Morphostructure Control Towards the Development of Mahawu

Indonesian Journal of Geology, Vol. 7 No. 1 March 2012: 39-54

Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi

Kontrol Morfostruktur Terhadap Perkembangan Kompleks Gunung Api Mahawu, Sulawesi Utara

S. PoedjoPrajitno

Centre for Geological Survey, Geological Agency, Jln. Diponegoro No. 57 Bandung, Indonesia 40122

AbstrAct

The studied area, situated in northeastern part of North Sulawesi Arm, is dominantly occupied by the Mahawu, Linau, Tompusu, and Kasurutan volcanic rocks. Using remote sensing data, such as landsat image, black and white panchromatic aerial photograph, and IFSAR image, morphology-origin unit and morphology lineament can be interpreted. Four morphology-origin units, those are Mahawu Volcano Complex, Intra-montane Plain structure, Linau Volcano Complex, and Lacustrine Plain are recognized. Furthermore, morphological lineament pattern was statistically processed to find out the general stress direction in the area to determine the probability of the structural morphology occurrence in the Mahawu Volcano Complex. The result shows that generally the development pattern of volcanic cones are irregular, except the Mahawu Volcano Complex showing a linear pattern. This lineament pattern is interpreted as a NW - SE fault pattern controlling the rise of magma. At least, two tectonic and two eruption periods occurred regularly at different time from the Quaternary age till the present.

Keywords: morphostructure, Mahawu Volcano cone, fault, lineament, magma, North Sulawesi Arm

Sari

Daerah penelitian, yang terletak di bagian timur laut Lengan Utara Sulawesi, didominasi oleh batuan vulkanik hasil kegiatan Gunung Api Mahawu, Linau, Tompusu, dan Kasurutan. Dengan menggunakan data inderaan jauh, yakni citra landsat, foto udara pankromatis hitam-putih, dan citra IFSAR, satuan bentukan- asal dan kelurusan morfologi ditafsirkan. Empat satuan bentukan-asal, yakni kompleks Gunung Api Mahawu, struktur dataran antar-gunung, Kompleks Gunung Api Linau, dan dataran danau telah terdeteksi. Selanjutnya pola kelurusan morfologi diolah secara statistik untuk penentuan arah umum tegasan dan kemungkinan kehadiran morfologi strukturnya. Hasilnya menunjukkan bahwa arah pertumbuhan kerucut gunung api tidak berpola, kecuali arah pertumbuhan kompleks kerucut Gunung Api Mahawu yang memperlihatkan garis lurus. Pola kelurusan kerucut gunung api ini ditafsirkan sebagai pola sesar berarah barat laut - tenggara yang mengontrol keluarnya magma ke permukaan. Dua periode tektonik dan dua periode erupsi yang teratur dan tidak pernah bersamaan telah terjadi di daerah kajian pada kala Kuarter hingga sekarang.

Kata kunci: morfostruktur, kerucut Gunung Api Mahawu, sesar, kelurusan, magma, lengan utara Sulawesi

IntroductIon

Mount Mahawu is a stratovolcano with an eleva-

tion of ± 1324 m asl., located at the east of Lokon Empung active Volcano. One of the volcanic cones was cut off and developing to become a crater lake

with 80 m width. Its surface temperature reaches ± 65.50 C, and the estimated depth is ± 10 m. A weak explosive eruption expelling white smoke occurred on April 1987 (SEAN, 1987). Beforehand, in 1974 outpouring of mud with 0.5 m height took place. Furthermore, in 1977, 1978, 1987, and 1990 there

Manuscript received: December 7, 2011, final acceptance: March 09, 2012 Coresponding Author: 08122482072/[email protected]

39

40 Indonesian Journal of Geology, Vol. 7 No. 1 March 2012: 39-54

were activities of fumarole, mudspot, and hot water outpouring along the crater lake periphery having green water (Sumpena and Djuhara, 1992).

The Mahawu Complex is located at the coordi- nates of 1240 49’ - 1240 54’ E and 10 19’ 30” - 10 21’ 18” N. Administratively, it is included into the Mina- hasa Regency, North Sulawesi Province (Figure 1).

Based on the geologic map of Manado Quadran- gle scale 1:250.000 (Effendi and Bawono, 1977) no geological structure exists in the Mahawu Volcanic Complex. That is why the morphological structure of Mahawu Volcano is need to be discussed here to find out its relation with the probability of the occurrence of Mahawu Fault.

