alubijid

Results of the Rapid Geohazard Assessment Survey of

Alubijid, Misamis Oriental

Collantes, M.G.B.1, Lucero E.S.1, Padrique, A.M.2, Brebante B.M.M.2, Asis, J.C.2 (1Senior Geologist, 2Geologist, Mines and Geosciences Bureau-Region X)

INTRODUCTION Background Information The Philippine Government has started a directive to the Mines and Geosiences technical staffs to map out areas in Philippines that might be susceptible to landslides and other geologic hazards. The project, which started right after the Southern Leyte Landslide incident, will enhance the government’s effort in educating people about geologic hazards or geohazards. As part of the project, geologists and support staffs from the Mines and Geosciences Regional Office 10 were deployed to visit each municipality within the Region 10 and assess areas at Barangay Level. These field activities aim to assess each barangay in terms of geomorphology, distribution of slopes, distribution of residential areas with respect to the slope, rivers, coast and susceptibility to geologic hazards such as floods, landslides, tsunami and earthquake. The Geohazard Assessment Team that visited Alubijid, Misamis Oriental last November 27 to December 2, 2006 is composed of Edward S. Lucero, Ma. Gracia B. Collantes, senior geologists; Beverly Mae M. Brebante, Abner M. Padrique and Joy Christine V. Asis, geologists; Elvert L. Eludo, Rodolfo L. Hidalgo, Salvacion N. Naranjo and Amalia P. Jayme, geologic aides; and Arlene M. Hernando, driver. The team was ably assisted by Mr. Joe Caminci from Municipal Planning and Development Office and “habal-habal” drivers who served as guides and mediator during interviews with the locals. Purpose, Scope and Limitations The fieldwork was done on a 6-day duration within which the team visited each barangay within the Municipality of Alubijid. The data for this rapid assessment were based on interviews, ocular inspection of slopes, fractures, faults whenever present and distribution of houses near slopes and other identified risky areas such as riverbanks, valleys etc. The team utilized Rapid Landslide Assessment Form from Mines and Geosciences Bureau Central Office which served as checklist during ocular inspection of the whole area. The other data concerning floods, earthquake and tsunami were obtained through interviews with the locals and previous works.

The secondary data and municipal maps were gathered from the Municipal Planning and Development Office. Specifically, the purpose of this study are the following: a.) assess the slope distribution within the municipality; b.) identify residential areas close to sloping terrains, rivers and coast; c.) interview barangay officials about the history of their barangay in terms of landslide, flood and earthquake occurrences using the standard checklist for landslide rapid assessment; d.) inform the barangay about the situation. Location and Accessibility The Municipality of Alubijid is located at the central portion of Misamis Oriental. Alubijid is about 21.6 Kilometers away from Cagayan De Or. It takes about 30 minutes by land travel via Maharlika Highway. Most barangays are accessible by all types of vehicles. Barangay Tula, which is the farthest barangay with respect to the highway, can be accessed using “habal-habal” or single motor type of vehicle. Tula Lake can be accessed by all types of vehicle via municipal road through the Municipality of Manticao, west of Alubijid. Alubijid is bounded by Alubijid Bay on the north, El Salvador on the east, Kitanglad Mountain Range and Caballero Mountain on the west and Manticao on the north. The Municipality of Alubijid is a 4th class municipality in Misamis Oriental. It has a total of 16 barangays namely Baybay, Benigwayan, Calatcat, Lagtang, Lanao, Loguilo, Lourdes, Lumbo, Molocboloc, Poblacion, Sampatulog, Sungay, Talaba, Taparak, Tugasnon and Tula. Methodology Prior to the field activity, the team went to Alubijid’s Municipal Planning and Development Office to obtain municipal maps and necessary data that would be essential to the assessment. The field assessment focused on barangays that are located on foot slopes, mid slopes, mountain ridges, riverbanks, and coastal areas. Each barangay was rated with low, moderate or high landslide susceptibility whereas areas

susceptible to coastal and riverine flooding were assessed in terms of flood height, recurrence interval (as per interview), extent of damage and turbidity. The rating parameters for landslides are as follows:

High

Presence of active and/ or recent landslides

Presence of numerous and large tension cracks that would directly affect the community

