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

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

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 with 80 m width. Its surface temperature reaches ± 65.50 C, and the estimated depth is ± 10 m. A weak Mount Mahawu is a stratovolcano with an eleva- explosive eruption expelling white smoke occurred tion of ± 1324 m asl., located at the east of Lokon on April 1987 (SEAN, 1987). Beforehand, in 1974 Empung active Volcano. One of the volcanic cones outpouring of mud with 0.5 m height took place. was cut off and developing to become a crater lake 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 was statistically processed to find out the general outpouring along the crater lake periphery having stress direction in the area. Supported by the result green water (Sumpena and Djuhara, 1992). of the aerial photograph interpretation and by finding The Mahawu Complex is located at the coordi- out the general stress direction, the probability of the nates of 1240 49’ - 1240 54’ E and 10 19’ 30” - 10 21’ occurrence of the structural morphology in Mahawu 18” N. Administratively, it is included into the Mina- Volcano Complex was determined. 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 regIonAl geology geological structure exists in the Mahawu Volcanic Complex. That is why the morphological structure The Mahawu Volcano Complex is situated in the of Mahawu Volcano is need to be discussed here to eastern part of the north arm of Sulawesi. The region find out its relation with the probability of the oc- is occupied by volcanic rocks composed of andesite currence of Mahawu Fault. bordered with basalt as the result of Lokon volcanic

activities. Both volcanoes are categorized as young stratovolcanoes of Quaternary age (Qv). The material Methodology produced is lava, bomb, lapilli, and ash. The oldest deposit around the studied area is Tertiary volcanics The research method was carried out by using re- (Tmv) (Figure 2). The studied area is included into mote sensing data, comprising landsat, panchromatic a volcanic arc due to the multiple subduction of the black-white aerial photograph, and IFSAR images. North Sulawesi subduction belt in the north, and of Morphological lineament was interpreted on landsat East Sangihe subduction belt located in the east and images which then the lineament interpretation result south parts of the north arm (Hall, 2001). The sub-

121° E 122° E 124° E 126° E

0 25 50 75 km MANADO

Sulawesi Sea . Mahawu Volcano

North Sulawesi Studied Area

Index Map 120º GORONTALO Studied Area S u la we s I Sea MANADO 0° 0°

GOR ONTALO Tomini Bay PALU Sula Islands

S u la we si Island Bu ru Sea

KENDARI

Central Sulawesi MAKAS AR

Ba n d a Sea 120º 121° E 122° E 124° E 126° E

Figure 1. Locality map of the studied area. Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 41 (S. Poedjoprajitno)

o 1 24 4 5 ’ E 1 25o 0 0 ’ E o o 1 30 ’ N 130’ N MANADO Qa l Qs La kit S a wa n ga n Ma u mbi Sulawesi Sea

Teling QTv Ka wa ng ko a n

Malalayang Qv

S a re n gs o n g

Mt. TETE MP ANGAN Qv Koka QTv

Ke n d e s

Mt. TATAWIR AN Ru me ng ko ko

Mt. LOKON Mt. MAHAWU

To n d a n o

QTv Tmv Mahawu Qv Ma ra wa s Volcano

Qs QTv Mt. KALUTA Lake Linau Mt. TOMBUS U Lake Ton da n o

o Ka s u ra ta n o 115’ N 1 15’ E 1 2 4 o 45 ’ E 1 2 5 o 0 0’ N

Legend:

Qs = Fluvial and lacustrine deposits Mount

Qv = Young volcanic rock Hot Spring Qtv = Tondano Tuff Studied Area 0 5 km Tmv = Tertiary volcanic rocks

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 regIonAl geoMorphology Mahawu, Lokon, Soputan, Klabat, Tongkoko, Tom- pusu, Lengkoan, and Batuangus Volcanic Complexes According to Suharsono et al. (2007) nearly 50 % (Figure 3). Based on the similar occurrences of the of the Manado area originated from a volcanic mor- volcanic distribution patterns in the North Sulawesi phology (Figure 4). The others were derived from arm and Sangihe subduction, it is inferred that the denudated, marine, fluvial, and structural volcanic Sangihe subduction belt more affected the formation morphology. The morphological origin is generally of volcanic cones than the North Sulawesi subduction. of young active volcano (Quaternary) of which its 42 Indonesian Journal of Geology, Vol. 7 No. 1 March 2012: 39-54

