ArticlePDF Available

The geological evolution of Merapi volcano, Central Java, Indonesia

July 2012
Bulletin of Volcanology 74(5)

DOI:10.1007/s00445-012-0591-3

Authors:

Ralf Gertisser

Keele University

Sylvain Charbonnier

University of South Florida

Xavier Quidelleur

University of Paris-Saclay

Merapi is an almost persistently active basalt to basaltic andesite volcanic complex in Central Java (Indonesia) and often referred to as the type volcano for small-volume pyroclastic flows generated by gravitational lava dome failures (Merapi-type nuées ardentes). Stratigraphic field data, published and new radiocarbon ages in conjunction with a new set of 40K–40Ar and 40Ar–39Ar ages, and whole-rock geochemical data allow a reassessment of the geological and geochemical evolution of the volcanic complex. An adapted version of the published geological map of Merapi [(Wirakusumah et al. 1989), Peta Geologi Gunungapi Merapi, Jawa Tengah (Geologic map of Merapi volcano, Central Java), 1:50,000] is presented, in which eight main volcano stratigraphic units are distinguished, linked to three main evolutionary stages of the volcanic complex—Proto-Merapi, Old Merapi and New Merapi. Construction of the Merapi volcanic complex began after 170 ka. The two earliest (Proto-Merapi) volcanic edifices, Gunung Bibi (109 ± 60 ka), a small basaltic andesite volcanic structure on Merapi’s north-east flank, and Gunung Turgo and Gunung Plawangan (138 ± 3 ka; 135 ± 3 ka), two basaltic hills in the southern sector of the volcano, predate the Merapi cone sensu stricto. Old Merapi started to grow at ~30 ka, building a stratovolcano of basaltic andesite lavas and intercalated pyroclastic rocks. This older Merapi edifice was destroyed by one or, possibly, several flank failures, the latest of which occurred after 4.8 ± 1.5 ka and marks the end of the Old Merapi stage. The construction of the recent Merapi cone (New Merapi) began afterwards. Mostly basaltic andesite pyroclastic and epiclastic deposits of both Old and New Merapi (<11,792 ± 90 14C years BP) cover the lower flanks of the edifice. A shift from medium-K to high-K character of the eruptive products occurred at ~1,900 14C years BP, with all younger products having high-K affinity. The radiocarbon record points towards an almost continuous activity of Merapi since this time, with periods of high eruption frequency interrupted by shorter intervals of apparently lower eruption rates, which is reflected in the geochemical composition of the eruptive products. The Holocene stratigraphic record reveals that fountain collapse pyroclastic flows are a common phenomenon at Merapi. The distribution and run-out distances of these flows have frequently exceeded those of the classic Merapi-type nuées ardentes of the recent activity. Widespread pumiceous fallout deposits testify the occurrence of moderate to large (subplinian) eruptions (VEI 3–4) during the mid to late Holocene. VEI 4 eruptions, as identified in the stratigraphic record, are an order of magnitude larger than any recorded historical eruption of Merapi, except for the 1872 AD and, possibly, the October–November 2010 events. Both types of eruptive and volcanic phenomena require careful consideration in long-term hazard assessment at Merapi.

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RESEARCH ARTICLE

The geological evolution of Merapi volcano, Central

Java, Indonesia

Ralf Gertisser &Sylvain J. Charbonnier &Jörg Keller &

Xavier Quidelleur

Received: 22 January 2011 / Accepted: 3 March 2012 / Published online: 26 April 2012

#Springer-Verlag 2012

Abstract Merapi is an almost persistently active basalt to

basaltic andesite volcanic complex in Central Java (Indone-

sia) and often referred to as the type volcano for small-

volume pyroclastic flows generated by gravitational lava

dome failures (Merapi-type nuées ardentes). Stratigraphic

field data, published and new radiocarbon ages in conjunc-

tion with a new set of

K–

Ar and

Ar–

Ar ages, and

whole-rock geochemical data allow a reassessment of the

geological and geochemical evolution of the volcanic com-

plex. An adapted version of the published geological map of

Merapi [(Wirakusumah et al. 1989), Peta Geologi Gunun-

gapi Merapi, Jawa Tengah (Geologic map of Merapi

volcano, Central Java), 1:50,000] is presented, in which

eight main volcano stratigraphic units are distinguished,

linked to three main evolutionary stages of the volcanic

complex—Proto-Merapi, Old Merapi and New Merapi.

Construction of the Merapi volcanic complex began after

170 ka. The two earliest (Proto-Merapi) volcanic edifices,

Gunung Bibi (109±60 ka), a small basaltic andesite volca-

nic structure on Merapi’s north-east flank, and Gunung

Turgo and Gunung Plawangan (138± 3 ka; 135 ± 3 ka), two

basaltic hills in the southern sector of the volcano, predate

the Merapi cone sensu stricto. Old Merapi started to grow at

~30 ka, building a stratovolcano of basaltic andesite lavas

and intercalated pyroclastic rocks. This older Merapi edifice

was destroyed by one or, possibly, several flank failures, the

latest of which occurred after 4.8 ± 1.5 ka and marks the end

of the Old Merapi stage. The construction of the recent

Merapi cone (New Merapi) began afterwards. Mostly basal-

tic andesite pyroclastic and epiclastic deposits of both Old

and New Merapi (<11,792± 90

C years BP) cover the

lower flanks of the edifice. A shift from medium-K to

high-K character of the eruptive products occurred at

~1,900

C years BP, with all younger products having

high-K affinity. The radiocarbon record points towards an

almost continuous activity of Merapi since this time, with

periods of high eruption frequency interrupted by shorter

intervals of apparently lower eruption rates, which is reflected

in the geochemical composition of the eruptive products. The

Holocene stratigraphic record reveals that fountain collapse

pyroclastic flows are a common phenomenon at Merapi. The

distribution and run-out distances of these flows have fre-

quently exceeded those of the classic Merapi-type nuées

ardentes of the recent activity. Widespread pumiceous fallout

deposits testify the occurrence of moderate to large (subpli-

nian) eruptions (VEI 3–4) during the mid to late Holocene.

VEI 4 eruptions, as identified in the stratigraphic record, are an

Editorial responsibility: H. Delgado Granados

Electronic supplementary material The online version of this article

(doi:10.1007/s00445-012-0591-3) contains supplementary material,

which is available to authorized users.

R. Gertisser (*):S. J. Charbonnier

School of Physical and Geographical Sciences, Keele University,

Keele ST5 5BG, UK

e-mail: r.gertisser@esci.keele.ac.uk

S. J. Charbonnier

Department of Geology, University of South Florida,

Tampa, FL 33620-5201, USA

J. Keller

Institut für Geowissenschaften, Mineralogie-Geochemie,

Albert-Ludwigs-Universität,

79104 Freiburg im Breisgau, Germany

X. Quidelleur

Université Paris-Sud, Laboratoire IDES,

UMR 8148,

Orsay 91405, France

X. Quidelleur

CNRS,

Orsay 91405, France

Bull Volcanol (2012) 74:1213–1233

DOI 10.1007/s00445-012-0591-3

order of magnitude larger than any recorded historical erup-

tion of Merapi, except for the 1872 AD and, possibly, the

October–November 2010 events. Both types of eruptive and

volcanic phenomena require careful consideration in long-

term hazard assessment at Merapi.

Keywords Merapi .Stratigraphy .Chronology .

Radiocarbon dating .K–Ar dating .Ar–Ar dating .Merapi-

type volcanism

Introduction

Merapi volcano (110.442° E, 7.542° S) is one of the large

Quaternary central volcanoes of the Sunda arc in Indonesia,

which has been formed by the northward subduction of the

Indo-Australian Plate beneath the Eurasian Plate (Hamilton

1979). The ~3,000-m-high, basalt to basaltic andesite vol-

canic complex lies ~25 km north of the city of Yogyakarta in

Central Java and is surrounded by the geologically young

stratovolcanoes Merbabu, Telomoyo and Ungaran to the

north, and Sumbing, Sundoro and the Dieng complex to

the northwest (Fig. 1). One of Indonesia’s most active and

dangerous volcanoes, Merapi is best known for the genera-

tion of small-volume pyroclastic flows from gravitational

lava dome collapses (commonly referred to as Merapi-type

nuées ardentes). Over the past two centuries or more, the

volcanic activity of Merapi has been dominated by prolonged

periods of lava dome growth at the summit of the steep-sided

volcanic cone and intermittent gravitational or explosive

dome failures to produce pyroclastic flows every few years

[see Voight et al. (2000) for a detailed summary]. These have

posed a persistent threat to life, property and infrastructure

within the densely populated areas on the flanks of the volca-

no, as the catastrophic eruptive events in 2010 have once more

demonstrated (Gertisser et al. 2011).

In contrast to the well-recorded historical activity since

the late eighteenth century, Merapi’s prehistorical eruption

Merapi

Dieng Ungaran

Merbabu

Sumbing

Sundoro Telo mo yo

7° 0' S

7° 30' S

8° 0' S

25 km

Yogyakarta

110° 30' E110° 0' E

250 km

Java

Sleman

Klaten

Muntilan

Pakem

Kali Gendol

Kali Woro

Kali Bedok

Kali Pabelan

Kali Krasak

Kali Batang

Kali Putih

Kali Lamat

Kali Senowo

Kali Trising

Kali Boyong

Kali Kuning

Kali Pabelan

Kali Apu

Kali Blongkeng

G. Wungkal

Menoreh

Mountains

Klaten

Yogyakarta

Magelang

Yogyakarta

Surakarta

Merapi

G. Turgo G. Plawangan

G. Bibi

G. Gendol

Salam

Kali Bebeng

Cepogo

G. Dengkeng

G. Patukalapalap G. Kendil

G. Gadjah Mungkur

G. Batulawang

G. Pusunglondon

G. Selokopo

Duwur

110° 20' E 110° 25' E 110° 30' E 110° 35' E

05 km

7° 30' S 7° 35' S 7° 40' S

G. Selokopo

Ngisor

Fig. 1 Topographic sketch map of Merapi volcano, showing major

towns (filled circles) and volcano observation posts (black squares):

Kaliurang (K), Plawangan (P), Ngepos (N), Babadan (B), Jrakah (J),

Selo (S). Dashed lines indicate major drainages leading from the

volcano. The summit of Merapi and a series of hills (Indon. 0Gunung

(G.)) rising from the volcanic complex are shown by black triangles.

