Volcano Hazard Management Using Digital Elevation Model

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Volcano Hazard Management Using Digital Elevation Model

Quantitative analysis of mudflow
Wholesale ejection of lake water (36 million m³) would not be expected in on go. However, even a fraction of water that rushes through the outlet is capable of creating mudflow. The hydraulic radius and velocity depict a linear relationship where the increase in the hydraulic radius (which is a function of flow path cross sectional area and wetted perimeter) is accompanied by a steady increase in the velocity. This is shown in figure 3i (a-f). For example at the distance of 4.7 km from the Crater Lake (figure 3id) the mudflow achieves a velocity of 16 m/s when the hydraulic radius extent to 12.4 m. Meanwhile, the relationship between discharge rate and the velocity of mudflow reveals that as the quantity of discharge increases the velocity also increases in a non- linear fashion (Figure 3ii (a-f)) For example near to the outlet, when the discharge rate increases from 20,000m³/s, 60,000 m³/s and 90,000 m³/s the mudflow travels rapidly at a velocity of 22 m/s to 28.5m/s and 31 m/s respectively. The higher rate of velocity near the outlet could be due to the steep slope at the volcanic flank. It is gradually decreasing when mudflow approaching the downhill side, mainly due to the slope of the topography. At the distance of 4700m the velocity of mudflow is comparatively lower because the flow path's width is wider than that of other areas. The velocity of mudflow is mainly depending upon the characteristics of topography such as slope and the quantity of discharge of water from the Crater Lake (figure 3(iii)).

Figure 2 shows the major mud flow paths. Flow paths and Landsat TM image (RGB:4 3 2) overlaid onto DEM to visualise the flow path in a 3D perspective view.

(i)

(ii)

(iii)
Figure 5 (i) to (f) Shows the relationship between the hydraulic radius and the velocity of mudflow at several areas along the flow path at various distances, Surface Profile a) in outlet area, 0.103 km distant from the crater lake, b) 1.64 km, c) 3.8 km, d) 4.7 km, e) 7.95 km, f) 10.8 km from the crater lake. Figure 5 (ii) shows the relationship between discharge rate and velocity of the mudflow at several cross sectional areas along the major mudflow path. Surface profile (a) nearer (0.103km) to the outlet of Kawah Ijen Crater Lake. (b) 1.64 km, (c) 3.8 km, (d) 4.7 km, e) 7.95 km. (f) at 10.8 km from the Crater Lake. Figure 5 (iii) shows the velocity of mudflow along the flow path.

Conclusion
Mudflow modeling of Ijen kawah volcano using DEM within a GIS environment is found to be useful in providing information pertinent to mudflow hazard. The velocity of the mudflow is directly proportional to the cross-sectional area of the flow path, hydraulic radius and bed slope of flow path and inversely proportional to the wetted area perimeter. Meanwhile, as the quantity of water discharge from the Crater Lake increases the velocity of mudflow also increases. Information pertinent to the routes of flows can provide precautionary measurement against mudflow hazards. In mudflow analysis, collecting more field data, improving DEM's grid element size and coupling GIS with hydraulic flow model can improve the mudflow model.

References

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