In many parts of the world debris flows are one of the most dangerous of all mass wasting events. Mountainous areas with high slope instability, high seismic activities and extreme rainfall condition are the main triggering factors. The Monday, May 12, 2008, mega-earthquake of magnitude 8.0 that struck the Wenchuan area, Northwestern Sichuan province in China was catastrophic. This event, led to co-seismic landslides and subsequent rainfall induced debris flow in Yingxiu catchment on August 14^th, 2010. The catchment has a very steep topography, an area of 5.35 km² and a channel length of 3.55 km. The aim of this research is to model the post seismic debris flow, Parameterize and calibrate the event. Two main initiation zones were identified based on susceptibility assessed from geomorhological mapping and formed the bases for input in the FLO-2D model. 161, 350 m³ (64.54%) of the debris flow volume was modeled with FLO-2D in a manner consistent within the limit of the data available. FLO-2D model do not incorporate entrainment of materials in the transport zone. Thus, limitation to the production of the total deposits volume on the debris flow fan. The model was parameterized and the result shows that, Sediment concentration and the coefficient of friction were the two main parameters that affected the velocity of debris flow, area of inundation and the impact force respectively. Finally, the debris flow was calibrated using a back analysis of the debris flow event of 2010.

Abstract:The environmental impact and potential health challenges resulting from artisanal mining inShango area of Minna, North Central Nigeria was put into perspective. The methodology adopted for the research includes field work and laboratory analysis. Results of field observation reveal that mining activity resulted in physical environmental impact such as land degradation, destruction of vegetation, erosion of soils and degrading water quality. Results from the laboratory analyses show that soils are contaminated with elements such as Cu (27.7 ppm), Cd (0.6 ppm), Hg (0.62 ppm) and Ag (0.35 ppm) and generally show high status when compared to published standard for upper continental crust. While, Zn (14.8 ppm), Ni (7.17 ppm), Mn (207 ppm), Pb (0.58 ppm), As (0.4 ppm), Co (0.55 ppm), Mo (0.16 ppm), and Zr (129.8 ppm) are rated low in line with the published standard; other determined elements such as Cr (37.8 ppm), Fe (31.1ppm) and Au (0.2 ppm) are high. These elements can easily be absorbed by plants and subsequently accumulate in their tissues. When such plants are eventually eaten by man, it may lead to different health problems such as slow growth rate, liver and kidney problem. High concentration of these elements in plant tissues may causes different problems.

A swarm of 14 landslides occurred spontaneously within the Azenge Mountain on November 13 th , 2010 between the hours of 1 and 6 am after torrential rains. The landslides were studied using interviews, field observations and laboratory study of the soil samples collected from the major landslide site. Results of the study show that the event that was reported by many local media in Nigeria as volcanic eruption was a spontaneous massive slope movement along the mountainous terrain of Imande Ukusu, Mon village. About 1,123,918 m 3 of rock and debris were moved along the sliding surface for more than 1.5 km to the toe of the mountain within a very few minutes. The size of the materials moved decreases from the top to the toe of the slope which range from 50 o to 5 o respectively. These materials range in size from block of rocks of various sizes, soil to mud. The largest boulders moved measured 71.2 m and 88.5 m respectively. The rock types in the area include gneisses, granites, basaltic rocks and dolerite dykes which have a general strike of 240 o NW with a dip of 038 o NE and are highly fractured. The fractures and dip are in the direction of the slope. Laboratory result of the soil samples reflect two types of grain sizes. Those with very high degree of susceptibility to sliding above the sliding surface which plot in the failure zone and those less susceptible from the sliding surface and plot outside the failure zone. Torrential rainfall towards the end of the year was the main triggering mechanism of the landslides. Other causes are attributed to geological, morphological and human factors. The landslides led to the death of 1 person, destruction of vegetation, soil structure and texture, farmlands and remodeling of the geomorphology of the area. It is recommended that human activities along the toe of the hills be reduced and settlements should be sited far away from the hills to avoid further loss of lives in future.

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