leyte landslide 2006 case study

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The disastrous 17 February 2006 rockslide-debris avalanche on Leyte Island, Philippines: a catastrophic landslide in tropical mountain terrain

S. g. evans, r. h. guthrie, n. j. roberts, n. f. bishop.

Abstract. In February 2006, a disastrous rockslide-debris avalanche occurred in tropical mountain terrain, on Leyte Island, Central Philippines. Over 1100 people perished when the village of Guinsaugon was overwhelmed directly in the path of the landslide. The landslide was initiated by the failure of a 450 m high rock slope within the damage zone of the Philippine Fault where the rock mass consisted of sheared and brecciated volcanic, sedimentary and volcaniclastic rocks. Tectonic weakening of the failed rock mass had resulted from active strike-slip movements along the Philippine Fault which have been estimated by other workers at 2.5 cm/year. The landslide involved a total volume of 15 Mm 3 , including significant entrainment from its path, and ran out a horizontal distance of 3800 m over a vertical distance of 810 m, equivalent to a fahrböschung of 12°. Run-out distance was enhanced by friction reduction due to undrained loading when the debris encountered flooded paddy fields in the valley bottom at a path distance of 2600 m. A simulation of the event using the dynamic analysis model DAN indicated a mean velocity of 35 m/s and demonstrated the contribution of the paddy field effect to total run-out distance. There was no direct trigger for the landslide but the landslide did follow a period of very heavy rainfall with a lag time of four days. The rockslide-debris avalanche is one of several disastrous landslides to have occurred in the Philippines in the last twenty years. In terms of loss of life, the Guinsaugon event is the most devastating single-event landslide to have occurred worldwide since the Casita Volcano rock avalanche-debris flow which was triggered by Hurricane Mitch in Nicaragua in 1998.

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Recovery status report: Southern Leyte Landslide

This study focuses on the 2006 landslide tragedy in the Philippines, where an entire community, including its people, its productive assets, and its socio-cultural resources, was totally buried. It reports on the various levels of recovery that have been achieved among the provision of community services and facilities such as health, education, recreation, infrastructure, livelihood opportunities and psychosocial services; and identifies the limitations of the principle of "build back better" as well as those areas of concern in which the principle can best be applied.

It affirms that disaster recovery has to be advocated for and mainstreamed in national and local development planning, education, and mass media programs so that the principle of "build back better" can be achieved. It also calls for available early warning systems for landslide hazards to become a part of the preparedness and recovery efforts.

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The 17 February 2006 rock slide-debris avalanche at Guinsaugon Philippines: a synthesis

• Original Paper
• Published: 22 April 2009
• Volume 68 , pages 201–213, ( 2009 )

Cite this article

• Richard H. Guthrie 1 ,
• Stephen G. Evans 1 ,
• Sandra G. Catane 2 ,
• Mark A. H. Zarco 3 &
• Ricarido M. Saturay Jr. 2  

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The paper presents a synthesis of the key findings of the conference and workshop convened to consider the causes of and lessons to be learned from the disastrous rockslide-debris avalanche on 17 February 2006 in southern Leyte, Philippines. Some 1,221 people died and the barangay of Guinsagon was buried. The geology, historical seismicity, progressive disintegration of the rock mass, development of smectite layers and the continuous development and movement of shears within the Philippine Fault Zone combine in the steep rugged terrain to produce massive landslides, of which the 15 million m 3 Guinsaugon event was the latest. The relevance of recent heavy rain and an almost synchronous seismic event are considered but it is concluded that the movement was the result of progressive failures and tectonic weakening while the landslide hazard was increased by the presence of rice paddy fields in the valley bottom. An anecdotal time to failure curve is presented, based on eyewitness accounts and observations of instability. Attention is drawn to the importance of both the education and training of the local people in the recognition of signs of potential movement and a reporting management system. Such simple measures could save lives and empower local communities to take some ownership of their level of landslide risk.

