Geomorphological Condition at Padang Pariaman Regency, West Sumatera Province, Indonesia

GEOMORPHOLOGICAL CONDITION AT PADANG PARIAMAN REGENCY, WEST SUMATERA PROVINCE INDONESIA Yustinus Adityawan Herlambang

1)

1)

e-mail : [email protected]  Undergraduate Student of Environmental Geography Department Geography Faculty Gadjah Mada University Yogyakarta, 2010

ABSTRACT

Sumatera Island is one of the biggest islands in Indonesia. It was formed by a lot of  geomorphic processes such as tectonic and volcanic activities. This research was carried out in Padang Pariaman Regency, West Sumatera Province, Indonesia. Padang Pariaman Regency located at 99 58’ 13’’ - 100 32’ 35’’ East Longitude and 1 18’ 56’’ - 1 34’ 56’’ North Lalitude. ˚

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˚

˚

The purpose of this research is to describe geomorphological conditions at Padang Pariaman Regency. This research consists of several steps such as literature study, secondary data in terpretation, and analysis. Literature study is the first step to know genetical process which occur at research area. Secondary data were used in this research are geologic map, topography map, and SRTM. Analytical approach was used to analyze geomorphological condition at research area. Analytical approach consists 4 geomorphological aspects, that are morphology, morphochronology, morfogenetic, and morphoarrangement. Volcanic, marine, fluvial, and complex landforms are the types of landform at Padang Pariaman Regency based on their genetical processes. Complex landform at this area was formed by configuration a lot of geomorphic processes such as tectonic, volcanic, karst, and denudational processes. Andesitic isolated hill is unique volcanic form. The genetic process which formed andesitic isolated hill didn’t know correctly yet, so the author made some scenario where it can be explained genetic process which formed andesitic isolated hill in research area

Keywords : Padang Pariaman Regency, Geomorphological Condition, Analytical Approach.

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1. Introduction

Geomorphology is the study of landforms and the processes that create them (Hugget, 2007). Lobeck (1939) stated that geomorphology had relevance with 2 sciences, that were geology and geography. Geomorphology in relation with geology science was a science which deals with surface features of the earth’s crust (Lobeck, 1939). It considered with mineralogy and petrology, paleontology, and stratigraphy. Stuctural and dynamic geology contribute toward an understanding of geomorphology by explaining evolution of the earth’s surface. Geography defined as the study of the relationship existing between life and physical

environment.

The

study

of

the

physical

environment

called

physiography. The meaning of physiography was a subject of geography science where it was a relationship between geomorphology, climatology, oceanography which it determined the distribution and behavior of the animal and human. Many scientists in the world disputed geomorphology was branch of physical geography or branch of

physical geology. But this controversion was back back from the

development of geomorphology around the world. For example in United State, geology science is the basic for all application in their sciences such as soil, hydrology, etc. Whereas in Europe, geography is the basic for natural sciences.

Figure 1. Indonesia Location, Red Box is Padang Pariaman Regency (Source: Badan Nasional Penanggulangan Bencana, 2009)

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Geomorphological condition at certain region has influence with resources and hazard

either from their type, type, quantity, quantity, and intensity. intensity. To analysis analysis

geomorphological condition at certain region, we can use 2 approaches, those are syntetic and analytical approach. Analytical approach was used by author for determining geomorphological condition in Padang Pariaman Regency. In analytical approach, geomorphology study based on 4 aspects in geomorphology, that are morphology, morphochronology, morfogenetic, and morphoarrangement. This time, the development in many areas around the world are increasing significantly. The development will be causing a lot l ot of problems either positive or negative problems. One of the negative problems is climate changing, in which it becomes world concern, either government, academic, and society around the world. A lot of hazards occurred at certain place around the world were an evidences of global climate changing such as landslide, flooding, sedimentation, drought, raising of sea level, etc. To reduce the impact of hazard at certain place, it needs intergration between science and technology, especially geomorphology. Sutikno (2007) stated that Indonesia was in collision zone of three tectonic plates (Eurasian, India-Australian, and Pacific Plates), between two oceans (Pacific and India), an between two big continents (Australian and Asian). According that fact, Indonesia has unique geologic and geomorphic features. Padang Pariaman regency located at West Sumatera Province, where genetical processes formed topography compotition and geologic features at this place. The purpose of this paper is to know geomorphological condition at Padang Pariaman Regency.

