Friday, November 5, 2010 Merapi eruption

A much larger and more explosive Merapi eruption occured on 1am, Friday, November 5, 2010 following Thursday eruption. Roaring sound and intensive volcanic tremor was heard and felt since 11pm on Thursday until several blasting sound heard around 12am to 1am. Pyroclastic surges associated with this eruption injures more than 20 people, the number expected to rise. Thick ash, sand and gravel hits nearby city of Yogyakarta, Magelang, Purworejo, Solo and Klaten. The authority expand the exclusion zone to 20km and move all evacuation center that were located in Sleman regency to Maguwoharjo stadium, located 30 km from the volcano.

Update: as released in November 15, the total causalities reaches 275. Currently as in December 1st, Merapi remains relatively calmed, the forbidden zone narrowed done to 15 km. However, the accumulation of volcanic material at the upper slope creates laharic flow hazard to the down-slope regions of Yogyakarta city. Many bridges and settlement damaged due to heavy rain in the past several day that followed by massive laharic flows. People lives near the banks of the river that comes from Merapi drainage system are advised to remain vigilant, especially during heavy rainfall.

Update: on December 3, 2010 the Volcanology Center of Indonesia lower the alert level of Merapi from its highest degree to the third level (alert level code chart)

Latest Merapi eruption, Thursday-November 4, 2010, the largest eruption over the past eight days

Merapi volcano spewed clouds of hot ash and lava in a violent explosive eruption on Thursday, November 4, 2010 around 6am . The eruption column reaches 4000 meters heights. It was the largest in a series of eruptions over the past eight days. There were no reports of new casualties. Forty two causalities recorded since the beginning of eruption in October 26, 2010 (updated as in Thursday, November 4, 2010).

Almost 80,000 people have been forced from their homes by the recent eruption into emergency shelters outside a 10 km exclusion zone around the volcano. On Wednesday, November 3, 2010, the authorities extended the radius of the zone to more than 15 km, ordering evacuations that could affect at least 100,000 people.

Figure caption: the latest Merapi eruption as seen from Yogyakarta city that located 25 km from the volcano. The picture was taken on 6 am, Thursday, November 4, 2010. The eruption column reaches 4000 meters height. (Photo courtesy of Reza Muzzamil Jufri)

Explosive eruption on Merapi, October 30, 2010

An explosive eruption occurred early on Saturday, October 30, 2010 around 00.40 am following precursor eruption on Wednesday. Loud blasting sound heard from 20 km away and produce eruption column that reach as high as 3.5 km. Yogyakarta city which is located 20 km south of the volcano covered by half cm thick of ash and sand, the pouring of ash and sand occurred until it ceased around 4am. More people flees to the evacuation center as the new eruption affecting broader area than predicted.

Update:
Another explosive eruption occurred on Monday, November 1, 2010 around 10am producing pyroclastic flow that traveled mostly to the southeast. The ash and fine volcanic material reach as far as 80km south of the volcano.

Pyroclastic flow produced by Merapi during Monday, November 1, 2010 eruption as seen from Pakem (Detik)

The death toll of Merapi eruption rise to 25 (updated: 34)

The death toll of the Merapi eruption at Indonesia's Mount Merapi rose to 25 on Wednesday, October 27, 2010, while 14 people still under treatment from severe burns and more than 19,000 villagers were moved to temporary shelters.

Mount Merapi spewed searing gas and volcanic debris on 5pm Tuesday, October 26, 2010 destroyed the village of Kinahrejo and Kaliadem. The volcano observatory recorded that the eruption start around 5 pm. Six pyroclastic surges were recorded before roaring and explosive sound occured around 6pm, and then two more pyroclastic surges occurred until around 7pm. The volcanic ashes reaches as far as 200 km west of the volcano.

Though the activity currently decreased, the authorities said that readings suggested that it is possible that the current activity is only foreshadow of a much more destructive explosion in the coming weeks or months, thus the residents were advised to continue to remain in shelters. Many lives were saved after authorities ordered thousands of them to evacuate the danger zone, after raising the alert level into its maximum level on Monday.

Destroyed house and vehicle at Kinahrejo (Kompas)

Volunteers carry the bodies of those who died after Mount Merapi erupted. (Yahoo News)

Update (as of Friday, October 29, 2010): the death toll rose to 34, and 44,986 people are still remain in the evacuation shelter.

Magnitude 7.7 - Kepulauan Mentawai, West Sumatra, October 25, 2010

A magnitude of 7.7 earthquake struck Kepulauan Mentawai region of Sumatra on Monday, October 25, 2010 at 09:42:22 PM local time. Tsunami warning reported but was lifted after an hour. No causalities and damage reported yet. The earthquake caused panic reaction to the residents of the island and nearby major city of Padang, strong shake also felt by the residents of nearby cities of Bengkulu and reach as far as Jambi region. The epicenter of the quake was in the position of 3.464°S, 100.084°E with the uncertainty of horizontal +/- 14.1 km (8.8 miles); depth +/- 14.2 km (8.8 miles). Aftershocks with magnitude range of 5.5 still happen in the region.

Maps

Update: tsunami hits the remote Mentawai Islands, destroyed villages in the south of the island chain and sweeping scores out to sea. The authority informs that the surge reached as high as three meters and advanced as far as half kilometer inland. The scale of the destruction did not become clear until Tuesday, October 26, 2010 as rescuers and local officials crossed a Sumatran strait to reach the islands. At least 113 people killed, more than 500 are still missing and thousands survivors left homeless, the death toll expected to rise. Electricity and telecommunication system in the area are currently disconnected.

