Adventure #4:
Porosity
What are Pores?
Pores are the space between sediment or dirt particles. The space between a pore or a little pocket of air does not let all of the different soils touch each other. In other words, a pore is a small pocket of space or air between the grains of sediment.
Often times pores are very small in sediment. In fact, you might need a microscope to see what is going on in the dirt.
Looking at the picture above this is what specific kinds of dirt would look like under a microscope.
The Space Between
What exactly is Porosity?
Porosity is the space between particles. It is the determining factor in how many holes or gaps are between different particles of dirt. Not all dirt is the same. As shown to the left some dirt has big pores and some has really small pores.
Porosity can also determine how resistant the soil is to flooding. An area with higher porosity soil has a lower chance of flooding because it is able to infiltrate into the water table as mentioned in the water storage section.
"Hold on, so geology is not just about what is solid... it includes air too?"
What happens when porosity is super high but water isn't going into the ground?
Source: Craig Miller
Option 1: Runoff
When the ground surface becomes saturated with water, it begins to generate runoff because it can't allow more water to infiltrate. On steep slopes, water is more likely to run off because gravity is quickly pulling the water down the hill instead of letting it soak into the ground.
Source: Chris Massey
Option 2: Landslide
Sometimes weather is very severe. When this happens, the water goes into the soil but it makes the soil very muddy. This is because the water is taking up all of the room between soil particles, so it is more water than soil in some areas.
Activity:
Porosity Rating
Look at the images below and rate the soil prosity on a scale of 1-5:
#1 = the most porosity (biggest spaces between grains)
#5= the least porosity (smallest spaces between grains or no space at all).
Record all of your answers in your Field Journal with an explanation of your thoughts and reasoning. Remember there are no wrong answers!
Source: Rodney Burton
This sediment has a mixture of some bigger sediments and some smaller sediments as well.
Source: Lance Vanlewen
Since the rocks are very big here they have a very hard time fitting together so the holes between them end up being decently big.
Source: Rodney Burton
This mound has very small holes between particles.
Source: Getty Images
The Boise Capital building where all of our legislation occurs for Idaho. The pavement and concrete have almost no space between particles.
Since you've completed the porosity section it is time to look at another factor of infiltration: Soil type. Click on the link below to see different types of soil and how they influence floods.