Methodology

The research method was carried out by using re-

mote sensing data, comprising landsat, panchromatic black-white aerial photograph, and IFSAR images. Morphological lineament was interpreted on landsat images which then the lineament interpretation result

was statistically processed to find out the general stress direction in the area. Supported by the result of the aerial photograph interpretation and by finding out the general stress direction, the probability of the occurrence of the structural morphology in Mahawu Volcano Complex was determined.

regIonAl geology

The Mahawu Volcano Complex is situated in the

eastern part of the north arm of Sulawesi. The region is occupied by volcanic rocks composed of andesite bordered with basalt as the result of Lokon volcanic activities. Both volcanoes are categorized as young stratovolcanoes of Quaternary age (Qv). The material produced is lava, bomb, lapilli, and ash. The oldest deposit around the studied area is Tertiary volcanics (Tmv) (Figure 2). The studied area is included into a volcanic arc due to the multiple subduction of the North Sulawesi subduction belt in the north, and of East Sangihe subduction belt located in the east and south parts of the north arm (Hall, 2001). The sub-

121° E 122° E 124° E 126° E

0 25 50 75 km Sulawesi Sea

MANADO . Mahawu Volcano

GORONTALO

North Sulawesi 120º

Studied Area Index Map

0°

Tomini Bay

Studied Area

PALU

S u la we s I Sea MANADO

0° GOR ONTALO

S u la we si

Island

Sula Islands

Bu ru Sea

121° E

Central Sulawesi

122° E

124° E

MAKAS AR

120º

KENDARI

Ba n d a Sea

126° E

Figure 1. Locality map of the studied area.

Qs Qv Qtv Tmv

Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 41 (S. Poedjoprajitno)

1o

30 ’ N 1 24

o

4 5 ’ E Sulawesi Sea

MANADO

Qa l

Qs

S a wa n ga n

Ma u mbi

La kit

1 25o 0 0 ’ E

1o30’ N

Teling

QTv Ka wa ng ko a n

Malalayang

Qv

S a re n gs o n g

Mt. TETE MPANGAN

Qv Koka

QTv

Ke n d e s

Mt. TATAWIRAN Ru me ng ko ko

Mt. LOKON Mt. MAHAWU

Ton d a n o

QTv Mahawu Volcano

Qv Ma ra wa s Tmv

Lake Linau

Mt. TOMBUS U

Qs

Lake Ton da n o

QTv

Mt. KALUTA

1o15’ N

1 2 4o 45 ’ E

Legend:

Ka s u ra ta n

= Fluvial and lacustrine deposits Mount

1o 15’ E

1 2 5o 0 0’ N

= Young volcanic rock

= Tondano Tuff

= Tertiary volcanic rocks

Hot Spring

Studied Area

0 5 km

Figure 2. Geological map of the Mahawu Volcano Complex and its vicinity, Minahasa Regency, North Sulawesi (part of the Geologi Map of Manado Quadrangle, scale 1: 250.000, Effendi and Bawono, 1977).

duction caused the magmatic activities to form the Mahawu, Lokon, Soputan, Klabat, Tongkoko, Tom- pusu, Lengkoan, and Batuangus Volcanic Complexes (Figure 3). Based on the similar occurrences of the volcanic distribution patterns in the North Sulawesi arm and Sangihe subduction, it is inferred that the Sangihe subduction belt more affected the formation of volcanic cones than the North Sulawesi subduction.

regIonAl geoMorphology

According to Suharsono et al. (2007) nearly 50 %

of the Manado area originated from a volcanic morphology (Figure 4). The others were derived from denudated, marine, fluvial, and structural volcanic morphology. The morphological origin is generally of young active volcano (Quaternary) of which its


6º N Mindano

0 130 260 km

4º N

Legend: Thrust fault of active fore-arc Subduction

Quaternary Volcano

Sangihe

Talaud Islands

2º N

Sulawesi Sea

Studied Area

Maluku mid-oceanic ridge

Mayu

North Arm

0º Una -una

Goronta lo Basin

Maluku Sea

Ternate

Tidore

Tomini Bay

Togia n Isl. East Arm

Sula Islands

Bacan

2º S

SULAWESI

Ba ngga i Island

Talabu Ma ngkole

Sula Besi 120º E 122º E 124º E 126º E

Figure 3. Geography and the main feature of the North Sulawesi tectonics (modified from Hall, 2001).

spread followed the regional tectonic pattern, in NE-SW direction beginning from Mount Lokon, Mahawu, Klabat, Duabersaudara, Batunuang, and Batuangus parasite.

The old volcanic tracks that can be observed among others are the old caldera walls of Tertiary Tondano Volcano shown by the series of Kawatak, Kaweng, Kamingtan, and Kaluta Hills. Suharsono et al. (2007) classified the hill series as dissected longitudinal volcanic ridge (VD3), while Verstap- pen (2000) called it as Tondano Escarpment. It is presumed that a paleoparasitary developed in the north flank of old Tondano Caldera. At present, the parasite is shown by a hill landform with dissected peak and wide plain in the middle part. Suharsono et al. (2007) classified the hill landform with dissected peak as a medium dissected crater wall (VD7), while the wide plain in the middle was classified as a medium dissected crater plain landform (VD8) (Figure 4).

