Dingalan Cherry Hills, Antipolo

LANDSLIDE 101 : “All ABOUT RAIN INDUCED LANDSLIDES IN THE ”

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- Road, Iligan City

Itogon, Benguet -

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 , 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 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.