Areas with drainages that are prone to landslides damming

Steep slopes Moderate

Areas with indicative and/or old landslides

Presence of small tension cracks and are located away from the community

Moderate slopes Low

Low to gently sloping

No presence of tension cracks PHYSIOGRAPHY The geomorphology of Alubijid is largely influenced by its underlying geology, structures such as fractures and faults and the dynamic processes along its watershed. The topography of Alubijid varies depending on the distribution of rocks underlying the area. There are at least four geomorphic zones in Alubijid. These are the upper valley section, lower valley section, karst and coastal area. The upper valley section is characterized by rolling to undulating topography (Photos 5 and 6) and narrow valleys. It is underlain by ultramafic rocks and Opol Formation. The ultramafic rock is part of the Caballero Mountain Range. Opol Formation is composed of lava flows and tuffaceous clastics. Lava flow served as water-bearing rock unit of Tula Spring (Photo 7). A small lake lies at the northernmost portion of Barangay Tula. This section includes Barangay Tula and portions of Barangay Sungay. The lower valley section is being shaped by the dynamic processes along Alubijid’s drainage system. Alubijid’s drainage system is moderate to sparse composed of small creeks such as Domanog creek, Lourdes creek and other unnamed creeks, Mahan-og and Alubijid Rivers. The morphology (sinuousity) of Alubijid River is largely influenced by the underlying rocks and the Alubijid Fault. Tributaries from Caballero Mountain Range and other elevated terrains join Alubijid River once it reaches lower valley section. Barangays within the lower valley section are Lourdes, Sungay, Taparak, Tugasnon. The karst area of Alubijid is composed of coralline limestone that exhibits undulating to sloping topography. Coralline limestone within this section form

cliffs and rolling hills that extends from Barangay Talaba, Lagtang, Lumbo, parts of Benigwayan and Poblaction all the way to coastal areas which includes barangays Baybay, Loguilo and Molocboloc. Small, intermittent creeks were observed within the karst area which is typical of such terrain. The coastal areas are gently sloping to flat and characterized by sand bars, estuaries, limestone buffs and flood plain. Portions of this area were converted to fish ponds (Photo 19) and residential areas.

METEOROLOGY

The province of Misamis Oriental falls below Type 3 (Table 1, Figure 1) of Corona Climate Classification system which means that seasons are not very pronounced, dry from November to April and wet during the rest of the year. The Municipality of Alubijid (shown by pink arrow in Figures 1, 2 and 3) receives 1000-2000 millimeters of rain per annual average (Figure 2) and 124.4 – 168.8 millimeters annual monthly average (Figure 3).

Strong winds from northeast monsoon hit the coastal areas of Iligan Bay from December to March.

Study Area

Figure 1 Corona Climate Classification distribution in Mindanao Island.

Table 1

Philippines’s Corona Climate Classification System

Type Description

Type

1

Two pronounced seasons, dry from Nov to Apr; wet during the rest of the year

Type

2

No dry season with a very pronounced rainfall from Nov to Jan

Type

3

Season not very pronounced, dry from Nov to Apr and wet during the rest of

the year

Type

4

Rainfall more or less evenly distributed throughout the year

Figure 2 Annual rain distributions in Mindanao. Shown by the arrow pink is the location of the

study area.

Study Area

Figure 3 Annual monthly averages in Mindanao. Shown by the pink arrow is the location of the

study area.

RESULTS AND DISCUSSIONS Based on the rapid geologic hazards/geohazard assessment study conducted in Alubijid, there are two barangays rated moderate, five barangays rated low and 10 barangays rated none in terms of Landslide Susceptibility Rating. Barangay Tula is cut by a number of active normal faults and slump structures associated with sag ponds and step like topography. These faults and slump structures (Photos 1, 2, 3 and 4) were observed to be associated with sag ponds. One of these slump structures were noted within the grounds of Tula Elementary School (Photo 2). Fortunately, no houses were observed directly below the downthrown or actively subsiding blocks. Old rock fall deposits were observed in Barangay Sungay (Photo 9). Although there hasn’t been any reported rock fall recently, recurrence of such type of landslide is a possibility considering that outcrops of limestone were observed in the area. Active quarry was observed along the highway in Barangay Loguilo (Photos 23 and 24). This quarry may result to slope instabilities and landslide in the future if proper benching is not done in the area.

