Volcano Hazard Management Using Digital Elevation Model
1D.John Prabaharan and 2Kasturi Devi Kanniah
1School of Spatial Science, Curtin University of Technology,
Perth,
W.Australia - 6845
E-mail: jdp27@yahoo.com
2Department of Remote Sensing
Faculty of Engineering and Geoinformation Science
Universiti Teknologi Malaysia, 81310 Skudai
Johor, Malaysia
E-mail: kdk21@yahoo.com
Keywords : GIS, DEM, mudflow, flow path, velocity, discharge rate, traveling time.
Abstract
GIS is being recognized as having applications for volcanic hazard assessment in early 90's. In this study digital terrain model within GIS environment was used to model the mudflow in Kawah Ijen volcano, Indonesia. With 36 million m3 of acidic water in its crater lake, Kawah Ijen is recognized as a potential threat to the surrounding population and properties. Using DTM, which was created by interpolating contours, two major mudflow paths were identified. Even a minor mudflow originated from the lake will flow through these paths. The topographic characteristics such as flow path's bed slope, width and depth were used to estimate the velocity and quantity of mudflow. The Manning formula with coefficient of 0.15 was used for calculating the velocity and quantity of mudflow.
Introduction
Volcanoes generate a wide variety of phenomena that can alter the earth's surface and atmosphere and endanger people and property. During the past 15 years volcanic activity killed more than 29000 people, forced over 830000 to flee from their homes and caused economic losses in excess of $3 billion (Simkin and Siebert, 1994). Countries like Indonesia which lies at the junction of three major plates with a population of 150 million face the greatest overall threat (Suryo et al, 1985). Most volcanoes related to deaths are associated with highly explosive eruptions involving pyroclastic flows and mudflows.
A flow composed of relatively small rock particles dominantly sand and silt size particles (less than 2 millimeters in diameter) are often called as mudflow. Mudflows have sediment concentration as great as debris flows and their sediment composition typically consists of at least 50% sand; silt and clay sized particles. Mudflows contain high concentration of rock debris to give them the internal strength necessary to transport huge boulders as well as buildings and bridges and to exert extremely high impact forces against objects in their paths (USGS, 1998).
Among the factors cause mudflow hazards, eruption through volcanic crater lakes represent a unique hazard because of the danger posed by the storage of large volume of water in proximity to near surface magma bodies the degree of hazard is proportional to the volume of water in the lake. This study is related to this category of mudflows. Eruptions in crater lake settings can result in deadly mudflows as seen at Mt. Ruapehu (New Zealand), Mt. Kelut (Indonesia) and etc (Oppenheimer, 1993). The most frequent reason for lake breakouts is the overflow of lake water across the dam and subsequent erosion and rapid down cutting into the loose volcanic rocks.
Since the impact posed by mudflow hazards is severe, it is vital to monitor, improve or lessen the impacts by utilizing GIS. Modeling the path of mudflow is fundamental to understand the areas affected by mudflow. The contribution of GIS in mudflow disaster ranges from identifying areas at risk, monitoring and forecasting hazards, to warning the possibly affected people or responsible teams to take precautions. All these strategies can be performed by utilizing the input, data analysis, modeling and display capability of GIS. This study was carried out by digitizing and interpolating the contours of Kawah Ijen area to create a DEM. Subsequently the DEM was used to identify the major mudflow paths that would carry the mud to the surrounding areas in a GIS environment. The velocity and quantity of mudflow from the crater lake was also estimated using hydraulic models.
Study Area
In this study, Kawah Ijen crater lake was selected because it is one of the largest and most active lakes that contain huge quantity of water. Any eruption through this lake would expel the water and create deadly mudflow that can claim hundreds of lives and properties (Oppenheimer, 1993). It contains about 36 million cubic meters of steaming, sulphurous acidic water. The floor is covered completely by a warm lake with the temperature ranges from 27 - 42°C. The outlet of the crater lake is located in western side that becomes the upper course of Banyupait - Banyuputih rivers. The size of the crater is about 960m x 600 m and has the surface area of 41x10
4 m
2 and 200 m deep. Kawah Ijen is placed on the summit of Mt. Ijen which is located in east Java. Ijen is one of the active volcanoes situated towards the eastern side of Ijen caldera The location of Mt. Ijen is shown in figure 1.
Figure 1 shows the location of Mt. Ijen in East Java, Indonesia and its aproximate outline of Ijen caldera.
(Source:http://www.lonelyplanet.com/dest/sea/graphics/map-indo.htm).
Data
For the above purposes the below data sets and methods were utilized.
- Toposheet map of Kawah Ijen area with a scale 1: 50,000 and Landsat 5 Thematic Mapper (TM) scene of Kawah Ijen dated on 5th October 1994 with World Referencing System of Path and row of 117/166.
- Arc info version 7.1 and Arc view 3.0 GIS software packages, Imagine image processing software 8.3 (all run on windows network system) and Microsoft excel.
Methodology
Flow path derivation
Firstly, a DEM was created by digitizing and interpolating contour map of Kawah Ijen area (1:50,000 scale). Subsequently, the DEM was used for deriving the mudflow direction. The direction of the flow is determined by finding the steepest descent, or maximum drop from each cellThe flow direction was found by Arcinfo "flow direction" command. The next step was to find the flow path. The flow accumulation process was utilized to find the gravity driven flow path.
The flow accumulation function calculates accumulated flow as the accumulated weight of all cells flowing into each down slope cell in the output grid. Cells with a high flow accumulation are areas of concentrated flow. The flow path was identified using 'stream network' and 'connects stream' functions available in arcinfo. The important flow paths were converted into arc coverage using arcview on screen digitization facility to drape over the DEM.
