Design of Volcanic Educational-based Natural Tourism at Giriloyo,

Wukirsari Village, Imogiri District, Bantul Regency,

Yogyakarta-Indonesia

Sri Mulyaningsih

, Nur Widi Astanto Agus Tri Heriyadi

, Desi Kiswiranti

dan Muchlis

1,2,3

Geological Engineering of FTM-IST AKPRIND Yogyakarta,Jl. Kalisahak No. 28 Yogyakarta

Keywords: design, nature, tourism, ancient, and volcano

Abstract: Previous study determined Giriloyo was Tertiary ancient volcano. Dyke, lava, and andesitic breccia which

comprise this region strongly support the geological conditions, but the central facies of the ancient volcano

had already associated with so many cracks, so that need further geotecnical handlings. Design technic for

the geotecnical engineering is required to support it. This study aims to develop a geotechnical planning design

in the context of a potential landslide management. On the other hand, Giriloyo has a potential volcanic

educational-based tourism, supported with beautiful landscapes. The geotechnical planning design was

packaged in the form of educational-based natural tourism development. Research related to the purpose has

been carried out supported with geotechnical mapping to describe the carrying capacity. The results found

southwest-northeast normal faults (N290-320

E), north-south shear faults (0-15

E), and oblique normal faults

(northwest-southeast). All of them have potentially move to generate landslides. In anticipate the active rock

movements, sloping terraces into 25-30

to obtain safety factors of at least 1.5-1.8 have been designed. Thus,

the technical design to reduce the potential mass movements is addressed to obtain the natural cruising

tourism. The terraces are designed to expose 5 ancient volcanic stratums, i e. Central Facies Stratum, Dyke

Stratum, Lava with Hydrovolcanic Stratum, Lava with Collumnar Joints Stratum, and Agglomerates with

Autoclastic Breccia Stratum. Each of these stratums is connected with a multilevel educational pathway to

reduce burden on the land.

1 INTRODUCTION

An ancient volcano was identified at Giriloyo,

Wukirsari Village, Imogiri District, Bantul Regency,

Yogyakarta Special Region (Figure 1). There was a

long periode of superimposed volcanism, building

Kebo-Butak Formation and Nglanggeran Formation,

during Early to late Middle Miocene (Mulyaningsih

et al., 2019). The exposed volcanic rocks were

deformed generating active cracks that potentially to

move. A big landslide was noted in 17 March 2019,

remaining very wide sloping plane of 47

(Figure 2).

The slope was progressing to erode time by time, not

only by running water but also by the active fault.

Figure 1: Situation map of study area.

Mulyaningsih, S.

Design of Volcanic Educational-based Natural Tourism at Giriloyo, Wukirsari Village, Imogiri District, Bantul Regency, Yogyakarta-Indonesia.

DOI: 10.5220/0009435703490356

In Proceedings of the Second International Conference on Science, Engineering and Technology (ICoSET 2019), pages 349-356

ISBN: 978-989-758-463-3

349

Dykes, lava, tuff, and andesitic breccia compose

Nglanggeran Formation, that covering older volcanic

rocks of Kebo-Butak Formation, exposed at

Watulumbung, near the landslide. While Kebo-Butak

Formation consists of black color of layered tuff,

palagonite tuff and lapillistone. About 40-60cm of

calcareous sedimentarry rocks of claystone and

sandstone intersected the Kebo-Butak Formation and

the Nglanggeran Formation, having ages of N5-6

(Early Miocene). So that the Kebo-Butak Formation

must be older than Early Miocene.

Actually, those volcanic rocks should strongly

support the geological conditions, but a high density

of deformations and weathering, so it become fragile.

It needs further geotechnical treatments. Design

technic after the geotechnical study in early step is

necesarry to assist the geotechnical engineering.

This study aimed to design the geotecnical

engineering, related to the mass movements

management. By the presence of the interesting

volcanic rocks of the central facies ancient volcano,

design of the geotechnical engineering should be

composed curously and arty. Those purpose to obtain

Giriloyo ancient volcano to be community-based

geotourism.

Figure 2: Landslaide happened on 17 March 2019 at the meter of 720th (a) and the potential landslides along the track of

Giriloyo (b,c).

2 METHOD

The study was started by geotechnical mapping with

surface and subsurface investigation. Those mapping

described lithology distributions, faults (deformation)

and the potential creeps, slumps and falls. Surface

mapping carried out by tracking, measuring and

compiling the geological data. Subsurface mapping

used microseismic soundings. This research used H/V

method, also called Nakamura technique. The device

was seismometer Lennartz Electronic with brand LE-

ICoSET 2019 - The Second International Conference on Science, Engineering and Technology

350

3Dlite, to describe the HVSR spectrum ratio

(~microzonation), following the formula is:

Site response analysis is important in seismic hazard

assessment such in earthquake prone zones (Bray and

Rodriguez-Marek, 2004) and mass movements.

