New Geological Overview of Gendol Hills, A Group of Isolated Hill Landform in the Southwestern Flank...

The New Geological Overview of Gendol Hills, a Group of Isolated Hill Landform on the Southwestern Flank of Merapi Volcano, Central Java, Indonesia

2nd AJ-BCEP Geo-Resources World Forum

By Alva Kurniawan Department of Geological Engineering Universitas Gadjah Mada Indonesia Email: [email protected]

Cambodia, December 16th, 2014

2nd AJ-BCEP Geo-Resources World Forum 2014

ABSTRACT

Gendol Hills is the name of a group of isolated hill landform which is located on Muntilan-Salam, southwestern flank of Merapi Volcano, Central Java, Indonesia. Recent studies of Gendol Hills has emerged controversy among geologist. There are three opinions related to the geology of Gendol Hills. The first opinion is the formation of Gendol Hills related to Merapi Volcano (van Bemmelen, 1949; Rahardjo et al., 1977; Camus et al., 2000). The second opinion is Gendol Hills as part of Menoreh Volcano (Murwanto & Subandrio , 1997; Prastistho & Soesilo, 1997; Prastistho & Soesilo 1998). The last opinion is Gendol Hills as volcanic remnant (Bronto, 2010; Commer et al., 2000; Newhall et al., 2000; Setijadji & Watanabe, 2009). Detailed geologic survey, petrography, and XRF were carried out to solve the controversy. The results of this research are very interesting. Upper part of Gendol Hills consists of rock which has similar characteristic with Merapi (High-K Hb-Px-basalt). Middle part of Gendol Hills consists of rock which has similar characteristic with Merapi (High-K Hb-Px-basalt) and Menoreh (Med-K Hb-andesite). The lower part of Gendol Hills comprises of unique rock (Complex Alkalinity Px-basalt with few olivines) which has not similar characteristic with both of Merapi and Menoreh. The unique rock was named as Gendol Basalt in this research. The controversy of Gendol Hills geology is reasonable since Gendol Hills contains three different groups of rock. The result measured structure on Gendol Hills suggest strong relation between Gendol Hills and Sentolo Fault. New idea about the geology of Gendol Hills was proposed in this research. Gendol Hills was formed by four stages. The first stage was the formation of Gendol Basalt. The second stage was burial of Gendol Basalt by Menoreh-type rock and volcanic product which possibly came from Merapi. The third stage was the further burial by volcanic product. The last stage was the uplifting of Gendol Basalt along with overlaid material formed hills morphology.


OUTLINE

• Introduction

• Geological Settings

• Methods

• Results

• Conclusions

• References


INTRODUCTION

Location of Study

Source: Google Earth


INTRODUCTION



INTRODUCTION


GENDOL HILLS

Grogolan Hill

Wukir Hill

Ndrakila Hill

Dali Hill

Guling Hill

Singobarong Hill

Pring Hill Sari Hill

Puguhan Hill

Gendol Hill Depok Hill

Tegal Hill

Lempong Hill

Tugel Hill


INTRODUCTION

• The geology of Gendol Hills is a controversy • Three opinions about the geology of Gendol Hills

• Gendol Hills was formed due to Merapi Volcano’s activity (van Bemmelen, 1949; Rahardjo et al., 1977; Camus et al., 2000)

• Gendol Hills was part of Menoreh Volcano (Murwanto & Subandrio , 1997; Prastistho & Soesilo, 1997; Prastistho & Soesilo 1998)

• Gendol Hills was a volcanic remnant (Bronto, 2010; Commer et al., 2006; Newhall et al., 2000; Setijadji & Watanabe, 2009)

• This research was conducted to solve the controversy


INTRODUCTION

Source: van Bemmelen (1949)


INTRODUCTION

after Murwanto & Subandrio (1997)


INTRODUCTION

Gendol’s Rock (Pliocene in age)

after Setijadji et al. (2008)


INTRODUCTION

Gendol

Menoreh

Sources: Tiede et al. (2005)


GEOLOGICAL SETTINGS

Map Source: Rahardjo et al. (1977)

Merapi Fault

Menoreh Fault

Sentolo Fault (Syafri et al., 2013)