Mindano 6º N

0 130 260 km

Legend: Thrust fault of active fore-arc Talaud Subduction 4º N Islands Quaternary Volcano Sangihe Sulawesi Sea Maluku mid-oceanic ridge Studied Area 2º N

Mayu

Te rn a te North Arm Tidore

0º Una -una Goronta lo Maluku Basin Sea

To m in i Togia n Isl. Bay Bacan Sula Islands East Arm Ba ngga i Ta la b u Ma ngkole 2º S SULAWESI Island 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 Geomorphology of the Mahawu Volcano NE-SW direction beginning from Mount Lokon, Complex and the surrounding Volcanoes Mahawu, Klabat, Duabersaudara, Batunuang, and On the basis of the interpretation result of the Batuangus parasite. black-white aerial photograph plotted on a topo- The old volcanic tracks that can be observed graphical map of the Mahawu Volcano and the sur- among others are the old caldera walls of Tertiary rounding volcanoes, scale 1:50.000 (Figure 5) four Tondano Volcano shown by the series of Kawatak, morphological origins are recognized in the area. Kaweng, Kamingtan, and Kaluta Hills. Suharsono et al. (2007) classified the hill series as dissected Unit of Morphological Origin of the Mahawu longitudinal volcanic ridge (VD3), while Verstap- Volcano Complex pen (2000) called it as Tondano Escarpment. It is Aerial photograph interpretation indicates that presumed that a paleoparasitary developed in the the unit consists of six volcanic cone landforms north flank of old Tondano Caldera. At present, the developing close to each other, grouped, and they parasite is shown by a hill landform with dissected occur almost in one line. The eruption product of peak and wide plain in the middle part. Suharsono et each Mahawu volcanic cone is difficult to be differ- al. (2007) classified the hill landform with dissected entiated. However, on the landsat image combined peak as a medium dissected crater wall (VD7), with DEM, twelve volcanic cones can be identified while the wide plain in the middle was classified (Figure 6). All eruption material of this Mahawu as a medium dissected crater plain landform (VD8) Volcano Complex is presumed to cover most of the (Figure 4). residual body of Paleo-Mahawu volcanic cone. The Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 43 (S. Poedjoprajitno)

125°18’ E 124°45’ E

N N

1°48’ Nain Besar Island

S U L A W E S I S E A 1°48’

Ta ra b ita n

M1 1 00 1 00 M1 M4

P ula u M a nte ha g e S 2 J a ya ka rs a Isl. Ta la b e Ke c il 0 2 4 6 8 10 km S on s ilo M1 Isl. Ta la be Be s a r Eh e M4 10 0 M1 100 Likupang Strait Isl. Ta m p e ron g 1 00 M4 20 0 M1 M4 20 0 Isl. Nya ripa nja ng Mu nte P ulis a n Cape Isl. Na p od a on g Ku lu M4 La bu a n Ma rins ow 20 0 10 0 100 100 100 We ro t M4 D1 W in e ru Kija ng M4 S 1 1 00 100 F2 1 00 Mia ya 1 00 F2 A M1 Ba tu 1 00 M4 M4 Ka lin a un VD7 F2 L I N G K U P A N G M4 Ku a la Wa ris a 2 00 M1 S 2 Te e p 2 00 D2 M5 200 200 2 00 Isl. P o n te ng VD8 M4 Kim a jo Kua la Ara re n M1 Ku a la Ta la w a a n 20 0 D1 F2 Ka we ru a n Bolun g 500 Tih owo Ku a la P a na w P in e ne k 20 0 Boh owo VD6 VD3 Ba tu putih M1 VD1 VD2 10 0

500 4 00 3 0 0 10 0 Ku a la Ka yu la we b e s a r 20 0 20 0 Tiwan Cape VD3 M1 P in a s u ngkula n V2 Mo la s 5 00 M4 Be n gko l 10 0 Ma pa ng e t V6 V3 G un un g Ba tua n gu s F1 Ta t e lu 5 0 0 F1 V1 0 V4 V7 4 00 V1 MANADO P a nilih V5 4 00 G un un g P ina ng unia n VD6 G un ung Ta ng koko 100 Ma p a n ge t V2 200 Ku a la Tunduka MANADO BAY V2 3 00 G. D u a s a u d a ra Kua la Airpra ng F2 Kua la Ton da n o 300 10 00 V8 400 600 V1 50 0 We na n g V2 F1 G u nu ng Kla ba t Ka lon g a n Kua la Tika la 100 1000 1200