Empty triangles denote hills of the surrounding plain. The three-

dimensional inset maps show the location of Merapi north of the city

of Yogyakarta and nearby Quaternary volcanoes in Central Java. The

maps were generated using GeoMapApp

1214 Bull Volcanol (2012) 74:1213–1233

record is more fragmentary and it was not until recently that

a more detailed picture of the mid to late Holocene eruptive

history emerged from detailed stratigraphic and geochrono-

logical investigations (Bahar 1984;delMarmol1989;

Berthommier 1990;Andreastuti1999; Andreastuti et al.

2000; Camus et al. 2000; Newhall et al. 2000; Gertisser

2001; Gertisser and Keller 2003a). These studies have

shown that Merapi is a very young volcanic complex, but

age information on the older Merapi units has remained

scarce and many aspects of the overall volcanological and

structural evolution of Merapi continued to be controversial

(Camus et al. 2000; Newhall et al. 2000).

This paper provides a synopsis of research on the geo-

logical evolution of Merapi since the early descriptions in

the eighteenth century. Considerable advances in our knowl-

edge of Merapi and Merapi-style volcanism were made in

the 1990s, when the volcano was designated as 1 of 16

Decade Volcanoes by the International Association of Vol-

canology and Chemistry of the Earth’s Interior as part of the

United Nations’International Decade for Natural Disaster

Reduction. The research efforts resulted in a collection of

landmark papers published in a special issue “Merapi vol-

cano”(Journal of Volcanology and Geothermal Research,

vol. 100; 2000). Since then, new efforts have been under-

taken to refine the Holocene and earlier volcanic history of

Merapi. Here, we present new geochronological (

K–

Ar,

Ar–

Ar) and previously unpublished stratigraphic data

obtained by the authors that add to the few published U–Th

and K–Ar ages (Berthommier 1990; Camus et al. 2000)anda

unique set of ~150 radiocarbon ages that are available for the

volcano (Andreastuti et al. 2000; Camus et al. 2000;Newhall

et al. 2000; Gertisser and Keller 2003a; Gertisser et al. 2012).

Building on the pioneering and fundamental works of van

Bemmelen (1949,1956), Bahar (1984), Djumarma et al.

(1986), del Marmol (1989), Berthommier (1990), Andreastuti

(1999),Andreastutietal.(2000), Camus et al. (2000),

Newhall et al. (2000), Gertisser (2001) and Gertisser and

Keller (2003a,b), this paper reassesses the temporal evolution

and past eruptive history of this high-risk volcano in the light

of the new chronological data. A comprehensive set of whole-

rock geochemical data for all volcano stratigraphic units

allows additional insight into the concurrent geochemical

variations of Merapi through time.

Previous work

Merapi has been the focus of geological investigations ever

since the first direct observations of F. Van Boekhold, who

might have been the first European to reach the summit of the

volcano in 1786 (van Boekhold 1792), and the pioneering

descriptions of the volcano and its eruptions by Junghuhn

(1853–1854) and Verbeek and Fennema (1896). Systematic

observations of Merapi’s eruptive activity have existed since

the first half of the twentieth century, with important contri-

butions from Escher (1933a,b), Grandjean (1931), Hartmann

(1934a,b,1935a,b,1936), Kemmerling (1921), Neumann

van Padang (1933,1936), Reck (1931,1935), Taverne (1925,

1933)andvanBemmelen(1949), amongst others, compre-

hensively summarised by Voight et al. (2000).

Van Bemmelen (1949,1956) was the first to describe the

structure of the Merapi volcanic complex, distinguishing a

deeply eroded, older part of the volcano (Old Merapi) and

the active Merapi cone, characterised by a youthful morphol-

ogy and the classic shape of a stratovolcano when viewed

from the west (Fig. 2). He proposed that a catastrophic erup-

tion in 1006 AD led to the collapse of the western flank of the

older volcanic edifice along a major fault zone, known as the

Kukusan fault, replacing its summit with a horseshoe-shaped

crater and leaving an avalanche caldera (or Somma) rim high

on the volcano’s northern and eastern flanks. He further pos-

tulated that the eruption forced the shift of the centre of the

Mataram Kingdom from Central Java to East Java. According

to van Bemmelen (1949,1956), the active cone of Merapi has

formed on the remains of the older volcanic edifice after the

inferred flank collapse event, which, in his original definition,

marks the end of the Old Merapi stage.

Subsequent investigations have complemented van

Bemmelen’s early work and added important details on the

overall geological evolution and eruptive history ofMerapi, in

particular over the past few millennia. Bahar (1984)presented

an outline of the lava sequences of Merapi, establishing their

geochemical compositions and stratigraphic relationships.

Djumarma et al. (1986) quoted new archaeological evidence

indicating that the Mataram Kingdom moved to East Java

several decades earlier (i.e. in 928 or 929 AD) than proposed

by van Bemmelen, but found no archaeological indications for

a catastrophic eruption of Merapi in either 928–929 AD or

1006 AD. They identified several moderately large eruptions

of Merapi in the eighth to tenth century AD, speculating that

the Somma of Merapi might have been due to one of these

eruptions, although no direct evidence for a westward directed

landslide from Merapi was found. Wirakusumah et al. (1989)

published a geological map that identifies an Old and a Young

Merapi edifice, as recognised by van Bemmelen (1949,1956),

distinguishing, within the former, older pyroxene andesite

lavas of Gunung (Indon.0hill or mountain) Turgo, Gunung

Plawangan and Gunung Bibi (their Ml 1 lavas) from those that

constitute the Somma-Merapi in the northern and eastern parts

of the volcanic complex (their Ml 2 lavas, Fig. 3).

Del Marmol (1989) and Newhall et al. (2000) established

the terms Old Merapi and New Merapi to refer to the

Somma-Merapi edifice and the active Merapi cone, respec-

tively. Del Marmol (1989) considered the rocks that were

deposited before the aforementioned catastrophic eruption

or large eruptions as part of Old Merapi and those erupted

Bull Volcanol (2012) 74:1213–1233 1215

afterwards as part of New Merapi. Despite earlier specula-

tion that one (or several) of these eruptions might have

formed the Somma of Merapi (Djumarma et al. 1986),

Newhall et al. (2000) argued that these eruptions were all

from New Merapi and too small to form a large sector

collapse, as suggested by the morphology and structure of

the volcanic complex, although a smaller partial edifice

collapse of New Merapi may have occurred <1,130± 50

C years BP. The eruptions were significant enough though

todestroyorburytemples,possiblycontributingtothe

eastward migration of the Mataram Kingdom in 928 AD.

Subsequent eruptions of New Merapi in the twelfth to

fourteenth century AD might have continued to affect major

temples in the area (Newhall et al. 2000). Using their youn-

gest pyroclastic flow deposit found on the east side of

Merapi, dated at ~1,900

C years BP, Newhall et al.

(2000) proposed that the inferred large avalanche caldera-

forming collapse of Old Merapi occurred at around this

time, assuming that the newly formed Somma rim stopped

all later pyroclastic flows from travelling in an easterly

direction. The subsequent discovery of a dome collapse

pyroclastic flow deposit with an age of 1,590±40

C years

BP on the north-east side of Merapi, new finds of pyroclas-

tic deposits as old as 8,380± 230

C years BP in the western

sector and the apparent lack of any young debris avalanche

deposits (Gertisser 2001; Gertisser and Keller 2003a) cast

doubts on a flank collapse event as young as or even

younger than 1,900

C years BP [see Gertisser (2001) for

a detailed discussion].

Newhall et al. (2000) also suggested that Gunung Turgo

and Gunung Plawangan, two conspicuous, steep-sided hills

rising above the villages of Turgo and Kaliurang on Mer-

api’s south flank (Fig. 2), represent the erosional remnants

of a Proto-Merapi cone (Very Old Merapi; del Marmol

1989), considered to be an older part of the Merapi volcanic

complex, preceding van Bemmelen’s Old Merapi. This in-

terpretation has been supported by an U–Th disequilibrium

age of 40±18–15 ka obtained from a lava flow of Gunung

(a)

(b)

New Merapi

New

Merapi

Somma-Merapi

(Old Merapi)

G. Kendil

G. Batulawang

G. Pusunglondon (post-Somma-Merapi)

Lava dome

(Sept. 1997)

Lava dome

(July 2007)

Kali Gendol

Kukusan fault

(c)

(d)

New Merapi

Gunung Turgo

(Proto-Merapi)

Gunung Plawangan

(Proto-Merapi)

Gunung Bibi

(Proto-Merapi)

Merapi-Somma

(Old Merapi)

Lava dome

(Nov.1995)

Fig. 2 Field photographs illustrating the main eruptive stages and

volcanic edifices of the Merapi complex. aThe symmetrical stratocone

of New Merapi, as seen from the west (photo taken in Sept. 1997). b

New Merapi (left) and Somma-Merapi, the remnants of Old Merapi

(right), as seen from the south. The Gendol river valley (Kali Gendol),

filled with block-and-ash flow deposits from the 2006 eruption, is in

the foreground (photo taken in July 2007). cGunung Turgo and

Gunung Plawangan, the erosional remnants of a Proto-Merapi edifice,

and the recent Merapi cone (New Merapi), as seen from the village of

Kaliurang on Merapi’s south slope (photo taken in Nov. 1995). d

Gunung Bibi, another ancient (Proto-Merapi) volcanic structure ex-

posed on the volcano’s north-east flank, as seen from Gunung Pusun-

glondon near the summit of Merapi (photo taken in 2006)

1216 Bull Volcanol (2012) 74:1213–1233

Plawangan (Berthommier 1990; Camus et al. 2000), which

is significantly older than the oldest age of 9,630 ± 60

years BP obtained by Newhall et al. (2000) for an explosive

eruption of Old Merapi.

Berthommier (1990) and Camus et al. (2000) presented

an alternative history of Merapi divided into four main

periods—Ancient, Middle, Recent and Modern Merapi.

