It is truly amazing that the Missoula Valley Aquifer can support more than 40,000 households! Do you ever wonder how all that groundwater moves around and gets stored below our feet? This science friday we are going to dive into properties of earth materials that allow this water to be present underground.
When you think of groundwater, what do you envision? A big pool or cave underground? I know I did growing up as a kiddo. I imagined digging deep enough that I would eventually dig my way to an underground cave. Although those do exist, most groundwater is stored in the tiny spaces in-between sand and gravel. Porosity and permeability control the distribution of water in these rocks.
The processes of earth materials that allows water to move underground is Permeability is a measure of the ability of a material to allow fluids to pass through it, and porosity is a measure of how much of the volume of a material is open space. Although there are many other variables that influence these processes...
The material with highest porosity (most open space) is clay, with those small little absorbent pieces. Sand and gravel have less porosity. What affects permeability is not just overall amount of space, but how big and well connected the individual spaces are. That’s why sand and gravel are more permeable than clay.
Information sourced from (1) MGA curriculum, (2) City of Missoula: Missoula Valleys Sole Source Aquifer, (3) Porosity & Permeability: Geosciences (on youtube). First two photos from WEN, final from educatorspages.com.