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Acknowledgments

The authors acknowledge the contributions from approximately 160 scientists, survivors, students and local elected officials who participated in the 2008 Guinsaugon conference and workshop, Leyte Island Philippines. The conference was convened by the University of Philippines and the University of Waterloo, and we acknowledge financial assistance from the National Science and Engineering Research Council of Canada, the city of Tacloban and the municipality of Saint Bernard. Finally this paper is respectfully dedicated to the memory of the people who lost their lives in the Guinsaugon landslide.

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Landslide Research Program, Department of Earth Sciences, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

Richard H. Guthrie & Stephen G. Evans

National Institute of Geological Sciences, College of Science, University of Philippines, Diliman, 1101, Quezon City, Philippines

Sandra G. Catane & Ricarido M. Saturay Jr.

Institute of Civil Engineering, College of Engineering, University of Philippines, Diliman, 1101, Quezon City, Philippines

Mark A. H. Zarco

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Correspondence to Richard H. Guthrie .

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Guthrie, R.H., Evans, S.G., Catane, S.G. et al. The 17 February 2006 rock slide-debris avalanche at Guinsaugon Philippines: a synthesis. Bull Eng Geol Environ 68 , 201–213 (2009). https://doi.org/10.1007/s10064-009-0205-2

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Received : 27 October 2008

Accepted : 21 February 2009

Published : 22 April 2009

Issue Date : May 2009

DOI : https://doi.org/10.1007/s10064-009-0205-2

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Philippines: An update on the Southern Leyte landslide

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A massive landslide buried an entire village in Barangay Guinsa-ugon, in the town of St. Bernard, Southern Leyte province on Friday, February 17, 2006 at around 10:00 am. The landslide roared down a mountainside burying around 500 houses and an elementary school packed with around 246 schoolchildren, six (6) teachers, a principal and two health and social workers. Classes were ongoing at the time of the landslide. A women's celebration was also being held in the barangay hall at the time of the landslide and the participants were believed to be trapped inside the hall.

The landslides had been triggered by more than two weeks of continuous heavy rainfall, estimated to be four times more than the normal recorded rainfall. The Philippine Institute of Volcanology and Seismology (Philvolcs) also recorded a 2.6 magnitude earthquake which hit the southwestern portion of Southern Leyte around 10:36 a.m

Barangay Guinsaugon, is around 7 kilometers away from the town proper and has an estimated population of 3,000.

Based on the report released by the Department of Social Welfare and Development (DSWD) on February 21, 2006, aside from Barangay Guinsa-ugon, 15 other barangays were also affected by the landslide. Four evacuation centers are serving at least 439 families with 1,645 persons while other families are currently staying with their friends and relatives. Eighty-one (81) dead bodies have been recovered from the landslide site, 19 survivors have been rescued while 996 persons are still missing.

A pastor of the United Church of Christ in the Philippines and his 6 month old daughter were among those killed in the landslide. According to Rev. Dominador Gulles of the UCCP St. Bernard Task Force, only nine (9) of the almost 70 members of UCCP Guinsaugon are in the survivors' list, the rest among those who are feared to be buried in the mud.

The ongoing search and rescue operations had been hampered by the heavy mud. Based on the readings of the special instruments, they were able to identify the location of the school building which lay beneath 25 to 30 meters of mud. Rescuers have not been able to use heavy equipment to dig in because the ground is still soft. The national highway leading to the village was also damaged.

One of the evacuation centers being used is the church of the United Church of Christ in the Philippines (UCCP).

The National Council of Churches in the Philippines (NCCP) is coordinating with the UCCP local church for emergency response. A team will also be dispatched to conduct needs assessment particularly on rehabilitation assistance.