Their Ancient Merapi (40–14 ka) comprises Gunung Turgo

and Gunung Plawangan as well as the oldest deposits of the

Merapi cone sensu stricto. Thus, Ancient Merapi corre-

sponds to the Proto-Merapi and part of the Old Merapi cone

in the sense of van Bemmelen (1949,1956), del Marmol

Mapt-Mlt

Ml 1

500

1000

1500

2000

2500

Boyolali

0 5 km

Young Merapi volcano Surficial deposits

Rocks of Merbabu volcano

Tertiary rocks of the Menoreh Mountains

(incl. the Gendol and Wungkal Hills) and

the Southern Mountains

Faults

Merapi Other units and symbols

Old Merapi volcano

Ml 3Ml 4 Mapm

Ml 2

Mjp

Key: MI 1: Pyroxene andesite lava flows (of Gunung (= hill)

Turgo, Gunung Plawangan and Gunung Bibi); MI 2: Pyroxene

andesite lava flows; Mapt-Mlt: Old pyroclastic flow and lahar

deposits; Mjp: Pyroclastic airfall deposits (of Young and Old

Merapi); Mapm: Young pyroclastic flow and avalanche

deposits; MI 3: Prehistoric pyroxene andesite lava flows; MI 4:

Pyroxene andesite lava flows erupted since 1888 AD

7° 30' S

Sleman

Klaten

Muntilan

Pakem

Salam

Cepogo

Merapi

G. Bibi

G. Turgo

G. Plawangan

110° 20' E 110° 25' E 110° 30' E 110° 35' E

7° 40' S 7° 35' S

Fig. 3 Simplified version of the 1:50,000 geological map of Merapi

volcano published in 1989 (Wirakusumah et al. 1989), using the

original terminology for the two major volcanic edifices distinguished

and the volcanic products of the different geological units. Some of the

original subdivisions were combined for clarity of presentation. Con-

tours are shown in 100 m intervals. Map symbols as in Fig. 1

Bull Volcanol (2012) 74:1213–1233 1217

(1989) and Newhall et al. (2000). Middle Merapi (14.0–

2.2 ka) consists of two thick andesitic lava sequences,

namely the Batulawang series, dated at ~6.7 ka using U–

Th disequilibria, and the Gadjah Mungkur series. The older

Batulawang series is cut by the Kukusan fault and therefore,

per definition, part of Old Merapi. By contrast, the Gadjah

Mungkur series forms a younger cone inside the presumed

avalanche caldera and consequently belongs to New Mer-

api. Recent Merapi (2.2 ka–1786 AD) and Modern Merapi

(since 1786 AD) overlie the lava sequences of Middle

Merapi and are the main units that constitute the active

Merapi cone or New Merapi. According to Berthommier

(1990) and Camus et al. (2000), the products of Ancient

Merapi overlie an even older (pre-Merapi) volcanic struc-

ture, Gunung Bibi, a prominent hill on the north-east flank

of Merapi (Fig. 2). A K–Ar age of 670± 250 ka for a lava

flow from Gunung Bibi (Berthommier 1990; Camus et al.

2000) has supported this hypothesis, but the reliability of the

age was later questioned by Newhall et al. (2000), who

instead interpreted Gunung Bibi as a younger flank vent of

Old Merapi.

Methods and results

Fieldwork and sampling

Most of the detailed stratigraphic fieldwork at Merapi was

conducted in the late 1990s (Gertisser 2001), with further

information added and samples for K–Ar dating collected

since 2006. During the field campaigns, many stratigraphic

sections were measured primarily in the pyroclastic (at

lower elevations predominantly epiclastic) apron (Cas and

Wright 1987) around the volcano. Much of the fieldwork

concentrated on the relatively thin pyroclastic successions

on the interfluve areas on the middle and lower flanks of the

volcano. These include widespread pumiceous fall deposits

alternating with finer grained ash deposits of plume fall or

ash cloud origin and locally with coarser grained overbank

pyroclastic flow, surge and reworked deposits. Stratigraphic

sections and a first comprehensive set of radiocarbon ages

for these successions were presented by Newhall et al.

(2000), who discussed the explosive eruptive activity of

Merapi over the past 10,000 years. Andreastuti (1999) and

Andreastuti et al. (2000) were able to identify and correlate a

number of widespread fallout and surge layers all around the

volcano and to establish a detailed tephrostratigraphic

framework with a total of 18 informally named tephra for-

mations less than 3,000 years old. Rather than attempting to

present an accurate account of the younger eruption chro-

nology, which was the approach taken by Andreastuti

(1999) and Andreastuti et al. (2000), the stratigraphic sec-

tions (Fig. 4) aim to complement previous work by

providing detailed stratigraphic relationships and age con-

straints for the interfluve pyroclastic successions across the

southern, western and north-western sectors of Merapi,

where the density of observations had been comparatively

low. We were able to identify five distinct pumiceous fallout

layers in these sectors that are widespread enough to serve

as easily recognisable stratigraphic marker horizons in the

field and to correlate sections. The stratigraphic relations are

typically demonstrated by superposition of at least two of

the recognised tephra layers in various stratigraphic sec-

tions. According to their type sections (Fig. 4), these tephras

were informally named, from oldest to youngest, Paten I,

Paten II, Trayem, Jurangjero I and Jurangjero II (Fig. 4). The

two oldest tephra layers (Paten I and II) are older than any of

the widespread tephra layers of Andreastuti (1999)and

Andreastuti et al. (2000) and may therefore represent previ-

ously unidentified units. The Trayem tephra crops out in a

stratigraphic level just above the base of Candi Asu on the

western slope of Merapi and may correlate with a coarse

tephra fall deposit that occurs above the floor level of nearby

Candi Lumbung (Newhall et al. 2000; their unit 15, strati-

graphic section M in Fig. 4). Based on the available radio-

carbon age ranges, the Jurangjero I and II tephras are

tentatively correlated with the Deles and Selokopo tephra

(Andreastuti 1999; Andreastuti et al. 2000), respectively,

although both correlations are considered provisional, as

neither the Jurangjero tephras nor the three older tephra

layers were recognised in the northern and eastern parts of

the volcano. As such, correlations of stratigraphic sections

beyond the area shown in Fig. 4depend heavily on the use

of radiometric age dates. Age ranges for the exposed

sequences are provided by radiocarbon dates of deposits of

flow origin or palaeosols within the successions and the

recognition that deposits of Merapi older and younger than

~1,900

C years BP are geochemically distinct, having

medium-K (MK) and high-K (HK) character, respectively

(Gertisser 2001; Gertisser and Keller 2003a,b).

In contrast to the interfluve pyroclastic successions, thick

and often exceedingly complex sequences of intercalated

valley-ponded pyroclastic flow deposits, fluvial and laharic

debris and minor fallout deposits are exposed in the incised

river valleys cut deep into the pyroclastic and epiclastic

apron. The stratigraphic information that can be extracted

from these successions is rather fragmented, as reliable

correlations of deposits between drainages and with thinner

and finer grained deposits on the interfluves are difficult.

Still, it is emphasised that each primary pyroclastic deposit

(or sequence of deposits closely associated in time) repre-

sents a single eruptive event or episode. As such, these

snapshots of eruptive activity are crucial for establishing a

complete eruption chronology of Merapi. Charred or

carbonised plant material suitable for radiocarbon dating in

the deposits provides a means for integrating these

1218 Bull Volcanol (2012) 74:1213–1233

701 ± 35

0.5 m

1614 ± 36

Jurangjero II

Tephra

Jurangjero I

Tephra

Jurangjero II

Tephra

1 m

458 ± 32

525 ± 46

706 ± 22

1426 ± 40

1643 ± 55

Jurangjero I

Tephra

Jurangjero II

Tephra

0.5 m

242 ± 28

Jurangjero I

Tephra

Jurangjero II

Tephra

704 ± 24

Jurangjero II

Tephra

1 m

762 ± 26

Jurangjero I

Tephra

Jurangjero II

Tephra

Tra ye m

Tephra

? Paten I

Tephra

Tra ye m

Tephra

Jurangjero I

Tephra

0.5 m

Tra ye m

Tephra

Jurangjero I

Tephra

Paten II

Tephra

Paten I

Tephra

344 ± 23

Jurangjero I

Tephra

Jurangjero II

Tephra

0.5 m

Tra ye m

Tephra

Paten II

Tephra

1 m

Tra ye m

Tephra

Jurangjero I

Tephra

1 m

952 ± 52

989 ± 51

1005 ± 45

Kali Batang

(E-1)

Jurangjero / Kali Putih

(E-2)

Kali Blongkeng

(E-3)

Beruttegal / Keningar

(F-1)

Kajangkoso / Kali Senowo

(F-2)

Kali Senowo

(F-3)

Tra y em

(F-5)

Paten

(F-9)

Kali Pabelan

(F-7)

Gowoksabrang

(F-10)

Klakah

(G-1)

458 ± 28

Tra ye m

Tephra

Jurangjero I

Tephra

1 m

Paten II Tephra

Paten I Tephra

14C date

from section F-8, Candi Asu /

Kali Trising (Gertisser 2001)

2264 ± 73

3868 ± 47

4153 ± 37

1865 ± 80

1947 ± 105

2260 ± 30

0.5 m

Muntuk

(F-4)

Jurangjero I

Tephra

Jurangjero II

Tephra

Kinarejo

(B-3 (2))

Tra ye m

Tephra

Blocks (predominantly lava dome components)

Scoriaceous components

(cauliflower and breadcrust bombs)

Fine ash

Vesiculated, pumiceous components

Coarse ash

Lapilli (lithics)

Lapilli (vesiculated)

Lithologies / components of pyroclastic deposits

110° 20' E 110° 25' E

Merapi

05 km

F-1

F-3 F-5

F-7 F-9

F-10

G-1

E-2

E-3

F-4

7° 30' S 7° 35' S

? Trayem

Tephra

F-2

E-1 B-3

Brown, partly weathered

ash/lapilli tuff; soil

Other deposits / units

Fluvial deposit (reworked)

Dark, humic-rich palaeosol Degassing pipes (lapilli pipes)

Lamination

Other symbols

Cross-bedding / cross-lamination

Conv. 14C age (years BP)242±28

Charred wood; charcoal

Key

Section shortened

MK/HK Geochemical character:

MK = Medium-K; HK = High-K

Fig. 4 Correlation of the mid to late Holocene pyroclastic successions in the southern,

western and north-western sector of Merapi (after Gertisser 2001). Prominent tephra layers,

which can be traced over large areas on the southern and western flanks and serve as

important stratigraphical marker horizons are highlighted using the informal names intro-

duced by Gertisser and Keller (2000) and Gertisser (2001)

Bull Volcanol (2012) 74:1213–1233 1219

successions into the stratigraphic record (Gertisser 2001;

Gertisser and Keller 2003a). In the western sector, the

deposits in the deep valley sides extend back to at least

8,380±230

C years BP (Supplementary Table 1)and,

thus, expose units that are significantly older than those on

the interfluves. The latter date back to 2,260± 30

C years

BP in the area of Kali Batang and Jurangjero/Kali Putih

(stratigraphic sections E-1 and E-2; Fig. 4), where they form

the base of the “Gumuk ashes”of Camus et al. (2000). The

maximum age for the interfluve deposits in the western

sector may be inferred from a palaeosol at the base of the

Paten I tephra near Candi Asu/Kali Trising dated at 4,153±

C years BP (Gertisser 2001; Fig. 4; Supplementary

Table 1).

