Costa Rica's Mass Wasting and Soil

Mass Wasting:

Heavy rains and the rich volcanic soils of Costa Rica make it a promise land for agriculture. The permeable slopes absorb water and make the land sustainable for growing food. This is other wise known as a transport limited landscape. Due to excessive rain during Costa Rica's rainy season (November - May) mass wasting is known to occur. Mass wasting is a downslope movement of angular material.

The photo above demonstrates a mudflow that occurred in December 2011.  The rain caused a release in the colluvium (angular slope material) and brought down mud and grasses.

A debris flow contains mud, boulders, and cobble. In 2010 this debris flow destroyed a small village.
Photo Source: Getty Images

In 2010 Costa Rica received excessive amounts of rain. At one time it rained 6.3 inches in two hours. This storm caused landslides across the country. The extreme rain caused the Pico Blanco mountains to soften and induce a major debris flow. Trees, mud, and boulders were swept away and stacked about 10 feet high at the end of the flow. The intense amounts of rain also caused a breach in a dam in Parrita. 

2010 Debris Flow. Photo Source: Getty Images

Soil:

The climate largely affects the soil. A majority of Costa Rica is rain forests and a large percentage of rainfall they receive per year really affects the soil. The soil becomes nutrient poor because of leaching due to the abundance of rainfall.  Leaching refers to the loss of soluble substances such as salt or nutrients. In this case leaching is the loss of nutrients in the soil. This action leads to very impoverished soils, causing aluminum and iron to accumulate; this process is referred to as laterization. The soil is normally a deep red color and the soil is classified as an oxisol. 

This is a picture of slashing and burning or swidden of a forest in Costa Rica, with the trees removed you can see the oxisol (deep red soil). Photo Source: Google Images

Without nutrients in the soil the tremendous amount of plant and tree growth comes from the vegetation. The rainforest's cycle of nutrients in rapidly changing. The decaying organic matter (dead wood, leaves and plants) are decomposed very quickly by bacteria, fungi termites, etc. that the organic matter never makes it past the O Horizon (the surface layer that contains living and decaying organic matter) and into the soil. The rapidly broken down nutrients are quickly taken up by plants and trees waiting for the cycle to begin again.

Sources:

• http://geography.about.com/od/costaricamaps/a/costaricageography.htm
• http://www.nbcnews.com/id/40009265/ns/weather/#.UTePdaUs_fY
• http://www.adventure-inn.com/articles/everything_grows_here
• http://creationwiki.org/Rainforest
• http://www.ehow.com/about_6404776_leaching-soils.html
• http://en.wikipedia.org/wiki/Laterite
• http://rainforests.mongabay.com/0502.htm
• Dr. Allen's Lectures