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2. Research Area

Geographic Condition Padang Pariaman Regency is a lot of regencies where it is a part of West Sumatera Province. Based on geomorphic processes which arrange Padang Pariaman Regency, Regency, these can be divided into 2 main groups that that are internal (geotectonic

and

volcanic

activities)

and

external

processes

(erosion,

sedimentation, and material transportation by water). Padang Pariaman Regency situated at zone 47 UTM, with UTM coordinate position 607966 mT – 671689 mT and 9902525 mU – 9966350 mU or 99 58’ 13’’ – 100 32’ 35’’ BT and 1 18’ 56’’ – 1 34’ 56’’ LU for geographic ˚

˚

˚

˚

coordinate position. Padang Pariaman Regency has 17 Districts and has width 2

1581,16 km . Batang Anai Sub District is a widely district in Padang Pariaman Regency. The area and width of Padang Pariaman Regency, can be saw at Table 1. Table 1. Area of District Administration In Padang Pariaman Regency No

District

Area of Administration ha

Km2

1

Batang Gasan

4276,944

42,76944

2

Sungai Limau

7933,210

79,3321

3

Batang Anai

35604,190

356,0419

4

Lubuk Alung

16876,749

168,76749

5

Ulakan Tapakis

5174,317

51,74317

6

Nan Sabaris

4993,406

49,93406

7

2X 11 Kayu Tanam

14663,654

146,63654

8

IV Koto Aur Malintang

11308,268

1 13,08268

9

II.X.XI.VI.Lingkung

4735,303

47,35303

10

Patamuan

5267,306

52,67306

11

Padang Sago

2043,312

20,43312

12

VII Koto Sungai Sarik

4338,093

43,38093

13

V Koto Timur

7897,011

78,97011

14

V Koto KP Dalam

8420,023

84,20023

15

Sungai Geringgi

13246,988

132,46988

16

Sintuk Toboh Gadang

5002,819

50,02819

17

VI Lingkung

6334,799

63,34799

158116,392

1581,1639

Total

(Source : Administration Map Analysis., June, 2010)

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In this research, the author used administrative area for the boundary of  research area. In figure 4, the author shown Padang Pariaman Regency Administration Map. The boundaries of this reseach area can be divided into 4 sections, that are : North : Padang Panjang Regency, Bukit Tinggi Regency. South : Pariaman Pariaman Regency, Mentawai Strait. West

: Agam Regency.

East

: Solok Regency, Padang Regency.

Figure 2. Padang Pariaman Regency Administration Map

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Topography Condition Padang Pariaman Regency have a lot of unique and variation of  topographic conditions. These variation of topographic conditions caused relief  differences, slope shapes, slope gradient, and drainage pattern. Topographic conditions in Padang Pariaman have a relationship with historical steps which formed this area with intergration between geomorphic agents - processes and climate conditions. Geotectonism and volcanism were energies below the earth’s which formed variation topographic conditions, geologic structure, the kind of  materials (types of rocks), and biophysic cultural of this area.

B

A

Figure 3. Elevation Map Padang Pariaman Regency At Raster Format (A); 3D Topography Padang Pariaman Pariaman VE = 4 (B) (Source : GIS Analysis, June 2010).

Geological Condition The forming process of Padang Pariaman Regency had relevance with the processes which formed Sumatera Island. Geologic and Geomorphic process activities can be saw by a lot of physical features in the field, such as Semangko Fault where it was lengthwise throughout Bukit Barisan mountains. The important concepts to identify those processes can be divided into 3 concepts. The important concepts are

1)

the same physical processes and laws that

operate today operated throughout geologic time although not necessarily always with the same intensity as now,

2)

Geomorphic processes leave their distinctive

imprint upon landforms and each geomorphic process develops its own

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characteristic assemblage of landform, and

3)

Geologic structure is a dominant

control factor in the evolution of landforms and is reflected in them (Thornbury, 1958 at Dibyosaputro, 1997).

Figure 4. Padang Pariaman Geological Map (Source : Bappeda Padang Pariaman, 2006)

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Katili and Marks (1953) stated that the processes who formed Bukit Barisan Mountains had been happened at Upper Cretaceous and Middle Tertiary Periods. Where, the relevance between magma activity and geologic structure have strong relationship with the process who formed Bukit Barisan Mountains. Subsidence process had been happened at young Mesozoic era. It was forming geosinclinal and ophilit intrusion. And then, the next processes were fold and uplift, where those processes occurred at Upper Cretaceous – Lower Eocene. When those processes occurred at the same time, another process happened in this area was granitic intrusion. At Oligocene-Miocene epoch, geologic and geomorphic processes were subsidence and volcanic activities. The intensity of volcanic activity was really strong, it made a lot of types of igneous igneous rocks such as andesite, basalt, basalt, and dacite, who known as old andesite formation.

