Risk Assesment of Lahar Flow Hazard in Merapi Volcano

8/10/2019 Risk Assesment of Lahar Flow Hazard in Merapi Volcano

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MODULE D

RISK ASSESSMENT AND MANAGEMENT

GROUP ASSIGNMENT

(For Volcanic Hazard)

Lecturer

Prof. Sutikno

By:

Pradiptya Setyahadi 14/370647/PMU/8191

Iriansa 14/370694/PMU/8198Siti Dahlia 14/373799/PMU/8418

Purwita Eka Sari 14/370504/PMU/8143

MAGISTER GEO-INFORMATION FOR SPATIAL PLANNING

AND DISASTER RISK MANAGEMENT

GRADUATE SCHOOL

UNIVERSITY OF GADJAH MADA

YOGYAKARTA2014


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Risk Assesment of Lahar Flow Hazard in Merapi Volcano

P.Setyahadi, Iriansya, S.Dahlia & P.E. Sari

Magister Geo-Information for Spatial Planning and Disaster Risk Management, Gadjah

Mada University, D.I.Yogyakarta, Indonesia.

ABSTRACT

Merapi Volcano in Sleman, D.I.Yogyakarta. The height of Merapi Volcano around 2,968

meters above sea level and has experienced 84 times (event) until 2010 within eruption average

is 5 years. Due to the active crater of Merapi volcano is now open to the west - southwest. So

that during the growth of the lava still in dome and not go beyond the walls of the crater, the

eruption will be heading west - south-west. The method in lahar flow assessing to settlement

used qualitative methode include with aprroch is spatial approach, ecological approach and

disaster approach with the technique of spatial multi-criteria analysis. Result analysis from this

research namely (a) potential hazards, (b) vulnerability, (c) element at risk, (d) capacity, (e) risk

assesment. We also given recommendation for mitigation in that area.

Keyword :Risk Assesment, Lahar Flow in Ginibangunharjo.

A. Introduction

One output of the eruption from Merapi volcanoe is lava, which then generates

became lahar flow. Lahar flow formed when in a volcano crater there is a crater, the

water in the lake will be very hot when it erupted. The hot water carrying mud material

and rocks, while the lava occurs when rain fell with high intensity rainfall mixed with

loose volcanic material to form a stream. Although lava material composed of volcanic

ash and rock fragments, but the flood of lava can flow more rapidly and faster when

compared with normal water flow (Daryono, 2011).

A lahar is a general term for a rapidly flowing mixture of rock debris and water

(other than normal streamflow) from a volcano and refers to the moving flow. Located

in the populated area of Central Java, the stratovolcano Merapi (2965 m) is prone to

lahar generation, due to three main factors: millions of cubic meters of pyroclastic

deposits are the product of frequent pyroclastic flows, which have occurred on 2- to 4-

year intervals, rainfall intensity is high (often 40 mm in 2 h on average) during the rainy

season, and drainage pattern is very dense.

The Boyong and Kuning river are river through the Hargobinangun village, and

one of the lines of lahar flow from Merapi Volcano, it is have material can be sand,

rocks and gravel where the lava material has a volume of 10 million m3. While the

flow along the Kuning and Boyong river, there are many seattlement areas. So that this

region could potentially have affected the risk of lahar flow hazard in Merapi volcano.


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B. Study Area

In this task, the area sampled for the identified impact on the settlement of the lava

flow is Hargobinangun village located in the northern District of Pakem. This region is

located in the northern district of Sleman, Yogyakarta. Distance sub-district to district

government center. Wide of Sleman is about 14 km. This area is located at the

coordinates 77.66708 'LS and 110.42011' BT and has an area of approximately

4384.04 ha, the total population of 32.561 people, with a population density reaches

1,551 / km2.

The geology of this region there are deposits surface of alluvium there are grovel,

sand, silt and clay along larger streams. Selected deposits of merapi volcano is

undifferented tuff, ash, breccia, agglomerate and lava flow. This region is located in the

highlands, precisely located at an altitude of 600 meters above sea level. Tropical

climate with cool weather as his trademark. The highest recorded temperature was 32C

with the lowest temperature of 18C. Expanse territory in the form of land area choppy,

hills and mountains. Based on the location, on the slopes of Mount Merapi. This region

is located in the highlands, precisely located at an altitude of 600 meters above sea level.

Tropical climate with cool weather as his trademark. The highest recorded temperature

was 32C with the lowest temperature of 18C. Expanse territory in the form of landarea choppy, hills and mountains. Based on the location,on the slopes of Merapi

volcano.