Kua la Wa lis uko Kua la Te nde ki 100 V3 400 V1 0 V1 1500 V3 B I T U N G 1400 Ta le ti 200 600 100 100 100 300 V3 Ku a la Tunduka V2 F1 M1 P a pus ung a n Ka le o s a n Airm a didi 200 Ku a la S e ge ra t VD5

300 Koh a 200 V3 200 S o s oa n R a n ora n o Le mb e h Island 400 400 200 300 M1 500 M3 400 200 Le m be a n P a ncu ra n Cape V2 Wa tu da m bo 300 200 M2

S a m piri S a wa ng a n Ka udita n 200 100 M2 M3 Dua Island 500 200 M1 Kua la S a wa n ga n 300 M6 1200 F1 Ke m a 2 Ke ntur V1 300 400 M3 Te t e m p a n g a n 400 500 M2 1500 700 1400 V1 1300 1200 M3 1100 V2 1000 1000 VD4 M1 700 Ka m a s i 700 Ku a la Lila n g S o s oa n Ra no wa ngko Wa le o VD3

700 V9 TONDANO 123° 124° 125° VD4 M1 1° 45’ 3° 5 0 50 0 6 0 0 m S os oa n Ra noa s a n S . To n d FL1 a n o 9 U 8

2°

7 Ma n a do MANADO 80 0 Ka la wira n 3 2 1° D. Lino w

B 1 00 0 1 D. Ta m p us u N

D. TO ND ANO S o s o a n B ulo D. P a n ga lo m bia n 50 0 1 000 Bulo Cape

6 N 50 0 0 ° S os oa n Ke we le wa ng ko 1 2 4 °45 ’ DAER AH P E METAAN 125°15’ 1 °1 5’ LIP UTAN F OTO UDARA MAP P ING AR EA AERIAL P HOTOGRAP H C OVE RAGE

1°15’

124°45’ E 125°18’ E 1°15’ Legend:

Volcanic cone Medium dissected volcanic cone Graben valley

Medium dissected volcanic flank Volcanic flank, upper part Tilting ridge

Medium dissected unseparated Volcanic flank, lower part volcanic series cone Alluvial plain

Medium dissected unseparated Intermontane plain volcanic series flank Flood plain

Laharic fan Laharic fan Beach sand

Solfatara field Residual hill Beach ridge

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

residual slope of the Paleo-Mahawu volcanic foot process, and now they left crater lakes (Figures 6 can still be seen especially in the southeastern part and 7) filled with water in rainy seasons (Figure 8). which is generally made up of trace of lava flow, The two of twelve recognized cones have the perfect gently sloping and jointed. Some of the Mahawu forms (Figure 9) occurring in the southern part of Volcano Complex cones have imperfect forms, pres- Mahawu Group. The perfect shape of the volcanic ent as dissected cones. It is assumed that the peaks cones can be formed, because the magma intruded of the cones had been damaged during eruption had been dormant before erupting. 44 Indonesian Journal of Geology, Vol. 7 No. 1 March 2012: 39-54

124º49’ E 124º54’ E N

N Kin ilo w 11 59 22’12’

1 22’12’ 22’12’

º 1 1 372 1 Ka ka s ke n 1 2 8

3 1328 93 9

7 4 Te m boa n 896

10 78 6

To m o h o n 5 126 2 12 34 Mt. Mahawu P la s a te n 1 1 237

12 16 Mahawu Volcano R.896 Ma ta ni Complex

Intra mountain

plain Ma s a ra ng PLASATAN FAULT VALLEY

760 683 Tum a ta ng t a ng 974 782 9 Plate a u 683

Kasoa ngan Ta ta a r a n 1

882 Lacustrine alluvial 68 3 9 84 plain La h e n d o n g Mt. Lin a u 6 88

13 783 R.902A-10 Lake Linau 12 To u n s a ru

899 Lake Tampusu

Lake Pangolumbian Linau Volcano Complex 11 1059 Mt. Ka s ura ta n 10

Ta m p u s u REMBOKEN N N 15’ 15’

