Science guides search and rescue after the 2006 Philippine landslide

Science guides search and rescue after the 2006 Philippine landslide

Alfredo Mahar A. Lagmay, Arlene Mae P. Tengonciang, Raymond S. Rodolfo,

Janneli Lea A. Soria, Eden G. Baliatan, Engielle R. Paguican, John Burtkenley

T. Ong, Mark R. Lapus, Dan Ferdinand D. Fernandez, Zareth P. Quimba and

Christopher L. Uichanco1

A rockslide-debris avalanche destroyed the remote village of Guinsaugon in Southern Leyte,

Philippines, on 17 February 2006. Although search and rescue procedures were implemented

immediately, the scale of the landslide and a lack of information about its nature resulted in

unfocused and imprecise efforts in the early days of the operation. Technical support was only

introduced five days after the event, provided by a team of volunteer geologists, geophysicists,

and meteorologists. By the time search and rescue operations were transferred to specific target

sites, however, the chances of finding survivors trapped under the rubble had diminished. In such

critical situations, speed, accuracy, and the maximum appropriation of resources are crucial.

We emphasise here the need for a systematic and technically informed approach to search and

rescue missions in large-scale landslide disaster contexts, and the formulation of better disaster

management policies in general. Standard procedures must be developed and enforced to improve

how civil authorities respond to natural calamities.

Keywords: avalanche, debris, Guinsaugon, landslide, Leyte, rockslide, search and

rescue, Southern Leyte

IntroductionA rockslide-debris avalanche occurred at 10:26 am on 17 February 2006 in Southern

Leyte, Philippines (Lagmay et al., 2006). This large-scale landslide devastated the

village of Guinsaugon, with a population of 1,857 (NDCC, 2006). Twenty survivors

were rescued from the front edge of the debris field within hours of the disaster,

but the majority of the village’s population was believed to have been buried by the

avalanche. For the next eight days, some 2,000 multinational rescuers scoured the

accessible portions of the landslide area, searching for survivors. On the evening of

24 February, the government authorities opted to switch from search and rescue

operations to the retrieval of fatalities. This decision was based on the consensus of

all parties involved in the search and rescue effort, who cited diminishing hopes of

finding survivors alive and concerns for the safety of the rescuers. In this paper, we

describe how scientific counsel provided both focus for the search effort and technically

supported strategies to ensure the welfare of those involved in the rescue operations.

The massive landslide happened along the steep scarp of the Philippine Fault Zone

(PFZ), a regional structure first recognised by Allen (1962). Numerous other slope

failures have occurred along the mountain range defining this segment of the PFZ,

especially in the week prior to the landslide, although none compares in volume and

doi:10.1111/j.0361-3666.2008.01047.x

Disasters, 2008, 32(3): 416−433. © 2008 The Author(s). Journal compilation © Overseas Development Institute, 2008.

Published by Blackwell Publishing, 9600 Garsington Road, Oxford, OX4 2DQ, UKand 350 Main Street, Malden, MA 02148, USA

Science guides search and rescue after the 2006 Philippine landslide 417

size to the Guinsaugon event (Presidential Inter-Agency Committee Report, 2006).

Landsat imagery and shaded relief maps generated by National Aeronautics and

Space Administration (NASA) Shuttle Radar Topography Mission (SRTM) data

(Figure 1) show the main trace of the PFZ, oriented N17°W. Older landslide scars

were identified in the area, verified both by field investigations (Presidential Inter-

Agency Committee Report, 2006) and analysis of available satellite images (Lagmay

et al., 2006). The presence of these scars further demonstrates the long-term suscep-

tibility of this mountain range to mass wasting.

Figure 1 Location of the 2006 Guinsaugon landslide*

* A shaded relief map generated from Shuttle Radar Topography Mission digital elevation data shows the location of the

landslide—outlined in dark grey—with respect to the trace of the Philippine Fault. The small black circles identify the

earthquake epicentres reported by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the

United States Geological Survey (USGS). The inset shows the location of Southern Leyte in the Philippines.

Source: authors.

Alfredo Mahar A. Lagmay et al.418

The timing of the landslide is still uncertain, although accounts of the events pro-

vided by witnesses converge at around 10:30 am (Lagmay et al., 2006; Suwa, 2006).

