LANDSLIDE 101 : “All ABOUT RAIN INDUCED LANDSLIDES in the PHILIPPINES”

Dingalan Cherry Hills, Antipolo LANDSLIDE 101 : “All ABOUT RAIN INDUCED LANDSLIDES IN THE PHILIPPINES” Compostela Valley Guinsaugon, Leyte LEARNING OBJECTIVES 1 -Understanding Rain-Induced Landslide -Understanding Types of Landslide Why is Philippines prone to various types of mass wasting or landslide GEOLOGIC CLIMATIC Geological Factors Various Topographies STEEP SLOPES ROLLING HILLS VAST PLAINS Climatic Factors • ~ 20 tropical cyclones per year enter PAR Numerous typhoons and extended rainy seasons/periods Strong and shifting wave currents Guinsaugon, Southern Leyte (February 2006) Downslope movementDownslope of earth materialsmovement aided of earth by materialsgravity aided by gravity ROLE OF GRAVITY August 1999 Sliding mass Sliding mass March 2001 LANDSLIDE Major topographic features What are the types of mass wasting? Very Slow Fast Very fast TYPE (<1 cm/year) (1mm/day to 1.0 km /hr) (>4km/hr) Flow CREEP EARTH OR MUDFLOW DEBRIS AVALANCHE Slip DEBRIS SLIDE OR SLUMP Fall ROCKFALL “LANDSLIDES” Creep Debris Flow Mudflow Debris Avalanche Creep DEBRIS FLOW • . Brgy Andap, Compostela Valley, 2012 Maco, Compostela Valley, 2009 . Debris Flow Dingalan, Aurora, 2004 Brgy Andap, Compostela Valley, 2012 Infanta,Quezon, 2005 Real, Quezon, 2005 2 Mudflow Infanta,Quezon, 2005 Former location of chapel Kapatagan, Lanao del Norte,2006 Kapatagan, Lanao del Norte,2006 DEBRIS AVALANCHE COMPLEX LANDSLIDE Cherry Hills Subdivision, Antipolo City, 1999 Slump Slide - Debris Slide - Rock Slide SLUMP Jagna, Bohol Kibawe, Bukidnon Kibawe, Bukidnon, 2006 Magsaysay, June 5, 2009 Mankayan National High School Ground June 9, 2009 SLIDES Debris Slide Carasi-Piddig Road, Ilocos Norte Iligan City Itogon, Benguet La Union-Ilocos Sur Rock Slide Rock Slide in Abigail Subdivision, Brgy. Del Carmen, Iligan City on July 2008 Rock Fall Benguet Bukidnon-Davao Highway LEARNING OBJECTIVES 2 -Understand the contributing factors to landslide incidence -To be able to know the factors to consider in selecting settlement sites nces between landslide and slope failure Contributory Factors to Landslide Incidence • Topography and Slope Angle • Rock Types, Composition and Physical Characteristics • Vegetation • Exacerbated by human activities • Anthropogenic (human activities) 1. Topography and Slope Angle Iloilo, 2008 Benguet, 2008 Maramag, Bukidnon 2008 Iloilo, 2008 Maramag, Bukidnon 2. Rock Types, Composition and Physical Properties Rock Type and Strength Brgys. Imbranga-an, Marirong and Tig-alaran. Antique being underlain by crushed rocks and unconsolidated soil, Effect of prolonged or intense rainfall on granular are prone to mass movement, especially during heavy, soils. continuous rains. Rock Types – Sedimentary Rocks sandstone –siltstone beds Brgy Mabileg, Sigay, Ilocos sandstone-siltstone beds Sur Brgy Poblacion, Burgos, LaUnion sandstone –siltstone beds Kalumsing, San Emilio, Ilocos Sur Degree of Alteration Volcanic rock area THE PLANES OF WEAKNESS Unaltered Volcanic rock OF GUINSAUGON DEBRIS AVALANCHE Altered Volcanic rock Argillized volcanic rocks, Hinobaan, Negros Occidental Degree of Weathering Degree of Weathering shallow landslide shallow landslide Deep-seated Landslide, Antipolo Bed contacts Fracture Orientation l.. Fault Fault Fault Joints 3. Vegetation Infanta, Quezon, 2004 No landslide despite cogon grass Landslide despite thick vegetation only vegetation Vegetation vs. slope angle “No amount of vegetation can hold the ground in the case of deep-seated landslides.” HUMAN ACTIVITIES 1. Deforestation 2. Overloading of slope surfaces by infrastructures 3. Overloading of slope surfaces by garbage dumps 4. Water leakage from utilities 5. Poor construction of roads and subdivision Illegal/Irresponsible mining Factors to Consider in Selecting Settlement Site Avoid settlements on steep to very steep slopes with thick soil overburden Restrict urban development including houses along unstable steep slopes unless properly mitigated using engineering measures. Avoid settlements at the base of mountainous slopes with small streams or drainage paths. Barangay Orquia San Remigio, Antique Avoid settlements Barangay Maparat, Compostela, on top of old ComVal Province landslide deposits. Barangay San Antonio, Tandag City, Surigao del Sur Avoid settlements on top of alluvial fan underlain by old debris flow and stream deposits Brgy. Andap, New Bataan, ComVal Province Avoid settlements near escarpments or faces of bedrock that have few joints and cracks developed within the masses..

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