Radiocarbon database

In contrast to the few published ages obtained by other

radiometric dating methods, an exceptional set of ~150

radiocarbon ages is now available for Merapi that extends

back to 11,792± 90

C years BP. These data were gathered

over many years by different researchers and research

groups. Larger sets of

C data can be found in the PhD

theses of Berthommier (1990), Andreastuti (1999)and

Gertisser (2001) and published in Andreastuti et al. (2000),

Camus et al. (2000), Newhall et al. (2000), Gertisser and

Keller (2003a) and Gertisser et al. (2012). A compilation of

these data is presented in Supplementary Table 1. Most of

the available radiocarbon ages were determined on charcoal

from carbonised plant material incorporated in pyroclastic

flow and associated ash cloud deposits. Other dated material

includes wood fragments in lahar deposits, charcoal par-

ticles from carbonised rootlets in soil horizons and dark,

organic-rich bulk soil samples. Most dated samples appear

to be from unknown parts of trees, although, where avail-

able, small-diameter twigs and the outer parts of larger

branches and tree trunks were used (Newhall et al. 2000;

Gertisser and Keller 2003a). Still, some samples may have

come from interior (i.e. older) parts of trees and, therefore,

the reported ages should generally be regarded as maximum

eruption ages. Analytical methods used for radiocarbon

dating include both conventional counting techniques and

accelerator mass spectrometry at different laboratories. All

published ages are expressed as conventional radiocarbon

years BP (before 1950 AD, Stuiver and Polach 1977) and,

thus, are directly comparable. However, different calibration

curves were used by different authors to convert the con-

ventional radiocarbon ages to calibrated ages, and different

methods were adapted for reporting calibrated ages and

ranges. In order to compare these data, all conventional

C ages were recalibrated using Calib Rev 5.0.1 (Stuiver

and Reimer 1993; Stuiver et al. 2005). All but the oldest

sample were calibrated with the Southern Hemisphere

calibration curve (SHCal04), which extends back to

11,000 cal years BP (McCormac et al. 2004). For the oldest

sample, the IntCal04 calibration curve (Reimer et al. 2004)

was used. Calibrated age ranges are 1-sigma and given both

in “cal years BP”(before 1950 AD) and in “cal years AD/

BC”. In the (standard) case of two or more intersections

with the

C calibration curve, the entire calibrated age

range is reported (Supplementary Table 1).

K–

Ar and

Ar–

Ar dating

For groundmass K–Ar dating, nine lava samples were care-

fully selected on the basis of sample freshness, as deter-

mined by petrographic examination of thin sections

(Table 1). The Cassignol–Gillot technique was chosen for

K–Ar dating, as it allows accurate age determination of both

ancient and young lavas, even with low radiogenic Ar

content (Cassignol and Gillot 1982; Gillot and Cornette

1986; Gillot et al. 2006). In order to remove any possible

gain of argon (excess argon) from fluid circulation or xen-

oliths and any possible loss of potassium due to weathering,

a careful mineralogical separation was performed. Based on

phenocryst size, jaw crushing and sieving was carried out in

the 125–250-μm grain size fraction. Grains were ultrasoni-

cally washed with deionised water and a 10 % nitric acid

solution. Heavy liquids were used to keep the groundmass

in a narrow density range of typically 2.80–2.85 g/cm

for

basalts, 2.70–2.75 g/cm

for basaltic andesites and 2.60–

2.65 g/cm

for andesites. Finally, residual minerals were

removed from the groundmass with a magnetic separator.

Potassium and Ar were measured in different aliquots of

the same groundmass separate at the Laboratoire de Géo-

chronologie Multi-Techniques (Orsay, France). Potassium

was measured by flame emission spectroscopy and Ar by

mass spectrometry using a 180° multi-collector instrument

similar to that described in Gillot and Cornette (1986). The

relative uncertainty of the K measurement is ~1% over a

range of K contents between 0.1 and 15.0 %. The detection

limit of the radiogenic Ar content is 0.1 % (Quidelleur et al.

2001), which makes the Cassignol–Gillot technique espe-

cially suitable for the dating of very young rocks (e.g. Gillot

et al. 2006). Such a performance can be achieved because of

the stable analytical conditions of the small-volume mass

spectrometer used, which allows an accurate atmospheric

correction by direct comparison of the dated sample with an

air aliquot measured under the exact same Ar pressure

conditions. The calibration of the system is obtained by

systematic measurements of an air pipette, which is routine-

ly compared to the GL-O standard with its recommended

value of 6.679×10

at/g of radiogenic

Ar (

Ar*, Odin et

al. 1982). This calibration introduces an additional relative

uncertainty of 1 %, which leads to a total relative age

uncertainty of ~1.4 % for samples older than ~1 Ma. For

1220 Bull Volcanol (2012) 74:1213–1233

younger samples, the relative uncertainty due to the atmo-

spheric correction dominates and can account for up to

100 % for zero-age samples (with

Ar* of 0.1 %). Potassi-

um and Ar were analysed at least twice in order to obtain a

reproducible age within the range of error determined from

periodic, replicate measurements of dating standards, such as

ISH-G, MDO-G (Gillot et al. 1992) and GL-O (Odin et al.

1982). For the age calculations (Table 1), the decay constant

and K isotopic ratios of Steiger and Jäger (1977)wereused.

All uncertainties quoted herein are given at the 1-sigma level.

In addition to the K–Ar age determinations, we also

attempted to date amphibole (hornblende) crystals from a

volcanic breccia near the top of Gunung Bibi using the Ar–

Ar method. For this purpose, amphibole grains were sepa-

rated from the lava clasts by gently crushing the rock sam-

ples followed by sieving and finally hand picking of

amphibole crystals under a binocular microscope. For the

inferred young volcanic mineral separate, “laser step-

heating”experiments were performed, where ~10 mineral

grains were melted with increasing laser power using a

focused infrared laser-automated argon extraction system

connected to a MAP 21550 mass spectrometer at The Open

University’s Argon-Argon and Noble Gas Research Labo-

ratory. Obtaining an accurate and precise age of the Gunung

Bibi amphibole separate was difficult, and the best age we

obtained yielded a large analytical uncertainty (109 ± 60 ka;

Kelley, personal communication 2004). The significance of

this age is discussed below.

Whole-rock geochemistry

Our Merapi whole-rock dataset currently comprises 205

samples that were analysed for major elements by

wavelength-dispersive X-ray fluorescence (XRF) spectrom-

etry at the Universität Freiburg (Germany) and The Open

University (UK), using a Philips PW 2404 and an Applied

Research Laboratories 8420+ XRF spectrometer, respective-

ly. Most of these samples were also analysed for a number

of trace elements (Ba, Rb, Sr, Zr, Ni, Cr, Co, V) with the

same technique. Before analysis, exposed portions and

weathered surfaces of the samples were carefully removed

and, where possible, fresh interior slabs of lavas and pyro-

clasts were processed. All samples were ground in an agate

mill. Major and trace elements were determined on fused

discs and pressed powder pellets, respectively. Reproduc-

ibility and accuracy for major elements are better than 1 %

relative. The analytical uncertainty for trace elements varies

from 1 to 10 ppm, depending on the specific element.

Accuracy and precision were monitored using several inter-

national rock standards. LOI was determined by weight

difference at heating the samples to 1,050°C for 90 min

and is the total effect of dehydration (loss of weight) and

oxidation (gain of weight). The complete dataset for sam-

ples from the main volcano stratigraphic units (see below) is

listed in Supplementary Table 2. The Merapi rocks range in

composition from 48.3 to 57.3 wt.% SiO

, with most sam-

ples falling into the basaltic andesite range. Merapi may

Table 1 K–Ar ages of Merapi lavas

Sample Sample location Latitude/longitude Map unit

K (%)

Ar* (%)

Ar* (at/g) Age± 1σ(ka) Mean age ± 1σ(ka)

M07-001 G. Pusunglondon

07°32.2326′S/110°27.1669′E 6 2.829 0.17 8.577E+09 2.9±1.7

0.03 1.351E+09 0.5± 1.6 1.7± 1.7

M07-002 E of G. Batulawang 07°32.3742′S/110°27.6094′E 3 2.459 0.39 1.492E+10 5.8± 1.5

0.28 9.743E+09 3.8± 1.4 4.8± 1.5

01ME07 N part of Somma-Merapi 07°30.6412′S/110°26.2661′E 3 2.503 0.54 2.064E+10 7.9±1.5

0.67 2.414E+10 9.2± 1.4 8.6± 1.4

M07-004 N of Deles 07°33.6119′S/110°27.8124′E 3 2.616 1.35 2.993E+10 11.0±0.8

1.49 2.831E+10 10.4±0.7 10.7± 0.8

M06-024 G. Batulawang 07°32.3154′S/110°27.4360′E 3 2.645 3.00 6.906E+10 25.0± 0.9

3.59 6.451E+10 23.4±0.7 24.2± 0.8

M07-005 E of G. Bibi 07°31.7590′S/110°28.6935′E 3 2.834 2.99 9.077E+10 30.7± 1.1

4.26 8.445E+10 28.5±0.8 29.6± 1.0

M06-032 G. Kendil 07°33.5525′S/110°27.1739′E 3 2.305 3.90 7.014E+10 29.1 ± 0.9

3.24 7.580E+10 31.5±1.1 30.3± 1.0

M06-002 G. Turgo 07°35.1401′S/110°25.6093′E 2 2.163 7.96 3.210E+11 142.1± 2.7

4.21 3.019E+11 133.6± 3.7 138± 3

M06-003 G. Plawangan 07°35.1905′S/110°25.6049′E 2 2.058 5.28 2.856E+11 132.9± 3.1

4.26 2.958E+11 137.6± 3.8 135± 3

Keyed to Fig. 5. For sample locations, see Fig. 6

GGunung (Indon.0hill or mountain)

Bull Volcanol (2012) 74:1213–1233 1221

therefore be regarded as a predominantly basaltic andesite

volcano. The implications of our whole-rock dataset for the

overall geochemical evolution of the volcanic complex are

discussed below.