Minnie Anne M. Calub Program Secretary Program Unit on Faith, Witness and Service National Council of Churches in the Philippines 879 EDSA, Quezon City Tel.No. (632) 922-91-41/ (+639189019359) Email: [email protected] / [email protected]

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Causal and Trigger Factors of Landslide Occurrences in Southern Leyte, Philippines: Its Implications to Disaster Risk Reduction and Management

Leyte and Southern Leyte are some of the provinces of the Philippines which had the worst landslide history. Several catastrophic landslides occurred in Leyte, the worst of which were the landslides in Ormoc City, Leyte in November, 1991 and in Panaon island in Southern Leyte on December 19, 2003. These series of massive landslides which claimed the lives of more than 5,000 and 200 people in Ormoc City, Leyte and Southern Leyte respectively were triggered by heavy and continuous rain. On February 17, 2006, massive landslides occurred also in Barangay Guinsaugon, St. Bernard Southern Leyte and more than 1,000 people were buried alive that made it the most catastrophic landslide event in the recent times. On January 2, 2011, landslides hit again the town of Saint Bernard, Southern Leyte which claimed the lives of about 5 people.

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The 2006 Guinsaugon landslide in Saint Bernard, Southern Leyte, is one of the largest known landslides in the Philippines in recent history. It consists of a 15–20 million m<sup>3</sup> rockslide-debris avalanche from an approximately 675 m high mountain weakened by continuous movement of the Philippine Fault. The catastrophic Guinsaugon landslide killed 1221 people and displaced 19 000 residents over its 4.5 km path. To investigate the present-day morphology of the scar and potential failure that may occur, analysis of a 5 m resolution InSAR-derived digital elevation model was conducted using Coltop3D and Matterocking software, leading to the generation of a landslide hazard map for the province of Southern Leyte in central Philippines. The dip and dip direction of discontinuity sets that contribute to gravitational failure in mountainous areas of the province were identified and measured using a lower Schmidt–Lambert color scheme. After measurement of the morpho-struct...

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Lessons from Guinsaugon: How do landslides happen?

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9 years after the landslide, how is Guinsaugon?

It was a Friday morning, February 17, 2006. Children were in school and parents were going about their daily chores. Suddenly, the mountain slope overlooking their village collapsed, burying many villagers alive in thick, slick mud.

In just about two minutes, a whole community was lost. The collapsed portion of the mountain took 1,500 lives.

There were signs. In a way, nature was trying to communicate little warnings days before the tragedy struck. In hindsight, experts say, many would have lived if people learned to read the signs and acted on them.

Here is a timeline of what happened on that tragic day:

December 2005 – Some residents start to notice the tilting of trees, and the appearance of springs that are not usually there.

February 1, 2006 – Heavy rains of 4 to 5 times the normal amount that used to fall on the area poured along the mountain slopes. This goes on for the next two weeks.

February 15 – After two weeks, the incessant rain subsides. Residents start returning to their houses.

Starting Over: the aftermath of the Guinsaugon landslide

February 16 – Aside from the small springs seen two months before, small rocks from the top of the mountain start falling from time to time, according to some residents.

February 17, around 10:30 am  – An earthquake of magnitude 2.6 occurs 21 kilometers near Guinsaugon village. Almost simultaneously, a massive landslide occurs on the mountain slope facing Guinsaugon, carrying with it 1.2 billion cubic meters of mud and boulders up to about 3 kilometers. Minutes after the landslide, rescue efforts start.

February 25 – Southern Leyte Governor Rosette Yñiguez Lerias announces that they are calling off rescue efforts. Only 137 bodies and 15 body parts have been recovered, while 937 people remained missing – all presumed dead.

What went wrong?

The building of Guinsaugon village, as well as the other villages located along the footslopes of the Mount Can-abag was a disaster waiting to happen.

“The land where the houses were built were old landslide deposits,” Mines and Geosciences Bureau (MGB) senior science research specialist Salvio Laserna said. “Maaring nagkaroon na ng malalaking landslides doon noong wala pang tao.” (It’s possible that big landslides had occurred in that place before the place became inhabited.)