Figure caption: Destroyed houses at Betumonga village, Sipora island, Mentawai (Kompas)

Figure caption: A rescue team loaded a ship in Padang, West Sumatra on Tuesday to prepare for the evacuation and rescue of victims of the 7.7-magnitude earthquake and resulting tsunami. (New York Times)

An Overview of Merapi Volcano, Central Java, Indonesia

Written by:
Gayatri Indah Marliyani
San Diego State University, USA
Gadjah Mada University, Indonesia

INTRODUCTION
Merapi is a strato-volcano located in Central Java, Indonesia, about 30 km north of Yogyakarta city which has more than one million inhabitants (Figure 1, Figure 2). It is part of the volcanic front of the Sunda-Banda magmatic arc produced by subduction of the Australian plate under the Eurasian plate. The Indonesian archipelago resulted from complex and diverse tectonic processes (Simandjuntak & Barber, 1996, Wilson 1989, Hamilton, 1979). The present phase of orogenic activity in Indonesia commenced in the mid-Miocene and is still in progress (Simandjuntak & Barber, 1996). In westernmost Sumatra, it involves strongly oblique convergence and major strike slip transcurrent fault movement within the magmatic arc (Figure 3). Continuing to the east, in Java and Nusa Tenggara, normal convergence produces an orogenic belt and Andean type subduction zone. This subduction zone is characterized by trench, accretionary complex, forearc basin and Quaternary active volcanoes built on the margin of the Sundaland continent. Merapi is one of these volcanoes. Further to the north east, convergences of oceanic plates set the Sangihe and Halmahera magmatic arc, while in Sulawesi, it involves collision of microcontinental blocks with subduction systems along the eastern margin of Sundaland. Moving to the south of Sumba, it involves collision of the northern margin of the Australian continent with the subduction system along the southern segment of the Banda Arc. A more advanced stage of collision of the northern margin of the Australian continent with a magmatic arc on the Philippine Sea plate forms the easternmost part of Indonesia, Irian Jaya.

Having an average eruption frequency of once every 4-5 years with more explosive and larger episodes every few decades, this volcano is considered one of Indonesia’s most active volcanoes. Despite the danger of living close to a volcano, many people occupy fertile land surrounding Merapi, risking exposure to pyroclastic flow and possible larger explosive eruptions. For this reason, Merapi was selected as one of the focus volcanoes during the International Decade for Natural Disaster Reduction (Newhall et al. 1994).

In this writing, I describe Merapi based on published data and limited personal field observation. This description includes morphological aspects, eruption type and history, rock types, and also includes monitoring for hazard assessment and recommendations.

Figure 1. Regional map of Merapi and its surroundings, modified from Camus et al, 2000

Figure 2. Morphology of modern Merapi, with Merbabu mountain behind, seen from approximately 20 km south of Merapi (http://discover-indo.tierranet.com/newsa.htm)

Figure 3. Map of the Indonesian subduction system shows general tectonic setting and distribution of active volcanoes (marked as circles). Arrows indicate the direction of movement (after Gertisser and Keller, 2003)

MORPHOLOGY
Merapi forms a bell-shaped topography that has a mean dip angle of 5° up to 1300 m and 15° up to the summit of 2911 m (Berthommier, 1990). The porphyric nature of the lava and alternating deposits of lahars and pyroclastic flows forms an un-compacted and highly porous material that is easily eroded. Merapi's morphology is characterized by steep erosional valleys of all sizes and radial ridges (Mizutani, 1990).

There are two high temperature fumarolic fields near the Merapi summit, Gendol and Woro, located 150 m and 250 m SE of the centre of the summit crater. The maximum fumarolic temperatures in the Gendol field are greater than 800°C, while those in Woro are higher than 600°C (Zimmer and Erzinger, 2003). The SO2 gas is continuously discharging from the fumaroles and the lava dome.

ERUPTIONS
Merapi has behaved as a classical strato-volcano, with alternating phases of effusion of lava flows and vertical vulcanian explosions that could generate scoria flows (Camus et al, 2000). The major event that interrupted this behavior was a sector collapse, with an inferred associated blast. Later, strong magmatic and probably phreatomagmatic events occurred, preceding the present dome-building phase.

The total Merapi eruption volume is estimated between 100 and 150 km3 (Berthommier, 1990) with present rate of effusions at about 105 m3 per month over the past 100 years (Siswowidjoyo et al., 1995). A strong uncertainty remains concerning the beginning of its activity. If the effusion rate is assumed to be constant since the beginning of its activity, Merapi could be between 8.300 and 125.000 years old (Camus et al, 2000). However the geological evidence, Camus et al (2000) suggests that the rate of flow may have decreased during the evolution of Merapi. Thick and long lava flows were progressively replaced by smaller ones, then by slow dome extrusions. If so, Merapi is much younger. According to Newhall et al (1995), Merapi shows evidence of over 7000 years of explosive eruptions, and Charbonnier & Gertisser (2008) give an age around 40.000 years.

Figure 4. A pyroclastic flow referred to Merapi type nuee ardente at 08:54:37 on 7 June 2006 traveling down Merapi's upslope region in a generally SE direction. (The Research and Technology Development Agency for Volcanology-BPPTK, Yogyakarta).