A telephone call made by Lita Siona, a Department of Agriculture technician and

one of the listed fatalities, probably offers the best approximation of the time and

duration of the incident. Siona placed a call to the Mayor of St. Bernard, Southern

Leyte, as the landslide transpired. According to the Mayor, the conversation started

with a query from the terrified technician: ‘Mayora, dakong anas . . . Aruy, asa mi

ron dagan?’ (Mayor, a big landslide . . . Oh no, where are we going to run?). The

records of the mobile telephone company show that this conversation started at

10:26:00, and that it lasted for 26 seconds. After a brief interruption, it was followed

by a second call, which started at 10:27:53 and lasted for 91 seconds before the con-

nection was cut again. These reported times, as verified by the mobile telephone

company, are based on the standard atomic clock time used by its computer servers.

* The figure shows the planform area of the landslide, reconstructed from an ASTER (METI-ERSDAC, 2006) image

and aerial photographs taken over the debris field. The landslide is overlain on a Landsat image of Guinsaugon (white)

and its vicinity. White dashed lines mark the trace of the Philippine Fault.

Source: authors.

Figure 2 Planform area of the landslide*


The landslide has a planform area of 3,324,400 million square metres, a maximum

width of 1.52 kilometres, and a distance of 4.1 kilometres from crown to toe (Figure 2).

Independent reports place the volume of the deposit at 15–20 million cubic metres

(Lagmay et al., 2006) and 21 million cubic metres (Araiba, in Suwa, 2006). Based on

the duration of the telephone calls and the extent of the landslide deposit, the ava-

lanche is estimated to have travelled with a velocity of about 100 kilometres per hour.

Three factors are suspected of having triggered the avalanche. First is the exces-

sive amount of rain that fell in the days before the disaster, even though the landslide

happened on a sunny morning. Multi-satellite precipitation analysis from the NASA-

JAXA Tropical Rainfall Measuring Mission reported that 500 millimetres of rain

fell on Southern Leyte between 4 and 7 February. The Philippine Atmospheric,

Geophysical, and Astronomical Services Administration (PAGASA) rainfall station

at Otikon, located seven kilometres southwest of the landslide head, recorded 683.6

millimetres from 8–14 February. The highest amount of rainfall over this duration

was 171 millimetres, recorded on 12 February (Lagmay et al., 2006).

Second is an earthquake that occurred in Southern Leyte on 17 February 2006.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) recorded a

2.6 magnitude (Ms) earthquake 21 kilometres west of Guinsaugon at 10:35:30.99,

using seven of its unmanned satellite-telemetred seismic stations (PHIVOLCS, 2006a;

2006b). An earthquake was also recorded by the United States Geological Survey

(USGS) at 10:36:32.59 (PDE-W 2006), about two kilometres north of the landslide,

at a depth of 35 kilometres, and with a magnitude (Mb) of 4.3 (USGS, 2006a). Records

obtained from the F-net broadband seismograph network established and operated

by the National Research Institute for Earth Science and Disaster Prevention, Japan,

measured the occurrence of ground motion at 10:37. Yamanaka (2006) interprets

this record of ground motion as the Rayleigh wave generated by the landslide event.

Third is deformation of the slope prior to the landslide. Accounts described by

Suwa (2006) indicate that the slope had been experiencing deformation due to

creep. This phase of creep motion may have developed from secondary to tertiary

creep at the end of 2005 or in early 2006.

By 28 February 2006, 139 bodies had been recovered from the landslide—56 have

been identified and 83 remain unidentified. Two victims died in hospital, out of

the 33 treated for injuries. The number listed as missing and presumed dead is 980

(NDCC, 2006). The remaining residents of the village were not in the area at the

time of the disaster. In total, the official number of fatalities is 1,221.

Search and rescue operationsA team of geologists, geophysicists, and meteorologists provided technical advice

during the search and rescue operations following the landslide. Their combined

efforts resulted in an ad hoc Geographic Information System (GIS) that was used to

narrow the rescue mission down to certain sites within the debris field. In particu-

lar, search parties were directed to transfer operations from the original position of

Guinsaugon to 550–600 metres down slope, where the avalanche transported it. By

the time rescuers concentrated their efforts on the new search sites, the local water


table had already risen due to persistent rainfall, decreasing the chances of finding

survivors trapped beneath the debris.

