Abstract
Mass movements are quite common in the Northern Andes and constitute one of the major hazards in the region. In particular, along valley flanks where the city of Medellin (Colombia) is located, rainfall is the main trigger of these phenomena, but little is understood about how water in the soil and subsoil behaves. In this study, we show data from some basic soil hydrology measurements and conventional geophysical surveys within a ~4 ha experimental plot that is experiencing soil creep. The seasonally wet study site has an average slope gradient of 33%, and its surface geology consists of a series of older deposits of debris flows. Our measurements show a low surface runoff, which ranges from 4 to 11% of the rainfall; infiltration is 89–96% of the rainfall, and 15–33% corresponds to drainage water at shallow levels in the soil (20–50 cm); piezometric measurements reveal a mostly steady-state water table. About 14–54% of the rainfall becomes subsurface flow within the first ~1–2 m below the surface. Geoelectrical and seismic surveys suggest small temporal changes in the properties of materials shallower than 2 m, consistent with the steady-state water table and the permanent and high subsurface flow. These geophysical surveys also indicate the presence of a major discontinuity at ~4–6 m below the surface, which we interpret as the limit between different prior debris flows.
Highlights
The tropical Andes of Northern South America is highly susceptible to mass wasting, due to widespread steep slopes, unstable and erodible soils, and heavy rain
Our intention in this study is to understand the water in the soil mass and relate it with the behavior of the mass movement; we focus on an dynamics of water in the soil mass and relate it with the behavior of the mass movement; area of slow downslope motion,motion where it is not possible establish a specific moment for a we focus on an area of slow downslope, where it to is not possible to establish a specific landslide occurrence
Our preliminary results demonstrate the feasibility of using measured hydrological fluxes to better understand the water behavior inside unstable hillslopes that experience slow soil movement
Summary
The tropical Andes of Northern South America is highly susceptible to mass wasting, due to widespread steep slopes, unstable and erodible soils, and heavy rain. Population pressures are increasing the areas prone to landslides, and the losses in infrastructure amount to several billions of dollars every year; in northern South America, more than 100,000 casualties in the last 50 years can be attributed to different kinds of landslides [1]. Several studies have identified rainfall and the resultant hydrologic processes as the major triggering factors for mass movements in tropical and subtropical areas [4,5,6,7]. The connection between the hydrologic cycle and the occurrence of mass wasting phenomena in the Aburrá Valley is
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