On the basis of field studies and geochronological data, Camus et al (2000) divided its history into four periods: Ancient, Middle, Recent and Modern Merapi. The Ancient Period may have begun around 40.000 y BP and lasted until 14.000 y BP as the Middle Period begun. The Recent Period begun around 2200 y BP and was replaced by the Modern Period after the eruption of 1786. During the Middle Merapi stage, a St. Helens-type edifice collapse occurred. During the Recent Merapi stage, two violent magmatic to phreatomagmatic eruptions interrupted the growth of the volcano.

The older phreatoplinian deposits cover the entire cone; charcoal found within these deposits gave 14C ages of 2200 and 1470 y BP (Camus et al, 2000). The overlying ash deposits, referred to as Sambisari ash deposits, were emplaced by violent pyroclastic surges directed towards the south, i.e. to the present location of the town of Yogyakarta, burying the Shivaitic temple of Sambisari at the start of the 15th century. Many other Shivaitic temples, such as Prambanan, Kadisoko, Kedulan, (Figure 7) were found buried under thick volcaniclastic deposits south of Merapi, indicating that the pyroclastic flow and surge deposits can reach as far as 25-35 km. It is believed that there are still many temples and other remains of ancient civilizations still undiscovered under the deposits. This distance makes it clear that Merapi produces not only dome-collapse pyroclastic flows, but also pyroclastic flows related to moderate to large explosive eruptions (Camus et al, 2000).

Modern Merapi is characterized by the persistent growth of a summit dome, known as Merapi-type activity, which is described as a semi-continuous outpouring of viscous lava producing a summit dome, interrupted by periodic gravitational dome collapse or total destruction triggering violent block-ash flows and associated surges. The ash produce is referred to as Merapi-type nuées ardentes (Figure 4) (Escher, 1933, Voight et al., 2000). Sometimes, a more exceptionally, fall-back St. Vincent type nuées ardentes (scoria flows) occurs.

Figure 5. The excavation process of Kedulan temples that were buried under at least 6 m thick volcaniclastic deposits approximately 25 km south of Merapi (http://media.photobucket.com/image/candikedulan.jpg/noncy_2008/candikedulan.jpg).

Since the mid-1500s, eighty eruptions have been recorded and almost half have been accompanied by the dome-collapse pyroclastic flow (Simkin and Siebert, 1994). About sixteen of Merapi's past eruptions, including the latest eruption episode in 2006, have caused fatalities (Charbonnier and Gertisser, 2008). Most pyroclastic flows events in the 20th Century that were produced by collapse domes produced limited amount of lava and traveled relatively short distances. Occasionally, as in 1930, unusually large collapse related flows traveled 10 km from the summit into populated areas. However, several studies on the older deposits revealed that many eruptions during the 7–19th centuries A.D. were substantially more violent and swept broad sectors of the volcano with explosion type pyroclastic flows (Kemmerling, 1931; Neumann van Padang, 1931, 1933, 1936/1937; Escher, 1933; Hartmann, 1934, 1935). These eruptions, much larger and more explosive and violent than any of the 20th Century, have occurred at irregular intervals of several decades as identified in 1768, 1822, 1849, 1872, and 1930–1931. The 1872 eruption is the only one of a St. Vincent-type during the Modern Period (Hartmann, 1934), but many deposits attest that it was a very frequent type during the preceding periods. In 1872, all the flanks of the volcano were covered by ash-and-scoria pyroclastic flows. An interesting fact quoted by Hartmann (1934) is that the building up of the volcanic column was progressive, and preceded by two days of spectacular events describes as roarings sounds, intensive volcanic tremor and smaller explosions, which explains the small amount of causalities recorded, since many inhabitants had left the danger zone before the climax of the eruption.

In contrast, the 1930–1931 eruption, in spite of an exceptionally high lava output, the eruption was quiet, without pyroclastic flows that last for 23 days. So, the cataclysmal explosive phase was unexpected, explaining the great number of fatalities. This unusual behavior was related to the opening of a vent at a place lower than usual, which is at the foot of the older summit domes. This opening can be caused by hydraulic fracturing, or by utilization of a pre-existing weak zone, or both (Camus et al, 2000). It is important to recollect that the eruption began after 11 months of increasing seismic activity. This type of sub terminal eruption seems to be exceptional at Merapi. If this type of eruption would occurs again, it could be on the same flank of the volcano, or on its south flank, where there is a fractured zone with fumaroles and small solfataras, at about 300 m below the summit (Camus et al, 2000).

The absence of large ignimbrite eruptions suggests both the absence of a large-deep reservoir and of a long stage of volcanic rest (Camus et al, 2000). Inferred from seismic observation, location of the magma reservoir which feeds the eruptions is estimated to be at 1.5 km below the summit (Ratdomopurbo, 2000).

By observing the long recorded behavior of Merapi, the occurrence of explosive eruptions during periods of less explosive dome growth and dome collapse is more likely than the occurrence new open-vent eruptions. An average low level activity of Merapi can be interrupted by a much larger explosive eruption and there is no reliable evidence to assume that the future activity will be as benign as that of the 20th century (Newhall, 2000).

CHRONOLOGY OF 2006 ERUPTION
To give a better understanding of the behavior of modern Merapi, I present here the sequence of the latest eruption of 2006 includes its chronology and deposits.

