Does rain cause Tarmac / asphalt pot holes? If so, how?
After a period of rain in my city there are plenty of fresh new pot holes in the Tarmac / asphalt surfaces. The immediate cause is obviously axle overloading, due to appalling regulations, but these holes are fresh from a fourtnights heavy rain.
I can comprehend erosion in dirt or gravel roads as I know these substances are penetrable by water. But my impression is that Tarmac is impenetrable to water.
What process am I missing?