The village of Guinsaugon lay directly in the path of the downward-moving mass

of earth, near the base of the fault scarp of the Philippine Fault (Figure 2). Rescuers

focused their efforts during the first six days on the original location of the village,

assuming that the landslide had buried the community. An elementary school build-

ing with 248 students and teachers, believed to be 30 metres below the surface, was

the primary target of the rescue effort. Despite the daunting task of excavating an

enormous amount of debris, rescue efforts were sustained because of reports that

victims had sent mobile telephone messages to relatives and friends up to two days after

the event. One text message reportedly called on rescuers to hurry because the water

level was rising.

Figure 3 GPR profile*

* The figure shows the GPR line located at the first search site before rescue operations were shifted. The penetration

depth of the survey was about 18 metres; the depth of the landslide deposit at this point was estimated to be 30 metres.

An elevated water table was identified, caused by the ponding of water at several levels within the debris field.

Source: authors.


The location of the school building was initially plotted on a 1:50,000 topographic

map by the first rescue teams that arrived. They used unscathed trees as triangulation

points to locate the original site of the school based on the accounts of local resi-

dents. The authors identified a more precise location on the sixth day by overlaying

a 2003 SPOT 5 JPEG satellite image and a cadastral plan on the topographic map.

The position of the school as determined after orthorectification of the SPOT image

and maps is 40 metres away from the earlier estimate determined through triangula-

tion. A ground control point measured with a differential global positioning system

(GPS) several years earlier was provided to the ground-based teams by PHIVOLCS

on the seventh day. This GPS point plots in the same position that was located by the

scientific advisory team using the co-registered satellite image, cadastral plan, and

topographic map.

After establishing the location of the school perimeter, a ground penetrating radar

(GPR) with a 100 megahertz (Mhz) antenna was used to identify buried structures,

while sound detectors and canine units were employed to detect signs of life. The

maximum depth of coherent penetration of the GPR within the landslide deposit was

only 18 metres, too shallow to reach the targeted 30-metre depth. The GPR detected

an elevated water table 14–15 metres beneath the surface of the deposit (Figure 3).

Observations within the debris field showed pools of water accumulating on the

surface at levels consistent with the water table identified from the GPR profile. This

* The figure shows a vertical aerial photograph of exposed clusters of houses within the debris field. Continuous rainfall

throughout the search and rescue operations further exposed these structures on the seventh day.

Source: authors.

Figure 4 Aerial photograph of debris in the landslide area*


suggested that any possible survivors buried below that depth might have already

drowned.

Vertical and oblique aerial photography carried out on the seventh day revealed

clusters of buried houses and building debris exposed by runoff from continuous

rains (Figure 4). These structures were believed to contain air pockets that could

possibly host survivors at depth, informing initiatives to assign priority sites.

An inventory (Table 1) of survivors, recovered bodies, personal articles, and houses

was plotted on the maps and aerial photographs with the assistance of the rescue

teams that conducted the retrieval. Four residents were also asked to identify the

building remnants in the debris field and to establish their original positions on the

cadastral map. They were able to identify a half-buried three-storey concrete build-

ing, which was originally located in front of the school compound. Remnants of other

houses adjacent to this concrete building were also recognised down slope and were

arranged as before the landslide. The inventory and field validation plotted on the

aerial photographs constituted a GIS, which strongly suggested mass transport of

the community, 550–600 metres from its original location (Figures 5 and 6). This

database helped in focusing the search and rescue operation in areas with a higher

probability of containing survivors.

Table 1 Partial inventory of rescued persons, fatalities and articles within the debris field

Recovery sites

Date recovered

Description Identification Origin

2 19 February Arm – –

2 19 February Leg, 10 metres away from the arm – –

2 20 February Adult – –

2 21 February Adult male buried under collapsed structure (house)

– –

1 22 February Adult, female, buried one metre deep, in the process of decomposition, hairless, skin intact, swelling

– –

1 22 February Child, buried one metre deep, decapitated on impact

– –

1 22 February Chicken (alive), buried under a roof – –

1 22 February Three children, hairless, bodies complete and intact, buried less than one metre, in the process of decomposition

– –

1 22 February Four adult, bodies complete and intact, buried less than one metre, in the process of decomposition

– –

1 22 February Dream Satellite Antenna – Barangay Guinsaugon

1 22 February Grills/roofs – Barangay Guinsaugon

1 22 February Motorcycle parts – –


1 22 February Large shelves – Barangay Guinsaugon

1 22 February Soft drink cans/bottles – –

3 22 February Intact body, child – –


3 22 February Body – –

4 22 February Adults, bodies complete and intact, buried approximately one-metre deep

