IV. RESULT AND DISCUSSION
4.1 Settlement Area
Settlement area was extracted from Landsat 7 ETM+ data which is recorded in year 2001.
Classification method being used is ISOCLASS Unsupervised Classification with the result showed on Figure 4.1. Cause of the limitation of
spatial resolution in Landsat imagery which is 1 pixel represents area around 30 m
2
, it is quite difficult to distinguish between settlement area and open land. Thus, the interpretation of settlement area was regarded from the calculation of
settlement class and open land class. Appendix 2.
Figure 4.1. Result of unsupervised settlement area over Landsat 7ETM+ Year 2001
4.2 Land Stability Risk Zone
39
One of many Landsat 7 ETM+ capabilities is used for alteration zone interpretation which geologically can explains general pictures of structural
condition and level of weathering in research area. Those information can be extracted from several satellite channels where placed in bands.
Alteration extraction results from soil and rock data which indicates the content of laterite minerals. Iron oxide interpretation was extracted from iron rich
soil gained from band 1 and band 3 which have good capabilities in iron anomaly recognition and band 5 and band 7 which have capabilities in clay rich soil
recognition. By means of principal component analysis PCA techniques, the anomaly
data of mineral features recorded in band 1, band 3, band 5 and band 7 could be enhanced with the calculation of statistic features data and performed as dominant
or majority data in population. Iron oxide and clay hydroxyl data is useful in order to interpret and predict stability zone.
Band ratio of mineral contents used for delineating areas which have contents of metal-oxide especially iron although clay-hydroxyl minerals.
Concentration of these minerals constitute alteration process of weathering and sedimentation. The area which contains of high iron-oxide shown by reddish color
whereas the higher content shown by red color. Additionally, the areas which have high contains of clay-hydroxyl are shown by blue color. While yellow color
consitute unification of them. Band ratio anomaly with circular distribution pattern generally related to
concentric volcano forms. Elongated distribution pattern possibility caused by weathered iron-oxide or clay-hydroxyl on structural zone in the term of fault zone,
40
where around the fault zone usually represent of weak zone and enable to occurring of alteration or weathering.
Based on alteration analysis for mineralization zone by means of principal component analysis PCA, West Java area shown some concentrated zones
Figure 4.2.. The mentioned result progressively supported some zones which has been interpreted lithologically and geomorphologicaly.
Figure 4.2. Mineralization Zone indicating Land Stability Risk Zone
Those iron-oxide possibility consitute result of weathered igneous rocks
which contains iron element in term of pyrite FeS
2
, chalcopyrite CuFeS
2
and
hematite Fe
2
O
3
minerals. Although those igneous rock weathered or oxidized, its characteristics still more stable than weathered rocks contains clay-hydroxyl
minerals like montmorillonite Mg
2
Al
10
Si
24
O
5
OH
12
+ Na,Ca, kaolinite
41
Al
2
Si
2
O
5
OH
4
and illite Al,Fe,MgSi,Al
2
O
5
OH + K, where those mineral elements have a plastic or unstable characteristics. Furthermore, the areas with
yellow and cyan colors, caused by weathered rocks which contains same percentage of iron-oxide and clay-hydroxyl, but the characteristics it self not more
stable than rock contains iron-oxide and more stable than rocks which contains clay-hydroxyl. Caused iron-oxide mineral that compose the rock indicating the
resistant rock than clay-hydroxile mineral. Therby, Land Stability Risk Zone can
be obtained by giving weight Table 4.1. toward those mineral distribution in an image.
Unstable
3
Clay I ntermediate
2
I ron-Clay Stable
1
I ron
Description Weight
Mineral Distribution
Table 4.1. Mineral Distribution Weighting
4.3 Slope Stability Risk Zone
Kategori