Tohwata (2008) argued that microzonation can

predict the response and behaviour of soil and rocks

by the external energy around the soils/rocks.

Fifteen spots have sounded using H/V method.

The microseismic device identifed vibration decays

along the identified surface fault planes. This method

was intended to identify the distribution of the faults

below the surface. Along with the broadband

seismometer measuring in the real time, the vibration

were recorded using the main sources of hits

sounding into the medium. The ground movements

were verified as a function of time in local site.

Analysis and synthesis of research data is based

on all data that is compiled using the library data

collection system, then synthesized using overlie

system. Calculation and simulation of slopes is

carried out manually and computed using ESRI and /

MapInfo Arc-GIS software.

3 RESULTS

3.1 Secondary Data

Secondarry study found stratigraphy of study area

from the bottom to the top were Kebo-Butak, Semilir,

Nglanggeran, Sambipitu, Oyo and Wonosari

Formations (Elliezer et al., 2019; Rahardjo et al.,

1995; and Surono et al., 1992). The third earlier

mention were volcanic constituents. Kebo-Butak

Formation and Nglanggeran Formation were exposed

at study area (Mulyaningsih et al., 2019).

3.2 Field Data Record

Surface field mapping described Kebo-Butak

Formation consists of black tuff intersects with

brecciated and compacted basalt lava in about 60m

thickness. Above them are less calcareous sedimen-

tarry rocks consist of laminated tuffaceous claystone

and sandstone in about 60cm. Creammy color of

coarse tuff and lapillistone lie on the sedimentarry

rocks. That volcanic rocks are coarsening upward and

replaced with intersectings of thick layers of breccia,

lava and lapillistone in pyroxene-rich basalt

composition. The thickness of the volcanic sequence

is ~200m. Above them are agglomerate, andesitic

lava and dike (Figure 3), which is interpreted as

Nglanggeran Formation, as a product of constructive

phase volcanism occured within central facies. The

last volcanic rocks are exposed in the top of the track,

i.e. in the meter of 1000th at Watulumbung (1927th).

These volcanic rocks strongly supported the

geological conditions, but the inflation and deflation

during the volcanism located at the central facies had

already associated with the deformations. Mapping

recognized geological structures, consist right normal

slip faults. There are south-west-northeast normal

faults (N290-320

E), north-south shear faults (0-

E), and oblique normal faults (northwest-

southeast) (Figure 4a-b). All of them have potentially

move to generate landslides.

3.3 Subsurface Mapping

The soil vulnerability index (Table 1, Figure 5)

displays soil and rocks stability; the greater the

vulnerability value the smaller the soil/rocks

structure. The high vibration decays of the lections of

micrometer are found at S04-S07 with 33.2-45.55kgs

in the elevation of 134-186m asl

(Table 1, Figure 5).

Those corners are described having small values of

the soil vulnerability index, so that interpreted as

unstable conditions (movable). Low vibration decays

are found at S012-S015; that zone are interpreted

having higher vulnerability index, so that calculated

as more stable blocks.

Table 1: The mass vulnerability index recorded during

microseismic measurements.

Sta-

tion

Coordinate (m) Eleva-

tion

(m)

Vulnerability

Index (kgs)

South East

S01. 434823 9124498 50 32.45

S02. 434778 9124451 104 23.68

S03. 434783 9124362 146 18.42

S04. 434786 9124312 145 45.55

S05. 435126 9124308 186 38.75

S06. 435044 9124366 137 37.56

S07. 434995 9124430 134 33.12

S08. 434922 9124450 115 27.49

S09. 434845 9124597 105 16.54

S010. 434881 9124518 94 17.77

S011. 434759 9124693 103 21.45

S012. 434920 9124600 157 19.87

S013. 435055 9124516 211 17.55

S014. 435238 9124359 244 15.45

S015. 435255 9124336 262 12.73

Design of Volcanic Educational-based Natural Tourism at Giriloyo, Wukirsari Village, Imogiri District, Bantul Regency,

Yogyakarta-Indonesia

351

Figure 3: The volcanic rocks exposed at study area; a. Agglomerate; b. Dike; c. Altered rocks with sulphid minerals, d.

Volcanic neck; and e. Lava with collumnar joints. Those are used to deposited very close to the crater or within the crater.

ICoSET 2019 - The Second International Conference on Science, Engineering and Technology

352

Figure 4a: The geological structure measured and computed at study area; the right normal slip faults.

Figure 4b: The distrubuted normal and right slip faults interpreted based on surface mapping and subsurface mapping using

dipole-dipole resistivity method and microseismic method.

Design of Volcanic Educational-based Natural Tourism at Giriloyo, Wukirsari Village, Imogiri District, Bantul Regency,

Yogyakarta-Indonesia

353

Figure 5. Map of vulnerability index at study area

interpreted from microseismic soundings.

