Geology and Soils
Emojis Have Meanings to Guide You!
📚--->Supplemental Resource!
📚 Pictured above is a cross section representative of Michigan's state soil - Kalkaska sand.
What do the terms mean?
Geology
"The science that deals with the earth's physical structure and substance, its history, and the processes that act on it. "
-Oxford University Press
Image Source: Wheeling Jesuit University
Soil
"The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. "
-Soil Society of America
"A natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment."
-Natural Resources Conservation Service
Noting that some things we covered in Hydrology would also fall under Geology and Soils.
In Focus: Lake Huron Watershed and Your Place
Ecoregions and Landforms (or Physiographic Regions)
These two classification systems for large land areas can help us understand the role abiotic and biotic factors play in what areas will support.
This document identifies the major physiographic regions of Michigan (Figure 4.6 and descriptions below). This map identifies the Level IV ecoregion (zoom to your area on the interactive map and note the number - ex. Alpena is 50ab) and then, read the accompanying description. We recommend using Ctrl-F to quickly locate the description in the PDF.
Texture, Horizons, Classification, Oh My!
Soil texture indicates the makeup of soil based on the size of particles (described as sand, silt or clay) present and helps us understand many other properties of soils.
Image Source: Central Michigan University
Soil horizons, or layers of soil, form what is called a soil profile. Horizons are defined based on properties such as texture, color, and chemical and mineral content.
The graphic below is an example of a soil profile: the surface horizon (A), the subsoil (B), and the substratum (C). The organic horizon (O) may be at the surface or buried.
Image Source: NRCS
Classifying soils is done similarly to plants and animals with a hierarchy that gets more descriptive at each level. This naming system (or taxonomy) allowed for soil maps to be fully developed. Soil maps help us understand what is under our feet, how to care for the soil and activities deemed most feasible for those soils.
📚 Web Soil Survey is an online mapping service that allows you to see what soil types are where. Your local conservation district office also has printed copies of the county soil survey.
Moisture and Infiltration
The driving factor of infiltration is the soil texture with larger pored soils (sandy) having a higher rate than smaller pored soils (clay). As soil moisture increases, infiltration will decrease as the pore spaces fill with water. Soil moisture is impacted by factors such as evaporation, use by plants, and human modification to an area (such as in irrigation or drainage practices).
📚 Explore various ways of measuring and tracking soil moisture via maps on this page.
Image Source: National Weather Service
Nutrients in the Soil
Sandy soils do not typically hold nutrients due to the highly-drained nature of large pore sizes. Silt and clay soils will hold both macronutrients and micronutrients necessary for plant growth.
Macronutrients are those that plants use the most, primarily for building cell components like proteins and nucleic acids. Nitrogen (N), potassium (K), and phosphorus (P) are needed in the largest quantities; hence the NPK rating on your fertilizer! Hydrogen, carbon, oxygen, calcium, magnesium and sulphur are also considered macronutrients.
Micronutrients are not used as frequently and are typically cofactors in enzyme activity. Theses include chlorine, iron, boron, manganese, zinc, copper, molybdenum and nickel.
Freeze-Thaw and Frost Heave
Michiganders: "We'd like to thank these weathering forces for their key role in this award of Pothole Capital of the US."
In Michigan, freeze-thaw contributes to the weathering of naturally occurring rocks which in the long term add material to our soils.
📚 This article highlights the connection between freeze-thaw impacts to Michigan's road and climate change.
Frost heave is caused by internal (both soil and rock) frost action. Not all soils are equal when considering frost heave; fine-textured soils (silt, loam and fine sands) experiencing this weathering more frequently due to their high capillary action.
📚 This article further explains the mechanisms of frost heave.
Image Source: Ahmad, T. & Khawaja, Hassan
Wind Erosion
👥 Community Partner Connections 👥
Who are some of the partners that focus on Soil in the Great Lakes basin and Michigan?
✅ USDA Natural Resources Conservation Service
📚 Find your local service center and more about tools for Michigan soils learning and work.
✅ Michigan Conservation Districts
📚 Find contact information and more about what they do here.
✅ MSU Soil and Plant Nutrient Laboratory
📚 Find contact information and more about what they do and soil testing here.
📚Supplemental Resources📚
Global Ecoregions
Rock or Mineral?
National Park Service digs into the differences between rocks and minerals. This page also has links at the bottom to deeper dives into rocks and minerals as material classes.