Gendol Hills (Pliocene; Newhall et al., 2000)

Merapi Volcano (Quartenary)

Menoreh Volcano (Upper Miocene; Setijadji et al., 2008)


METHODS

• Geological survey • Petrographical analysis • XRF data analysis


RESULTS

Strike N 280°-300° E, Dip 24-29°, Dip Direction N 190 E to N 210° E


Merapi Fault

Menoreh Fault

Sentolo Fault (Syafri et al., 2013)

Gendol Hills

Merapi Volcano

Menoreh Volcano

RESULTS

Map Source: Rahardjo et al. (1977)


RESULTS

Tuffaceous sandstone

Open fabric lahar breccia

Tuff

Interbedded tuff, sandstone, and lappili tuff

Polimic breccia

Red and black tuffaceous claystone lens in lappili tuff with pumice intercalation

Open fabric breccia interfingering with closed fabric breccia

Lava flow

Upper part of Gendol Hills

Middle part of Gendol Hills

Lower part of Gendol Hills

1

2

3 4 5

6


RESULTS

1 2 3

4 5 6


RESULTS

6 mm

1 2 3

4 5 6

Aug Pl

Hb

Pl

Hyp Aug

Hb

Hb

Hb

Pl

Pl

Pl Aug

Hyp

Aug Hyp

Ol Pl

Hyp

Crossed Nikols


RESULTS

10 mm Crossed Nikols

Aug

Hb

Hb

Hyp

Pl

Pl

Hb

Hb

Pl

MERAPI BASALT MENOREH ANDESITE


RESULTS

TAS after Lebas et al. (1986)


RESULTS

Data were plotted on Alkalinity Diagram after Wheller et al. (1987), Merapi-Menoreh-Kulonprogo data from Setijadji et al. (2008)

Gendol’s Rock (Setijadji et al., 2008)


RESULTS

1. High K Hb-Px-Basalt – Fragment of lahar breccia

2. High K Hb-Px-Basalt – Fragment of polimic breccia

3. Med K Hb-Andesite – Fragment of coarser breccia

4. Med K Hb-Andesite – Fragment of coarser breccia

5. Complex K Px-Basalt – Fragment of less coarse breccia

6. Complex K Px-Basalt with olivine – Fragment of lava flow

1

2

3 4 5

6 Gendol Basalt


RESULTS

Tuffaceous sandstone

Lahar breccia with basalt fragment

Tuff

Interbedded tuff, sandstone, and lappili tuff

Polimic breccia with basalt fragment

Breccia with andesit fragments interfingering to breccia with basaltic fragments

Basaltic lava flow (Gendol Basalt)

Merapi’s Rock (?) Quaternary

Gendol Hills’s Rock (?) Pliocene

Menoreh’s Rock Fragments (?)

Red and black tuffaceous claystone lens in tuff lappili with pumice intercalation

Up

pe

r M

idd

le

Lo

we

r

Age data after Setijadji et al. (2008)


CONCLUSIONS

• Controversy about Gendol Hills is reasonable since Gendol Hills consist of different rock

• Measured structure available on Gendol Hills suggest strong relationship between Gendol Hills and Sentolo Fault

• Gendol Hills consist of three different group of rock such as: High K Hb-Px-Basalt (Probably belongs to Merapi’s

Rock) Med K Hb-Andesit (Probably belongs to Menoreh’s

Rock) Complex Alkalinity Px-Basalt with olivine (Gendol

Basalt) • Gendol Hills was formed by four stages


CONCLUSIONS

• Gendol Hills was formed by four stages 1. Formation of Gendol Basalt. 2. Burial of Gendol Basalt by rock which probably came

from Menoreh and Merapi. 3. Further burial by volcanic product. 4. The uplifting of Gendol Basalt along with overlaid

material formed hills morphology


REFERENCES

• van Bemmelen, R. W. (1949). The Geology of Indonesia, Vol IA, General Geology of Indonesia and Adjacent Archipelagoes. The Hague: Martinus Njhoff.

• Bronto, S. (2010). Geologi Gunungapi Purba, Publikasi Khusus. Bandung: Badan Geologi, Kementrian Energi dan Sumberdaya Mineral.

