GEOMORPHOLOGICAL CONDITION

AT PADANG PARIAMAN REGENCY, WEST SUMATERA

PROVINCE INDONESIA

Yustinus Adityawan Herlambang 1) 1) e-mail : killrockforfun@yahoo.co.id 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.

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 interpretation,

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 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, quantity, and intensity. To 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 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, these can be divided into 2 main groups 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

1581,16 km2. 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

Area of Administration No District

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 11308,268 113,08268

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

Total 158116,392 1581,1639

(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 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.

A B

Figure 3. Elevation Map Padang Pariaman Regency

At Raster Format (A); 3D Topography Padang 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 rocks such as andesite, 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 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 mapTopography Map

SRTM

Literatures

Interpretation

Morphology

Morphochronological

Morphoarrangement

Morphogenetical

Geomorphological Map

Figure 7. Geomorphological Methodology Flowchart.

4. Results and Discussion

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 Landform Km2 % 1 Upper Slope of Andesitic Mountain Range 39.77 2.51 2 Coastal Plain 60.35 3.80 3 Middle Slope of Andesitic Mountain Range 82.15 5.18 4 The Peak of Mountain with Volcanic Lava flow 21.67 1.37 5 The Peak of Mountain with quartzite material 1.22 0.08 6 Upper slope of complex mountain with limestone, granite, quartzite

materials 18.66 1.18

7 The valley between mountains with volcanic lava flow material 10.51 0.66 8 Upper slope of mountain with volcanic lava flow material 89.26 5.63 9 Middle slope of complex mountain with volcanic lava flow, quartzite,

granite, andesitic, limestone materials 185.92 11.72

10 Foot Slope of complex Mountain with volcanic lava flow, Tutut Geologic Formation, Andesitic, Granite materials

328.23 20.69

11 Andesitic Isolated Hill 5.46 0.34 12 Colluvial Plain 160.70 10.13 13 Alluvial Plain 582.74 36.73

(Sources : Geomorphological Analysis, 2010)

0

350

700

1050

1369

6275 12550 18825 25100 31375 37601

Topography ProfileBatang Anai District - Ulakan Tapakis District

Vertical Exaggeration = 18

Elevation(m)

Distance(m)

0

325

650

975

1300

5400 10800 162000 21600 27000 32269

Topography ProfileKayu Tanam District - Ulakan Tapakis District

Vertical Exaggeration = 15

Elevation(m)

Distance(m)

0

225

450

675

900

5025 10050 15075 20100 25125 30091

Elevation(m)

Distance(m)

Topography ProfileKota Aur Malintang District - Sungai Limau District

Vertical Exaggeration = 19

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.

The scope of volcanic landform is 127.38 km2 or approximately 8.03 % of

the total reseach area. Morphological condition in this landform highly varied, it

was shown with the 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.

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 and river.

Material transportation by river including rolling, sliding, traction,

suspended matter, and dissolve matter (Dibyosaputro, 1997; Hugget, 2007).

Alluvial plain has scope 582.74 km2 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 river flow with concentrated or 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 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 are compaction and 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,

with 60.35 km2 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 such as material sorting and deposition by 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 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 rocks, 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

was 655.46 km2 or approximately 41.31 % of the total research area.

The chronological complex landform figuration phase can be 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, who known as old andesite formation. Third 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 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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