500

1000

1500

2000

2500

Boyolali

New Merapi

Old Merapi 3

Proto-Merapi 1 2

Merapi - Volcano-stratigraphic units

Cenozoic rocks of the Menoreh

and Southern Mountains

Faults

Other units and symbols

Merapi - Eruptive stages / edifices

Rocks of Merbabu volcano

7° 30' S

7° 40' S 7° 35' S

Sleman

Klaten

Muntilan

Pakem

Salam

Cepogo

Merapi

G. Bibi

G. Turgo

G. Plawangan

Surficial deposits

HPS*

Pyroclastic-flow and lahar deposits

[< 11,792 ± 90 14C y BP (14C)]

Pyroclastic-fall deposits

[< 11,792 ± 90 14C y BP (14C)]

Lava flows of the Somma-Merapi

[30.3 ± 1.0 ka; 29.4 ± 1.0 ka; 24.2 ± 0.8 ka; 10.7 ± 0.8 ka; 8.6 ± 1.4 ka; 4.8 ± 1.5 ka (K-Ar)]

Lava flows of Gunung Turgo and Gunung Plawangan

[138 ± 3 ka; 135 ± 3 ka (K-Ar)]

Lava flows of Gunung Bibi

[109 ± 60 ka (Ar-Ar)]

Lava domes of the recent episode

[1888 AD - Present (direct observation and historical accounts)]

Recent and mostly historical pyroclastic-flow and lahar deposits

[? ≤ c. 1550 AD - Present (historical accounts and 14C dating)]

Young (post-Somma-Merapi) lava flows

[1.7 ± 1.7 ka (K-Ar)]

* HPS = Holocene Pyroclastic Series

0 5 km

110° 20' E 110° 25' E 110° 30' E 110° 35' E

1222 Bull Volcanol (2012) 74:1213–1233

Discussion

Geological evolution of Merapi

Based on field studies, the volcanic structure and new ra-

diometric age dates, the following eight main volcano strati-

graphic units, linked to three eruptive stages and volcanic

edifices, are distinguished and keyed to the adapted version

of the geological map of Merapi (Wirakusumah et al. 1989)

presented in Fig. 5. The description of the units follows,

where possible, the stratigraphic sequence, although there is

partial overlap in the age ranges of some of the lava and

pyroclastic sequences identified.

Volcano stratigraphic units

Lava flows of Gunung Bibi (map unit 1) Gunung Bibi

(Fig. 2) is a morphologically distinct, heavily forested hill

some 3.5 km to the north-east of the summit of Merapi. It

consists of highly weathered, mostly basaltic andesite brec-

cias and lava flows that resemble the surrounding lavas of

the Somma-Merapi. Exposures at Gunung Bibi are rare, and

the hill remains a poorly known part of the Merapi volcanic

complex. It has been interpreted as a residual hill of a pre-

Merapi volcanic structure (Berthommier 1990; Camus et al.

2000) or, alternatively, as a vent or volcanic plug that

erupted through and built itself on the upper flank of the

Merapi Somma volcano (Newhall et al. 2000).

The high degree of weathering of the Gunung Bibi lavas

compared to the surrounding lavas of the Somma-Merapi

suggests that Gunung Bibi could indeed be an older volca-

nic structure. However, providing new radiometric ages to

4.8 ± 1.5

29.6 ± 1.0

24.2 ± 0.8

10.7 ± 0.8

30.3 ± 1.0

1.7 ± 1.7

138 ± 3

135 ± 3

8.6 ± 1.4

2 km

109 ± 60

Lava flows of the Somma-Merapi

Lava flows of Gunung Turgo and Gunung Plawangan

Young (post-Somma-Merapi) lava flows

Lava flows of Gunung Bibi

Fig. 6 Digital elevation model of Merapi showing the locations of

samples dated using the K–Ar (cf. Table 1) and Ar–Ar (shown in

italics) techniques. Used colour codes and map units correspond to

those in Fig. 5. All age dates are reported in kiloannum. Digital

elevation model courtesy of Carl Gerstenecker (TU Darmstadt,

Germany)

Fig. 5 Adapted version of the geological map of Merapi (Wirakusumah

et al. 1989), distinguishing eight main volcano stratigraphic units linked

to three main evolutionary stages—Proto-Merapi, Old Merapi and New

Merapi. The reported dates for the Gunung Bibi, Gunung Turgo and

Gunung Plawangan, Somma-Merapi and post-Somma-Merapi lavaflows

are from this study. The oldest age for the HPS is from Gertisser (2001),

published in Gertisser and Keller (2003a). Stratigraphic data from Bahar

(1984), del Marmol (1989), Berthommier (1990), Andreastuti (1999),

Andreastuti et al. (2000), Camus et al. (2000), Newhall et al. (2000),

Gertisser (2001) and Gertisser and Keller (2003a) are considered. Map

symbols as in Fig. 1

Bull Volcanol (2012) 74:1213–1233 1223

test such a hypothesis and help resolve the controversy

above has proved to be difficult. Our attempts to date two

samples from Gunung Bibi using the K–Ar Cassignol–Gil-

lot technique were unsuccessful. Loss of K due to weather-

ing and release of radiogenic Ar due to the scoriaceous

nature of one of the samples are possible reasons for this.

However, amphibole crystals derived from relatively fresh

basaltic andesite blocks from a volcanic breccia exposed in

the late 1990s by a small landslide ~100 m below the

summit of Gunung Bibi yielded an Ar–Ar age of 109±

60 ka (Fig. 6). The value of this new age is somewhat

limited due to the large analytical uncertainty. Still, it sug-

gests that Gunung Bibi is younger than 170 ka and, there-

fore, substantially younger than the only other available date

suggests. The newly obtained age of 109±60 ka (>50 ka)

indicates that Gunung Bibi predates the lava sequences of

the Somma-Merapi (see below). Thus, in accordance with

previous studies by Berthommier (1990) and Camus et al.

(2000), Gunung Bibi is regarded as an ancient (Proto-Mer-

api) volcanic structure older than the Merapi edifice sensu

stricto. A different ancient volcanic structure exists in the

form of Gunung Turgo and Gunung Plawangan, two prom-

inent hills on the south side of Merapi. The age relation of

Gunung Bibi to Gunung Turgo and Gunung Plawangan in

the light of new radiometric age dates for the latter is

discussed in the following section.

Lava flows of Gunung Turgo and Gunung Plawangan (map

unit 2) Gunung Turgo and Gunung Plawangan are two

steep-sided hills on either side of the Boyong valley on

Merapi’s south flank, some 5 km from the summit

(Fig. 2). They mainly consist of basaltic lava flows with

similar petrographic and geochemical characteristics, sug-

gesting that they are the same volcanic edifice that has been

subsequently eroded and incised by the Boyong river. The

basaltic nature of their lavas, with a typical mineral assem-

blage of plagioclase, clinopyroxene, olivine and magnetite

that characteristically lacks amphibole (hornblende), is a

notable feature that distinguishes the two hills from the rest

of Merapi (Gertisser 2001). A first attempt to date a lava flow

from Gunung Plawangan, using a U–Th mineral isochron,

yielded an age of 40±18–15 ka (Berthommier 1990;Camus

et al. 2000), indicating that the two hills might be considerably

older than the main Merapi edifice. They were interpreted as

either basaltic flank vents of Old Merapi (van Bemmelen

1949), slightly tilted megablocks related to a sector collapse

during the Middle Merapi period (Berthommier 1990;Camus

et al. 2000) or, as mentioned above, erosional remnants of a

Proto-Merapi edifice (Newhall et al. 2000). Our field

observations corroborate the interpretation of the two

hills as ruins of an ancient volcano. Both consist mostly

of intact sequences of basaltic lava flows and intercalated soil

horizons, occasionally oxidised by the overlying flow, that dip

slightly towards the north. There is no evidence for a crater or

any near-vent pyroclastic depositsthat would suggest that they

are eccentric vents. In order to constrain the age of Gunung

Turgo and Gunung Plawangan, two lava samples of basaltic

lava flows were taken from the basal successions of either hill

exposed in the Boyong valley. The basaltic flow at the base of

the western slope of Gunung Plawangan yielded a K–Ar age

of 135± 3 ka and is within error of the lava dated at the foot of

the eastern flank of Gunung Turgo, for which an age of 138±

3 ka was obtained (Fig. 6). The lava flows from Gunung

Turgo and Gunung Plawangan are the oldest rocks of Merapi

dated by the K–Ar method in this study. The new ages suggest

that the two hills are considerably older than previously

thought and precede the main edifice of Merapi by ~100 kyr

(see below).

Lava flows of the Somma-Merapi (map unit 3) Thick suc-

cessions of massive, predominantly basaltic andesite lava

flows and minor pyroclastic deposits are exposed in the

deeply incised valleys on the southeastern, eastern and

northern flanks of the volcanic complex (Fig. 2).These

sequences are remnants of a partly destroyed older volcanic

edifice with a horseshoe-shaped crater open to the west that

has been related to one or several sector collapses in the past

history of Merapi (Camus et al. 2000; Newhall et al. 2000).

The lava sequences constitute the main part of van Bemme-

len’s Old Merapi and the Batulawang series of Berthommier

(1990) and Camus et al. (2000), named after Gunung Batu-

lawang, the highest peak of the Somma-Merapi. Chronolog-

ical information on the lava sequences of the Somma-

Merapi has been essentially nonexistent prior to this study,

with only a single available U–Th mineral isochron age of

6.7 ka for a lava flow near the base of the Batulawang series

(Berthommier 1990; Camus et al. 2000). The six new K–Ar

ages obtained for lava flows of the Somma-Merapi yielded

ages between 30.3±1.0 and 4.8 ± 1.5 ka (Table 1). The oldest

ages are from samples collected at the base of Gunung

Kendil (30.3±1.0 ka), a lava flow near the base of the pile

southeast of Gunung Bibi (29.6± 1.0 ka) and from Gunung

Batulawang near the summit of Merapi (24.2±0.8 ka). No-

tably younger ages were obtained for lavas in the upper

parts of the Somma-Merapi above the village of Deles

(10.7±0.8), east of Gunung Batulawang (4.8 ± 1.5 ka) and

on the lower northern slopes of the volcano (8.6 ± 1.4 ka,

Fig. 6). From these new ages, it can be inferred that the

construction of the older Merapi cone (Old Merapi) began at

~30 ka with the emplacement of massive lava flows building

a large central volcano that was subsequently destroyed by

collapse(s) of the western sector of this edifice. The youn-

gest age of 4.8±1.5 ka is interpreted to provide an upper age

limit for the latest inferred flank collapse of the older Merapi

edifice and, as such, marks the end of Old Merapi and the

beginning of the recent cone (New Merapi).