C. Methodology

The purposed method in lahar flow assessing to settlement in the Hargobinangun,

Pakem Distrik of Sleman Yogyakarta by used qualitative methode include with aprroch

is spatial approach, ecological approach and disaster approach with the technique of

spatial multi-criteria analysis. Spatial approach and ecological approach is intended to

identify the characteristics of the physical environment and the characteristics of the

study area includes the settlements, topography, slope, rainfall, river flow, settlement

patterns, the distribution of settlements, building the model and direction to the direction

of flow. Disaster approach is intended to identify the characteristics of lava flow scoring

the study area, volume, period, distance, and direction of flowIn the review process

generally includes four processes namely, study literature, data collection, data analysisand reporting, as shown in the diagram below:


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Figure 1: Framework process for the study

1. Study of Literature

This process is the first step in this study are intended to seek and understand a

variety of approaches, methods and data analysis in risk analysis lahar flow. It is

from book, journal and internet.

2. Data Colection

After understanding the concept and scope of the study area, is the determination

of variables and collecting data required for the analysis of both primary data and

secondary data.

3. Data Analysis

This process is divided into three phases: phase analysis petensial lava flow hazard,

vulnerability level analysis phase of the residential building of the lava flow, and

risk assessment.

a. Analysis Potential Lava Flow Hazard

This process include several stage: at this stage include; Identification of the

characteristics of lahar flow, clasification of danger level and the danger level

of committing lahar flow zone.

Table 1 : Potential of Lahar Flow Hazard Zone

Zone

Distance from the vents

of Mount Merapi Carateristic o f the region Hazard

Zone 1 Radius 5 kmlocatedin the basin area, located in a radius

of 100 meters from the river high

Zone 2 Radius 10 km

locatedin the basin area and slope area,

located in a radius of 100 meters from the

river medium

Zone 3Outside a radius of 10

km

located in a radius of 100 meters from the

river low

Study Literature

Data Colection

Data Analysis

Report


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b. Vulnerability level analysis phase of the residential building of the lava flow

This stage covers, identification and classification of building types based

materials, building of age, the building to the flow direction, the distance from

the road. As for the classification can be seen in Table 2.

Table 2: Potential of Vulnerability

NO

CHARACTERISTIC OF BUILDING

Vulnerability

Material

Age of

Building Direction to strem

1 Woodvery high

2 Stone > 40

50 - 90

(Perpendicular)

3 Stone >40 < 50 (Diretion)

High

4 Stone 20 - 40

50 - 90

((Perpendiculars)

5 Stone 20 - 40 < 50 (Diretion) Medium

6 Stone < 20

50 - 90

((Perpendicular) Low

7 Stone < 20 < 50 (Diretionh) Very Low

c. Risk Assesment data analysis

In this process, the results of the potential hazard zone that be overlay with

lava flow for the results of the vulnerability residential buildings

classification to the lava flow. The overlay results, will be analyzed by using

the formula of risk assessment and risk assessment matrix.

Risk = Hazard x Vulnerability


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Table 3: Risk Assesment Matrix of Value

Table 4: Risk Assesment Matrix of Data Analysis

Hazard

zone 1

(A)A1 A2 A3 A4 A5

zone 2

(B)B1 B2 B3 B4 B5

zone 3

(C)C1 C2 C3 C4 C5

very low

(1)low (2)

medium

(3)

high

(4)

very high

(5)

Vulnerabilty

Very Low

Low

Medium

High

Very High

0

1

2

3

4

5

HighMedium

Low

Risk Assessment Value

Hazard

HighLow Risk

Medium

Risk

High

risk

Very

high risk

Very high

risk

MediumVery low

risk

Low

Risk

Medium

Risk High risk

Very high

risk

LowVery low

risk

Very

low risk Low risk

Medium

Risk High risk

very low low medium high very high

Vulnerabilty

Where, Hazard = probability of occurrence of a given area being

affected by cause damage, loss, and death of people

in residential areas within a given period of time.

Vulnerabilty = proportion of settlement threatened likely to be in a

given hazardous event; degree of damage resulting

from the hazard.


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Figure 2: Framework Risk Assesment of Lahar Flow

D.

Result and Analysis

1. Potential Hazard

Hazard is a potentially damaging physical event, phenomenon or human

activity thay may cause the loss of life or injury, property damage, social and

economic disruption or environmental dagradation (C.J.Van Western. 2011.

Multi-hazard risk assessment. ITC).

Potential hazard that used in this task is lahar flow in Hargobinangun village,

because in Hargobinangun village through by Boyong and Kuning river, and it is

one of the lines of lahar flow from Merapi Volcano, taht have material can be sand,

rocks and gravel where the lava material has a volume of 10 million m3. And

there are many settlemen areas, So that this region could potentially have affected

the risk of lahar flow hazard. The following below map to the potential hazard

of lahar flow by Merapi volcano:


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Figure 3: Potential of Lahar Flow Hazard


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2. Vulnerability

Vulnerability is a human condition or process resulting from physical, social,

economic, and environmental factors which determine the likelihood and scale of

damage from the impact of a given hazard(UNDP, 2004) .

