Potholes - the Road Variety

A recent question came up the other day....

How do potholes form?

This is a good question as it relates directly to geology. We don't cover it specifically in Earth Systems but it does relate to several concepts in the course. It is covered directly in World Geography.

Potholes, the types we see often in our roads in springtime, are a result of physical weathering.

During the winter, water underneath the road freezes and expands giving a frost heaving or frost action effect. The result would be slightly bumpier road or at least areas where the surface would be raised and uneven.

This would leave the pavement more easily broken if it were contacted by the force of a snow plow for example. Over several rounds of snow clearing, the pavement would be more and more broken, starting as several small chips which would lead to wider and wider holes.

Once the pavement is broken and increased water runoff occurs during late winter and early spring, further erosion occur and deepens the hole leading to the types of potholes that cause so much damage to cars.

The pothole problem is quite common in Canadian cities. Here is a brief news story published recently by the CBC.

 CBC Story - Potholes

Of course, there are other types of potholes that form around river beds due to the swirling motion of pebbles as flowing water carries them, but that's a discussion for another post.