15’ º 1 1º 124º49’ E 124º54’ Legend : 0 1 2 3 km

Volcano Lava fan Lava flow track Crater lake

11 Observation point Contour line Inferred fault R.902A-1 0 Central point

River channel Geomorphological 1059 Elevation point Road main unit boundary

Figure 5. The result of geomorphologic interpretation of Mahawu Volcano area and the surrounding volcanoes from the black- white aerial photographs (panchromatic). Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 45 (S. Poedjoprajitno)

705000 mE 710000 mE

150000

150000 Mt. MAHAWU

mN mN

145000 145000

Lake Linau

140000

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 Unit of Morphological Origin of Intramountain cone pattern is divided into two groups: the North Plain Structure and South Mahawu Groups (Figure 9 and 10). The The terminology of morphological structure or North Mahawu Group consists of series of five morphostructure firstly introduced by Gerasimov volcanic cones having craters and one residual pa- (1976) and Gerasimov and Mescherikov (1968; in leovolcanic body; whilst the South Mahawu Group Faibridge, 1981) is used to describe the landform comprises six cones. Based on the landform bound- topography constructed by neotectonic activities. ary distribution, the chronological construction of This morphology, generally, has a coarse relief each cone in each group can well be followed in but flat in some places, hemmed in amongst morpho- concomitance with the order number shown in Fig- logical units of Mahawu, Linau, and Lokon Volcano ure 9. Hence, due to the abundance of volcanic ma- Complexes (outside the studied area). This morpho- terial and repeatedly overlain each other lead to the logical unit surface is covered by very thick deposits presence of difficulties in identifying the structural of pyroclastic fall from the surrounding volcanoes, pattern since many structural morphologic indicator difficult to be differentiated. The boundaries with covered by the volcanic deposits. the surrounding morphological units among others

(the result of landsat ETM+ landsat of result (the Figure 7. A Tentative 46

150000 mN 140000 mN 145000 mN f

Legend: Gunungap Pyrodastic Pyroclastic Mahawu f

Lake Lake fall

Foot of Limau [a] geomorphological geomorphological fall

[a] crater [a] crater [b] crater [b] crater Linau

[d] crater [d] crater [c] crater crater [c] [e] volcanic [e] volcanic

Caldera wall trace Linau [b]

7 image and DEM IFSAR image). Indonesian Indonesian Journal of Geology, Vol. 7 No.1March 2012: 39-54 f [c] [c] floor lake wall rim Alluvial Paleo-volcano Paleo-volcano cone Plain [d]

[e]

f [b]

[e]

Alluvial

Plain Bk. of 705000 mE 705000 705000 mE 705000

map of Mahawu Volcanomap of and other volcanoes Young paleolava paleolava old lava old lava young lava Pyroclastic flow lava [e]

Plateau

fiow flow [b] fall fiow

]

Mt. Tompusu

Structural terrace pyroclastic Linau Old lava valley scarp terrace a [a]

fall Dissected

flow plateau [e]

of [b] [c]

[b] f

[b]

[b] [b]

[c]

[e] [d] boundary of of boundary unit landform Pyroclastic

1 a a [b] [b] f

=inferred =subboundary

[a]

f [b] [e]

flow f

Alluvial in its vicinity, Manado, SulawesiNorth 2

Paleo-lava plain Paleo - lava flow 710000 710000 710000 710000

f f

mE mE flow

Pyroclastic inferred inferred track lineament fault

Swampy fault Lake fall

4km Lake

140000 mN 145000 mN 150000 mN Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 47 (S. Poedjoprajitno)

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 Figure 8. One of Mahawu volcanic craters with Mount Lokon fault facilitating the rise of Linau Volcano Complex at the background. The camera faces west, location 8. is Linau Fault in NE - SW direction.