Laserna explained that old tension cracks, scars, and cat-like scratches on the surface of the mountain indicate that there had been major landslides before.

He also said that, prior to the disaster, MGB had been giving advisories to local government units that those communities were very prone to landslides since they were located at the footslopes of the mountain.

“’Yun ang problema kasi namin eh, wala kaming police power para paalisin ‘yung mga tao. kami ay sa recommendation lang,”  Laserna said. (That’s our problem. We don’t have the police power to force people to leave. We can only recommend.) 

The top of the mountain, according to Laserna, is also full of gullies – small channels along the mountain slope where water passess through and where landslides start to develop.

Philippine Institute of Volcanology and Seismology (Phivolcs) Director Renato Solidum said the mountain’s proximity to the Philippine Fault Zone also adds to its vulnerability to landslides.

“If there are earthquakes, [mountain] slopes can be [easily] fractured. So, essentially, the [mountain] slope [facing Guinsaugon] was already fractured. Maraming bitak .”

According to Malyn Tumonong , senior science research specialist at MGB and spokesperson for the team of geologists that the bureau sent to St Bernard, rocks that made up the mountain overlooking the village were shattered when the Philippine Fault—which runs from Luzon to Mindanao—cut across Leyte Island around 5 million years ago.

This made the rocks prone to weathering, erosion, and alteration. Movements in the fault zone also caused the rocks to continuously grind against each other, pulverizing them in the process.

Observe nature, communicate warning signs

The signs that were already visible days, even months, prior to the big landslide could have saved lives, Solidum said.

As early as two months before the disaster, some people familiar with the mountain had been noticing significant changes, such as tilting of the trees and appearance of springs, not normally seen in certain parts of the mountain.

Signs as such have significant meanings. Normally, rainwater seeps through the soil, depending on the original layers. If there is ground movement, the original path of the water becomes disrupted and so it has to find another opening, which is through the cracks formed from such movement, according to Solidum.

Other signs of ground movements according to MGB and Phivolcs are:

Had the information been shared, residents would have been more prepared.

“People see but they don’t share the information. I think communities need to have a good network among the residents especially those [who] frequently [go to the] slopes. [Once they notice changes], they should report to the barangay official,” Solidum said.

Climate change and landslides

“I use Guinsaugon landslide as an example of a condition that would happen during climate change – global warming,” Solidum said.

As the years go by, the effects of climate change become more and more evident all over the world. In the Philippines, whose location along the typhoon belt and the Pacific Ocean’s Ring of Fire exposes it to major hazards, its effects could be much worse.

Landslides can be triggered by rain or earthquake alone, “but if you have a combination, then it is easier for landslides to happen,” Solidum explained.

Solidum says it is important to look at how climate change could exacerbate the effects of natural hazards. As the world gets warmer, the more evaporation happens, thus more rain forms. Frequent and more intense rainfall will make the mountain slopes wetter, making it easier for landslides to occur.

With the country being seismically active, earthquakes could occur and aggravate the situation.

It is also important for people to be familiar with the different types of landslides that could occur. What happened in Guinsaugon, for instance, was a deep-seated landslide, according to Solidum.

Deep-seated landslides are those which do not occur immediately during a heavy rain. “There’s a lag time [during which] the water would have to pass through and seep in through the soil, and then at some point it gets saturated,” Solidum said. But because of the earthquake, it became sooner.

“[Yung landslide ay] para bang buntis na nanganak na kahit hindi pa due,”  Solidum added. (The landslide was like a pregnant woman who gave birth prematurely.)

Using hazard maps

Had there been detailed geohazard maps before, the damage caused by the landslide would have been minimized and the loss of life could have been prevented.

Geohazard mapping and the Guinsaugon landslide

While MGB had started its geohazard mapping way before the tragic event, it is only recently that government agencies are able to actually produce hazard maps. 

In 2010, MGB was able to complete 1:50,000 scale rain-induced landslide hazard maps for the whole country. Higher resolution maps at a scale of 1:10:000 are already around 85% complete.

