Landslides Paralyze a Village

By Vic Odarve

Like volcanoes, earthquakes, and tsunamis; landslides also paralyze a village where it occurs.

Landslide is characterized by a descent of a mass of earth and rock down a mountain slope due to gravity. The instability of the slope is sometimes triggered by earthquakes and heavy rains. Earthquakes may have caused stress, damage, and eventually weaken the foundation of rocks and earth of the mountain slopes. And during heavy rain, water seeps through cracks and pore spaces in underlying foundation, and encounters a layer of slippery material, such as limestone or clay. Thus, water-saturated soil becomes like liquid mud, an effect called liquefaction, and finally cracks the earth and stone formation of the slopes. If the support is not strong, the upper surface of these softened and well-lubricated layers of mass of earth and rock slides down due to gravity, thus a landslide occurs.

Cracks at Mayana Mountain Slope

Cracks at Mayana Mountain Slope

This is exactly what happened on July 11, 2005 in a village Mayana, a 17 km from a town of Jagna, Philippines. At around 3 am, on that fateful day, residents heard rocks were falling along a nearby mountain slopes in Sitio Balikbayan. A mass of earth of width about 400 m, and consists dominantly of blocks of limestone slowly moving down from the slopes. The debris, moving in a single mass at about average rate of 22 m/day caused great destruction when it passed in an area of dense human habitation in Sitios Balikbayan, Ilaud, and Pangabay. More than 103 families and 200 hectares of agricultural land were affected. No casualty was recorded. Total damage was estimated at Php 14,519,790. For many months the landslide had masked its potential tragedy until the debris stopped and stabilized. Since then, the affected populace was struggling in pain to make their both ends meet.

Path of the Landslide Debris

Path of the Landslide Debris

The earthquake of magnitude 5.3 with epic center 8 km from this landslide area which occurred at 8:25 pm on March 31, 2005 may have contributed to the instability of the rock formation of the Balikbayan mountain slopes. Then the prolonged spell of heavy rain of high intensity that followed worsens the situation. These factors triggered the Mayana landslide.

In most parts of the world, landslides usually occur on mountains with steep slopes trigger by many factors. Some of the most common causes include geological such as rainfall, and earthquakes; morphological such as slope angle, wave erosion and uplift; physical such as prolonged precipitation, volcanic eruption; and human such as mining, quarrying, deforestation, and excavation.

The Mayana case is one of the common pictures of landslides in the Philippines. The worst landslide recorded in history occurred in December 16, 1920 in Kansu, China where over 180,000 were reportedly dead.

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1 Comment

  1. vicodar

     /  March 18, 2014

    Reblogged this on ODARVE'S NOTEBOOK IN AFRICA.

    Reply

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