Geomorphology of the Mahawu Volcano Complex and the surrounding Volcanoes

On the basis of the interpretation result of the black-white aerial photograph plotted on a topo- graphical map of the Mahawu Volcano and the surrounding volcanoes, scale 1:50.000 (Figure 5) four morphological origins are recognized in the area. Unit of Morphological Origin of the Mahawu Volcano Complex

Aerial photograph interpretation indicates that the unit consists of six volcanic cone landforms developing close to each other, grouped, and they occur almost in one line. The eruption product of each Mahawu volcanic cone is difficult to be differentiated. However, on the landsat image combined with DEM, twelve volcanic cones can be identified (Figure 6). All eruption material of this Mahawu Volcano Complex is presumed to cover most of the residual body of Paleo-Mahawu volcanic cone. The

F2

3

V3

1

1°15

’ N

1°

48’

N

1°15

’ N

1°

48’

N

V2


124°45’ E 125°18’ E

Nain Besar Island

S U L A W E S I

S E A

Ta ra bita n

P ula u M a nte ha g e

M1 1 00

1 00 M1 M4

M1

M4

M1

Ku lu

J a ya ka rs a

M4 1 00

S 2 S on s ilo

10 0

100

20 0 20 0

10 0

Eh e

Mu nte

Isl. Ta la b e Ke c il

Isl. Ta la be Be s a r

M1 M4

Isl. Ta m p e ron g

Isl. Nya ripa nja ng

Isl. Na p od a on g

M4

Likupang

La bu a n Ma rins ow

Strait

20 0

0 2 4 6 8 10 km

P ulis a n Cape

M4

A Mia ya

M1

We ro t 100 100

S 1 1 00

Ba tu

100

M4

Kija ng

1 00 F2

W in e ru

D1

1 00

100

M4

M4

M1 M4

M4 F2

M1

Kim a jo

Ku a la Ta la wa a n

200

VD7

Kua la Wa ris a

VD8

Te e p

S 2 2 00

2 00

20 0

1 00

200

L I N G K U P A N G

D2 2 00

D1

M5

Kua la Ara re n

F2

Ka lina un Isl. P on te ng

Ka we ru a n

Boh owo

Tih owo Bolun g

VD6

Kua la P a na w 500

VD3

20 0

P in e ne k Ba tu putih

M1 VD1 VD2 10 0

10 0

M1

500 4 00 0 0

Mo la s

20 0

VD3

P in a s u ngkula n

5 00

Kua la Ka yu la we be s a r

20 0

V2

Tiwan Cape

M4 10 0

F1 F1

Be n gko l

V6 Ma pa ng e t

Ta te lu

5 0 0

4 00

V3

G un un g Ba tua n gu s

V1 V4

V7 V1 0

MANADO

MANADO BAY

Ma pa n ge t

100

VD6

200

P a nilih

V2

4 00 Kua la Tundu ka

3 00

V5 G un un g P ina ng un ia n

G un ung Ta ng koko

G. Dua s a u da ra

F2 Kua la Ton da n o

F1 We na n g

Kua la Tika la

100

Ka long a n

300

400 1000

1200

G u nu ng Kla ba t

600

10 00

V1 V2 50 0

V8 Kua la Airpra ng

Ta le ti

Koh a

300

100 V3

200

Kua la Wa lis uko

100

100

V3

Ka le o s a n

100

200

200

400 V1 0 600

300

Airm a didi

V1 1500 1400

Kua la Te nde ki

V2

Kua la Tundu ka

Kua la S e ge ra t

V3

F1 M1

B I T U N G P a pus ung a n

VD5

400 500

400

V2 300

200 300 400

S o s oa n R a n ora n o

200

S a m piri

200

200

Le m be a n

M1 M3

Wa tu da m bo M2

Le mb e h Island

P a ncu ra n Cape

Ke ntu r

Te te m pa n ga n

V1

1200

500

500

400

300

400

S a wa ng a n

300

200

200

Kua la S a wa n ga n

Ka udita n

F1

Ke m a 2

100

M2 M3

M1

M6

M3 M2

Dua Island

700 1500

1400 300 1200 1100

1000

700

S o s oa n Ra no wa ngko

V2

Ka m a s i

V1 1000

700

VD3

Ku a la Lila n g

VD4

M3

M1

Wa le o

VD4 50 0

V9

S os oa n Ra noa s a n

700

TONDANO

FL1

M1 123° 124° 125°

3°

S . To n d a n o

9

5 0 6 0 0 m

U

1° 45’

8

4

2°

D. Lino w B

D. Ta m p us u

D. P a n ga lo m bia n

1 000

D. TONDANO

1 00 0

80 0 50 0

Ka la wira n S o s o a n B ulo

Bulo Cape

7 Ma na do

3 2

1°

1

6

MANADO

50 0

124°45’ E

Legend:

S os oa n Ke we le wa ng ko 0 °

1 2 4 °45 ’ DAER AH P E METAAN 125°15’ MAP P ING AR EA

1 °1 5’ LIP UTAN F OTO UDARA AERIAL P HOTOGRAP H C OVE RAGE

125°18’ E

Volcanic cone

Volcanic flank, upper part

Volcanic flank, lower part

Intermontane plain

Laharic fan

Solfatara field

Medium dissected volcanic cone Medium dissected volcanic flank

Medium dissected unseparated volcanic series cone Medium dissected unseparated volcanic series flank Laharic fan