705000 mE 710000 mE

f 43 mN 40 14 42 [e] 41 Young lava flow 150000 mN 150000 150000 39 [b] [a] [e] 6 [d] Trace of paleo 10 13 38 [b] 9 lava flow paleo 37 [e] 5 Mahawu Vo l c a n o [e] f [c] Mt. MAHAWU [b1] 2 Undulated area 36 pyroclastic fall 12 11 of Mahawu [b] 44 North Mahawu [c] 7 Mahawu upper flank

11 Mahawu lower flank 35 8 pyroclastic fall [b6] 1 45 34 f 2 Mahawu foot [b] 4 pyroclastic fall 15 10 7 3 30 South Mahawu [b] 31 [b] 4 Structural terrace 9 [a] 33 32 49 23 [b] 24 3 5 22 25 f [d] 48 21 Alluvial plain [e] 26 47 Young lava flow 46 Trace of paleo lava 2 flow of paleo f Mahawu Volcano 28 15 20 1 27

19 29 16 mN 0m 500m 1000m 0m 500m 1000m 17 18 mN

145000 705000 mE 710000 mE 145000 Legend: Vo l c a n o

[a]= crater lake f fault [b] break-in-slope boundary of landform unit inferred fault [b]= crater floor young lava field f [a] [c] scarp a= subboundary [c]= crater wall old lava field fault lineament [d] valley b= inferred [e] [d]= crater rim paleo lava field [e]= volcanic cone 1-12 inferred Mahawu Volcanic growth fault scarp 1-49 fault lineation order

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

result result of DEMIFSARimage). Geomorphology VolcanoMahawu Figure 10. the of Complex de and IFSAR image showthat the plateau landform is DEM with combined 457 RGB composite ETM+7 terrace landform (Figure 7). The landsat image minor fault scarps develop as part of a structural eastern andsoutheastern pa ishigherthelandforms. than Inthe surrounding with ± 974 m high asl., ha 48 The southeastern part unit occurs as a plateau

145000 mN 150000 mN F olcano c l Vo Legend: [e] [a]

[d] [b] [c] [c]

Indonesian Indonesian Journal of Geology, Vol. 7 No.1March 2012: 39-54 [b]= crater floor

[c]= crater wall [a]= crater lake [d]= crater rim [e]= volcanic cone ving a fine relief which rts of the plateau, some [e] [e]

[a]

[b]

[c]

[e] [e]

[e] [c]

[e]

[c] [b]

[b] [b]

[b]

[c] [c] F [e]

inferred boundary inferred sharp boundary boundary sharp

[e]

[e] F [e] [c] [b]

[e] 0 as morphostructure. cal type formed by a structural process or known valley, river offset, and elements suchas fault scarp, fault terrace, fault is strongly dissected (Figure 7). Morphological Thesouthern part of the plateau hassubsided and boundaryofthe two plateau parts is afaultscarp. NE SW in - The into two parts direction. faulted [e] [b] [b]

[f]

[e] [b]

veloping pattern of fault st fault ofveloping pattern

[e] [e] [e]

F F 1 F

inferred fault fault fault scarp

plateau are a morphologi-

ructure (the interpretation ructure (the 2km

145000 mN 150000 mN South Mahawu Group North Mahawu Group

facilitated by the Linau Fault in NE -SW direction. Tompusu volcanicpresumedbeenhavecones is to having a wide craterriseof lake.having a The Tamposu), Linau cone volcanic young the is only it the threeOf conesno. young (Linau,Kasuratan,and with specific grass and other shrubs. als (fine sand, silt, clay, and peat), swampy locally, Unit of Morphological Origin ofLacustrine Plain as the results of the activities of Village andRemboken Sub-Regency are presumed landforms of lava flows situated around Tounsaru and Tompusu volcanic conesdevelop inside.Some VolcanoKasuratan,Linau, calderayoung wherethe this unit ismade upof the residual Paleo-Linau cano Complex Unit of Morphological of the Origin Linau Vol- movement. Figure 11. A displacement ofariver channel in the flank of and almost Based on the aerial photograph interpretation, interpretation, photograph aerial the on Based This morphology dipalowunitNW inthe has Morphostructure Control Towards the Development of Mahawu Volcanic Mahawu Sulawesi of North Development Complex, Morphostructure Control Towards the

1º20’ 30’ N 1º22’12’ N flat 124º49’ 124º49’ E

towards SE, comprising E Legend:

1078 Rungku

Lembuyang Elevation point river arc shift Dextral Dextral arc river shift Location Kinilo Kamasi

of R. Panuraan

Paleo-Linau Kakaskasen3

S Sinambe Kasuratan S Ranowangko Plasaten2

fine Matani

Contour

slip

materi- materi- (S. Volca- fault Poedjoprajitno) and S Plasaten strike-

line

the foot ofMountMahawuindi

Kentur Kentur sion azimuth) plotting on the rosette diagramazimuth)the showssion plotting on - SW,- some others areto NW mainly to is fracture the of direction general The for thePaleo-Mahawu lava age combined with DEM IFSARimage, especially ETM+7 landsat im- faultand iswellor recorded by Lineament Pattern rosette diagramrosette (Figure12). regionalMahawulineation fault of plotteda are on ments (Table distribution theof analysis result and 1) quency version,lineament the direction measure- a used asguide. morphostructurebecause no indication that can be currence of N-Sfault (presumed) is still doubtful, DEM IFSARimage (Figure 10). Therefore, the oc- cones 2,4,(Figure 5 9)is notwell identified on Kentur Kentur 1371 Mahawu The morphologicThe lineamentfracture pattern of The result of lineamentThe result of Using the azimuth calculation method fre- of fault system (inferred) N-S joiningThe volcanic

1324 Masarang

1328

1262 1078

Road

1299 1234 1216

1237

S Raong

1 0

Masarang NE-SW NE-SW 900 S Sumalangka cates dextral horizontalfault

939

analysis (frequency ver-

flow

and N-S directions. N-S and 896 deposit (Figure 9).

124º54’ 124º54’ 2 km E E

1º20’ 30’ N 1º22’12’ N 49

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

LINEATION DATA

Measurement Measurement Measurement Azimuth Group Frequency Length (km) Length (%) No. Direction No. Direction No. Direction

1 N302°E 19 N320°E 37 N336°E 0° - 10° 181° - 190° 2 2.450 7.99 Indonesian Journal of Geology, Vol. 7 No.1March 2012: 39-54 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 Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 51 (S. Poedjoprajitno)

N 0 N 0

A B A

D B C C E F D E F W 12 9 6 3 3 6 9 1 2 E W 1 6 12 8 4 4 8 1 2 16 E

1 80 18 0 S S

Figure 12. A rose diagram of general direction of Mahawu Figure 13. A rose diagram as the measurement result of length regional fault lineation. A, B, and C are the main directions version azimuth of fault lineament showing an active fault of fault lineation (N 3300 E – N 1500E) which are more active zonation in Mahawu, ranging between N 1200 E - N 1600 E compared to fault lineation D, E, and F. and N 3000 E - N 3400 E.

that the main fault direction in Mahawu area varies E inferred as thrust fault with “H” notation on the between N 3200 E - N 3400 E and N 1400 E - N1600 E rose diagram (Figure 12), while in Figure 13, it is (“A” and “B” on the rose diagram, Figure 12). This shown by “C” notation. variation confirms to right-hand offset of some river Poedjoprajitno et al. (2004) on a structural channels at the west foot of Mahawu Volcano as the and distribution pattern map of active fault of the structural morphological feature of Plasaten Fault. Manado Quadrangle included the studied area into Therefore, the stress direction is inferred to be from the structural area of Manado domain with the N - S. If the main stress direction is from N - S, “D” Malalayang right lateral fault in the NE and Sonder and “H” notations on the rose diagram represent the upthrust dextral strike-slip fault in the SW. Both 0 type of thrust with direction ranging between N 60 faults are included into the main faults in the Manado E - N 900 E and N 2400 E - N 2700 E. Quadrangle, acting as a divider of Tondano structural Moreover, “E”, “C”, and “F” notations on the blocks; whereas the fault structure divided by the rose diagram represent normal fault direction rang- two big faults are called as subsidiary faults (Figure ing between N 1600 E - N 1700 E and N 3400 E - N 14). The N-S subsidiary fault is located at the east of 3500 E. Sinistral strike-slip fault is represented by Mahawu Volcano Complex, categorized as a dextral fault lineation with direction between N 00 E - N strike-slip fault. A sinistral strike-slip fault crossing 100 E and N 1800 E - N 1900 E with “G” notation the Mahawu Volcano Complex (Poedjoprajitno et on the rose diagram. al., 2004) (Figure 14) is represented on the rose The result of lineament analysis (length version diagram with “D” notation (Figure 12). Therefore, azimuth) on the rose diagram means that the activity it confirms to the abovementioned discussion that 0 zone of Mahawu Fault occurs on a range of N 120 the division of Mahawu Complex into two groups E - N 1600 E and N 3000 E - N 3400 E, while the most is probably caused by the activity of sinistral strike- active fault at the present is inferred to occur within slip fault. a direction between N 1350 E - N 3150 E or written Both Effendi and Bawono (1997) on the Geo- by “A” notation (Figure 13). A fault categorized as logic Map of Manado Quadrangle and Lecuyer potentially active (Cluff, 1972; in Slemmons, 1982a) (1998) with SPOT image do not estimate the occur- 0 0 is the one having a direction of N 65 E and N 245 rence of this fault.