1224 Bull Volcanol (2012) 74:1213–1233

Holocene Pyroclastic Series (map units 4 and 5) Merapi is

surrounded by an extensive apron of predominantly Holo-

cene pyroclastic and epiclastic deposits (Andreastuti 1999;

Andreastuti et al. 2000; Camus et al. 2000; Newhall et al.

2000; Gertisser 2001; Gertisser and Keller 2003a). For the

most part, the exposed successions appear stratigraphically

younger than the Somma-Merapi lavas, which is confirmed

by the new K–Ar ages we obtained for these lavas (Table 1;

Fig. 6). On the interfluve areas, these consist of relatively

thin pyroclastic flow, surge and reworked deposits, interbed-

ded with numerous lapilli and ash fall layers. The sides of

the valleys that cut into the pyroclastic and epiclastic apron

are dominated by thick sequences of intercalated valley-

ponded pyroclastic flow deposits, fluvial and laharic debris

and minor fallout deposits. Gertisser and Keller (2003a)

introduced the term Holocene Pyroclastic Series (HPS) to

describe these successions, a term that is adopted in this

study. The age range of the HPS is constrained by ~150

radiocarbon ages (Supplementary Table 1). A palaeosol in

the northern sector of Merapi that underlies a succession of

pyroclastic deposits from, presumably, both Merapi and

Merbabu, the volcano immediately north of Merapi, limits

the HPS to <11,792± 90

C years BP. The oldest age for an

explosive eruption is 9,630± 60

C years BP obtained from

a pyroclastic flow deposit in the eastern sector of Merapi

(Newhall et al. 2000). Important for the younger eruptive

history of Merapi is the recognition of relatively old ages for

the pyroclastic successions on the interfluves on the western

flank which, in the area of Kali Batang (820 m a.s.l.) and

Jurangjero/Kali Putih (970 m a.s.l.), date back to 2,260±30

C years BP and, in other places, back to 3,868 ± 47

years BP (Kajangkoso-Kali Senowo; 690 m a.s.l.) and 4,153

±37

C years BP (Candi Asu/Kali Trising; 700 m a.s.l.),

respectively (Fig. 4; Supplementary Table 1). Comparative-

ly old pyroclastic deposits up to 3,453±33 and 8,380 ± 230

C years BP are also found in the south-west inside the

valleys of the Bedok (980 m a.s.l.) and Bebeng (1,100 m

a.s.l.) rivers, respectively (Supplementary Table 1). The

youngest dome collapse pyroclastic flow deposit east of

Merapi was dated at 1,590 ± 40

C years BP (Supplemen-

tary Table 1), which contrasts with the youngest age for a

pyroclastic flow deposit on the east or southeast side of

Merapi reported by Newhall et al. (2000). In view of an

inferred avalanche caldera-forming event at around (or

somewhat younger than) 4.8± 1.5 ka (see above), the oldest

ages on the west side signify the minimum western

extent of pyroclastic deposits of the pre-collapse (Old

Merapi) edifice and suggest that any young debris ava-

lanche deposit could be exposed and may not necessarily

been buried by rapid sedimentation around the base of

Merapi, as suggested by Newhall et al. (2000). By con-

trast, the (perhaps surprisingly) young ages of pyroclastic

flows on the eastern slopes indicate that ~1,900 years

ago (or even earlier), the post-collapse (New Merapi)

cone was already large enough for dome collapse pyro-

clastic flows to overflow the avalanche caldera scar,

although the predominant pyroclastic flow direction has

continued to be to the west. The younger successions of

the HPS are generally well exposed around the volcano,

and the recognition of a few stratigraphic marker hori-

zons have allowed a relatively detailed reconstruction of

the past 2,000–3,000 years of eruptive activity at Merapi

(Berthommier 1990; Andreastuti 1999; Andreastuti et al.

2000; Camus et al. 2000; Gertisser and Keller 2000,2003a;

Newhall et al. 2000;Gertisser2001).

Young (post-Somma-Merapi) lava flows (map unit 6) Apart

from the thick basaltic andesite lava sequences of the

Somma-Merapi, geologically younger lava flows occur near

the summit of Merapi in the area of the Pasarbubar crater

(Gunung Selokopo Ngisor, Gunung Selokop Duwur,

Gunung Gadjah Mungkur, Gunung Pusunglondon), high

on the south-western and western flanks (Gunung Deng-

keng, Gunung Patukalapalap) and farther downslope in the

Kuning and Gendol river valleys in the south (Fig. 1). These

lavas constitute the Gadjah Mungkur series of Berthommier

(1990) and Camus et al. (2000), a geologically young lava

sequence unaffected by and therefore younger than the

Kukusan fault. A K–Ar age of 1.7±1.7 ka for a lava flow

from Gunung Pusunglondon (Fig. 6) and a “zero”age for

another flow from Gadjah Mungkur (not listed in Table 1)

confirm the young age of these lavas in absolute terms and

in comparison with those of the Somma-Merapi east of the

Kukusan fault, although many of these lavas still remain to

be dated.

Recent and mostly historical pyroclastic flow and lahar

deposits (map unit 7) and lava domes of the recent episode

(map unit 8) Pyroclastic flow deposits from historical to

recent eruptions cover large areas on the south-west flank

of Merapi and fill the deep river valleys in the southern,

western and north-western sectors to distances up to 10 km

from the summit. Farther downstream, lahar deposits dom-

inate, resulting from reworking of the primary pyroclastic

material. At Merapi, historical accounts of scattered eruptive

activity date back as far as the sixteenth century and the

record only becomes more complete since the mid to late

eighteenth century (Fig. 7). Most of these young pyroclastic

flow deposits are associated with lava dome collapse, al-

though some are more likely to be related to fountain or

eruption column collapse during more explosive events (see

below). The present day lava dome complex at the summit

of Merapi constitutes domes extruded since 1888 AD within

the larger Pasarbubar crater (Voight et al. 2000). Eccentric

vents and flank eruptions are unknown for the younger

eruptive episodes of Merapi.

Bull Volcanol (2012) 74:1213–1233 1225

Eruptive stages and volcanic edifices

In the previous section, we have deliberately not related the

volcano stratigraphic units, as shown on the geological map

(Fig. 5), to distinct evolutionary stages of Merapi, as defined

by previous authors. Taking into account the new radiomet-

ric ages obtained during the course of this study, we distin-

guish three temporal eruptive stages and volcanic edifices in

the evolution of the Merapi complex—Proto-Merapi, Old

Merapi and New Merapi (Figs. 2and 5). The erosional

remnants of two Proto-Merapi edifices are represented by

Gunung Bibi and Gunung Turgo/Gunung Plawangan, re-

spectively. Both edifices are older than the main part of

the volcanic complex, and the ages obtained suggest that

the earliest Merapi edifices started to grow less than 170

thousand years ago. However, the new ages for Gunung

Bibi, and the Turgo and Plawangan hills are within error

of each other (Table 1), so that the exact age relationships

between these two petrographically and geochemically dis-

tinct earliest volcanic edifices cannot be ascertained with the

available data. In fact, it is possible that both edifices were

active contemporaneously. In a recent study, Gomez et al.

(2010) discussed a potential link between volcanic rock

samples from drill cores taken near Candi Borobudur

~30 km west of Merapi and dated at ~119 and 31 ka,

respectively, and possible collapse events of Proto-Merapi

in the sense of Newhall et al. (2000) or the older Ancient

Merapi stage (Camus et al. 2000). With the new ages for

Gunung Turgo and Gunung Plawangan presented in this

study, a Merapi origin for these drill core samples from the

Borobudur basin remains a possibility, although another

volcanic source is equally feasible. A partly destroyed vol-

canic edifice, Old Merapi (van Bemmelen 1949; del Marmol

1989; Newhall et al. 2000), constitutes most of the Merapi

complex. The oldest lavas of Old Merapi (Batulawang

Series; Berthommier 1990; Camus et al. 2000)aredated

at ~30 ka (K–Ar), which shows that Old Merapi is

significantly older than inferred previously (Camus et

al. 2000; Newhall et al. 2000). The oldest of only a

small number of hitherto documented explosive erup-

tions of Old Merapi are younger than 11,792± 90

years BP, and some of these may have left deposits in

the Borobudur basin (Gomez et al. 2010). Our youngest

ageforalavaflowfromtheSomma-Merapi(4.8±

1.5 ka) indicates that the destruction of Old Merapi

occurred after 4.8± 1.5 ka. With an age of 1.7± 1.7 ka

(i.e. <3.4 ka at 1σconfidence level) obtained for one of the

earlier post-collapse lava flows from Gunung Pusunglondon,

the lower age limit for the end of the Old Merapi eruptive

stage, as inferred from the lava flow chronology in Merapi’s

summit area, remains poorly constrained. Still, an important

implication of these new ages is that pyroclastic deposits of

the HPS older than 4.8±1.5 ka are part of Old Merapi, while

those that are younger erupted from the recent cone and,

therefore, belong to the New Merapi stage.

Geochemical evolution of Merapi

Most of Merapi consists of basaltic andesite lavas and

pyroclastic rocks. Basaltic rocks also occur, but are volu-

metrically less significant (Supplementary Table 2). The

Merapi rocks are typical calc-alkaline basalts and basaltic

andesites of medium-K and high-K affinity (Fig. 8).

MK and HK series were initially defined based on varia-

tions in K

O content observed in lavas of the Somma-

Merapi, pyroclastic rocks of the HPS and the historical

and recent eruptive products (Gertisser and Keller 2003b).

Here, we expand the discussion of the compositional varia-

tions of the Merapi rocks to the earliest eruptive products of

the two Proto-Merapi edifices (Fig. 8). Our data show that

the lava flows of Gunung Bibi and the Turgo and Plawangan

hills are geochemically distinct, consisting of MK basaltic

andesite and HK basalt, respectively. While the HK charac-

ter of the basaltic lavas of Gunung Turgo and Gunung

Plawangan appears to be unusual for the earliest eruptive

stages of Merapi, the Gunung Bibi lavas show geochemical

affinity to the surrounding younger lavas of the Somma-

Merapi, which may suggest that Gunung Bibi is a precursor

to the main Merapi edifice fed by the same magma system.