Vulnerability is the degree of the loss to a given element or set of elements

at risk resulting from the occurrence of a natural phenomenon of a given magnitude

and expressed on a scale from 0 (no damage) to 1 (total loss). In lay terms, it means

the degree to which individual, family, community, class or region is at risk from

suffering a sudden and serious misfortune following an extreme natural event. To

determinate value of vulnerability based on building characteristic of settlement.

The following in table 2.

Table 2: Potential of Vulnerability

No

Characteristic Of Building

Vulnerability

Material

Age of

Building Direction to strem

1 Woodvery high

2 Stone > 40

50 - 90

(Perpendicular)

3 Stone >40 < 50 (Diretion)

High

4 Stone 20 - 40

50 - 90

((Perpendiculars)

5 Stone 20 - 40 < 50 (Diretion) Medium

6 Stone < 20

50 - 90

((Perpendicular) Low

7 Stone < 20 < 50 (Diretionh) Very Low

Based on the above data, characteristic of a settlemen building with very high

vulnerability criteria, namely the building of wood, this was due to the wooden

buildings are more vulnerability to the of lahar flow hazard from the shape of the

building stone, so of wood with very high vulnerability premises given a score of

1 and for a stone with a low vulnerability values given a score of 0.2. Other than

building materials, other factors that determine vulnerability, namely: the age of

the building, the shape of the building to the flow direction and distance to the

river.


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Figure 4: Seattlement Vulnerability of Lahar Flow Map


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3. Element at Risk

Population, properties, economic activities including public service or any

other defined value exposed to hazard in a given area. Also referenced to as

assets. The amount of element at risk can be quantified either in numbers (of

buildings, people, etc), in monetary value (replacement costs, market costs, etc),

area or preseption (importance of element at risk). (Western, etc. 2011. Multi-

hazard risk assessment. ITC)

Element at risk which used on this task is settelmen in Hargobinangun Village.

it is chosen as the location of this settlement has the potential hazard of the lava

flow. The following below table of number and distribusi of seattlement in

Hargobinangun Village.

Table 5: Number of Seattlement in Hargobinangun Village

4. Capacity

Capacity is the positive managerial capabilities of individuals, households, and

comunnities to confront, the threat of disasters (eg through awaerenes raising, early

warning and preparedness planning). (Western, etc. 2011. Multi-hazard risk

assessment. ITC)

0

500

1000

1500

Upper ZoneMiddle ZoneLower Zone

Total Seattlement

Zona Total Seattlement

Upper Zone 487

Middle Zone 327

Lower Zone 1186

Total 2000


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Indonesia is a country that is prone to geological disasters earthquakes,

landslides, volcanic eruptions, and tsunamis. As a consequence of the state's

obligation to protect its people, the government is expected to take appropriate

measures to reduce the risks and have contingency plans to minimize the impact of

disasters.

Currently available legislation on national disaster management UU No. 24 of

2007. The Act serves as the basic guidelines governing authority, rights, obligations

and sanctions for all providers and stakeholders in the field of disaster management.

According to UU No. 24 of 2007, the implementation of disaster management in

the event of a disaster potential conditions include: (a) preparedness (b) early

warning and (c) disaster mitigation.

Organizations that are in this region is the area of disaster management agency

(BPBDs) and BPPTK. Implemented through coordination BNPB. The organization

runs in accordance with the work program, one of which is the dissemination of

information, forums of Merapi and mandatory practice. That is a sustainable

program that is expected to form a culture of preparedness in communities

5. Risk Assessment

Risk assessment is a methodology to determine the nature and extent of risk

by analyzing potential hazard and evaluating existing conditions of vulnerability

that could pose a potential threat or harm to people, livelihoods and the

environment on which they depend.

The process of characterizing hazard within risk area, analyzing them for

their potential mishap consequences and probabilities of occurrence and

combining the two estimate to reach a risk ranking.