Sulawesi (modified from Poedjoprajitno structural of domain of 14. Apart Figure 52

1º 07 ’00” N 1º 20 ’00” N 124º47 124º47 FAULT P Mt. Kawa ngko A au ut La L Normal fault U Right normal slip fault Left normal slip fault Left reverse slip fault Right normal slip fault Dextralfault slip Simistral slip fault Right reverse slip fault slip reverse Right S

ulawe S R

SYMBOL ’00” INDEK ’00” E ulawe GORO I ND s i E s MAP Indonesian Indonesian Journal of Geology, Vol. 7 No.1March 2012: 39-54 Island

N i

an M E T

A ANAD

A Mt. Mt. V Mahawu

O olcano

L ADDITIONAL ADDITIONAL i n map and structural spread patternmap and activ of Structural Block: Structural

T M au S et al et Mt. Mt. Tondano Block Manado Block Soputan Block

Main fault Subsidiary fault . 2004). Ka s s Ka Studied area T DESCRIPTION GEOMORPHOLOGICAL GEOMORPHOLOGICAL

u S

r a

t an Re mbo Mt. Mt.

ACTIVE FAULT Active volcanoes: T a. a.

k o Lake c. e .b.

Volcanic cone with Active volcanic cone eruption crater pu b. Fault scarp surface a. Upper fault scarp line c. Lowerc. fault scarp lin SYMBOL Ma h a wu V wu a h Ma su T Ka ka ka Ka

ondano

SCARPS s

e faultstructure, Manado Quadrangle, North T

olcano o

nda nda INACTIVE V INACTIVE n

c o U a

r is

Residual volcanic cone Residual lavaplug Lava flow a. Crater rim Crater a. c. Caldera plain b. Crater wall

OLCANOES 124º57 124º57

M ’00”

’00”

1º 07 ’00” N 1º 20 ’00” N

Morphostructure Control Towards the Development of Mahawu Volcanic Complex, North Sulawesi 53 (S. Poedjoprajitno)