Residual hill

Graben valley

Tilting ridge

Alluvial plain

Flood plain

Beach sand

Beach ridge

Figure 4. Geomorphological map of Manado area modified from Suharsono et al. (2007).

residual slope of the Paleo-Mahawu volcanic foot can still be seen especially in the southeastern part which is generally made up of trace of lava flow, gently sloping and jointed. Some of the Mahawu Volcano Complex cones have imperfect forms, present as dissected cones. It is assumed that the peaks of the cones had been damaged during eruption

process, and now they left crater lakes (Figures 6 and 7) filled with water in rainy seasons (Figure 8). The two of twelve recognized cones have the perfect forms (Figure 9) occurring in the southern part of Mahawu Group. The perfect shape of the volcanic cones can be formed, because the magma intruded had been dormant before erupting.

R.902A-1 0

1º 2

2’1

2’ N

1º

15’

N

1º 1

5’ N

1º

22’

12

’ N


124º49’ E

Kin ilo w

11 59

124º54’ E

Ka ka s ke n 1 1

2

1 372

8

3 1328

93 9

4

7 Te m boa n

896

To m o h o n

10 78

6

5

126 2 12 34

P la s a te n 1

Mt. Mahawu 1 237

R.896

Ma ta ni

12 16

Mahawu Volcano Complex

Intra mountain plain

PLASATAN FAULT VALLEY

Ma s a ra ng

Tum a ta ng t a ng

Plate au

974

760 782

683

9

683

Kasoa ngan Ta ta a r a n 1

La h e n d o n g

Mt. Lin a u

9 84

882 Lacustrine alluvial 68 3

plain 6 88

13

Lake Linau 783

12

899

11

1059

Lake Tampusu

Lake Pangolumbian

Linau Volcano

Complex

R.902A-10

To u n s a ru

Mt. Ka s ura ta n 10

Ta m p u s u

REMBOKEN

124º49’ E

Legend : 0 1 2 3 km

124º54’

Volcano Lava fan Lava flow track Crater lake

Contour line Inferred fault

River channel Geomorphological

main unit boundary

11

1059

Observation point Central point

Elevation point Road

Figure 5. The result of geomorphologic interpretation of Mahawu Volcano area and the surrounding volcanoes from the black- white aerial photographs (panchromatic).

1400

00 m

N

1450

00 m

N

1500

00 m

N

1400

00 m

N

1500

00 m

N

1450

00 m

N


705000 mE 710000 mE

Mt. MAHAWU

Lake Linau

705000 mE 710000 mE

Figure 6. Landsat image ETM+7 combined with DEM IFSAR image of the Mahawu Volcano and the surrounding volcanoes.

The distribution of Mahawu Volcano Complex

cone pattern is divided into two groups: the North and South Mahawu Groups (Figure 9 and 10). The North Mahawu Group consists of series of five volcanic cones having craters and one residual pa- leovolcanic body; whilst the South Mahawu Group comprises six cones. Based on the landform boundary distribution, the chronological construction of each cone in each group can well be followed in concomitance with the order number shown in Fig- ure 9. Hence, due to the abundance of volcanic material and repeatedly overlain each other lead to the presence of difficulties in identifying the structural pattern since many structural morphologic indicator covered by the volcanic deposits.

Unit of Morphological Origin of Intramountain Plain Structure

The terminology of morphological structure or morphostructure firstly introduced by Gerasimov (1976) and Gerasimov and Mescherikov (1968; in Faibridge, 1981) is used to describe the landform topography constructed by neotectonic activities.

This morphology, generally, has a coarse relief but flat in some places, hemmed in amongst morphological units of Mahawu, Linau, and Lokon Volcano Complexes (outside the studied area). This morphological unit surface is covered by very thick deposits of pyroclastic fall from the surrounding volcanoes, difficult to be differentiated. The boundaries with the surrounding morphological units among others

1500

00 m

N

1400

00 m

N

1450

00 m

N

1400

00 m

N

1450

00 m

N

1500

00 m

N


705000 mE 710000 mE

Alluvial Plain

[e]

[a] [d]

[b] [e]

[c]

[e]

Pyroclastic fall

[b]

Pyrodastic fall

[b] [c]

Pyroclastic fall

[b] [b]

f [b]

[b]

f

[a]

Alluvial f Plain

[b]

f

Old lava flow f

Paleo - lava flow track

Pyroclastic fall Mahawu

Plateau

Foot of Limau Paleo-volcano

Dissected plateau

Swampy

Lake

Caldera wall trace of Linau Paleo-volcano

Young lava

flow

Structural terrace of

Linau pyroclastic fall

Pyroclastic flow

Alluvial plain

[a] [b] [c] [d] [e] Lake Linau

f [e]

[b]

[c ]

Mt. Tompusu

Paleo-lava flow

f

[b]

[e]

Bk.

f

f 705000 mE 710000 mE

Lake

Legend: 0 1 2 3 4km

Gunungap [a] crater lake [b] crater floor

young lava fiow

terrace

boundary of landform unit f

fault

[c] crater wall old lava fiow scarp a =subboundary f inferred fault [d] crater rim [e] volcanic cone

paleolava flow

valley a =inferred lineament

Figure 7. A Tentative geomorphological map of Mahawu Volcano and other volcanoes in its vicinity, Manado, North Sulawesi (the result of landsat ETM+7 image and DEM IFSAR image).