Middle Miocene

Lower Eocene

Figure 5. Geologic Time (Source : International Stratigraphic Chart)

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The second processes was same with the first, where the second processes occurred at Middle Miocene. In the beneath of Sumatera Island, granitic rock was formed. Eruption process took place at the surface, it made some rocks such as pumice, dacite, rhyolite, etc. This process occurred lengthwise throughout Semangko Fault. At upper Miocene, those processes took place again, where those were identified by basalt and andesite. The kind of rocks in Padang Pariaman Regency were alluvium, andesite, granite, lava flows, limestone, quarsite, etc. Limestone and igneous rocks were an evidence, where in this area had been happened 3 processes, that were tectonic, volcanic, hydrothermal alteration activities. Intergration between physical and climatic conditions will be making a lot of geomorphic processes such as weathering, mass wasting, erosion, sedimentation, etc.

3. Research Methods Geomorphological Geomorphological Method

There are 2 approaches to determining geomorphological condition and to analysis, that are analytical and syntetic approach. Analytical approach was used by author for determining geomorphological condition in Padang Pariaman Regency. In analytical approach, geomorphology study based on 4 aspects in geomorphology, that are morphology, morphochronology, morfogenetic, and morphoarrangement. Morphology can be divided into morphometry and morphography. Morphometry aspect including size aspect and the form of unsures which formed landform. Morphography was a formation from natural object in the earth surface (Dibyosaputro, 1997). Morphogenetic were the processes which forming landform and their development, whereas morphoarrangement was the relevance of  landform in some place with their spatial function. Morphological data and types and rock distribution were obtained from SRTM and geologic map. And the morphogenetic and morphochronology aspects were obtained from literature or researches in this area.

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Data

Geologic map

SRTM Topography Map Literatures Inte Interr reta retati tion on

Morphology

Morphoarrangement

Morphochronological

Morphogenetical

Geomorphological Map

Figure 7. Geomorphological Methodology Flowchart.

4. Results and Discussion Geomorphological Geomorphological Conditions

Geomorphology is the study of landforms and the processes that create them (Hugget, 2007). Landform is a part of earth surface which it’s unique forms, as the result from geologic structure, time, and processes (Dibyosaputro, 1997). Landform was included geologic structure, rocks, relief, and geomorphic process. Based on genetic geomorphic process which formed Padang Pariaman topography composition, can be divided into 6 processes, those were volcanic, tectonic, denudation, marine, solutional, and fluvial processes. Those processes contribute at landscape characteristic and evolution. The important object in Geomorphology was landform, where it discussed 4 aspects, those were morphology, morphogenetic, morphocronology, and morphoarrangement. The kind of landforms at research area were 4 landforms considered on genetical processes which those formed this area. Four genetical landforms can be classified in detail into 13 forms, where those forms were classified and delineated based on topography, geomorphic processes, and types of rocks. The name and distribution of those landforms can be seen at Table 2.

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Table 2. The kind of Landforms And Width No 1 2 3 4 5 6 7 8 9 10 11 12 13

Landform Upper Slope of Andesitic Mountain Range Coastal Plain Middle Slope of Andesitic Mountain Range The Peak of Mountain with Volcanic Lava flow The Peak of Mountain with quartzite material Upper slope of complex mountain with limestone, granite, quartzite materials The valley between mountains with volcanic lava flow material Upper slope of mountain with volcanic lava flow material Middle slope of complex mountain with volcanic lava flow, quartzite, granite, andesitic, limestone materials Foot Slope of complex Mountain with volcanic lava flow, Tutut Geologic Formation, Andesitic, Granite materials Andesitic Isolated Hill Colluvial Plain Alluvial Plain (Sources : Geomorphological Analysis, 2010)

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Km 39.77 60.35 82.15 21.67 1.22 18.66

% 2.51 3.80 5.18 1.37 0.08 1.18

10.51 89.26 185.92

0.66 5.63 11.72

328.23

20.69

5.46 160.70 582.74

0.34 10.13 36.73

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Topography Topo graphy P rofile Kota Aur Malintang District - Sungai Limau District

1300

Topography Topog raphy P rofile Kayu Tanam District - Ulakan Tapakis District

900

975

675

Vertical Exaggeration = 19 Elevation (m)

Vertical Ve rtical Exaggeration = 15 650

450

Elevation (m) 325

225

0

5025

10050

15075

20100

25125

30091

0

5400

10800

Distance (m)