– –



8 22 February Female, teenager – –

8 22 February Male, adult – –


1 23 February Body of a schoolgirl – –

1 23 February Relatively intact desktop computers – –

2 23 February Picture Evangellel Paler Barangay Guinsaugon

2 23 February School identification Obralen Miravales

Barangay Guinsaugon

2 23 February Algebra notes Joellen Miravalles Barangay Guinsaugon

2 23 February Old documents – –

2 23 February Letters Tortillano Cabadbad Bolasco

Barangay Guinsaugon

2 23 February Bible with identification Anecita Rubio Barangay Guinsaugon

2 23 February Income Tax Return, receipts Tortillano Cabadbad Bolasco

Barangay Guinsaugon

3 23 February Teenager (15 years old) – –

3 23 February Male, female – –

3 23 February Mother Geralyn Gorine Pagulong (?dead)

–

3 23 February Father, alive with three children (survivors) Libby Pagulong –

3 23 February Three missing children –

3 23 February One child of nine-member family is dead and retrieved, female, three years old

Kwin2/Ching2 Pagulong

–

1 24 February Helmet Jonhson Monghit Barangay Guinsaugon

1 24 February Picture frames – –

1 24 February Picture album Judy Labis, Venus Baylan

Barangay Guinsaugon


1 24 February Books – –

1 24 February Lesson plans – Barangay Guinsaugon

1 24 February Pasugo articles/prayer books – –

1 24 February Picture album with identification of the person in the picture

Virgilio Monghit –

– – Identified dead Agapito Timkang Barangay Guinsaugon

– – Identified dead Abdolio Lasquito Barangay Guinsaugon

– – Identified dead Juanito Samcol Barangay Guinsaugon

– – Identified dead Absalon Libaton Barangay Guinsaugon

– – Identified dead (two bodies) Melicio Navos Barangay Guinsaugon

– – Identified dead Jorge Velasco Barangay Guinsaugon

– – Identified dead Cresencio Medilio Barangay Guinsaugon

– – Identified dead Candido Peligro Barangay Guinsaugon

– – Identified dead (two bodies) Teodoro Pia Barangay Guinsaugon

– – Rescued Felipe Arcay Barangay Guinsaugon

– – Rescued Loreta Marqueda Barangay Guinsaugon

– – Personal articles Agapito Timkang Barangay Guinsaugon

– – Personal articles Antonio Arbiol Barangay Guinsaugon

– – Personal articles Teodoro Pia Barangay Guinsaugon

– – Personal articles Jorge Velasco Barangay Guinsaugon

8 – Intact body, child – –

1 – Three-storey building Rogelio Araullo Barangay Guinsaugon

2 – Notebooks – –

2 – Test papers – –

2 – Teacher’s record book – –

2 – Cedula Melanie Coquilla Barangay Guinsaugon

2 – Diploma – –

2 – Birth certificate – Barangay Guinsaugon


2 – Pencil case – Barangay

Guinsaugon

2 – Textbooks – Barangay

Guinsaugon

2 – Pasugo publication – Barangay

Guinsaugon

2 – Bible – –

2 – Philippine Benevolent Missionaries

Association (PBMA) booklets and

publications

– Barangay

Guinsaugon

2 – Wedding Invitations Judy Labis and

Venus Baylan

Barangay

Guinsaugon

2 – PBMA identification cards Virgilio Monghit Barangay

Guinsaugon

Note: Barangay Guinsaugon was the only community directly in the path of the debris avalanche.

Figure 5 Inventory of debris from the landslide field*

* A) Database of survivors, recovered bodies, personal articles, and houses. B) University of Philippines geologist

Raymond Rodolfo examining recovered items, and a three-storey building belonging to Rogelio Araullo, formerly

located in front of the school compound, and a mail pouch belonging to one of the former residents. C) Building

remnants and personal items that were concentrated near the toe of the landslide. D) Advanced Spaceborne Thermal

Emission and Reflection Radiometer (ASTER) image draped over a digital elevation map shows that Guinsaugon

moved 550–600 metres down slope from its original location.

Source: authors.


Figure 6 Transport of buildings and debris*

* Recovery sites 1–6 were identified from aerial photography for the refocused search and rescue mission. Additional

bodies and articles were recovered from sites 7–9. The three-storey building was transported relatively intact approxi-

mately 550–600 metres from its original location.

Source: authors.

