On November 4th, 2010 the San Antonio de Escazu suburban region of Costa Rica was impacted by a mudslide. This populated city is surrounded by many steep mountain and volcano slopes, which are prone to events of mass wasting (downward movement of rock and sediment that transports materials). Mudflows can be very damaging, as they destroy and bury whatever is in their path. The mudslide of 2010 had lots of water in the flow due to heavy rains, and it was very destructive as the fast stream that did not give residents time to prepare. 23 people died trying to escape the flow and several homes were buried.
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A picture of a house caught in the middle of the 2010 mudslide. The power of the mudslide has destroyed the house, and will integrate its remains into the stream as it moves material further down the slope. After the mudslide stops as the water seeps out of the sediments, the bonds will restrengthen as the mud solidifies, and the house will be buried underneath a solid material. (Photo credit: srnnews.townhall.com)
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This mudslide was offset by heavy rains in the area, which loosens the bonds holding the soil and sediment together. The loose ground then forms a thick muddy fluid that quickly flows down the slope and solidifies after the water stops flowing through.
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Excess water from heavy rains mixes with soil and flows downhill in the pictured mudslide from 2010. Since the flow had so much water, it moves very fast has the power to destroy what is in its path as the telephone pole is destroyed. This picture also shows that mudslides accumulate material such as branches, plants, and any rocks and moves this material downslope with the flow. (Photo credit: www.welovecostarica.com)
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The soil composition and structure in Costa Rica was the “perfect recipe” for a mudslide to occur. Based on a study, the main soil types consist of loam, sandy loam and silty loam, which create a porous soil. This soil is less flocculant (particles that stick together) than others, which means that it is more prone to water particles slipping between soil particles.
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Soil Ternary chart showing the different types of soil compositions. Since Costa Rica consists of mainly sandy loam, medium loam, and silty loam. All consist of little clay and more silt, with varying levels of sand. Clay is the most flocculant, and sand is the least, so this chart shows that Costa Rica’s soil composition is porous. Photo Credit: Oneplan.org
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The layers of soil in Costa Rica have a thick O horizon, which is the organic matter consisting of decaying material (leaves, dead animals, ext.). There is also a thick A horizon, which is dark in color from the nutrients and supports plant growth. The B horizon consists of minerals that have trickled down from the O and A horizons. These minerals have been compressed in a blocky form, which are clusters of soil that allow water infiltration.
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The soil horizons are shown. Photo Credit: llrs.co.nz
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A soil profile taken from the Charles Schembre study. You can see the many horizons as discussed above. The top O horizon is where you can see vegetation, and the dark soil underneath is the Topsoil. Below these, the lighter colored soil is the B horizon. If you were to keep digging, you would also be able to see the C and R horizons.
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