162000

21600

27000

32269

Distance (m) 1369

Topography P rofile Topography Batang Anai District - Ulakan Tapakis District

1050

Vertical Exaggeration = 18

700

Elevation (m) 350

0 6275

12550

18825

25100

31375

37601

Distance (m)

Figure 8. Topography Profiles

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Volcanic Landform Volcanic landform at research area can be divided into 3 landform, that were upper slope of andesitic mountain, middle slope of andesitic mountain, and andesitic isolated hill. Delineation process of those landforms used topography classification based on elevation map. Determining volcanic landform consider on dranaige pattern, where the type of drainage pattern in this landform was radial. Volcanic process was an important thing process who formed this area. Magma activity worked intensively, where it formed a lot of types of  igneous rock such as andesite, granite, lava flow, and quartzite. Based on petrology classification, andesite is a dark-colered, fine grained volcanic rock that is the extrusive equivalent of diorite. Granite is light colored, typically gray or pink, coarse grained, plutonic rocks with abundant quartz, in which the dominant feldspar is potassium feldspar rather than plagioclase. Granitic was commonly found at continental crust, especially in the cores of mountain ranges. 2

The scope of volcanic landform is 127.38 km or approximately 8.03 % of  the total reseach area. Morphological condition in this landform highly varied, it was shown with the class class of slope ranging from 8 – 55 %. The class of slope has influence to morphological condition, where morphological forms at this area were moderately steep, steep, and very steep. Andesitic isolated hill feature was a special phenomena where it can be classified into 2 landforms, those were volcanic and denudational landforms.

The genetic process which formed

andesitic isolated hill didn’t know correctly yet, so the author made some scenario where it can be explained genetic process which formed andesitic isolated hill in research area. First scenario is dynamic magma movement activity, where it will be making preasure on earth surface. Preasure on earth surface influences to their form and shape. When the preasure become higher and endurance of the material is higher, it will be making unique form like dome. If the preasure is higher than the endurance of the material, it will making volcano form.

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Another option is anticline form, who formed by the preasure bellow the earth energy. Anticline form can be detected by measuring dip and strike on the outcrop in the field. This form is like Gendol Hill at Muntilan District, Magelang Regency, Central Java Province. Where Dutch geologist (Bammelen) stated that this form was made from large mass sliding of Merapi volcano. But that statement contestable by Kurniawan (2008) who spoke Gendol hill was anticline. Second scenario, andesitic isolated hill is a result old volcanic activity like large eruption or great mass sliding of southeastern part of the lake. It based on volcanic lake or caldera of volcano at that time. The dranaige pattern is radial, where it is the type of drainage pattern on volcanic landform. Third scenario, andesitic isolated hill is denudational landform, where denudation processes such as erosion and mass wasting are working actively. Those scenario just were the author argument, where needed field observation and laboratory activity to prove the genetic process who fomed andesitic isolated hill. hill .

Figure 9. Radial dranaige pattern in volcanic lake (red circle is andesitic isolated hill, not scaled)

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Fluvial Landform Fluvial landform is a types of landforms, who formed characteristic landscape of Padang Pariaman Regency. Fluvial landform in research area was alluvial plain. Based on genetic process which formed this landform, the important agent was river process. A lot of processes occurred at this landform such as erosion, transportation, and sedimentation. Erosion process can be happened by overlandflow overlandflow and river. Material transportation by river including rolling, sliding, traction, suspended matter, and dissolve matter (Dibyosaputro, 1997; Hugget, 2007). 2

Alluvial plain has scope 582.74 km or approximately 36.73 % of the total scope of research area. Morphological condition at alluvial plain relatively flat until moderately, with class slope ranging from 3 – 13 %. Commonly, material on this landform was a transportation result by water flow such as overland flow and and river flow with concentrated or unconcentrated unconcentrated flow. Sorting depends on three factors: the viscosity, velocity of the transporting medium and the durability of the particles. The material sorting in this landform has good particles, where large particles deposited in the bottom and small particles on the top. The chronological alluvial plain figuration phase was long process with intergration some geomorphic agents. Material transportation process by river or overland flow depended on local geophysical condition, such as rainfall, slope, the width of channel, and external disruption. Rainfall played role as geomorphic agent who carried decay material where it was transported into river or transported into flat slope area. Slope condition has influence to velocity and the rate of flow from overland flow and river flow. Whereas the example for external disruption is vegetation, who can be disturbed transportation in the channel of  river. Material transportation process has directly proportional with slope condition and the width of

the channel of river. Those Those have influence with

velocity and the rate of river flow. Decreasing of the rate of river flow will be causing sedimentation process.

