Helen DIAS, University of São Paulo, Brazil
Vivian DIAS, University of São Paulo, Brazil
Carlos GROHMANN, University of São Paulo, Brazil
Mass movements are common in the Brazilian south and southeast regions. On January 12 of 2014 shallow landslides and debris flows occurred in Itaóca city, São Paulo state, Brazil, causing damage to local infrastructure, and 25 deaths. The aim of this research is to make a morphometric characterization of the event and to provide shallow landslides and debris-flow inventories. Morphometric analysis was derived from a Digital Elevation Model (DEM) from the SRTM mission processed to remove outlier data, re-sampled to a 12.5 m spatial resolution. Shallow landslides and debris flow mapping were made based on a post-event free access image of Google Earth Pro, dated 2014/08/10. The visual criteria for shallow landslides mapping were the absence of vegetation, format and size, drainage network distance, slope position, planar rupture surface, and altimetric variation. The debris-flow runout was made considering visible erosion on stream, which creates a path through where the flow passed, and the presence of deposits (e.g. Large boulders), which have been identified in the image. The results demonstrated shallow landslides scars (SLS) were concentrated in slopes between 20,1 – 30°, South and Southeast orientation, 600 – 800m of elevation, concave curvatures, and in Quartz-Monzonite and Biotite Monzogranite rocks. SLS occurred in several watersheds, but only one of them has also debris flow occurrence. The watershed with the highest number of SLS was Gurutuba with 288 and no evidence of an expressive debris-flow occurrence able to be identified through the images. On the other hand, the Guarda-mão watershed had an expressive debris-flow occurrence but a smaller number of SLS, with only one landslide being responsible for the initialization of the debris flow in the main channel and with most part of the volume generated by the entrainment of material through the channel. The results helped to improve our knowledge about mass movement in a tropical environment.
Mots clés : Mass movement|morphometric analysis|Google Earth|South America
A102953HD