Risk assessment in the analysis in this task is the level of risk of damage

settlements caused by lava flow from Mount Merapi. With the purpose of risk

assessment outcome data, can be used as a form of preparedness so as to reduce

the impact of hazards. Based on Table 1 and Table 2, it can be determined the

value of a risk assessment based on the characteristic of the potential hazards and

vulnerabilities value. Below are the results of the calculation of the combined

value of the potential hazards and vulnerability:


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Table 6: Qualitative matrix of consequences

HAZARD

Zone 1

(A)

radius 5 km by

road, located in thebasin area, located

in a radius of 100

meters by the river,

material stone with

< 20 age of

building, and < 500direction to stream

radius 5 km by


in a radius of 100


material stone with

< 20 age of

building, and 50 -900 (perpendicular)

direction to stream

radius 5 km by

road, locatedin the basin

area, located

in a radius of

100 meters by

the river,

material stonewith 20 - 40

age of

building, and

< 500direction

to strem

radius 5 km by


in a radius of 100


material stone with

20 - 40 age of

building with 50 -900 (perpendicular)

direction to strem,

and material stone

with > 40 age of

building with < 500direction to strem

radius 5 km by


in a radius of 100


material stone with

> 40 age of building

with 50 - 900(perpendicular)

direction to strem,

material wood

Zone 2

(B)

radius 10 km by

road, located in the

basin area and slope

area, located in a

radius of 100

meters by the river,material stone with

< 20 age of

building, and < 500

direction to stream

radius 10 kmby



area, located in a

radius of 100


< 20 age of

building, and 50 -

900 (perpendicular)

direction to stream

radius 10 km

by road,

located in the

basin area and

slope area,

located in aradius of 100

meters by the

river, material

stone with 20 -

40 age ofbuilding, and

< 500direction

to strem

radius 10 km by



area, located in a

radius of 100


20 - 40 age of

building with 50 -

900(perpendicular)

direction to strem,and material stone

with > 40 age of

building with < 500

direction to strem

radius 10 km by



area, located in a

radius of 100


> 40 age of building

with 50 - 900

(perpendicular)

direction to strem,material wood

Zone 3

(C)

outside a radius of

10 km by road,

located in a radiusof 100 meters by

the river, material

stone with < 20 age

of building, and 40 age of

building with < 500

direction to strem

outside a radius of

10 km by road,

located in a radiusof 100 meters by

the river, material

stone with > 40 age

of building with 50

- 900

(perpendicular)

direction to strem,

material wood

Very low (1) Low (2) Medium (3) High (4) Very High (5)

VULNERABILITY


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Figure 5: Risk Assessment of Lahar Flow Map


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E. Conclusion

One result of the eruption of Merapi volcanoe is lava, which then generates lahar

flow. The Boyong and Kuning river are river through the Hargobinangun village, and one

of the lines of lahar flow from Merapi Volcno, it is have material can be sand, rocks and

gravel While the flow along the Kuning and Boyong river, there are many settlemen

areas. So that this region could potentially have affected the risk of lahar flow hazard.

Representation of risk assessment that caused by lahar flow, it can determinate using

vulnerability value and potential hazard using formula by UN-ISDR. Value of

vulnerability base on element at risk ie settelmen, so data analysis used characteristic

building and spatial analysis using GIS. And than, of potential hazard which selected is

lahar flow, so that the required data is lava volume and intensity of rainfall.

Based on calculations of UN-ISDR, for the risk assessment of settelmen by lava flow

hazard in HargobinangunVillage, then there are three zones, namely the risk of high,

medium and low. Where Hargobinangun village in general are at high and medium zones.

But the biggest risk in the medium zone. This is due to the location of the village is located

in Zone II based maps Disaster Prone Areas. so as to risk vulnerability to hazards lava

flow that is middel.

Based on the risk assessment of the lava flow in Hargobinangun Village, so we theauthors provide recommendations to the community to:

1. Building a house in the location on the radius of> 100 m from the river, with a view

to avoiding vulnerable areas impacted. because lava flow generally follows the

direction of the river.

2. The shape of the house building should extends to the north - south, to avoid the

lava flow direction of flow. Thereby reducing the damage to the house when in

passing lava flow.

3. The Material houses of building suggested of bricks, because bricks material

stronger to withstand lava flow compared with wood material where higher levels

of vulnerability.


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F. Refference

Andreastuti1, S, etc. 2006.Menelusuri kebenaran letusan Gunung Merapi 1006.Jurnal

Geologi Indonesia, Vol. 1 No. 4 Desember 2006: 201-207.

BNPB dan BAPPENAS. 2011.Rencana Aksi Rehabilitasi dan Rekonstruksi:Pascabencana Erupsi Gunung Merapi Provinsi D.I.Yogyakarta dan Provinsi Jawa

Tengah Tahun 20112013.

Daryono. 2011. Ancaman Banjir Lahar Merapi. (on www.bmkg.go.id (Badan

Meteorologi Klimatologi dan Geofisika) access on 13November 2014 (Risk

Modelling of Lahar Hazard in Kali Putih, Magelang).

UNISDR. 2004. Terminology: Basic terms of disaster risk reduction. Available at :

http://www.unisdr.org/files/7817_7819isdrterminology11.pdf. Access on 13

November 2014.

Western, etc. 2011.Multi-hazard risk assessment. ITC

Risk Assesment of Lahar Flow Hazard in Merapi Volcano

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