Study Area

In Barangay Lumbo, Alubijid Fault (Photo 16) has been active for the last 20 years or so based on interview with Barangay 2nd Kagawad Ruth Antig. According to her, the national highway (Photo 15) used to be located at Purok 4 of Lumbo but was relocated to Purok 1 because of the active subsidence around Alubijid Fault which unfortunately traverses the said purok. The Lumbo end of Alubijid Fault appears to be a Normal Fault that cuts through Indahag Limestone. Surrounding the displaced road is evidence of subsidence (topographic lows) and slump structures (step-like morphology, Photo 17) that are not clearly visible due to vegetation cover. Houses were observed along the fault zone (Photo 18) particularly along the subsiding block with slump structures. There has been occurrence of riverine and coastal floods in the past within the Municipality of Alubijid. Although rainfall data in Alubijid shows that it receives 1000-2000 millimeters of rain per annual average (Figure 2) and 124.4 – 168.8 millimeters annual monthly average (Figure 3) only, abnormal climatic conditions can lead to excess precipitation which may result to flash floods along the major drainage system of the area such as the Alubijid River and its tributaries and Mahan-og River. In August 11, 2002 for instance, Alubijid River overflowed in some portions of Barangays Lourdes and Benigwayan flooding houses and school along it. This happens when increase in volume of water and soil content or turbidity causes the river to deviate from its original path attenuating houses along its banks and floodplain. Increase in turbidity of water is due to several factors such as deforestation along the banks and source area and loosening up of sand by quarry within the river bed (Photo 14) as in the case of Barangay Lourdes. Garbage dumped along the riverbanks (Photo 13) to some degree may also cause clogging of the drainage. In Barangay Taparak, sheet flood is common during heavy rains as most of the houses are concentrated along the road opposite outcrops of Opol Formation. In addition, the area has very poor or absent drainage system. Mahan-og River overflowed in 2004 affecting portions of Barangay Calatcat particularly Purok 6. Some portions of Alubijid coastal area is attenuated occasionally by strong waves resulting to flood and erosion such as that in Barangay Baybay, Loguilo and Molocboloc. Houses get damaged by strong waves from December to March during which northeast monsoon hit the coastline of Iligan Bay. In Purok 3, Barangay Baybay houses constructed makeshift seawall (Photo 20) made up of bamboo and old car tires to protect their properties from strong waves. Mangroves were also planted along the beach (Photo 21). In Barangay Molocboloc, coastal flood supplies water to their fish ponds (Photo 19) during rainy season. These fish ponds are converted to salt flats during summer.

Photo 1 Sharp termination in grass growth indicates the fault line in Barangay Tula. Left side of the

fault is actively subsiding. Note the creep failure shown by the coconut trees.

Photo 2 The right side block of this normal fault (red hashed line) within the school grounds in

Barangay Tula has been actively subsiding since 1980’s based on interviews.

Photo 3 Actively subsiding block (as in photo 1) and associated sag pond at Barangay Tula. Photo

taken from the other side of the road.

Photo 4 Same sag pond from Photo 3 on a closer view. Similar sag ponds were observed along the

downthrown block within the school ground in Barangay Tula.

Photo 5 Volcanic cone (?) at Barangay Tula.

Photo 6 Hinterlands in Barangay Tula. The barangay proper is situated at the footslope proximal to

Tula Spring (Photo 7).

SUBSIDING BLOCK

SAG POND SAG POND

Photo 7 Lava flow deposit is the water bearing unit in Tula Spring.

Photo 8 Creek at Purok 2, Barangay Sungay overflows during heavy rains and attenuates these

houses.

Photo 9 Very old rock fall deposits in Barangay Sungay composed of limestone boulders.

Photo 10 Houses were observed along the footslope of a hill in Barangay Lourdes.

Photo 11 More houses were found along the footslope of another hill in Barangay Lourdes.

Photo 12 A house is being built at the footslope of a hill showing debris slide in Barangay Lourdes.

Photo 13 Garbage dump site in Barangay Lourdes is quite proximal to Alubijid River.

Photo 14 The Alubijid River is being quarried for sand by the municipality.

Photo 15 This part of Lumbo, Alubijid is where the old highway used to be located. The road’s

continuity got terminated about 20 years or so ago when the active normal fault (red line and arrow)

resulted to more than 20 feet of displacement of the downthrown block.

Photo 16 Closer look at the fault scar (red line of Photo 16) along a limestone wall (horst).

Photo 17 Corn fields proximal to the fault in Lumbo, Alubijid is slumping based on step-like

configuration of the soil (actively subsiding?).

Photo 18 Small houses were observed along the subsiding block within the fault zone in Barangay

Lumbo, Alubijid.

Photo 19 Fish ponds along coastal area in Barangay Molocboloc, Alubijid. Arrow is pointing to the

sea.