En-masse flow transport (Takarada, 1994) is consistent with the initial identifica-

tion of the Guinsaugon landslide as a rockslide-debris avalanche, characterised by a

fault plane at the head scarp, hummocks, and jigsaw cracks (Ui, 1983; Glicken, 1996)

in the debris field, and an unusually long runout (Dade and Huppert, 1998). Such a

type of non-turbulent mass flow (Takarada, 1994; Melendez and Takarada, 2006) is

capable of moving surface objects downward without significant scattering of debris.

Some of the transported houses were found with their roofs and beams still attached,

as well as with a relatively intact personal computer and refrigerator. Text messages

received from the victims corroborated this en-masse transport hypothesis. It is more

likely though, that victims who were able to send text messages were buried at

shallower depths down slope rather than under 30 metres of material at the original

site of Guinsaugon.

On the eighth day, rescue operations were moved to the priority sites closer to

the distal part of the landslide deposit. More bodies were found in the rain-drenched

debris and mud, but no survivors (Figure 7). The assessment of the ground condition

suggested that remaining air pockets necessary for the survival of the victims were

https://www.researchgate.net/publication/223624454_Volcanic_dry_avalanche_deposits_-_Identification_and_comparison_with_nonvolcanic_debris_stream_deposits?el=1_x_8&enrichId=rgreq-e785e8a8a1960d2fdebbbdcf29a73143-XXX&enrichSource=Y292ZXJQYWdlOzIyOTg4OTkyOTtBUzoxNDQ1NzA5ODU3NTA1MjlAMTQxMTQ3OTgxNzkyMQ==

https://www.researchgate.net/publication/249520524_Long-runout_rockfall?el=1_x_8&enrichId=rgreq-e785e8a8a1960d2fdebbbdcf29a73143-XXX&enrichSource=Y292ZXJQYWdlOzIyOTg4OTkyOTtBUzoxNDQ1NzA5ODU3NTA1MjlAMTQxMTQ3OTgxNzkyMQ==


already flooded, precluding the chances of finding any more survivors. On the evening

of 24 February, it was decided that the operations should shift from search and rescue

to the retrieval of fatalities.

Hazards and safety concernsThe safety of the rescuers was also a primary concern because of imminent hazards

identified at the site: steep unstable slopes and hanging debris were apparent at the

head scarp, and continuous rains created ponds of water at several levels of the land-

slide deposit and generated thick mudflows (Figure 8). In the absence of rainfall

monitoring stations in the vicinity, the intensity and amount of rainfall were meas-

ured on an hourly basis using improvised rain gauges made of calibrated tin cans

(Figure 9). Rescuers in high-risk areas of the debris field were advised to pull out

when the intensity of the rainfall reached a critical level of 20 millimetres within a

period of one hour.

This threshold rate of rainfall was determined from previous studies of landslides

in the Southern Leyte region and Surigao, which showed that a rainfall intensity of

Figure 7 Recovered bodies in mud*

* Portions of the debris field were saturated as the local water table rose due to persistent rainfall. Bodies were retrieved

from waterlogged mud.

Source: Philippine Air Force 505th Search and Rescue Group.


Figure 8 Ponding of water at multiple levels*

* The figure shows water ponding at several levels and remobilisation of loose debris. Thick mudflows presented dan-

gers to search and rescue personnel.

Source: authors.

Figure 9 Onsite rainfall data*

* In the absence of detailed rainfall data, rainfall intensity was measured using calibrated tin cans (see inset image).

This data formed the basis of the decision to halt search and rescue operations, after the rainfall intensity exceeded the

threshold for landslides in the region.

Source: authors.


about 15–20 millimetres per hour and sustained for six hours is required for land-

slides to occur (Daag et al., 2005). Short duration rainfall, requiring an intensity of

13.8 millimetres per hour, is known to trigger shallow soil slips and debris flows

(Larsen and Simon, 1993).

United States Marines witnessed at least two mudslides during the first suspension

as rescuers were airlifted out of the area. The intensity of rainfall decreased briefly

after the suspension and those who were still in the debris field continued their

operations. After the waning of rainfall for approximately one hour, the intensity

suddenly increased to 10 millimetres in six minutes, translating to a rate of 100 milli-

metres per hour. At this point, all of the rescue teams were ordered to halt their

search and rescue operations completely for the remainder of the day.

