is the Rock Outcrop-Biscayne-Chekika soil association.

Woman and dog near limestone outcrop.

Rock outcrop made of limestone in southeast Florida. Source: Sepmstrata.org

I remember years ago watching city or county employees “planting” trees in this material. The first step was to set off a dynamite cap to open a hole in the limestone. The second step was to plant the tree in the rubble. While Florida is often thought of as white sand and water, it is a state whose soils vary significantly across its 37.5 million acres.

For more information about soils in Florida, see our Dec. 2013 post: https://soilsmatter.wordpress.com/2013/12/10/florida-sandbox-of-the-u-s/

Answered by Nick Comerford, University of Florida

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