Photo 20 This house in Purok 3, Baybay constructed a makeshift seawall composed of bamboo and

old car tyres to protect it from incoming strong waves that are common in the area during December

to March northeast monsoon.

Photo 21 Mangroves that were planted along the coast in Purok 3, Baybay may help break the strong

waves caused by northeast monsoon in the future.

Photo 22 Coconut trees fell when strong waves hit the area in Loguilo near Don Ben beach resort.

Photo 23 and 24 Active limestone quarry along the highway in Barangay Loguilo, Alubijid.

Table 2 Summary of the Rapid Geohazard Assessment in Alubijid.

Barangay Landslide

Susceptibility

Rating

Other

Geohazards

Remarks

Tula Moderate Flood (rare,

very low risk)

No houses along the riverbanks; houses

concentrated on elevated terrains. Tula

spring/waterfall (Photo 7) appears to have step-

like structure wherein each “landing” contains

shallow water pools; active tension cracks and

normal faults and slumps associated with sag

ponds (Photos 1, 2, 3 and 4) where observed

within the area. Progress of these structures should

be monitored. Areas along slope (Purok 4 and 6)

and creeks (Purok 6) should monitor for landslide

and creek water levels.

Lagtang Low Flood (very

rare, very low

risk)

Purok 1-along slope so should monitor for

landslide and tension cracks. Purok 4 is proximal

to Mahan-ob creek so should monitor for water

level and soil content.

Lumbo Low to

Moderate

(Purok 4 and 1)

Flood (very

rare)

Active normal fault which resulted to

abandonment of old highway in Purok 4, Lumbo

(Photos 15, 16, 17 and 18); limestone blocks

along the fault are actively moving for the last 20

years or so as per interview. No houses should be

built along the fault zone and constant monitoring

of any movements, cracks along the area is strictly

advised.

Lourdes Low Riverine Flood

(along Alubijid

River)

August 11, 2002-flood along Alubijid River

affected several houses and school at Purok 1.

Sheet flood is common during heavy rains.

Monitor river water level especially during rainy

days. Purok 3 and 4 (Sikiton) are situated at the

footslope of Caballero Mountain so monitoring for

landslides, tension cracks is strictly advised.

Houses found at the footslope of some hills

(Photos 10, 11 and 12) within the barangay are

likewise advised to monitor the slope for tension

cracks and landslide during rainy days. Garbage

dumpsite (Photo 13) is situated near Alubijid

River. Sand quarry along Alubijjd River was

observed (Photo 14); Sand quarry may increase

turbidity of water during flood.

Sungay Low Old rock fall deposits (Photo 9) composed of

limestone boulders were observed, possible

recurrence may happen in the future. Purok 2 is

near a creek that overflows during heavy rains so

monitoring for water level is strictly advised.

Taparak Low Riverine Flood

(along Alubijid

River)

Area is rolling to sloping in some parts so sheet

flood during heavy rains affect some of the houses

along the road (usually at the foot slope). Purok 1

is near Alubijid River whereas Purok 4 is near a

creek so both areas should monitor for water level

and soil content (turbidity).

Tugasnon Low Riverine Flood Puroks 1, 2 and 6 are along the creeks, namely,

Burakan, Bongbongon and Luasi respectively, so

monitor creek water level during heavy rains.

Baybay None Riverine

Flood; Coastal

flood and

erosion

Purok 7 and Purok 2 are situated near and at the

mouth of Alubijid River, respectively so prone to

riverine + coastal flood; Purok 3 is prone to

coastal erosion and flood (Photos 20 and 21)

when strong waves caused by northeast monsoon

hit the beaches affecting houses in the area.

Northeast monsoon is experienced from

December to March.

Benigwayan None Riverine Flood Purok 2 and 6 are near Alubijid creeks that got

flooded in 2002. Puroks 4 and 7 are situated near

slopes so monitor for tension cracks and

landslides.

Calatcat None Riverine Flood Purok 6 is situated near Mahan-ob River that got

flooded in 2004 affecting livestock so monitor for

creek water level especially during heavy rains.

Lanao None Puroks 1, 3 and 6 are situated near the coast;

Lanao creek gets flooded during heavy rains

affecting portions of Purok 1 and 3. Monitor creek

water level especially during heavy rains.

Loguilo None Sheet Flood Alubijid River lies at the boundary between

Poblaction and Loguilo; Purok 4 is along the

coast where coastal erosion during northeast

monsoon was observed (Photo 22); monitor water

level and soil content along Alubijid River.