The 2006 eruption of Merapi consisted of three eruption phases that produced a complex sequence of block-and-ash flows directed mainly towards the south-western (May 2006) and southern flanks (June 2006) of the volcano (Charbonnier and Gertisser, 2008). After a dormant period of nearly five years, volcanic activity at Merapi resumed in July 2005 with an increase in the number of volcanic tremor and deformation of the summit area. This renewed episode of activity ended with the extrusion of a new lava dome in March 2006. In contrast to summit lava domes predating the 2001 eruption, which were mainly located inside the 1961 crater, the 2006 lava dome of Merapi was emplaced near the eastern rim of the 1931 crater, locally known as Gegerbuaya (Figure 6). The period of lava-dome growth that started in March 2006 increased during April and was rapidly followed by periods of multiple rockfalls and dome-collapse pyroclastic flows during May and June 2006.

Due to the presence of a topographic barrier in the south-eastern sector of the 1931 crater (Gegerbuaya ridge; Figure 5), the rockfalls and dome-collapse pyroclastic flows of the first eruption phase from May 5–27, were mainly directed towards the southwestern flank of Merapi into the Krasak, Bedok and Boyong River valleys, with runout distances of <4>6 m3.

The second eruption phase was associated with a magnitude 6.3 earthquake on May 27, whose epicenter was located 35 km south of Merapi (Fig. 1). Immediately after this event, lava extrusion rates at Merapi increased to 0.1×106 m3/day. On June 4, the summit lava dome reached a volume of >4.0×106 m3 and a height of 116 m above the summit peak (BGVN 32:02). Following partial collapse of the eastern part of the Gegerbuaya ridge (Fig. 5), an increase in the volume of successive pyroclastic flows and associated collapsed material was observed. This succession of events allowed flows to take a different path and travel down the southern and south-eastern flanks of Merapi, which were not affected by pyroclastic flows for more than a century.

During the third eruption phase in June, the activity occurred in two distinct periods. Between June 3 and 12, several dome-collapse pyroclastic flows affected the southern and south-eastern flanks towards the Gendol River valley with runout distances <4.5 km. On June 14, the activity peaked with two sustained dome-collapse events produced at least two pyroclastic flows with maximum runout distances in the Gendol River valley of 5 and 7 km. The largest of these flows caused two fatalities and partially buried the village of Kaliadem (Figure 7). This peak collapse event was preceded by a high lava extrusion rate and over-steepening, creeping and deflation of the lava dome (Merapi Volcano Observatory BPPTK, 2006). After June 14, the number and frequency of pyroclastic flows decreased until the end of the eruption in early July.

Figure 6. Ikonos satellite image of the summit area of Merapi on May 10, 2006. Lava domes and viscous flows are labeled with the year of extrusion. The white dotted line corresponds to the 1931 crater rim. The Gegerbuaya ridge is formed by 1911 lavas (Charbonnier and Gertisser, 2008).

Figure 7. Destroyed houses and dislodged ash and volcanic rocks from Merapi in the village of Kaliadem (SE flank ~ 5 km from the summit) shortly after the 14 June 2006 pyroclastic flows passed through the settlement. (http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-25=&volpage=var#bgvn_3310)

ROCK TYPES
Most of the lavas of Merapi are calc-alkaline, high-K basaltic andesites, with a restricted compositional range from 52–57% SiO2 (Camus et al, 2000). Some basalts and andesites occurred, but scarce, extending the compositional range to 49.5–60.5% SiO2 (Figure 8). The lavas are highly porphyritic, with phenocryst and microphenocryst contents ranging from 22–62% (Camus et al, 2000).

The mineralogy throughout Merapi's history is generally very similar, and the characteristic assemblage is plagioclase, clinopyroxene (augite–salite), brown hornblende, olivine, titanomagnetite, and hypersthene (only in basaltic andesites), embed in a clear to brown glassy matrix (Camus et al, 2000). The main accessory minerals are apatite, which occur as microphenocrysts, alkali-feldspar and tridymite as interstitial phases in the groundmass. The groundmass is partly crystalline, with mainly microlites of plagioclase and pyroxenes.

Figure 8. Total alkalies versus silica diagram for Merapi volcanic rocks (Camus et al, 2000). Fields represent the volcanic rock classifications of LeBas et al (1986).

The complex zoning of plagioclase, the wide compositional range of plagioclase for a single sample and disequilibrium textures for amphibole and pyroxene, suggest thermal and chemical disequilibrium (Camus et al, 2000). The additional macroscopic and microscopic evidence for mixed glass indicates the occurrence of a magma mixing process. Magma mixing may have buffered the compositions of lavas at Merapi, resulting in the restricted range of whole-rock composition (52–57% SiO2). Typical phenocryst assemblage is plagioclase > clinopyroxene > amphibole, orthopyroxene, olivine, titanomagnetite. A general trend toward more evolved magmas, from Recent to Modern Merapi is recognized (Camus et al, 2000).

Deposits from the explosive phases of the Modern Merapi period can be classified into three types (Kemmerling, 1832; Escher, 1933, Camus et al, 2000):
(1) Block and ash flow deposits of the Merapi type, commonly produced by dome collapses (Figure 9). These deposits are characteristic of the Modern Merapi Period and, to a certain extent, also occur in the Middle Period. They have not been recognized as the products of the Ancient Period eruptions.
(2) Block and scoria flow deposits, produced by fall-back nuees ardentes of the Saint Vincent type.
(3) Surge-like “pelean” deposits. Grandjean (1931) suggested that the 1930–1931 eruption could have generated violent “pelean” surges; deposits related to such eruptive processes have not been described before 1994 at Merapi.