Detailed stratigraphic fieldwork, whole-rock geochemistry

and radiocarbon dating of the pyroclastic successions of the

HPS have revealed a change from older MK to younger HK

Volcanic Explosivity Index (VEI)

1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000

Merapi - Historical eruptions (AD)

Fig. 7 Historical eruptions of

Merapi compiled with data

from Venzke et al. (2002) and

Siebert et al. (2011). The two

VEI 4 eruptions are those that

occurred in 1872 and 2010

1226 Bull Volcanol (2012) 74:1213–1233

series products at ~1,900

C years BP, a trend that has

continued into the recent episode (Fig. 8; Gertisser and

Keller 2003a). This increase in K

O at a given SiO

content

of the eruptive products is accompanied by changes in other

element concentrations, such as Rb and Ba, and Sr isotopic

ratios, and has been attributed to variations in the source

characteristics of the primary magmas of the two series

(Gertisser and Keller 2003b). The timing of the MK to HK

transition appears to hold with the new geochemical data

obtained for the lava samples dated by the K–Ar method,

although, as already pointed out, age information for post-

Somma-Merapi lavas is still limited.

The Holocene eruptive history of Merapi

The radiocarbon record

The radiocarbon record of Merapi comprises presently ~150

published ages that provide important chronological con-

straints on the younger activity of the volcano over the past

nearly 14,000 years (cal. years BP). The majority of the

exposed pyroclastic successions on the volcano’slower

flanks span a period from ~2,000 cal. years BP to the

present. Older deposits are comparatively rare due to burial

by younger material, particularly in the west (Fig. 4). This

means that the stratigraphic record of eruptions that are

older than 2,000 years is less complete and the radiocarbon

record more fragmentary (Fig. 9a). By contrast, the radio-

carbon record provides a more complete and detailed picture

of the past 2,000 years of explosive activity. A total of 126

radiocarbon ages (84 % of all radiocarbon dates available)

indicates that the eruptive activity of Merapi over the past

2,000 years has been almost continuous. Assuming that

each radiocarbon date reflects a single eruptive event, it

can be inferred that Merapi has had, on average, 6.3 erup-

tions per 100 years (1 eruption every 15.9 years) over the

past 2,000 years. The apparent eruption frequency over this

period, based on the radiocarbon record, may have been

lower due to potential multiple dating of single eruptive

events, which cannot be ruled out completely due to the

integration of multiple data sets. An incomplete eruption

record and addition of the numerous historical eruptions

since the mid to late eighteenth century would lead to a

higher eruption frequency over the past 2,000 years

(Fig. 9b). The eruptive frequency estimated from the radio-

carbon record compares to 29 eruptions in the nineteenth

century (1 eruption in every 3.4 years) and 25 episodes of

eruptive activity in the twentieth century (1 eruption every

4 years, Venzke et al. 2002; Siebert et al. 2011). The fre-

quency of eruptions has probably not been constant through

time. The steepening of the trend in Fig. 9b indicates a

decreasing number of radiocarbon ages with increasing

age. This could either reflect an increase in eruptive activity

in more recent time or, more likely, a less complete record of

older eruptive events. Based on a smaller radiocarbon data-

set, Gertisser and Keller (2003a) defined three periods of

increased eruptive frequency over the past 2,000 years inter-

rupted by periods of apparently reduced eruptive frequency

from 1,300 to 1,150 and 700 to 550

C years BP. Each

period of high eruptive frequency started with the most

SiO

-rich whole-rock compositions, produced by differenti-

ation processes in the preceding period of apparently re-

duced eruptive activity, and ended with the least evolved

rock compositions. In order to test this model with the larger

radiocarbon dataset presented here (Supplementary Table 1),

the conventional radiocarbon ages younger than 2,000

years BP are shown on an age probability plot commonly

used in K–Ar or Ar–Ar geochronology (Deino and Potts

1992) that takes into account the errors of individual anal-

yses (Fig. 9c). While such an approach is affected by the

smaller number of dates available for older deposits, it

allows the identification of the same successive alternation

of periods of apparently higher and lower eruption frequen-

cy over the past 2,000 years.

50 52 54 56 5848 60

K2O (wt%)

SiO2 (wt%)

High-K

Basalt Basaltic Andesite Andesite

Medium-K

Low-K

(g)

(f)

(e)

(d)

(c)

(b)

(a)

Fig. 8 K

O versus SiO

classification diagram (Le Maitre et al. 2002)

for Merapi lavas and pyroclastic rocks. All analyses are recalculated to

100 wt%, free of volatiles. Symbols (keyed to Fig. 5): aLava flows of

Gunung Bibi (map unit 1); blava flows of Gunung Turgo and Gunung

Plawangan (map unit 2); clava flows of the Somma-Merapi (map unit

3); d–epyroclastic deposits of the Holocene Pyroclastic Series (map

units 4 and 5), subdivided into eruptive products older than ~1,900

years BP (d) and younger than ~1,900

C years BP (e). Pre- and post-

1,900

C years BP eruptive products have medium-K and high-K

compositions, respectively; fyoung (post-Somma-Merapi) lava flows

(map unit 6); grecent and mostly historical pyroclastic flow and

lahar deposits (map unit 7), and lava domes of the recent episode

(map unit 8)

Bull Volcanol (2012) 74:1213–1233 1227

Pyroclastic deposits and eruption types

The recent and historical activity of Merapi has been dom-

inated by frequent eruptions generating small-volume pyro-

clastic flows from the gravitational collapse of basaltic

andesite lava domes (Merapi-type nuées ardentes, Voight

et al. 2000). Lahars are frequent during the rainy seasons

in the years following an eruption, transporting farther

downstream the primary pyroclastic material from distances

typically less than 10 km from the volcano (e.g. Lavigne et

al. 2000). Pyroclastic flow and associated ash cloud deposits

(and reworked deposits thereof) also dominate the Holocene

stratigraphic record. Apart from the classic block-and-ash

flow deposits (resulting from Merapi-type nuées ardentes),

the juvenile component of which is dominated by dense to

poorly vesicular dome fragments, we have identified three

other types of pyroclastic flow deposits based on their

principal juvenile component in the larger (lapilli to block

sized) clast range. These include pyroclastic flow deposits

dominated by moderately vesicular bread crust bombs, mod-

erately vesicular clasts with characteristic cauliform surface

textures and moderately to highly vesicular, light grey pu-

miceous clasts (Fig. 10).

Each of these deposits may contain variable proportions

of dense (lithic) blocks and are considered endmembers of a

continuum of small-volume pyroclastic flow types at Mer-

api. The lithic component in these deposits may either be

juvenile by a mechanism of vent clearing or disruption of a

volcanic plug or dome at the summit, older collapsed dome

masses or, as observed during the 2006 eruption, derived

from crater wall or small cone collapses (Charbonnier and

Gertisser 2008). Direct observations or historical accounts

of eruptions generating these different types of deposits at

Merapi are rare. As such, possible generation mechanisms

may best be inferred from observations made at other vol-

canoes, such as Arenal, Costa Rica (Alvarado and Soto

2002;Coleetal.2005); Aso, Japan (Miyabuchi et al. 2006);

Mayon, Philippines (Moore and Melson 1969); Soufrière

Hills, Montserrat (e.g. Cole et al. 2002) and Tungurahua,

Ecuador (Hall et al. 1999; Le Pennec et al. 2008). At Merapi,

pyroclastic flow deposits with bread crust bombs or blocks of

cauliform external morphologies are associated with magmas

that are more basic than the typical dome-forming basaltic

andesite (Gertisser 2001). The most prominent bread crust

bomb-rich pyroclastic flow deposit at Merapi was described

0 400 800 1200 1600 2000

Conventional 14C a

e (14C

BP)

Relative probability (n = 126)

Calibrated 14C age (cal. y BP)

200

400

600

800

1000

1200

1400

1600

1800

2000 15 10

Samples in chronological order (n = 126)

Samples in chronological order (n = 150)

Calibrated 14C age (cal. y BP)

2000

4000

6000

8000

10000

12000

14000 (a)

(b)

(c)

Fig. 9 The radiocarbon record of Merapi volcano (Supplementary

Tab le 1). aPublished radiocarbon ages for Merapi plotted in

chronological order (total number of analyses, n0150). All ages

are shown as their maximum 1σrange in calibrated years BP (i.e.

before 1950). bA close-up of figure (a) showing the subset of

samples with calibrated ages <2,000 years BP (total number of

analyses n0126). Illustrated are the median probability and the

maximum calibrated 1σage range. The dashed lines indicate the gra-

dients expected from the number of samples (as indicated) per 100 years.

cCumulative probability plot obtained by summing the probability dis-

tributions of all conventional radiocarbon ages <2,000

C years BP (total

number of analyses, n0126). The thick black bars indicate the two

periods of reduced eruptive activity proposed by Gertisser and Keller

(2003a). See text for discussion. Data sources: Andreastuti et al. (2000),

Camus et al. (2000), Newhall et al. (2000), Gertisser and Keller (2003a)

and Gertisser et al. (2012)

1228 Bull Volcanol (2012) 74:1213–1233

by Newhall et al. (2000) and tentatively ascribed to the VEI 4

(Newhall and Self 1982) 1872 AD eruption. As one of the

youngest pyroclastic flow deposits on Merapi’s south flank, it

canbetracedoveralargeareabetweentheBoyongriver,

south of the village of Kaliurang, in the west, to the Woro river

in the east, and to distances of ~11 km from Merapi (Gertisser

et al. 2011,2012). It is widespread across the interfluve areas

on the south slope, but also occurs as young valley fills in the

Gendol and Opak valleys. An even wider distribution may be

indicated by the presence of a similar deposit on the south-

west flank at Jurangjero (Kali Putih) that correlates petro-

graphically and geochemically with the south flank deposit

(Gertisser 2001). While fragments of the exterior surfaces of

the Merapi domes are occasionally bread crusted, our pre-

ferred mechanism for the generation of the bread crust bomb-

rich pyroclastic flow deposits at Merapi is that of fountain

collapse related to Vulcanian-type explosive activity, which,

in some cases, involves solidified lava dome material and

fresh, partially molten material from the dome’sinterioror

conduit. Such a process may also be capable of producing a

similar type of pyroclastic flow rich in blocks characterised by

cauliform external morphologies, well-preserved examples of

which occur in the upper Kali Boyong north of the Turgo and

Plawangan hills and in Kali Apu in the northern sector of

Breadcrust bombs, typically dark-

coloured (mafic), glass-rich, vesicular,

subangular to rounded

Juvenile component characterised by

clasts / bombs with cauliform external

morphology, typically dark-coloured

(mafic), glass-rich, vesicular, subangular

to rounded

50 cm

Essential juvenile component

Eruptive mechanism

Dense to poorly vesicular andesite lava

dome fragments / blocks, highly

crystalline, but may contain glass in

groundmass, angular, occasional with

prismatic cooling joints

Lavadome collapse

(gravitational)

Fountain collapse Fountain to eruption column collpase

Block-and-ash

flow deposit

Breadcrust-bomb-rich

pyroclastic flow deposit

Cauliflower-bomb-rich

pyroclastic flow deposit

Pumice-rich

pyroclastic flow deposit

Type of pyroclastic-flow deposit

ABCD

Pumiceous juvenile clasts, light

coloured, glass-rich, highly vesicular,

strongly rounded through abrasion

during lateral transport

Vulcanian (Sub-)Plinian

Fig. 10 Different types of small-volume pyroclastic flow deposits identified at Merapi based on the dominant juvenile component they contain.