• Camus, G., A. Gourgaud, P.-C. Mossand-Berthommier, & P.-M. Vincent. (2000). An Outline of The Structural and Magmatological Evolution, with A Special Emphasis of the Major Pyroclastic Events. Journal of Volcanology and Geothermal Research, 100, p. 139-163.

• Commer, M., S. L. Helwig, A. Hordt, C. Scholl, & B. Tezkan. (2006). New Result on the Resistivity Structure of Merapi Volcano (Indonesia), Derived from 3D Restricted Inversion of Long-Offset Transient Electromagnetic Data. Geophys. J. Int., p. 142.

• Hall, R. (2009). Indonesia, Geology. South East Asia Research Group, p. 454-460.

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REFERENCES (Cont. 1)

• Kurniawan, A. (2011). Identifikasi Struktur Bedding Bentuklahan Berdasarkan Metode ERT Konfigurasi Double Dipole di Bukit Gunungsari Kecamatan Salam Kabupaten Magelang. Skripsi. Yogyakarta: Fakultas Geografi, Universitas Gadjah Mada.

• Lebas, M. J. &, R. W. Lemaitre, A. Streckeisen, B. Zanettin. (1986). A Chemical Classification of Volcanic-Rocks Based on Total Alkali Silica Diagram. Journal of Petrology, 27(3), p. 745-750.

• Murwanto, H. & A. Subandrio. (1997). Kajian Geologi dan Sejarah Terhadap Hipotesa Terbentuknya Perbukitan Gendol, Kabupaten Magelang, Jawa Tengah. Laporan Penelitian. Yogyakarta: UPN Veteran.

• Newhall, C.G., S. Bronto, B. Alloway, N.G. Banks, I. Bahar, M.A. del Marmol, et al. (2000). 10,000 Years of Explosive Eruptions of Merapi Volcano, Central Java: Archaeological and modern implications. Journal of Volcanology and Geothermal Research, 100, p. 9-50.

• Prastistho, B. & J. Soesilo. (1997). Data Baru Gunung Gendol, Muntilan Jawa Tengah. Laporan Penelitian. Yogyakarta: UPN Veteran.


• Prastistho, B. & J. Soesilo. (1998). Penafsiran Baru Terhadap Perbukitan Gendol, Muntilan Jawa Tengah. Abstraksi, Prosiding Pertemuan Ilmiah Tahunan XXVII, Ikatan Ahli Geologi Indonesia.

• Rahardjo, W., Sukandarrumidi, & H. M. D. Rosidi. (1977). Peta Geologi Lembar Yogyakarta, Skala 1:100.000. Bandung: Pusat Penelitian dan Pengembangan Geologi.

• Setijadji, L. D., D. H. Barianto, K. Watanabe, K. Fukuoka, S. Ehara, W. Rahardjo, et al. (2008). Searching for the Active Fault of the Yogyakarta Earthquake of 2006 Using Data Integration on Aftershocks, Cenozoic Geo-History, and Tectonic Geomorphology. The Yogyakarta earthquake of May 27, 2006, p. 4.1–4.18.

• Setijadji, L. D. & K. Watanabe. (2009). Updated Age Data of Volcanic Centers in the Southern Mountains of Central-East Java Island, Indonesia. Proceeding, International Conference Earth Science and Technology, B18, p. 1-7.



• Syafri, I., E. Budiadi, & A. Sudradjat. (2013). Geotectonic Configuration of Kulon Progo Area, Yogyakarta. Indonesian Journal of Geology, 8 (4), p. 185-190.

• Tiede, C., A. G. Gamacho, C. Gerstenecker, J. Fernández, & I. Suyanto. (2005). Modeling the Density at Merapi Volcano Area, Indonesia, Via the Inverse Gravimetric Problem. Geochemistry Geophysics Geosystems, 6 (9), p. 1-13.

• Wheller, G. E., R., Varne, J. D. Vaden, & M. J. Abbott. (1987). Geochemistry of Quaternary Volcanism in the Sunda-Banda Arc, Indonesia, and Three-Component Genesis of Island-Arc Basaltic Magmas. Journal Volcanology and Geothermal Research, 32, p. 137-160.

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