Figure 9. The 2006 block-and-ash flow deposits in the upper Gendol River valley (http://www.esci.keele.ac.uk/merapi/about.htm)

Figure 10. Detailed map of the June 2006 block-and-ash flow deposits on the southern flank of Merapi. Typical longitudinal profile along the pre-2006 topographic surface with the distribution of individual lobe deposits is shown in the inset. Contour heights are in meters (Charbonnier and Gertisser, 2008)

Surface particle assemblage analyses on 2006 block-and-ash flow deposits were performed by Charbonnier and Gertisser (2008) as presented in Table 1. They grouped the assemblages lithologically into six main types, which are representative of the rock types found within the different flows generated during this eruption period (Figure 10). The juvenile component is a porphyritic basaltic andesite that can be divided into four main lithologies: (1) light grey scoria (2) dark grey scoria, (3) light grey dense clasts, and (4) dense, prismatically jointed clasts. These juvenile components range in density from 1.7 to 2.6 g/cm3 (mean 2.2 g/cm3, n=25). The two other components identified as hydrothermally altered and oxidized clasts are lithologically distinct from the juvenile material and represent accidental lithics which were incorporated into the flows. Their density ranges from 1.8 to 2.4 g/cm3 (mean 2.1 g/cm3, n=20). These clasts represent the old dome fragments and/or lava flows which constitute the south-eastern part of the summit area as it has similarity with the material taken from Gendol solfatara field and the 1931 crater wall.

MERAPI MONITORING
The institution that is responsible for monitoring the activity of Merapi is Volcanological Survey of Indonesia (VSI). The monitoring encompasses these parameters: seismicity, volcanomagnetism, deformation, geochemistry, visual monitoring of summit morphology and dome evolution, and also lahar detection during episodes of eruption.

Seismicity is considered the most important parameter for estimating the probability of an eruption. The seismic signals observed at Merapi volcano are classified as A-type, B-type, multiple phase events, long-period events, tremor and rock fall (Ratdomopurbo, 1995). Currently, the network of eight seismographs established around the volcano, allows volcanologists to accurately pinpoint the hypocenters of tremors and quakes.

Geomagnetic monitoring in Merapi has been carried out since 1977 with a total of four sensor stations established. Those sensors continuously measure the total geomagnetic intensity with a sampling rate of one data sample/minute.

Geochemical monitoring of Merapi has been carried out since 1984. Several fixed points are located at two main solfatara fields of Gendol and Woro for a continuous sampling.

Since 1961, the only change in the morphology of the summit has taking place inside the crater. Alternation of dome formation and dome collapse occurs frequently. As the direction of pyroclastic flows depends strongly on summit morphology and the condition and position of the dome, visual observation of the summit and the dome is necessary. Detailed observations of the crater were conducted by a team sent to the summit to take photographs of the crater and the dome. From the successive photographs, the evolution of the dome can be reconstructed.

The VSI also established six observation posts: Kaliurang, Ngepos, Babadan, Jrakah, Krinjing and Selo. Every observation post is equipped with a telescope to observe changes in the upper part of the volcano, including rock fall activity; source, direction and distance traveled by avalanches, location of dome build up and height of the volcanic smoke.

Lahar is one of the important secondary hazards in Merapi. In 1975, lahar in the Krasak River destroyed the bridge on the main road connecting the provinces of Yogyakarta and Central Java. On December 5, 1996 at Boyong River, 14 mining trucks were buried under the lahar flow. The measurement of the lahar volume based on estimates of the volume of loose material at the slope. Some detectors also placed near some river channels as an early warning system. A lahar event is usually triggered by heavy rainfall, and so the system must be more alert under conditions in which the volume of material reaches a threshold and there has been rainfall of around 50-mm/hour.

All of the data is sent directly to the base station of Merapi Volcano Observatory, Volcanological Survey of Indonesia (MVO-VSI) which is located in Yogyakarta City. The data is processed to maintain the alert level of the volcano on a daily basis. The MVO-VSI is also responsible for producing a volcano hazard map of Merapi and for revising it when necessary.

DISCUSSION
There are more than one million inhabitants endangered by Merapi. The prominent hazards of this volcano come from the direct and secondary effects of the eruptions. The direct effect is related to block and ash pyroclastic flow and associated surges that are produced by gravitational dome collapses. Secondary effects include laharic flow produced by mixing of its loose material with water and by aerial and water pollution. The areas expected to experience the effect of eruption are mapped by the MVO-VSI. This map divides the area surround the volcano into several zones based on susceptibility to danger from future eruptions. This prediction is largely based on the present morphological condition of Merapi.

In addition, predicting the eruption hazards of Merapi must be estimated not only based on the eruptions observed during the Modern Period, which are relatively small, but also from the much larger eruptions that preceded it. There is a broad spectrum of scenarios describing the large eruptions of the past. The prediction of future eruptions must take this into account, bearing in mind that the scenario likely will differ. For example, the location of the vent could change, or a new dome be created with associated pyroclastic flows going in different direction from eruptions in the past.

Many villages and towns around Merapi are built on deposits of Merapi’s large explosive eruptions. At least 80,000 and perhaps as many as 100,000 people live inside the so-called Forbidden Zone defined by Pardyanto et al (1978). This area lies roughly within a 10 km radius of the summit, mainly on the west and south sides of the volcano. Several hundred thousands more live just a few kilometers outside that zone. The residents are familiar with small dome-collapses but not many realize that their homes and schools are built on deposits of much larger, relatively young, lethal explosive eruptions.