7

24

1450

00 m

N

1500

00 m

N

1450

00 m

N

1500

00 m

N

Sou

th M

ahaw

u N

orth

Mah

awu

11

22


Figure 8. One of Mahawu volcanic craters with Mount Lokon at the background. The camera faces west, location 8.

are Plasaten Fault valley in the northeast (Figure 5), structural terrace in the south (Figure 7), and Paleo- Linau volcanic foot slope in the west. The fault is called as Plasaten Fault because among others it bended the Plasaten River channel in the Plasaten Village. Based on the appearance of the displacement of some river channels, the Plasaten Fault is categorized as right lateral fault (Figure 11) with inferred stress in north-south direction. The Plasaten Fault in Matani Village branches off to the west forming Matani Fault. Besides the main Plasaten and Matani Faults, it is presumed that another main fault facilitating the rise of Linau Volcano Complex is Linau Fault in NE - SW direction.

705000 mE

8 f 40 14

41 42

710000 mE

43

Young lava flow 39

[b]

[e]

[a] [d]

6

[e]

Trace of paleo

13 38 10

37 [e]

[b]

f

[e]

9 lava flow paleo 5 Mahawu Volcano

Mt. MAHAWU Undulated area pyroclastic fall 12 of Mahawu

[c] [b1] 2

36

[b] 44 [c]

Mahawu upper flank

11 Mahawu lower flank

8 pyroclastic fall

34

35 [b6] 1

f 45 Mahawu foot pyroclastic fall

10

Structural terrace 9

15

7 3 [b]

49

[b]

[b2] 4[a]

4 30 31

33 32

48 Alluvial plain

3

f [e]

23 [b]

5 25 [d] 21 26

47 2

Young lava flow 46

15 f

Trace of paleo lava

flow of paleo Mahawu Volcano 28

20 1

0m 500m

1000m 0m

500m

1000m

16 19

17 18 29

27

705000 mE

Volcano

Legend:

[a]= crater lake

break-in-slope

boundary of landform unit f

710000 mE

fault

[b] [a] [c]

[d] [e]

[b]= crater floor [c]= crater wall [d]= crater rim

young lava field

old lava field

scarp

valley

a= subboundary

b= inferred

f inferred fault

fault lineament

[e]= volcanic cone paleo lava field 1-12 inferred Mahawu Volcanic growth

1-49 fault lineation order

fault scarp

Figure 9. A tentative geomorphological map of the interpretation result of landsat ETM+7 image combined with DEM IFSAR image.

1500

00 m

N

1450

00 m

N

1450

00 m

N

1500

00 m

N

Sout

h M

ahaw

u G

roup

N

orth

Mah

awu

Gro

up


F [e]

[c]

[e]

[a] [c]

[e]

[b] [c]

[c] [e]

[e]

[b] [e]

[b]

[e] [c] F

F

[e] [c]

[b]

[e]

[e]

[b]

[e]

[b] [e]

[e]

[b]

[b] [f]

[e]

[e]

[e] F [b]

Legend:

Volcano [b]

[a]= crater lake [b]= crater floor

0 1 2km

[a] [c] [d]

[e]

[c]= crater wall [d]= crater rim [e]= volcanic cone

sharp boundary

inferred boundary

F fault

F inferred fault fault scarp

Figure 10. Geomorphology of the Mahawu Volcano Complex and developing pattern of fault structure (the interpretation result of DEM IFSAR image).

The southeastern part unit occurs as a plateau with ± 974 m high asl., having a fine relief which is higher than the surrounding landforms. In the eastern and southeastern parts of the plateau, some minor fault scarps develop as part of a structural terrace landform (Figure 7). The landsat image ETM+7 composite RGB 457 combined with DEM IFSAR image show that the plateau landform is

faulted into two parts in NE - SW direction. The boundary of the two plateau parts is a fault scarp. The southern part of the plateau has subsided and is strongly dissected (Figure 7). Morphological elements such as fault scarp, fault terrace, fault valley, river offset, and plateau are a morphological type formed by a structural process or known as morphostructure.