DiscussionThe role of government agencies

The Federal Emergency Management Agency (FEMA) is the US government organi-

sation tasked with disaster mitigation, preparedness, and response, as well as with

recovery planning. Under US law, FEMA, the USGS, and other appropriate federal

agencies are mandated to provide technical assistance to national and local govern-

ments to ensure the provision of timely and effective disaster warnings (FEMA, 2006;

USGS, 2006b).

In the Philippines, the nearest thing to FEMA is the National Disaster Coordinat-

ing Council (NDCC), which is composed of several national and local government

agencies. Among these agencies are three institutions that are capable of offering geo-

logical and meteorological advice during search and rescue operations: PHIVOLCS;

the Mines and Geosciences Bureau (MGB); and PAGASA. A review of their institu-

tional mandates shows that none is formally tasked with providing technical support

during the search and rescue phase of a landslide disaster.

During the February 2006 search and rescue operations, geologists from the MGB

were present in the calamity area but they were more involved in mapping existing

and potential landslides within Southern Leyte—10 other landslides occurred in the

region but these were smaller in scale (Presidential Inter-Agency Committee Report,

2006). Volunteers from the US Army Corps of Engineers were assisting the MGB

team. For this reason, the authors found themselves supplying onsite geological and

meteorological information to the search and rescue teams, in addition to conducting

GPR surveys to locate the elementary school building. In effect, instead of solely

providing peripheral support, the authors became technical advisors to the search

and rescue operations.

Lessons learned from the disaster

Our experience of the search and rescue operations pointed up critical points of con-

cern that need to be addressed. Government authorities can use them to improve

policies on disaster management.

https://www.researchgate.net/publication/271788360_A_Rainfall_Intensity-Duration_Threshold_for_Landslides_in_a_Humid-Tropical_Environment_Puerto_Rico?el=1_x_8&enrichId=rgreq-e785e8a8a1960d2fdebbbdcf29a73143-XXX&enrichSource=Y292ZXJQYWdlOzIyOTg4OTkyOTtBUzoxNDQ1NzA5ODU3NTA1MjlAMTQxMTQ3OTgxNzkyMQ==


An immediate and efficient response by search and rescue missions to landslide

disasters requires a systematic approach. As learned from Guinsaugon, technical

advice can focus rescue efforts and lead to maximisation of employment of man-

power, equipment, and other resources. Scientists should be deployed to a site within

a few hours of a landslide event. A characterisation of the landslide must be provided

at the earliest possible time to determine the transport mechanism and its effect on

populated areas.

Ad hoc GIS strongly suggested the en-mass transport of the village of Guinsaugon,

about 550–600 metres down slope. Debris in high-energy landslides has been re-

ported as razing structures, rather than just burying them—see, for example, the

2005 La Conchita landslide in California ( Jibson, 2005). Furthermore, internal

structures found within deposits of large-scale volcanic debris avalanches suggest that

this type of landslide travels en-masse rather than as a turbulent flow (Takarada, 1994).

An aerial survey should be conducted immediately and used to plot the inventory

of recovered bodies, personal articles, and remnants of buildings. High-resolution

digital cameras can be used to take vertical photographs of the affected area. This

exercise does not necessarily require highly technical aerial survey equipment, such

as that used by professional surveyors. Available satellite imagery, existing topo-

graphic maps, and cadastral plans can be utilised to co-register the location of aerial

imagery. If available, ground control points determined from a differential global

positioning system (DGPS) of landslide-prone areas should be made readily acces-

sible and used along with all available maps and imagery. These initial steps narrow

down the search areas within a large debris field to specific sites.

To secure the safety of the search and rescue teams, instruments to monitor debris

flow hazards should be deployed on site without delay. Intense rainfall may cause

mudslides and trigger the collapse of unstable slopes. The threshold of rainfall can

vary from place to place. As noted, studies done prior to the Guinsaugon disaster

highlight that a rainfall intensity of about 15–20 millimetres per hour and sustained

for six hours is required for debris flows to occur (Daag et al., 2005).

Conclusions and recommendationsAfter a landslide disaster, a scientific team must be deployed at the earliest possible

moment to determine its characteristics. A description can be produced from aerial

and ground surveys and used to establish the extent of the disaster and the level of

damage. Subsequent aerial surveys can also be conducted to monitor the debris field

and to assess how it changes in the wake of additional rainfall and further mass move-

ment. Other data pertinent to the investigation of the devastated area, such as detailed

long-term climate data, satellite images, topographic maps, geohazard maps, cada-

stral plans, and ground control points, should be made readily available to the

technical advisors working at the site of the disaster. Additional information can be

collected from the site, including the relative positions of structures before and


after the landslide, the state in which structures and private property are found, and

the position at which the highest numbers of survivors were recovered, in order to

illustrate the transport mechanism of the landslide. A synthesis of all these data can

be used to refine ongoing search and rescue operations, to redeploy them at loca-

tions where there is the highest probability of finding more survivors, and to iden-

tify other potential hazards that can endanger the personnel working within the

debris field.