3.4 Geomorphological Analyses

Geomorphology of study area are characterized by

gently to undulating topography sloping to 5-10

(at

Giriloyo), undulating to steeply at Cengkehan to

Nogosari (sloping between 10-30

), roughy elevated

hills near upper Nogosari, Watulumbung and

Grenjeng (~30-60

) and very steeply scarpments with

~60-70

on upper cliffes (Figure 6). The scarpments

are impending to fall (Figure 2). Creeps are

recognized along Grenjeng and lower Bukit Makbul

(Figure 2).

Figure 6: Digital Elevation Model (DEM) at study area.

4 DISCUSSION

Both surface and subsurface mappings recorded

active faults that potential moving at study area.

According to the data, whenever and at any time, such

in water saturated condition (in rainny sesion), it will

immediately collapse. Sloping will reduce the rate of

mass movement. Design for the hazard mitigation is

necesarry following the potential landslide/ rock falls.

It’s following the internal shear angle (ɸ), the density

of soil/rocks (γ),

cohesion (c) and water contents (ω).

Terraces will be also able to minimize the impact

caused by the mass movements. Technically,

designing terrace are following Figure 7.

The problems are how to manage the slope

stability, at once the kinds of strategic management in

protecting the geoheritage related to the Giriloyo-

Cengkehan’s ancient volcano phenomenon. Safe

storage with good aesthetics can be done through the

terracing. Making artistic terraces will not only

reduce the rate of mass movements but also add to the

aesthetics of the study area. Slope management can

be improved through risk analysis and systematic

assessment of slope stability.

Terrace morphometry has been analyzed based on

size, width (horizontal/horizontal interval (HI)) and

distance of each edges (vertical distance/vertical

interval (VI)). The terrace interval (HI) was assumed

according to the ease of anthropogen activities. The

size of terrace (VI) was calculated using the equation

of FAO (1986, in Blanco, 2008) as follows.  

∗

∗

= where as VI = vertical distance (m), Wb =

terrace width (m), hereinafter referred to as HI (m); S

= slope (%) and U = HI and VI ratio (using 0.75 for

manually built terraces (Blanco, 2008). So that it was

calculated that slopes of ≤20

is advisable a distance

to be 15m; while slopes of ~30

should be more than

10m distance. Bennett's criteria to calculate distances

between terraces are the more advisable being closely

related with experimental results in the area. Each

terrace consists of 5m for landfill, 5m bamboo parks

with landfilling to the top, the last 5m is keep to be

the original slopes. The overall slope has changed to

~20

in the teak garden, and ~35

around the 1.5-5m

and obtain safety factor of 1.5-1.8 for the sloping

terraces.

Bamboo park is chosen to be an effective soil

conservation at study area. Bamboo groves can

maintain land and groundwater stability. The dense

bamboo root system, which spreads in all directions,

is able to strengthen the stability of the land, and rain

water is easier to infiltrate into bamboo-covered soil.

Bamboo stems have advanced natural capillary,

which absorbs and stores water. Bamboo is able to

release 35% oxygen and is a very useful plant in terms

of reforestation of unproductive or degraded land.

Planting bamboo at study area as land conservation is

designed take place in the tarrace planes (Figure 7.a),

while the hillslopes are designed as a retaining walls

(Figure 7.b).

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354

Figure 7: Design for the terracing (grounding) the slopes in reducing mass movements

Figure 8: Design of the volcanic educational-based tourism at study area; as a conservation plan to manage landslide and

other potential mass-movements.

Design of Volcanic Educational-based Natural Tourism at Giriloyo, Wukirsari Village, Imogiri District, Bantul Regency,

Yogyakarta-Indonesia

355

5 CONCLUSIONS

Study area has potential mass-movements, such as

landslides. It threats to the civilization below the

slopes. But study area also potential with special

interest of ancient volcanological tourism. Land

conservaton and developing heritages (land, culture

and geology) is designed following the natural

resources and their potential movements. Terracings

are chosen to be developed at study area. Those are

, to obtain

slope stability under safety factor of 1.5-1.8.

ACKNOWLEDGEMENTS

Our greetings attend to the Ministry of Research

and High Education (RISTEKDIKTI) which was

funding the research by the first and second years of

Penelitian Terapan Unggulan Perguruan Tinggi

(PTUPT Scema) on 2018-2019. Special gratitudes

tend to the goverment of Bantul Regency, the head

and staff of Wukirsari, the Giriloyo and Cengkehan

communities, POKDARWIS, as well as FORCIB

ARYABHATA, who have provided the research

facilities, accompanied the research and gave a

variety of very warm supports. A big appreciation is

supervised to LPPM IST AKPRIND Yogyakarta for

the opportunities to reach the PTUPT grant.

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