There is no assurance from the geologic record that Merapi will remain as quiet in the next century as it was during the 20th Century. Rather, it is suspected that a major explosive eruption will occur within the coming decades. Large numbers of people, both within and beyond the Forbidden Zone will be at serious risk. Public education and discussion of the intent of the Forbidden Zone, a willingness among all parties to accept some false alarms, and an ongoing search for precursors of a larger explosive eruption are needed to limit the risk.

REFERENCES
Berthommier, P., 1990. Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et Chronologie. Mécanismes éruptifs. Thèse Doct. III ème cycle, Univ. Blaise Pascal, Clermont–Ferrand, 115 pp
Camus, G., Gourgaud, A., Mossand-Berthommier, P.-C. and Vincent, P.M., 2000. Merapi (Central Java, Indonesia): an outline of the structural and magmatological evolution, with a special emphasis to the major pyroclastic events. J. Volcanol. Geotherm. Res. 100, pp. 139–163.
Charbonnier, S.J. and Gertisser, R., Field observations and surface characteristics of pristine block-and-ash flow deposits from the 2006 eruption of Merapi Volcano, Java, Indonesia, Journal of Volcanology and Geothermal Research 177 (2008), pp. 971–982.
Escher, B.G., 1933. On a classification of central eruptions according to gas pressure of the magma and viscosity of the lava. On the character of the Merapi eruption in central Java. Leidsche Geol. Meded. VI 1, pp. 45–58.
Gertisser, R. & Keller, J. (2003): Trace element and Sr, Nd, Pb and O isotope variations in medium-K and high-K volcanic rocks from Merapi Volcano, Central Java, Indonesia: evidence for the involvement of subducted sediments in Sunda Arc magma genesis. Journal of Petrology, 44: 457-486.
Hamilton, W, 1979. Tectonics of the Indonesian regions. U.S. Geol. Surv. Prof. Pap. 1078.
Hartmann, M., 1934. Die Vulkanische Tatigkeit des Merapi Vulkanes (Mittel Java) in seinem ostlichen Gipfelgebiete zwischen 1902 und 1908. De Ingenieur in Nederlandsch Indie, IV. Mijnbouw en Geologie 1ste Jaargang (5), 62–73.
Hartmann, M., 1935. Die Ausbruches des Gunung Merapi (Mittel Java) bis zum Jahrey 1883.
Kemmerling, G.L.L., 1931. Beshouwingen over de hernieuwde werking van den Merapi der Vorstenlanden van December 1930. Tijdschr. Kon. Ned. Aarddr. Genoot. 48 (2), 712–743.
Mizutani, T., Longitudinal profiles of radial valleys on the Merapi Volcano in central Java, Indonesia, Geographical Reports of Tokyo Metropolitan University, 25, 183-194, 1990.
Neumann van Padang, M., 1936. Die Tatigkeit des Merapi-Vulkans (Mittel Java) in den Jahren 1883–1888. Z. Vulkanol. 17, 93–113.
Neumann van Padang, M., 1931. Der ausbru¨ch des Merapi (mittel Java) im jahre 1930. Z. Vulkanol. XIV, 135–148.
Neumann van Padang, M., 1933. De Uitbarsting van den Merapi (mittle Java) in de Jahren 1930–1931. Vulk. en Seis. Med. 12, 1–117.
Pardyanto, L., Reksowigoro, L.D., Mitromartono, F.X.S., Hardjowarsito, S., Kusumadinata, 1978. Volcanic hazard map, Merapi volcano, Central Java (1/100 000). Geol. Surv. Of Indonesia, Bandung, II, 14 (reed. 1982).
Ratdomopurbo, A., Poupinet, G., 1995. Monitoring a temporal change of seismic velocity in a volcano: application to the 1992 eruption of Mt Merapi (Indonesia). Geophys. Res. Lett. 22, 775–778.
Simkin, T. and Siebert, L., 1994. Volcanoes of the World (2nd ed.), Geoscience Press, Tucson, AZ 349 pp.
Simandjuntak, T.O. and Barber, A.J., 1996, Contrasting tectonic styles in the Neogene orogenic belts of Indonesia, Geological Society, London, Special Publications; 1996; v. 106; p. 185-201; DOI: 10.1144/GSL.SP.1996.106.01.12
Siswowidjoyo, S., Suryo, I. and Yokoyama, I., 1995. Magma eruption rates of Merapi volcano, Central Java, Indonesia, during one century (1890–1992). Bull. Volcanol. 57 2, pp. 111–116.
Voight, B., Constantine, E.K., Siswowidjoyo, S., Torley, R., 2000. Historical eruptions of Merapi Volcano, Central Java, Indonesia,1768–1998. J. Volcanol. Geotherm. Res.100, 69–138.
Wilson, M., 1989. Igneous Petrogenesis: a Global Tectonic Approach, Unwin Hyman, London.
Zimmer, M.; Erzinger, J., Geochemical Monitoring on Merapi Volcano, Indonesia, 1st Merapi-Galeras-Workshop, Potsdam, 25 June 1998, DGG Special Issue, 1999.

