... trapezium‐shapedmeander(Fig.1 and 2):on the onehandbecauseofhighlevel of tectonic fissuration, on the other handowing to the presenceof the erodibleshales and silty sandstone (T2-3 ... instability of the east slope of the Nam Lay valley and consequently why within the studiedarea only the sectioncorresponding to the territoryof the LayNuaCommunehad to sufferfrequently the wave ... conditionssuchasclimate,relief,lithologic and tectonicfeatures,which are consideredrelevant to debris and mudflows activities, are analyzed, and then come to the conclusions on determinant agents ofdebris and mudflashfloodinthisarea.Keywords:MuongLay;Landslide;Mudflow;Debrisflow;Mudflashflood.1.Introduction*Debris...