Last February 25-26, my team mate Bevs and I left Cagayan De Oro City for Lanao del Norte for yet another fieldwork. With our usual field tools, we set out for the adventure in the manner of Lara Croft looking for treasures (thanks Denz for the idea!) except that we weren’t after any treasures but landslides.
The following are snap shots of our fieldwork:
*Our accommodation was soo nice and comfortable that I was still sleepy by the time we need to hit the road for the field.. :-)*
*The weather was good as shown by these cirrus clouds. Shot taken from the MCCI ground at 5:30 in the morning.*
Okay, let’s go to the serious stuffs.
*This corn field was flattened when water overflowed towards Cabuyao River banks.*
The dense and strong onrushing water along Cabuyao River destroyed partially this spillway/submarine bridge that used to connect two barangays.
*The truss bridge connecting Barangay Poblacion and Daligdigan was damaged by the flood along Cabuyao River. The abutment’s foundation was eroded by the debris-laden flood water*
Brace your self for more serious observations we had in Lanao:
Yeah, that’s a spring. What’s amazing about this spring is that it’s new and that it gushed right out of a house’s kitchen’s floor in Barangay Inasagan!
According to the interviews we conducted, water gushed out of their floor after nine days of continuous rain. Formation of new intermittent (meaning water is not permanently gushing out) springs in Barangay Inasagan started after a weak earthquake days before the 9-day deluge. But these springs formed along the foot slopes of the hills proximal to the houses. During the 9-day deluge, springs started developing right inside people’s homes with water gushing out and flooding houses and streets. Portions of Barangay Inasagan now looked like a housing development with bad drainage system. Creeks formed between houses as shown by the following photos:
* I borrowed this Styrofoam boat from a kid, played with it and took a picture*
After assessing flood and spring occurrences in Barangay Inasagan and vicinities, we hit the road again to go to Barangay Buntong where landslides were said to have occurred and killed 6 people. The purpose of our visit was to traverse around landslides, plot them on the map by locating through GPS device and identify areas susceptible to recurrence of geohazards.
*This portion of the road was scoured by sediment-laden sheet flood water (sheet flood is a flood along flat surface such as roads where no river is in proximity and where water from rain just spread like a “sheet” in the absence of a drainage system)*
*A portion of a ridge showing debris flows that damaged crops. Note that the materials are greyish and appeared to have “flowed” as water would along a valley. This characteristic of the landslide indicate water saturation as the primary cause of the landslide. On close examination, the materials were mostly composed of sand with pebble to cobble-size volcanic rocks such as pumice, andesite and scoria.*
*More landslides! The hill interior of Barangay Buntong is actually prone to landslide due to the nature of its topography and geology. We rated the area as “High” in terms of susceptibility to landslide and flood. In this area’s case, the type of landslide is debris flow as the materials flowed downslope similar to water flowing along a valley (but slower) indicative of rain saturation. Debris flows, mud flows actually run faster along a slope compared to say, debris slide or mud slide (slide vs flow with the former having less water content compared to the latter) so there’s little chance of survival if you happen to be in its path. A sad fact.*
*This is a rill or something like a small dike that forms along the foot of a landslide where water flowed through. So this rill is another evidence of water saturation during the 9-day deluge as the primary cause of the debris flow occurrence in Barangay Buntong. This rill is about one meter deep.*
*I’ve merged two pictures of a ridge cut by numerous debris flow and debris slides (I hope by now you know the difference between the two)*
*These low lying hills are cut by recent landslide scarps whose debris meet in between them forming a valley of sand, pebbles and organic materials (grasses in this case)*
*After looking at several debris, we looked at the exposed face of the rock and found out that the area is underlain by an old lahar deposit (by old I meant a layman’s definition of the word but the lahar deposits look recent to us Geologists, which means it could be hundreds of years old).*
*This is the “killer” debris flow. In two minutes after the residents heard a bursting sound from the mountainside, the debris flow hit their houses killing 6 people on its path instantly.*
*Note that the trees are actually standing erect in spite of the high erodibility character of the sand comprising this mountain. This indicates that the movement of the debris downslope was fast (as opposed to creeping soil failure which is a slow downslope movement of materials and hence be indicated by slowly tilting trees or posts).*
*Some of the materials from the “killer” debris flow reached the river causing a temporary damming of water.*
*This is where the two young girls were buried by the debris. They were moved from their original position by about 10 meters. What you see here were their mat (what some Filipinos use for sleeping) and part of their house that was totally damaged by the debris flow.*
*The survivor named Tatah as he tells us the horrors of that night the debris flow hit them.*
The following shots are the not-so-serious photos of my team and me during the fieldwork. But before that, I’d like to express my deep and heart-felt condolences to those who lost their loved ones during the landslide and flood occurrence. One person is still missing……
*Our escort and me posing for the picture on the start of our trek.*
*My team! Congratulations for a job well done!*
*I took a photo of two Muslim kids chatting along the road.*
*This is a view of the garden from our corridor in MCCI where we stayed*
*2 comfortable beds for two tired geologists.*
*MY tired tired feet*
Rock_Angel_Grass 