Website references
Global Volcanism Program-BGVN, http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-25=&volpage=var#bgvn_3310
Keele University Merapi Research http://www.esci.keele.ac.uk/merapi/about.htm
The Research and Technology Development Agency for Volcanology-BPPTK, Yogyakarta http://portal.vsi.esdm.go.id
http://discover-indo.tierranet.com/newsa.htm

A new episode of Merapi eruption begin

The Indonesian Center for Volcanology has issued a third-degree warning on the possible eruption of the Merapi volcano in densely populated Yogyakarta City, Central Java. The status of Merapi was raised on September 21, 2010 from the second degree 'warning' to the third degree 'expectation'. All activities in the threatened area around the volcano will be banned for safety reasons. The official said the volcano's activity had been rapidly increasing, accompanied by tremors and frequent lava spills. According to the Indonesian Center for Volcanology the current condition has reached the point of no return. They expected that the new eruption will produce pyroclastic flows that could travel up to 15 miles.

Updates:
Indonesian Geological Agency has raised the alert level for Merapi volcano on 6 am of October 25, 2010 into its maximum level.

The un-expected Mount Sinabung eruption in North Sumatra, August 29, 2010

After a dormant period of 400 years, Mount Sinabung in North Sumatra erupts on Sunday, August 29, 2010 at 00.08pm. The ejected materials, seen as thick black smoke, consist of sands, small stones and sulfur gas reach as high as 1,500 meters (about 5,000 feet) and prompting the evacuation of at least 12.000 residents. One people reported died of breathing difficulties. The ash spread to a distance of 30 kilometers from the volcano. Evacuated resident are staying in government buildings, houses of worship and other evacuation centers in two nearby towns.

The volcano erupts after rumbling for several days. On August 29, 2010, the increasing activity manifest by white smoke and fumarola solfatara in the active crater. On the following day, Sunday at 00:08 pm, roaring sound heard from the summit area, remarking the main eruption stage. Center for Volcanology and Geological Hazard Mitigation (PVMBG) immediately raised the level alert into its highest level. This volcano previously classified as type B volcano, and after the eruption, PVMBG raised its type into type A.

The 2,460-meter Sinabung volcano located in District Tanah Karo, North Sumatra. The nearest major city is Medan. There is no flight disruption reported yet. The eruption was unpredictable, caused by lack of knowledge in terms of its eruptive patterns and general forms; the last activity recorded in this volcano was that in 1600.

A villager covers her nose and mouth from volcanic ash as Mount Sinabung spews smoke in the background in Karo, North Sumatera, Indonesia, Saturday, Aug. 28, 2010. (Image source: Associated Press)

Update: Second, more forceful eruption occurred early on Monday, August 30, 2010, forcing more than 20.000 people to remain in evacuation centers. The eruption occurred at 6.30 am create a column of smoke up to 2000 meter into the sky.

Mount Sinabung's second eruption on Monday, August 30, 2010 (Image source: The Jakarta Post)

Update: Third and even more forceful eruption occurred on Friday, September 3, 2010 around 4.38am. Covering nearby area with thick, black smoke. The sound and volcanic tremor felt by residents at 12 km away from the volcano.

Magnitude 5.0 Yogyakarta Earthquake

A magnitude 5.0 struck Yogyakarta region on Saturday, August 21, 2010 at 06:41:38 PM local time. The epicenter located 6 km southwest of the damaging M 6.2 earthquake of May 26, 2006, onshore at position 8.034°S, 110.380°E (BMG). It is not clear if this events is related to 2006 events but by looking at alignment location of the epicenter, there is a big possibility that this earthquake occurred at the same fault system. The 2006 events caused more than 6.000 fatalities and a massive infrastructure destruction, leaves traumatic memories to the residents and causing panic reaction to this particular event. The shakes felt as a strong ground motion for about 5 seconds by the residents of Yogyakarta city, Bantul and Gunungkidul regency. No damaged and fatalities reported yet.

Location of this event related to 2006 event

Landslide In Cianjur, West Java

Another devastating landslide has occurred in West Java, following Ciwidey landslide that were happened 18 days before. The landslide occurred at Kampung Ciawi Tali, Cianjur, West Java Province on Thursday, 11 March 2010 at 6.30 pm. Seven people were confirmed dead and four others still buried under the debris and subject for search and rescue. At least 20 houses and school damaged and 100 people have been evacuated.

The prominent factors of landslide in Indonesia are lithology and morphology. Highly weathered material can be easily found in Indonesia. If it occurred on the steep morphology and water penetrate into the material, it will weaken the slope and increase the potential of mass movement as it cross the threshold. The increasing of precipitation rate during the late monsoon season should raise alert of the potential similar hazard near in the future. People living on unstable areas should be warned, prepared and trained to face it. A map of the susceptible-to-landslide area are available for most of Indonesian region (low resolution of the West Java image can be found here), that the government, from high to low level should be familiarize themselves with this map and socialized it to the people in the area. As published before in this website, applying a simple-low cost early warning system could be considered to reduce the causalities of landslide at high susceptible area, if relocation is not possible.

Magnitude 6.5 Earthquake, Southwest of Sumatra

A magnitude-6.5 earthquake struck the western shore of Indonesia's Sumatra island on Friday, March 05, 2010 at 11:06:57 PM. The epicenter located offshore at 4.032°S, 100.806°E at 22 km depth, about 165 km (100 miles) West of Bengkulu and 345 km (215 miles) South of Padang, Sumatra. This event causing panic but no casualties or damage yet reported. No tsunami potential being issued.

Epicenter location on Google Earth map

Moment tensor solution for this event can be found here.
Base map (topographic map scale 1:10.000) of Padang, Jambi, Bengkulu and surrounding area can be found here.

