Formation Birth of a pothole Explanation provided by the Michigan Department of Transportation. The Birth of a Pothole - Step 1 Potholes begin after snow or rain seeps into the soil below the road surface. The Birth of a Pothole - Step 2 The moisture freezes when temperatures drop, causing the ground to expand and push the pavement up. The Birth of a Pothole - Step 3 As the temperatures rise, the ground returns to normal level but the pavement often remains raised. This creates a gap between the pavement and the ground below it. The Birth of a Pothole - Step 4 When vehicles drive over this cavity, the pavement surface cracks and falls into the hollow space leading to the birth of another pothole Videos Low resolution video clip (0.5 MB, Windows Media File) Medium resolution video clip (1.7 MB, AVI File) High resolution video clip (12.6 MB, MPG File) Photos Photos taken from a video by the Minnesota Local Road Research Board. Step 1 Here's a cross section of a typical pavement. The weight of each vehicle bends the pavement slightly. Step 2 Small cracks form, first on the bottom of the asphalt because that gets stretched the most. As the asphalt is fatigued cracks also form on the top surface. Step 3 Now water on the pavement from rain or melted snow gets into the cracks. When the temperature drops the water freezes and expands, making the cracks deeper and wider. Step 4 With more precipitation, more freeze thaw cycles and the continued vehicle loading sooner or later the cracks go all the way through the pavement Now water can get underneath the surface. When this subsurface water freezes and expands it pushes the pavement up and weakens it even more. When the ice melts and contracts it leaves a space so we have a have weakened pavement layer over a cavity. Step 5 All that's needed now is a good sized vehicle … and there's your pothole.