If such procedures had been implemented early in the search and rescue phase at

Guinsaugon, we believe that more people could have survived. The rise of the local

water table several days after the catastrophic landslide is believed to have killed

people who were possibly still alive under the rubble. For the first five days after the

landslide, search and rescue operations focused on the original location of the village.

Operations only shifted down slope on the sixth day after GIS revealed the mass

transport of the community. Unfortunately, the decision to transfer operations came

much too late.

We emphasise the need for a systematic, technically informed approach to search

and rescue missions, as well as the formulation of better disaster management poli-

cies. The response of search and rescue units should befit the nature of the calamity.

For example, a large-scale landslide presents different challenges than an earthquake

disaster in terms of locating possible survivors. In such critical situations, speed,

accuracy, and the maximum appropriation of resources are crucial. Standard pro-

cedures must be developed and enforced to improve how civil authorities react to

natural hazards.

AcknowledgmentsWe would like to thank the following for supporting the search and rescue effort:

Southern Leyte Governor Rosette Lerias, the Luis A. Yulo Foundation, the Philippine

Army, the US Marines, the Philippine Long Distance Telephone Company, the

Philippine National Red Cross, the Provincial Disaster Coordinating Council, the

Armed Forces of the Philippines Reserve Command, the Department of Environment

and Natural Resources of the Philippines, Secretary Angelo Reyes, the Asian Disaster

Preparedness Center, Deutsche Gesellschaft für Technische Zusammenarbeit (German

Technical Cooperation, GTZ), Earthprobe Inc., the Republic Biscuit Company, the

civilian volunteers, and the rescue teams from Indonesia, Malaysia, the Philippines,

Spain, Taiwan, and Turkey. We are also grateful to Francia B. Avila, Armelle Reca

C. Remedio, Genevieve Rose H. Lorenzo, Jose Ramon T. Villarin, S.J., Daniel J.

McNamara, S.J., Emmanuel G. Anglo, Mariano A. Estoque, Dr. Celine Vicente,

Tristan Calasanz, Gerald A. Galgana, and Gemma T. Narisma of the Manila Observa-

tory for providing the field team with daily weather reports and technical advice.

The comments of David Petley, Carlo Bartolini, and an anonymous peer reviewer

significantly improved this manuscript.


CorrespondenceAlfredo Mahar Francisco A. Lagmay, National Institute of Geological Sciences, C.P.

Garcia, University of the Philippines, Diliman Quezon City 1101, Philippines. E-mail:

[email protected].

Endnotes1 Alfredo Mahar A. Lagmay, Associate Professor, National Institute of Geological Sciences, Univer-

sity of the Philippines, Philippines; Arlene Mae P. Tengonciang, MSc Student/Geologist, National

Institute of Geological Sciences, University of the Philippines, Philippines; Raymond S. Rodolfo,

MSc Student/Geologist, National Institute of Geological Sciences, University of the Philippines,

Philippines; Janneli Lea A. Soria, MSc Student/Geologist, National Institute of Geological Sciences,

University of the Philippines, Philippines; Eden G. Baliatan, MSc Student/Geologist, National

Institute of Geological Sciences, University of the Philippines, Philippines; Engielle R. Paguican,

MSc Student, National Institute of Geological Sciences, University of the Philippines, Philippines;

John Burtkenley T. Ong, Researcher/Geophysicist, Manila Obervatory, Ateneo de Manila Univer-

sity, Philippines; Mark R. Lapus, MSc Student/Geologist, National Institute of Geological Sciences,

University of the Philippines, Philippines; Dan Ferdinand D. Fernandez, Researcher/Geologist,

Manila Obervatory, Ateneo de Manila University, Philippines; Zareth P. Quimba, MSc Student/

Geologist, National Institute of Geological Sciences, University of the Philippines, Philippines;

Christopher L. Uichanco, Geologist, National Institute of Geological Sciences, University of the

Philippines, Philippines.

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Science guides search and rescue after the 2006 Philippine landslide

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