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LAHAR RISK MAPPING OF BANAHAW VOLCANO, SOUTHERN LUZON USING laharz
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INTRODUCTION
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• Banahaw Volcano is considered as one of the Philippines’s 24 active volcanoes (PHIVOLCS, December 2017).
• Geographic Information System (GIS) tools are useful and have great potential in assessing volcanic hazards (Yeats, 2014).
Figure 1. Active and Potentially Active Volcanoes in the Philippines. From DOST-
PHIVOLCS, November 2016.
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To map the extent of potential lahar flow/s around BanahawVolcano by using LaharZ
To estimate the volume of potential lahar flow/s by determiningthe type of deposits identified and delineated based onexisting geologic maps and field validation
To assess the risk of the municipalities and barangays that willbe affected by the potential lahars from Banahaw Volcano
Specific Objectives
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Local Government Units (LGUs)
Future Researchers
Field of Geology
General Public
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• Sampling was limited along the volcano’s gulley
• Volume of lahar input in LaharZwas limited to 10,000,000 to 50,000,000m3
• SRTM 3-Arc Second Global
• Risk assessment based on population and land area
• Results were limited to syn-eruption lahar
• Buildings and infrastructures were not considered
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Review ofrelated literature
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Banahaw Volcano Lahar Hazard-modelling using GIS
Risk assessment on volcanic
hazards
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Figure 2. Conceptual Framework of the study
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N
VOLCANO HAZARD LEVEL:
1-2
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methodology
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Figure 3. Study area
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• Quantitative research
• A methodology designed tocorrelate data gathered in theoutcrop description and samplescollected with the existinggeologic and hazard maps toproduce risk maps of Banahawvolcano.
Figure 4. Flowchart showing methodology of the study
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RESULTS AND DISCUSSION
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FIELD OBSERVATIONS
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Figure 8. Map showing the stations where samples were collected.
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The area within the basement of the volcano was closed off andinaccessible, which made the area for rock sampling focused andlimited to the southern flank of the volcano, along its gulley.
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Figure 9. Station 1
• The walls along the gulley had been observed to have a coarsening upward sequence
• The field ID for the rocks were identified as Andesite Porphyry
Figure 10. Station 2
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LAHARZ
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Proximal Hazard Zone
Figure 5. Preliminary Hazard map
Distal Hazard Zone
• Defined by the lahar path with a volume ranging from 10,000,000 to 50,000,000m3
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Figure 6. Preliminary Lahar Hazard Map of Banahaw Volcano
*Shows affected barangays
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Figure 13. Preliminary Lahar Hazard Map of Banahaw Volcano
*Shows affected district
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Table 1. Population Exposure Index (PEI)
Weighted Summed
Population
Population Exposure
Index
0 0
<3,000 0.5
3,000 – 9,999 1
10,000 – 29,999 1.5
30,000 – 99,999 2
100,000 – 300,000 2.5
>300,000 3
Volcano Hazard Level
Population Exposure Index 1 2 3
0, 0.5 1 1 1
1 1 2 2
1.5 1 2 3
2 2 2 3
2.5, 3 2 3 3
Table 2. Population Risk Level (PRL) cohorts
VOLCANO HAZARD LEVEL:
1 – Lowest hazard and uncertainty
2 – Moderate hazard and uncertainty
3 – Highest hazard and uncertaintySource: From GFDRR, Volcano Risk Study: Volcano Hazard and Exposure in
GFDRR Priority Countries and Risk Mitigation Measures, p. 19 by Aspinall, W., et al.,
University of Bristol.
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FACTOR CERTAIN RANGING UNCERTAIN
Volcano type 1
Crater lake/Snow cap 1
Pyroclastic flow hazard 1
Lahar hazard 1
Lava flow hazard 2
Number of subfeatures 3
Maximum VEI 2
Eruption frequency 2
Exact Volcano Hazard Level 1.625
Apparent Volcano Hazard Level 2
Table 3. Scoring of factors determining Volcano Hazard Level. From GFDRR, Volcano Risk Study: Volcano Hazard and Exposure in GFDRR
Priority Countries and Risk Mitigation Measures, p. 18 by Aspinall, W., et al., University of Bristol.
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Volcano Hazard Level
Population Exposure Index 1 2 3
0, 0.5 1 1 1
1 1 2 2
1.5 1 2 3
2 2 2 3
2.5, 3 2 3 3
VOLCANO HAZARD LEVEL:
1 – Lowest hazard and uncertainty
2 – Moderate hazard and uncertainty
3 – Highest hazard and uncertainty
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Based on population of affected districts
Figure 14. Preliminary Lahar PRL Risk Map of Banahaw Volcano.
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SUMMARY AND CONCLUSION
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• Banahaw Volcano’s VEI ranges from2-4 due to its andesitic composition
• The lahar flow path traversed andaffected 22 municipalities and 456barangays.
• Comparing with existing geologicand lahar hazard maps, most of thelahar paths conformed, while newpaths were created.
• The risk levels of the affectedbarangays ranged from 1-2 due tohaving a Volcano Hazard Level 2.
Figure 8. Volcanic Hazards Map for Banahaw Volcanic Complex (PHIVOLCS, 2008)
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• Include post-eruption lahar
• Field validation of laharhazard and risk maps
• Conduct more comprehensiveresearches about BanahawVolcano
• Run models with greatervolume input using higherresolution DEMs
• Installation of evacuationcenters, and water, power andfood source facilities outsidethe proximal hazard zone andaffected barangays
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Dr. Ma. Mylene M. Villegas
Mr. Daniel Jose L. Buhay
Dr. Arturo S. Daag Mrs. Charmaine V. Villamil
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THANK YOU