Meanwhile, Phivolcs, the agency in charge of producing earthquake-induced hazard maps, has been granted by the Department of Science and Technology a program called the “Development and Deployment of Early Warning System for Deep-seated Catastrophic Landslides and Slope Failures.” It will allow them to place sensors in slopes that have a potential of being affected by deep-seated landslides.

The University of the Philippines (UP) National Institute of Geological Sciences and the UP Institute of Electrical and Electronics Engineering are also part of the project.

So far there are 11 sites in Benguet, Surigao del Sur, Negros Oriental, Iloilo, and Southern Leyte where these sensors have been installed.

But disaster prevention and mitigation does not end with mapping and understanding the hazards.

Now that the maps are available, the next challenge is for communities to use them for development planning and coordinated action to make sure that disasters like the one that happened in Guinsaugon will never happen again. – Rappler.com

Sources: Philippine Institute of Volcanology and Seismology, Mines and Geosciences Bureau, various news websites

Editor’s Note:

February 17, 2015, is the 11th anniversary of the landslide that practically wiped out the village of Guinsaugon in Saint Bernard, Southern Leyte. This series on Rappler digs into what happened, what have been done since, and what can communities do to prevent future tragedies.

This series is part of Project Agos, a collaborative platform that combines top-down government action with bottom-up civic engagement to help communities learn about climate change adaptation and disaster risk reduction.

Project Agos harnesses technology and social media to ensure critical information flows to those who need it before, during, and after a disaster. It is a partnership between Move.PH, Rappler’s civic engagement unit, and agencies such as the Philippine Institute of Volcanology and Seismology (PHIVOLCS), the Mines and Geosciences Bureau (MGB), the Office of Civil Defense, the Department of Interior and Local Government (DILG) and other key stakeholders.

Project Agos is supported by the Australian Government.  

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Recovery Collection: Philippines: Southern Leyte Landslide

Aerial View of Mudslide St Bernard, Philippines

Introduction

The Guinsaugon rockslide-debris avalanche is the second major landslide of this kind to be described in the twenty-first century and the volume of its deposit falls within the range generated by debris avalanches from the twentieth century.

A massive landslide devastated the commu­nity of Barangay Guinsaugon, Municipality of St. Bernard, Southern Leyte Province, Philip­pines, at about 10:30 local time on 17 February. The landslide occurred along the steep fault scarp of the Philippine Fault Zone (PFZ) , a large and active tectonic structure that traverses the entire length of the Philip­pines. Barangay Guinsaugon is located at the foot of the scarp, directly in the path of the downward moving mass of earth.

Knowledge base

Philippines: 9 years after the landslide, how is guinsaugon.

Recovery status report: Southern Leyte Landslide

Rising to the call: Good practices in Disaster Risk Reduction and Climate Change Adaptation in the Philippines

Community-driven disaster intervention: Experiences of the Homeless People’s Federation Philippines, Incorporated (HPFPI)

From tragedy to resiliency: A journey from the 2006 Guinsaugon Landslide

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Philippines: Southern Leyte Landslide 2006

Introduction

The Guinsaugon rockslide-debris avalanche is the second major landslide of this kind to be described in the twenty-first century and the volume of its deposit falls within the range generated by debris avalanches from the twentieth century.

A massive landslide devastated the commu­nity of Barangay Guinsaugon, Municipality of St. Bernard, Southern Leyte Province, Philip­pines, at about 10:30 local time on 17 February. The landslide occurred along the steep fault scarp of the Philippine Fault Zone (PFZ) , a large and active tectonic structure that traverses the entire length of the Philip­pines. Barangay Guinsaugon is located at the foot of the scarp, directly in the path of the downward moving mass of earth.

Knowledge base

Recovery status report: Southern Leyte Landslide

Is this page useful.

Thank you. If you have 2 minutes, we would benefit from additional feedback (link opens in a new window) .