dIscussIon had never recommended the presence of a main fault in NW - SE direction. However, Siahaan et Based on the remote sensing approach con- al. (2005) decided the occurrence of NW-SE major fronted with the previous works, in the Mahawu fault located between Mount Lokon and Mount Complex of the Quaternary age till the present time, Mahawu till cutting Lake Tondano in the west of at least there were two tectonic periods and two Mount Kamingtan. eruption periods. Eruption 2 Tectonics 1 This stage produced small cones which could The Tectonics 1 produced a morphostructure chronologically be followed from the cone number occurring as a plateau between Tumatatang and Ta- 2 till number 12 (Figure 9). 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 conclusIons by a NE - SW fault (Figure 10), while in the eastern part it is bordered with the Plasaten Fault scarp in 1. The development occurrence of volcanoes in the NW - SE direction. Lecuyer (1998) using SPOT im- studied area is dense enough, especially in the age regionally interpreted the geological structure of Mahawu Volcano Complex. The developments North Sulawesi arm and plots a main fault crossing between the first and the next cones are not far the south of Mahawu Complex in E - NE direction. to each other, and some cones follow a straight The fault cuts the lower slope of the southern part line. Some morphostructure elements present as of Klabat Volcano till the north coast of Lembeh the past tectonic tracks can still be recognized, Island in the south of Bitung. Through a SPOT im- such as fault scarp, structural terrace, plateau, age, Lecuyer (1998) did not detect a normal lateral and fault lineament. This volcanic complex fault in the Mahawu Volcano Complex. Therefore, it condition tends to raise a thought that probably needs another image to cover the less accurate SPOT the development of Mahawu Volcanic Cone was image in recording the detailed morphostructure data. facilitated by a fault (Mahawu Fault). A fracture system (faulting) developing in the 2. The dynamics of tectonic events and volcanic tectonic activities has facilitated the rise of magma eruptions in the studied area were in order and to the surface which then continued to eruption 1. have never occurred at the same time. 3. Tectonics and eruptions are interrelated. The first Eruption 1 tectonic phase is proved by a wide plateau con- The construction of the Paleo-Mahawu Volcano struction which was also followed by voluminous and Paleo-Linau is shown by the residual diatrema eruptions shown by the wide lava distribution. and Paleo-Mahawu lava tongue around Masarang In the second phase, the tectonic intensity was till Tataran 1 Villages and around the northeast of lower which was also followed by the lower Lake Tondano. eruption intensity shown by the limited eruption product or by the narrower diameter of the Tectonics 2 volcanic cone bodies. Furthermore, the Paleo-Mahawu lava was 4. The remote sensing usages with different tak- densely jointed with the main direction of NW-SE. ing modes have covered the lack of data with The density of the joint is very obvious especially their recorded ones. Therefore, more than one around Masarang Village which then developed remote sensing data are needed in interpreting to become a fault in the NW - SE direction. These earth sciences. faults facilitated the rise of twelve volcanic cones in the Mahawu Complex (entering the second eruption Acknowledgments---The author thanks Ir. Sidarto, M.Si. stage). The condition can be proved by the volcanic for valuable discussion, critique, and input, so this paper cone lineament number 2, 4, and 5 along with num- can better be written. Gratitude is also expressed to Dr. A.D. ber 6 and 7 (Figure 10). Lecuyer (1998) regionally Wirakusumah. 54 Indonesian Journal of Geology, Vol. 7 No. 1 March 2012: 39-54

references Siahaan, E.E., 2005. Tectonism and volcanism study in the Minahasa compartment of the north arm of Sulawesi Effendi, A.C. and Bawono, S.S., 1977. Geologic Map of related to Lahendong geothermal field, Indonesia. Pro- the Manado Quadrangle, scale 1:250.000. Geological ceedings World Geothermal Congress, Antalaya Turkey, Research and Development Centre, Bandung. 5 pp. Fairbridge, R.W., 1981. The Concept of Neotectonic. Zet- Slemmon, D.B., 1982. A Procedure for Analyzing Fault- schrift fur Geomorphologie, Neue Folge, Bd.631-7, Controlled Lineaments and The Activity of Fault. In: Berlin-Stuttgart, 6pp. O’Leary, D.W. and Earle, J.L. (Eds.), Proceedings 3rd Hall, R., 2001. Extension during Late Neogene collision International Conference on Basement Tectonics, Inter- in East Indonesia New Guinea. Journal of the Virtual national Basement Tectonics Association, 33 pp. Explorer, 4. Suharsono, Mulyana, H., Hidayat, S., and Marjiyono, 2007. Lecuyer, F., 1998. Relations entre le volcanism actif et la Geomorphologic Map of Manado Area, scale 1: 100.000. tectonique actuelle dans la région de Tondano au nord Geological Research and Development Centre, Bandung. de Sulawesi (Indonésie). Thèse Doct., Université Blaise Sumpena, A.D. and Djuhara, A., 1992. Pemetaan daerah Pascal Clermont-Ferrand, 163 pp. bahaya G. Mahawu, Sulawesi Utara. Report No. 109, Poedjoprajitno, S., Lumbanbatu, U. M., and Suryono, N., Directorate of Volcanology, Bandung. 2004. Dinamika Bentuklahan Semenanjung Manado Verstappen, H.Th., 2000. Outline of the geomorphology of Sulawesi Utara (Studi dengan pendekatan penafsiran Indonesia. A case study on tropical geomorphology of a potret udara dan citra satelit kaitannya dengan analisa tectogene region, ITC-Division of Applied Geomorpho- pola struktur geologi). Jurnal Sumber Daya Geologi, logical Survey (AGS), The Netherlands, 212 pp. 1(1), Pusat Survei Geologi, Bandung, p.145-166. SEAN, 1987. Monthly Reports are organized chronologically of Mahawu. Bulletin, 12(7), 22 pp.