1º20

’ 30

’ N

1º

22’1

2’ N

1º20

’ 30

’ N

1º

22’1

2’ N


124º49’ E 124º54’ E

Kinilo S Sinambe

Kentur Mahawu

1371

1324

1299

Rungku

Kakaskasen3

1328 939

896

S Lembuyang

1078

900

Kamasi

1262 1234

Kentur Masarang

S Sumalangka

Plasaten2

1237

S Ranowangko

S Plasaten

1216

R. Panuraan

Matani

S Raong

Masarang

124º49’ E

Legend:

Location of river arc shift Dextral strike-

slip fault

Road

124º54’ E

0 1 2 km

1078 Elevation point Contour line

Figure 11. A displacement of a river channel in the flank of the foot of Mount Mahawu indicates dextral horizontal fault movement.

Unit of Morphological Origin of the Linau Vol- cano Complex

Based on the aerial photograph interpretation, this unit is made up of the residual Paleo-Linau Volcano caldera where the young Linau, Kasuratan, and Tompusu volcanic cones develop inside. Some landforms of lava flows situated around Tounsaru Village and Remboken Sub-Regency are presumed as the results of the activities of Paleo-Linau Volca- no. Of the three young cones (Linau, Kasuratan, and Tamposu), it is only the young Linau volcanic cone having a wide crater lake. The rise of Kasuratan and Tompusu volcanic cones is presumed to have been facilitated by the Linau Fault in NE - SW direction.

Unit of Morphological Origin of Lacustrine Plain

This morphology unit has a low dip in the NW and almost flat towards SE, comprising fine materi- als (fine sand, silt, clay, and peat), swampy locally, with specific grass and other shrubs.

Lineament Pattern The morphologic lineament pattern of fracture

and or fault is well recorded by ETM+7 landsat image combined with DEM IFSAR image, especially for the Paleo-Mahawu lava flow deposit (Figure 9). The general direction of the fracture is mainly to NW - SW, some others are to NE-SW and N-S directions.

The N-S fault system (inferred) joining volcanic cones 2, 4, 5 (Figure 9) is not well identified on DEM IFSAR image (Figure 10). Therefore, the occurrence of N-S fault (presumed) is still doubtful, because no morphostructure indication that can be used as a guide.

Using the azimuth calculation method of frequency version, the lineament direction measure- ments (Table 1) and the analysis result of distribution of Mahawu regional fault lineation are plotted on a rosette diagram (Figure 12).

The result of lineament analysis (frequency version azimuth) plotting on the rosette diagram shows

Direction No. No. Measurement

50 Indonesian Journal of G

eology, Vol. 7 N

o. 1 March 2012: 39-54

Table 1. Measurement Data of Lineament Direction, Frequency, and Length of Mahawu Volcano and Its Vicinity

No. Measurement

Measurement

Direction

LINEATION DATA

Direction Azimuth Group Frequency Length (km) Length (%)

1 N302°E 19 N320°E 37 N336°E 0° - 10° 181° - 190° 2 2.450 7.99 2 N247°E 20 N315°E 38 N307°E 11° - 20° 191° - 200° - -

3 N247°E 21 N320°E 39 N307°E 21° - 30° 201° - 210° - -

4 N235°E 22 N314°E 40 N307°E 31° - 40° 211° - 220° - -

5 N250°E 23 N322°E 41 N325°E 41° - 50° 221° - 230° 1 0.300 0.978

6 N247°E 24 N319°E 42 N319°E 51° - 60° 231° - 240° 2 2.450 7.99

7 N188°E 25 N319°E 43 N351°E 61° - 70° 241° - 250° 5 3.650 11.9

8 N338°E 26 N314°E 44 N348°E 71° - 80° 251° - 260° 1 0.900 2.93

9 N275°E 27 N321°E 45 N234°E 81° - 90° 261° - 270° - - -

10 N320°E 28 N336°E 46 N010°E 91° - 100° 271° - 280° 1 1.150 3.75

11 N335°E 29 N333°E 47 N255°E 101° - 110° 281° - 290° - - -

12 N328°E 30 N313°E 48 N250°E 111° - 120° 291° - 300° - - -

13 N320°E 31 N317°E 49 N230°E 121° - 130° 301° - 310° 7 4.050 13.21

14 N303°E 32 N345°E 131° - 140° 311° - 320° 14 5.680 18.528

15 N335°E 33 N310°E 141° - 150° 321° - 330° 7 3.750 12.23

16 N322°E 34 N311°E 151° - 160° 331° - 340° 6 4.625 15.08

17 N322°E 35 N314°E 161° - 170° 341° - 350° 2 1.200 3.91

18 N325°E 36 N307°E 171° - 180° 351° - 360° 1 0.450 1.467 Total Length 30.655 100


N N 0

0

A B A

B C

F D E

W 12 9 6 3 3 6

9 1 2 E

F W 1 6 12 8 4

D

E C

4 8 1 2 16 E

1 80 S

18 0 S

Figure 12. A rose diagram of general direction of Mahawu regional fault lineation. A, B, and C are the main directions of fault lineation (N 3300 E – N 1500E) which are more active compared to fault lineation D, E, and F.