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Futhermore

material

sedimentation

had

been

taking

lithification.

Lithification refers to processes that convert loose sediment to hard rock. Two of  the most important processes processes are compaction and cementation. cementation. Sedimentation process makes geologic structure feature such as cross-bedding, ripple marks, graded bedding, and mud cracks.

Figure 10. Geomorphological Map

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Marine Landform Marine landform is a part of landforms at research area who formed by marine activity. The type of marine landform at research area was coastal plain, 2

with 60.35 km or 3.8 % of the total scope of this area. At coastal area, we can see a lot of gisik features, where the shorelines almost form linear/straight lines. Marine landform commonly has 2 types, that were depositional and erosion types. Erosion type was a type of marine landform who occurred because of cutting process by waves activity. Whereas depositional type was a type of marine landform who occurred because of depositional process by waves. The marine landform at research area has depositional type. It can be proven with morphological criteria, where the slope was ranging form 0 – 7 % and the topography was relatively flat until moderately. The forming of coastal plain processes have relevance with geomorphic agents like waves, river, and overland flow. The chronological coastal plain figuration phase get started with weathering process caused by climate condition, biologic activity, and endurance of rock by weathering. The result of volcanic weathering was transported by overland flow into the river. Futhermore material transportation by river was deposited and transported around estuary or was deposited by river which had small rate of flow. In ocean, the material through a lot of geomorphic processes processes such as material material sorting and deposition by waves waves and current in shorelines. Those processes took long time and have directly proportional with layers and relative age of stratum. The color of materials in this landform commonly light until dark colored; with silica, sodium, and pottasium compositions relatively high. It was caused by rock genetic, in which the material was a result of weathering process of igneous rock. According to Bowen’s reaction series, mineral figuration fi guration at coastal plain can be classified into felsic and intermediate phases. The sorting of the material at coastal plain was same with alluvial plain, where the layer of materials composed with good deposite based on their size.

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Complex Landform Complex landform was a landform where it formed by a lot of geomorphic processes such as structural, volcanism, and solutional (karst). Classification those processes consider on type of rocks. Based on type of r ocks, we can explain about genetic processes which formed this landform. Configuration among those processes bring relatively unique at this landform, include physical and ecological side. Complex landform at research area can be divided into 7, those were the peak of mountain with volcanic lava flow; the peak of mountain with quartzite material; upper slope of complex mountain with limestone, granite, quartzite materials; the valley between mountains with volcanic lava flow material; upper slope of mountain with volcanic lava flow material; middle slope of complex mountain with volcanic lava flow, quartzite, granite, andesitic, limestone materials; and foot Slope of complex mountain with volcanic lava flow, Tutut Geologic Formation, andesitic, granite materials. The scope of complex landform 2

was 655.46 km or approximately 41.31 % of the total research area. The chronological chronological complex landform figuration phase can be divided divided into 3 phases. First phase was subsidence process and then the second phase was uplift process. The evidence of uplift process was limestone feature, in which limestone was the commonest and most important biogenic rock. Limestone consist of  lithified shells and reef constructed of calcite by marine organisms. While uplift process took place, another geomorphic process as volcanic process occurred too.

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Figure 11. Lineament Rose Diagram

Volcanic process as intrusion produced a kind of igneous rocks such as basalt,

and dacite, dacite, who known as old andesite andesite formation. Third phase phase was

volcanic activity produced andesitic, pumice, rhyolite, and lava flow. Volcanic and uplift processes caused variation of geologic structure indirectly, one of the geologic structure was lineament pattern. Lineament pattern was a shape of  geologic structures, who described fracture or fault f ault lines. Morphological of complex landform are mountain with moderately slope until steep slope. The slope of this landform ranging from 14 – 55 %. The complexity of geomorphic processes on this landform causing 2 type of rock, those were igneous and sedimentary rock. The type of igneous rock at this area can be classified into 3 group, those were felsic, intermediate, and mafic based on mineral configuration which formed igneous rock at this place. And for the type of sedimentary rock were biotic and clastic sedimentary rocks.

5. Conclusion

Tectonism and volcanism were an important processes which formed landform at Padang Pariaman. The type of landform in research area divided into 4 based on genetic processes, those are volcanic, marine, fluvial, and complex landforms. Field observation and laboratory test needed to compare the result of  interpretation and the fact in the field.

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nd 

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