Ciwidey-West Java landslide, 23 February 2010

A landslide buried a village in West Java early on Tuesday, 23 February 2010 around 7am. The site located in a tea plantation village of Ciwidey, about 90km south of Bandung, West Java and 150 km southeast of the capital, Jakarta. At least 45 people were killed, 21 people were confirmed died while 24 others still buried under the debris, houses occupied by 35 families working in the tea plantation buried by the landslide.

Weathered layers of lava, tuff and andesitic breccias made up the lithology of the area. Morphology of the area in general are hilly and steep. The area were included in the landslide hazard map of West Java province as high to medium risk zone. Heavy rain in the area during the week prior to landslide possibly was the main triggering factors beside the morphology and the lithology of the area.

The government investigates whether the land clearing practices by one of a tea plantation company at the 740-acre hillside were to blame, while the company owner blames the September 7.0 earthquake cause the cracks on the foothills that weakening the hillside.

Base Map and Initial Assessment

Picture showing the village before landslide (left) and after landslide (right). (Indonesian Geology Agency)

Villagers walk at a neighborhood hit by a landslide in Ciwidey district, West Java, Indonesia, Thursday, Feb. 25, 2010. Days of heavy rain prompted the landslide Tuesday afternoon at the mountainous tea plantation destroying scores of homes. (AP Photo/Irwin Fedriansyah)

Triangle of Life? How to Survive During an Earthquake

In recent years, an e-mail has been circulating which describes an alternative to the long-established "Drop, Cover, and Hold On" advice. The so-called "triangle of life" and some of the other actions recommended in the e-mail are potentially life threatening, and the credibility of the source of these recommendations has been broadly questioned (http://earthquakecountry.info/dropcoverholdon/).

Earthquakes occur without any warning and may be so violent that you cannot run or crawl; you therefore will most likely be knocked to the ground where you happen to be. Given the dynamics of earthquakes and their effects on structures, "Drop, Cover, and Hold On" is the single most useful instruction that you can follow to protect yourself in the majority of situations. It gives you the best overall chance of protecting yourself during an earthquake... even during quakes that cause furniture to move about rooms, and even in buildings that might ultimately collapse.

Studies of injuries and deaths caused by earthquakes over the last several decades indicate that you are much more likely to be injured by falling or flying objects (TVs, lamps, glass, bookcases, etc.) than to die in a collapsed building. The "Drop, Cover, and Hold On" position will protect you from most of these injuries. If there is no nearby space beneath a table or other furniture that can provide protection from these objects, ONLY then you should get next to furniture such as a sofa that won't tip over, cover your head, and hold on to the furniture and be ready to move with it as it shifts in the shaking. If there is no furniture, get down next to an interior wall if possible (exterior walls are more likely to collapse and have windows that may break) and cover your head and neck with your arms. If you are in bed, the best thing to do is to stay where you are and cover your head with a pillow. Studies of injuries in earthquakes show that people who moved from their beds would not have been injured if they had remained in bed.

In many seismically active parts of the U.S. and other countries, strict building codes reduce the potential of structure collapse. However, there is the possibility of structural failure in certain building types, especially unreinforced masonry, and in certain structures constructed before the latest building codes. Rescue professionals are trained to understand how these structures collapse in order to identify potential locations of survivors. The ONLY exception to the "Drop, Cover and Hold On" rule is if you are in a country with un-engineered construction, and if you are on the ground floor of an unreinforced mud-brick (adobe) building, with a heavy ceiling. In that case, you should try to move quickly outside to an open space. This cannot be recommended as a substitute for building earthquake-resistant structures in the first place!

If you do become trapped in a collapsed building, it will be important to immediately protect your airway against dust and debris by breathing through clothing or material (preferably a dust mask if one has been stored near their desk, bed, or other accessible location); check yourself for injuries and control any bleeding; find a source of light if possible; and make your location known to rescuers by tapping on a solid object with a rock or other instrument. Save your breath and energy. Delay yelling for help until you hears rescuers very nearby.

If a building does collapse, rescue teams will methodically search through the rubble for victims, using tools, search dogs, and electronic instruments that can detect the presence of live people. Survivors are usually found in spaces large enough for a human within the collapse debris, called "Survivable Void Space." It can be as large as an adult, or in the case of small children or infants, a very small space. The main goal of "Drop, Cover, and Hold On" is to protect you from falling and flying debris and other nonstructural hazards, and to increase the chance of your ending up in a Survivable Void Space if the building actually collapses.

The "triangle of life" advice is based on several wrong assumptions:
• buildings always collapse and crush all furniture inside (wrong);
• residents can always anticipate how their building might collapse and anticipate the location of survivable void spaces (wrong); and
• during strong shaking people can move to a desired location (wrong).

Experts agree that in the rare case that a building collapses, residents inside will not be able to anticipate the location of void spaces nor move to them during the strong shaking before the collapse. Some other recommendations in the "triangle of life" email are also based on wrong assumptions and very hazardous. For example, the recommendation to get out of your car during an earthquake and lay down next to it assumes that there is always an elevated freeway above you that will fall and crush your car. Of course there are very few elevated freeways, and laying next to your car is very dangerous because the car can move and crush you. A compilation of rebuttals from many organizations to these alternative recommendations, as well as news articles about the controversy, is online at www.earthquakecountry.info/dropcoverholdon.

In conclusion, the "Drop, Cover and Hold On" protocol, when performed correctly with an awareness of your surroundings, remains the most effective single piece of advice that you can follow when an earthquake occurs. More detailed information about what to do during an earthquake can be found here.