Figure 13. A rose diagram as the measurement result of length version azimuth of fault lineament showing an active fault zonation in Mahawu, ranging between N 1200 E - N 1600 E and N 3000 E - N 3400 E.

that the main fault direction in Mahawu area varies between N 3200 E - N 3400 E and N 1400 E - N1600 E (“A” and “B” on the rose diagram, Figure 12). This variation confirms to right-hand offset of some river channels at the west foot of Mahawu Volcano as the structural morphological feature of Plasaten Fault. Therefore, the stress direction is inferred to be from N - S. If the main stress direction is from N - S, “D” and “H” notations on the rose diagram represent the type of thrust with direction ranging between N 600

E - N 900 E and N 2400 E - N 2700 E. Moreover, “E”, “C”, and “F” notations on the

rose diagram represent normal fault direction ranging between N 1600 E - N 1700 E and N 3400 E - N 3500 E. Sinistral strike-slip fault is represented by fault lineation with direction between N 00 E - N 100 E and N 1800 E - N 1900 E with “G” notation on the rose diagram.

The result of lineament analysis (length version azimuth) on the rose diagram means that the activity zone of Mahawu Fault occurs on a range of N 1200

E - N 1600 E and N 3000 E - N 3400 E, while the most active fault at the present is inferred to occur within a direction between N 1350 E - N 3150 E or written by “A” notation (Figure 13). A fault categorized as potentially active (Cluff, 1972; in Slemmons, 1982a) is the one having a direction of N 650 E and N 2450

E inferred as thrust fault with “H” notation on the rose diagram (Figure 12), while in Figure 13, it is shown by “C” notation.

Poedjoprajitno et al. (2004) on a structural and distribution pattern map of active fault of the Manado Quadrangle included the studied area into the structural area of Manado domain with the Malalayang right lateral fault in the NE and Sonder upthrust dextral strike-slip fault in the SW. Both faults are included into the main faults in the Manado Quadrangle, acting as a divider of Tondano structural blocks; whereas the fault structure divided by the two big faults are called as subsidiary faults (Figure 14). The N-S subsidiary fault is located at the east of Mahawu Volcano Complex, categorized as a dextral strike-slip fault. A sinistral strike-slip fault crossing the Mahawu Volcano Complex (Poedjoprajitno et al., 2004) (Figure 14) is represented on the rose diagram with “D” notation (Figure 12). Therefore, it confirms to the abovementioned discussion that the division of Mahawu Complex into two groups is probably caused by the activity of sinistral strike- slip fault.

Both Effendi and Bawono (1997) on the Geo- logic Map of Manado Quadrangle and Lecuyer (1998) with SPOT image do not estimate the occurrence of this fault.

1º 0

7 ’0

0” N

1º

20

’00”

N

1º 0

7 ’0

0” N

1º

20

’00”

N


124º47 ’00” E

T

Ma ha wu Volcano

124º57 ’00” E

M

Laut S ulawe s i MANADO

Mahawu Volcano

PALU

GORONTALO To nda no

S ulawe s i Island

INDEK MAP

Mt. Linau

U Mt. To mpusu

Mt. Kas ura tan

Re mbo ke n

Kawa ngko an

Lake Tondano

ris

Ka ka s

S

Mt. RINDEKA

124º47 ’00” E 124º57 ’00” E

GEOMORPHOLOGICAL SYMBOL

FAULT SYMBOL ADDITIONAL DESCRIPTION ACTIVE FAULT SCARPS INACTIVE VOLCANOES

Left reverse slip fault

Dextral slip fault

Main fault

Subsidiary fault

a.

b. c.

a. Upper fault scarp line b. Fault scarp surface c. Lower fault scarp lin

a a. Crater rim

c b b. Crater wall c. Caldera plain

Right normal slip fault

Right reverse slip fault

Structural Block:

T Tondano Block

Active volcanoes:

Residual lava plug

S Soputan Block Volcanic cone with eruption crater

Residual volcanic cone

Simistral slip fault

Left normal slip fault

Right normal slip fault

Normal fault

M Manado Block

Studied area

Active volcanic cone

Lava flow

Figure 14. A part of domain of structural map and structural spread pattern of active fault structure, Manado Quadrangle, North Sulawesi (modified from Poedjoprajitno et al. 2004).


dIscussIon

Based on the remote sensing approach con-

fronted with the previous works, in the Mahawu Complex of the Quaternary age till the present time, at least there were two tectonic periods and two eruption periods.

Tectonics 1

The Tectonics 1 produced a morphostructure occurring as a plateau between Tumatatang and Ta- taran1 Villages, and some tectonic terraces located in the south of the plateau, southern Tomohon. The plateau is ± 3 x 4 km wide divided into two parts by a NE - SW fault (Figure 10), while in the eastern part it is bordered with the Plasaten Fault scarp in NW - SE direction. Lecuyer (1998) using SPOT image regionally interpreted the geological structure of North Sulawesi arm and plots a main fault crossing the south of Mahawu Complex in E - NE direction. The fault cuts the lower slope of the southern part of Klabat Volcano till the north coast of Lembeh Island in the south of Bitung. Through a SPOT image, Lecuyer (1998) did not detect a normal lateral fault in the Mahawu Volcano Complex. Therefore, it needs another image to cover the less accurate SPOT image in recording the detailed morphostructure data.

