Photo by E. Sohn
Oct. 6, 2004
Triggering Landslides
A Hidden Factor Sparks Landslides
Fernando J. Cordero Vázquez, 14, Sabana Grande, Puerto Rico
Intel Achievement Award, Intel International Science and Engineering Fair, 2004
Category: Earth Science
During November, 2003, a large amount of rain fell in an area of southwestern Puerto Rico, causing landslides and slumps. Because this area is heavily populated, many homes were destroyed or damaged.
Fernando's research looked at what factors, besides the amount of precipitation and gravity, were responsible for the landslides and slumps in the Bélgica sector of Guánica, Puerto Rico. He hypothesized that the soil composition of the area was one of the responsible factors.
Three samples of soil were collected from the affected area. Three other samples were collected from a nearby sector that was not affected. After conducting percolation tests, Fernando found that the affected soil retained 89 percent of water after 24 hours. The other samples of soil retained around 50 percent of water for the same period of time. The affected soil had a 9.9 alkaline pH, while the samples from the non-affected area were slightly acidic.
The affected-area samples were tested in a diffractometer. The x-ray diffraction test showed the presence of montmorillonite. The molecules of this kind of clay have the ability to expand when in contact with water, thereby increasing the volume and mass of the soil. This made it easier for the gravitational pull to act upon it.
The study shows that it is risky for people to construct houses on hillsides with this kind of soil composition.
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