Inferred flow generation mechanisms are also indicated (after Gertisser 2001). The scraper is 25 cm long

Bull Volcanol (2012) 74:1213–1233 1229

Merapi (Fig. 1). Alternatively, collapse from slugs of magmas

that rise a few hundred metres following an explosion may

also be envisaged (Newhall, personal communication 2011).

As observed during the ongoing Soufrière Hills eruption on

Montserrat (e.g. Cole et al. 2002), pyroclastic flows rich in

pumiceous clasts may also be associated with Vulcanian-type

(or more sustained Plinian-type) fountain or eruption column

collapses. At Merapi, such pyroclastic flows may be associat-

ed with the build-up of gas overpressure in a sealed conduit

due to the relatively fast ascent of volatile-rich basaltic andes-

ite magma.

Widespread pumiceous tephra fall deposits are equally

prominent among the Holocene volcanic products of Mer-

api, but essentially absent during the more recent activity in

the twentieth and at the beginning of the twenty-first centu-

ry, although lapilli-sized pumiceous tephra was produced

during the 2010 eruption. In the stratigraphic record these

tephra fall deposits form distinct strata of coarse ash and

pumiceous lapilli ranging in thickness from more than one

to a few tens of centimetres. They are separated from each

other by finer grained ash deposits of tephra fall or ash cloud

origin and locally by coarser overbank pyroclastic flow,

surge and lahar deposits. A few widespread and distinct

tephra- fall deposits (Paten I, Paten II, Trayem, Jurangjero

I, Jurangjero II) allow the lateral correlation of pyroclastic

successions in the southern, western and north-western sec-

tor of the volcano to distances of 20 km from the source

(Fig. 4). The distribution and thickness variations of each

tephra layer are shown in Fig. 11. The isopach maps give the

minimum extent of each tephra layer based on detailed field

mapping. Although lateral correlation of tephra units at

Merapi is often hindered by poor exposure and low

preservation potential in the tropical climate, we were

able to map these deposits down to the 10- or 5-cm

isopach. The volumes for the five tephra layers were

determined by extrapolating the deposit thicknesses be-

yond the 10- or 5-cm isopachs following the method of

Pyle (1989) and, as such, are considered minimum

estimates. The volumes obtained are 0.13 km

(Paten

I), 0.23 km

(Paten II), 0.16 km

(Trayem), 0.07 km

(Jurangjero I) and 0.28 km

(Jurangjero II, Gertisser and

Keller 2000; Gertisser 2001).

These deposits record large subplinian-type eruptions of

Merapi [VEI 3 (<0.1 km

) and VEI 4 (>0.1 km

) events]

during mid to late Holocene times (<4,153 ± 37

C years

BP), which differ fundamentally from the dome-forming

eruptions of the twentieth century. VEI 4 eruptions, as

described here and in Andreastuti (1999) and Andreastuti

et al. (2000), are an order of magnitude larger than any

recorded historical eruption of Merapi, except for the

1872 AD eruption and, possibly, the explosive events in

October–November 2010 (Venzke et al. 2002; Siebert et

al. 2011).

Summary and conclusions

A new set of

K–

Ar and

Ar–

Ar ages suggests that

construction of the basalt to basaltic andesite volcanic com-

plex of Merapi began after 170 ka. The Merapi cone sensu

stricto was preceded by two earlier Proto-Merapi volcanic

edifices. Proto-Merapi, as defined in this paper, constitutes

Gunung Bibi (109±60 ka), a small basaltic andesite volca-

nic structure on the north-east flank, and Gunung Turgo and

Gunung Plawangan (138±3 ka; 135 ± 3 ka), two basaltic

hills in the southern sector of Merapi. Old Merapi started

to grow ~30 thousand years ago, building a stratovolcano of

basaltic andesite lavas and intercalated pyroclastic rocks. A

major sector collapse, which we believe occurred sometime

after 4.8±1.5 ka, marks the end of the Old Merapi stage.

Thus, the recent Merapi cone (New Merapi) is younger than

4.8±1.5 ka. An apron of predominantly basaltic andesite

pyroclastic and epiclastic deposits younger than 11,792 ± 90

C years BP covers the lower flanks of Merapi and, thus,

comprises products of both Old and New Merapi. A shift

from medium-K to high-K character of the eruptive products

occurred at ~1,900

C years BP, with all younger products

having high-K affinity. The radiocarbon record reveals that

Merapi has been almost continuously active since then, with

periods of high apparent eruption frequency interrupted by

periods of apparently lower eruption frequency that are

mirrored in changes in the geochemical composition of the

eruptive products. Merapi’s recent activity has been charac-

terised by the extrusion of viscous lava domes and genera-

tion of small-volume pyroclastic flows by gravitational

dome failure (Merapi-type nuées ardentes) every few years.

These flows are typically characterised by run-out distances

of less than 10 km and usually restricted to the deep drain-

ages radiating from the volcano, where they leave spatially

confined, but thick block-and-ash flow deposits. Associated

with such eruptions may be partial cone collapses that can

lead to sudden shifts in the directions of pyroclastic flows

during prolonged dome-forming eruptive periods, as ob-

served, for example, in 2006 (Charbonnier and Gertisser

2008). While this type of activity poses a considerable

and permanent threat to the population close to the

volcano and has caused fatalities and severe damage in

the past, the Holocene stratigraphic record of Merapi

reveals the occurrence of more mobile fountain collapse

pyroclastic flows with lower aspect ratios, the distribu-

tion and run-out distances of which have now and then

exceeded those of the classic Merapi-type nuées

ardentes. One of the most striking examples of such

flows is a young bread crust bomb-rich pyroclastic flow

deposit that may have inundated all main river valleys

on Merapi’s south (and perhaps south-western) flank

and swept the entire, now heavily populated interfluve

areas between the Boyong and Woro valleys to at least

1230 Bull Volcanol (2012) 74:1213–1233

11 km from the summit. Plinian-style eruptions and

associated tephra falls (Andreastuti 1999; Andreastuti

et al. 2000; Gertisser and Keller 2000; Gertisser 2001)

maybeahithertolessrecognisedhazardatMerapi.

Several pumiceous fallout deposits testify the occurrence

of major explosive eruptions during the past ~4,000 years,

4153 ± 37

1047 ± 36

2264 ± 73

361 ± 22

762 ± 26

3868 ± 47

385 ± 65

7˚ 35' S

7˚ 30' S

110˚ 20' E 110˚ 25' E

Muntilan

Gendol

Hills

Salam

Merapi

11 13

13 14

12.5

10 712

2000

1600

1200

800

Jurangjero I

7˚ 35' S

7˚ 30' S

110˚ 20' E 110˚ 25' E

Muntilan

Gendol

Hills

Salam

Merapi

50 52

25 30 32

28 24

26 34

2000

1600

1200

800

Trayem

7˚ 35' S

7˚ 30' S

110˚ 20' E 110˚ 25' E

Muntilan

Gendol

Hills

Salam

Merapi

22 23

2124

15 10

2000

1600

1200

800

Paten II

7˚ 35' S

7˚ 30' S

110˚ 20' E 110˚ 25' E

Muntilan

Gendol

Hills

Salam

Merapi

1315 25

18 15

11 8

2000

1600

1200

800

Paten I

7˚ 35' S

7˚ 30' S

110˚ 20' E 110˚ 25' E

Muntilan

Gendol

Hills

Salam

Merapi

40 30

22 28

38.5

12*

25*

37.5

10*

22-24

2000

1600

1200

800

Jurangjero II

05 km 05 km

05 km

0 5 km

4000

5000

3000

2000

1000

Conventional 14C age (14C y BP)

Paten I

Paten II

Trayem

Jurangero I

Jurangjero II

Fig. 11 Isopach maps, field photographs and conventional radiocar-

bon ages (obtained from underlying and overlying deposits or palae-

osols) of the five prominent pumiceous tephra layers highlighted in

Fig. 4. Isopach thicknesses are in centimetres (after Gertisser and

Keller 2000; Gertisser 2001). The scraper is 25 cm long

Bull Volcanol (2012) 74:1213–1233 1231

which can be qualitatively described as moderate (VEI 3) to

large (VEI 4) subplinian events, which are an order of mag-

nitude larger than any recorded historical eruption of Merapi,

except for the 1872 AD and, possibly, the October–November

2010 events (Venzke et al. 2002; Siebert et al. 2011). For these

reasons, both lower aspect ratio pyroclastic flows associated

with Vulcanian-type explosions or more sustained eruption

columns, which are more widely distributed than the dome

collapse pyroclastic flows of the recent activity, and larger,

subplinian explosive eruptions generating widespread pumi-

ceous tephra fall deposits should be given careful consider-

ation in long-term eruption forecasting at Merapi.

Acknowledgments We gratefully acknowledge our colleagues at the

Merapi Volcano Observatory (BPPTK) in Yogyakarta for their gener-

osity and support over many years. Sutisna, Dedi, Budi, Sony and

Biyanto are thanked for the logistical support in Indonesia and for

bringing us to the most remote parts of Merapi. Pierre-Yves Gillot

(Université Paris-Sud, Orsay) and Simon Kelley (The Open Universi-

ty) kindly provided access to their K–Ar and Ar–Ar dating facilities,

respectively. We appreciate the stimulating discussions about Merapi

with Supriyati Andreastuti, Sutikno Bronto, Mary-Ann del Marmol,

Alain Gourgaud, Chris Newhall, Lothar Schwarzkopf, Valentin Troll

and Barry Voight, and the insightful reviews by Chris Newhall and

Alain Gourgaud. Funding was provided primarily by the Deutsche

Forschungsgemeinschaft (German Research Foundation). Financial

support from the Natural Environment Research Council (UK), the

Mineralogical Society of Great Britain and Ireland, and the Research

Institute for the Environment, Physical Sciences and Applied Mathe-

matics (EPSAM) at Keele University is also acknowledged.

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Jan 2004
RADIOCARBON

A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0–24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0–26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0–12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4–26.0 cal kyr B P. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14 C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

Reporting of 14C data

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