A fracture system (faulting) developing in the tectonic activities has facilitated the rise of magma to the surface which then continued to eruption 1.

Eruption 1

The construction of the Paleo-Mahawu Volcano and Paleo-Linau is shown by the residual diatrema and Paleo-Mahawu lava tongue around Masarang till Tataran 1 Villages and around the northeast of Lake Tondano.

Tectonics 2

Furthermore, the Paleo-Mahawu lava was densely jointed with the main direction of NW-SE. The density of the joint is very obvious especially around Masarang Village which then developed to become a fault in the NW - SE direction. These faults facilitated the rise of twelve volcanic cones in the Mahawu Complex (entering the second eruption stage). The condition can be proved by the volcanic cone lineament number 2, 4, and 5 along with number 6 and 7 (Figure 10). Lecuyer (1998) regionally

had never recommended the presence of a main fault in NW - SE direction. However, Siahaan et al. (2005) decided the occurrence of NW-SE major fault located between Mount Lokon and Mount Mahawu till cutting Lake Tondano in the west of Mount Kamingtan. Eruption 2

This stage produced small cones which could chronologically be followed from the cone number 2 till number 12 (Figure 9).

conclusIons

1. The development occurrence of volcanoes in the

studied area is dense enough, especially in the Mahawu Volcano Complex. The developments between the first and the next cones are not far to each other, and some cones follow a straight line. Some morphostructure elements present as the past tectonic tracks can still be recognized, such as fault scarp, structural terrace, plateau, and fault lineament. This volcanic complex condition tends to raise a thought that probably the development of Mahawu Volcanic Cone was facilitated by a fault (Mahawu Fault).

2. The dynamics of tectonic events and volcanic eruptions in the studied area were in order and have never occurred at the same time.

3. Tectonics and eruptions are interrelated. The first tectonic phase is proved by a wide plateau construction which was also followed by voluminous eruptions shown by the wide lava distribution. In the second phase, the tectonic intensity was lower which was also followed by the lower eruption intensity shown by the limited eruption product or by the narrower diameter of the volcanic cone bodies.

4. The remote sensing usages with different tak- ing modes have covered the lack of data with their recorded ones. Therefore, more than one remote sensing data are needed in interpreting earth sciences.

Acknowledgments---The author thanks Ir. Sidarto, M.Si. for valuable discussion, critique, and input, so this paper can better be written. Gratitude is also expressed to Dr. A.D. Wirakusumah.


references

Effendi, A.C. and Bawono, S.S., 1977. Geologic Map of

the Manado Quadrangle, scale 1:250.000. Geological Research and Development Centre, Bandung.

Fairbridge, R.W., 1981. The Concept of Neotectonic. Zet- schrift fur Geomorphologie, Neue Folge, Bd.631-7, Berlin-Stuttgart, 6pp.

Hall, R., 2001. Extension during Late Neogene collision in East Indonesia New Guinea. Journal of the Virtual Explorer, 4.

Lecuyer, F., 1998. Relations entre le volcanism actif et la tectonique actuelle dans la région de Tondano au nord de Sulawesi (Indonésie). Thèse Doct., Université Blaise Pascal Clermont-Ferrand, 163 pp.

Poedjoprajitno, S., Lumbanbatu, U. M., and Suryono, N., 2004. Dinamika Bentuklahan Semenanjung Manado Sulawesi Utara (Studi dengan pendekatan penafsiran potret udara dan citra satelit kaitannya dengan analisa pola struktur geologi). Jurnal Sumber Daya Geologi, 1(1), Pusat Survei Geologi, Bandung, p.145-166.

SEAN, 1987. Monthly Reports are organized chronologically of Mahawu. Bulletin, 12(7), 22 pp.

Siahaan, E.E., 2005. Tectonism and volcanism study in the Minahasa compartment of the north arm of Sulawesi related to Lahendong geothermal field, Indonesia. Pro- ceedings World Geothermal Congress, Antalaya Turkey, 5 pp.

Slemmon, D.B., 1982. A Procedure for Analyzing Fault- Controlled Lineaments and The Activity of Fault. In: O’Leary, D.W. and Earle, J.L. (Eds.), Proceedings 3rd

International Conference on Basement Tectonics, Inter- national Basement Tectonics Association, 33 pp.

Suharsono, Mulyana, H., Hidayat, S., and Marjiyono, 2007. Geomorphologic Map of Manado Area, scale 1: 100.000. Geological Research and Development Centre, Bandung.

Sumpena, A.D. and Djuhara, A., 1992. Pemetaan daerah bahaya G. Mahawu, Sulawesi Utara. Report No. 109,

Directorate of Volcanology, Bandung. Verstappen, H.Th., 2000. Outline of the geomorphology of

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Documents

Morphostructure Control Towards the Development of Mahawu