Susceptibility map of mass movements in the southern slope of Avila

28 March, 2018 | by Mayra

The mass movements that originate on the southwestern flank of the Avila, as observed in the analysis of the risk carried out in this work, cause numerous economic losses since many neighborhoods in the area are very susceptible to this threat, in view of the urban expansion of the city that has caused many settlements

Constraints, triggers and erosive factors affecting mass movements in the mountainous south area of Ávila in Venezuela, are spatially analyzed through ArcGIS software 10.0 a synthetic methodology that performs the analysis of these factors in each movement type (rock falls, landslides, road slope and flows) and then synthesize on a single map areas with increased susceptibility.

The main cause of mass movements in this area relates to geological conditions which are reactivated by active seismicity, heavy rainfall, and artificial changes to the ground. Only in Caracas city has registered more than 500 landslides with important effects in the last 60 years.

While the study of the risk of mass movements is elaborate, (a dispersed event in space-time and with low intensity) is one of the most costly threats at a socio-economic level.

Most of the movements studied are mainly controlled by the slope and lithology, observing that most of the most frequent instabilities occur in the metamorphic rock of the San Julián and Esquistos las Brisas Complex type and in alluvial quaternary.

Slope, altitude and orientation vary depending on the type of movement. Observed for rock falls and slopes that go from 20º to 35º and altitudes from 740 m.a.s.l. to 1110 m.a.s.l. Northeast facing mostly for landslides and southeast to the southwest of rock falls.

On the other hand, for edge faults and debris flows it is very variable, with a much lower slope and altitude for flows (0 to 10º) and a higher one for landslides, with slopes of up to 40º of dip being observed. They coincide in the maximum orientation that goes from southeast to southwest and in the fact that they are movements controlled by the adjacent hydrographic networks.

It is recommended that Venezuelan authorities take a forecast of the most frequent climatic threats and keep a forecast and control of dry vs. wet periods as these are the most frequent triggers that cause mass movements. This can be done by expanding the meteorological stations since there is currently the Maiquetía airport station, whose climatic variation contrasts with that of the southern flank of Avila, and the Caracas Valley.

As far as vegetation control is concerned, a good spatial analysis is recommended to determine the current vegetation type and thus to take vegetation as a conditioning factor. It is known that from the end of 2015 to March 2016 the ENSO has hit the Ávila mountain range causing major droughts and fires, which are triggering factors for mass movements but due to a lack of spatial information could not be included in the present work.

In addition, if urban expansion were to be controlled, the most vulnerable communities could be organized and warned of the danger that exists in this study. The most susceptible neighbourhoods are Plan de Manzano, Macayapa, Blandín, Araguaney and La Cortada.

Periodic awareness campaigns and visits to such communities can maintain areas potentially susceptible to threats from movements of evicted or prevented masses depending on the level of probability.

LA GUAIRA,,Distrito Federal,Venezuela
1 September 2016
Tutor of the Master thesis: Dr. Juan Antonio Marco Molina
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