Active limestone quarry at Purok 1 (Photos 23

and 24) along the highway may result to slope

instabilities so monitor for rock falls, debris slides

and tension cracks.

Molocboloc None Coastal Flood Coastal flood is common in Purok 4. (Photo 19)

Poblacion None Riverine Flood

(rare)

Puroks 2, 5, 6, 7 and 8 are near Alubijid River so

monitor for water level during heavy rains.

Sampatulog None

Talaba None Riverine Flood Purok 4 is situated near Mahan-og River so

monitor water level and soil content (turbidity).

CONCLUSIONS AND RECOMMENDATIONS There are at least two types of countermeasures to disasters, the long term and immediate. Long term countermeasures involve solutions that will reduce if not annihilate completely the impact of geologic hazards. Immediate countermeasures are the instantaneous response during disasters such as floods, earthquakes, landslides and storm surges. In this report, both types of solutions will be discussed but with emphasis on the long term countermeasures. Immediate Countermeasures Residents living near the river should evacuate immediately if the water level within the valley has increased to considerable height. Although the rainy season is not pronounced throughout the year, heavy rains occur during the

months January, February, June, September and December. Residents should be extra alert and watchful during these months. A warning device should be developed within the community to alert residents should flood occur. Warning devices come in different forms such as cellular phones, radios, church bells etc. Evacuation centers should be situated far from rivers and creeks, if possible, located on elevated areas. These centers should also be complete in facilities, First Aid Kits, food, blankets and other basic necessities. In areas prone to landslides, tension cracks, landslide scars, rock falls and other landslide indicators should be reported to the Barangay Disaster Coordinating Council or BDCC. BDCC should then report these to Municipal Disaster Coordinating Council so that proper authorities will be alerted. The authorities shall then help facilitate in the evacuation and relocation of landslide victims. A rescue team should be organized within each barangay. Landslide occurs in such a short time that time is essential in saving lives. It will therefore save more lives if immediate help from within the barangay is available. During storm surge, residents should immediately evacuate to an elevated area far away from the coast. Avoid going near the coast and river mouths as these areas are inundated by incoming strong waves. Long Term Countermeasures Rain triggers movement of unstable soil, rocks and vegetation along slopes and increases the water level along rivers and creeks. Determining the volume of rain in the atmosphere using radar has been utilized in other countries. Unfortunately, this kind of technology is not available in Philippines due to operation and maintenance cost it requires. Nevertheless, during heavy rains, river or creek water level and increase in turbidity or soil content should be monitored. A rain gauge for each barangay would have been helpful in monitoring the distribution of rain throughout the year. But since, rain gauges are expensive, improvised rain gauges in the form of bottles, buckets with known volume are enough. These rain gauges should be put in areas where evaporation by heat is minimal. In areas where flood is common, artificial levees built along the river bank may help protect the community from the flash flood. However, these levees should be well-designed to withstand extreme flooding. Sediments that pile up along the channel should be dredged every now and then so that depth of the valley is maintained. Garbages should not be thrown near or towards the rivers (Photo 13) and creeks as these clog the channel. Clogged channels results to deviation of the water from its natural path and increases its level worsening flood situations. Although residential houses are concentrated on the plains, a number of houses have been found situated along the slopes. Occurrences of landslides in some

areas in Alubijid are signs of slope instabilities. Therefore, recurrence of slope failures and landslides is a big probability. Houses should not be built at the foot slope or along the slope of hills, mountains and ridges particularly in areas where rocks are highly fractured, faulted or sheared or where soil thickness exceeds one meter. However, for areas that are already used for housing development, constant monitoring of slopes is strictly recommended. Proper drainage system should be built so that excess water will not be absorbed into the soil to avoid down slope movement and slope failures. Since most residents refuse evacuation for livelihood-related reasons, maintaining stability of slopes and monitoring for landslides become their responsibility. Karst areas are prone to ground subsidence. This is because limestone is easily weathered and eroded by rainwater. Development along karst areas should be limited to small houses and establishments only. Areas with known caves underneath should not be developed for housing as these are naturally unstable and prone to ground failure. Flash floods are also common in such terrain so people should be ready during heavy rains. Constant monitoring of rain fall volume and duration and vigilance are highly recommended. If possible, a good drainage system should be built in the area to constantly drain it from excess water. These alternative countermeasures may not totally annihilate the risk caused by geologic hazards but these will help prime movers in planning land use and development. Risk increases as population along areas highly susceptible to geologic hazards increases. This report should therefore serve as guidelines for any future community development plans.