It's caused by a displacement of the substrate, causing a break or buckle, like a ridge, in the road surface.

Here's a photo with a "columpio", and caption "Uno de los múltiples columpios en la carretera":
http://reydocbici.com/blog/wp-content/uploads/2012/03/a31.jp...
From this page:
http://reydocbici.com/blog/2012/03/amealco/

A TC discussion on the translation of "heaving and soft track". Someone claiming long experience of Mexican roads suggests "columpios y lavaderos en la carretera/vía", and adds:
"Así llamamos el resultado de este tipo de suelos en México. [...]
"un columpio en la carretera es el resultado de un levantamiento del suelo debajo del pavimento, levantamiento más o menos largo en comparación con un lavadero, que es de cadencia más corta. Se usa una cimentación de piedra, por así decirlo, para corregir el suelo y evitar que se formen esas cosas. Creo que después de haber manejado durante más de 35 años en las carreteras de México se de que estoy hablando."
http://www.translatorscafe.com/tcterms/es-ES/mobile/qtn.aspx...

Here's another photo from a blog, this one referring to "heaves and breaks" being well marked:
http://www.explorenorth.com/library/roads/images/065-akhwy-0...
From:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/2568...

Heaves are often caused by frost damage, and "frost heave" is a common expression, but they can be caused by anything (including subsidence, as in your case). In the following case it's actually heat (there's a video):
http://www.wgal.com/news/susquehanna-valley/lancaster/Part-o...