Mass Wasting of Oaxaca

Of the several different geographical regions in Oaxaca, the mountain ranges specifically are covered by lush forests of a diverse range of plant species. The high density of vegetative ground cover make this region a perfect example of a transport limited landscape.  In this area, the rate of transport of weathered material limits the rate of erosion, as opposed to in a non-vegetative weathering limited landscape, where the rate of rock decay limits the rate of erosion.  

The town of Tlahuitoltepec was built on the steep slopes of
a transport limited landscape. 

Liquefaction occurs when extensive
saturation increases the water filled
spaces between particles, decreasing friction
that normally holds sediment together.

In September of 2010, record rainfall in conjunction with previous deforestation led to a devastating mass wasting event in the town of Tlahuitoltepec, Oaxaca.  Transport limited landscapes are, by nature, permeable slopes as they must provide a medium through which plants can absorb water and nutrients.  By removing vegetation that normally limited the downslope movement of weathered material, the landscape became even more susceptible to liquefaction, allowing material to flow.

This photo of the Tlahuitoltepec mudflow exhibits thixotropic material flowing
downslope due to gravity.

With its swift speeds, the Tlahuitoltepec
mudflow was capable of carrying
cars in its flow.

Mudflows can be incredibly devastating to communities that lie in their path. While mudflows generally carry mostly clay and silt particles and not much rock content, they are still extremely dangerous and can travel at speeds ranging from 10-30 miles per hour. With their viscous properties and high velocity, mudflows are capable of swallowing entire villages. The mudflow of Tlahuitoltepec burried 80% of the town and killed 32 people.

 

Citizens, police, and military worked day and night to rescue victims
trapped by this geographical disaster.

References:

Bricker, K. (2010, September 29). Corruption and deforestation caused oaxaca's mudslide disaster. Retrieved from http://upsidedownworld.org/main/mexico-archives-79/2712-corruption-and-deforestation-caused-oaxacas-mudslide-disaster

CBN News. (2010, October 01). Mexico mudslide death toll raised to 32. Retrieved from http://www.cbn.com/cbnnews/world/2010/October/Mexico-Mudslide-Death-Toll-Raised-to-32-/