Forum about Merapi Volcano

Reported from the VOLCANO Listserv (Arizona State Univeristy)

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Patrick ALLARD

Date: Fri, 25 Nov 1994 20:20:43 MST
From: Patrick Allard 85.42
Subject: Merapi eruption

    Short comment about the new eruption:

    Although precise information from VSI (Volcanological Survey of Indonesia) is still needed, the November 22 eruption may signify an important change in the location of future magma extrusion and the distribution of related hazards at Merapi.
    Over the past hundred years at least, glowing block avalanches, pyroclastic flows and lahars associated with extrusion of the lava domes were entirely confined to the W and SW flanks (last major eruptive phases in 1969, 1976, 1984 and 1992). Now, in 1979 (ref.1) and 1983 (ref.2) attention had been drawn on the potential risk of new magma outbreak towards the South (from the Gendol-Woro breach), that would threaten a more densely populated area including the northern suburb of Yogjakarta city. This concern was based on the following observations: increase and then persistency of very high temperatures in the Woro and Gendol fumarolic fields (implying a close proximity to the top of the magma column, as later verified from magnetotelluric measurements), appearance of scattered but new fumaroles on the Woro downslopes in 1979, and above all extreme fumarolic alteration of this sector of the edifice (weakening its stability or/and resistance to any magma intrusion).
    The present events seem to verify it, south-eastward migration of the eruption site being facilitated by magma blockage in the SW Batang breach due to the presence of the huge 1992-94 lava dome.

    1. Allard P. & Tazieff H., Phenomenologie et cartographie thermique des principales zones fumerolliennes du Merapi (Indonesie). C.R. Acad. Sci. Paris, D-288, 747-750, 1979.
    2. Tazieff H., Monitoring and interpretation of activity on Mt. Merapi, Indonesia, 1977-1980: an example of practical, civil defense, volcanology. In: Forecasting Volcanic Events (eds H. Tazieff & J-C Sabroux), Elsevier, Amsterdam, 485-492, 1983.

    Dr Patrick ALLARD
    Centre des Faibles Radioactivites, CNRS-CEA
    91190 Gif/Yvette, France
    Tel. 33-1-69088542; fax: 33-1-69087716;

Charlie WATSON

Date: Sun, 27 Nov 1994 22:08:11 MST
From: Charlie Watson
Subject: Re: Merapi eruption

    In response to the suggestion that the top of the Merapi magma column may be "closer" to the surface because of increased of temperature and fumarolic activity, I would put forth another suggestion that the hydrothermal conduits to the magma chamber may have been facilitated in some fashion. I really don't see a major case of magma movement developing from just fumarolic activity. There may indeed be an increased "hazard" due to the facilitation of these conduits, hence, leading to an eruption event, but without additional evidence (ie; seismicity, induced geophysical investigations, etc.), I would be cautious on reporting movements of the magma.

    Happy Holidays!

    Charles Watson
    Advanced Geologic Exploration/Seismo-Watch


Date: Tue, 29 Nov 1994 10:19:20 MST
From: Dario Tedesco and Greg Bignall
Subject: Re: Merapi VSI report, 28 Nov 1994

    Among volcanologists there are often moments in which some models are more in fashon than others.
    The suggestion of P. Allard (geochemist) about the presence of a magma column close to the surface at Merapi volcano, prior to the recent eruption, based on the high temperature of the fumarolic field, is "rejec- ted" by C. Watson (geophysicist). The latter proposes, if we understood him, a better thermal efficiency of the fumarolic conduits (he said hydrothermal cobsuits ...) most likely produced the higher surface fumarolic temperature.
    We feel this is a continuation of the eternal controversy between geophysicists and geochemists.
    Neither of the two researchers point out the actual fumarolic temperatures before the occurrence of the recent pyroclastic flow. We feel to avoid any misinterpretation by readers, it is better the temperatures be reported. Merapi fumaroles, Gendol fumarolic field reached more than 900 degrees C in August (measured by one of us D.T.).
    The magnitude of the temperatures leads us to the following conclusions: (1) It is inappropriate to talk in term of hydrothermal system or conduits (cf. C. Watson) because there had been no water (liquid) in the system for some time.
    (2) The high measured temperature is evidence that the magma was already there ... just below the surface.

    The temperature was already high sometime before the recent eruption. We suggest our Indonesian friends belonging to M.V.O. should be consulted since they have conducted remarkable work on Merapi. They visit the area one or two times per month, to the dome, to collect fumarolic fluids and measure temperature.

    One more thing; the very high temperature, together with the presence of very aggressive (acidic) fluids could also be factor which helped trigger the eruption. A partial collapse of the dome occurred in September, and continuous destabilization of the whole dome, then sudden depressurization is clearly possible.

    Furthermore, we do not think that high temperatures alone can be used to argue that the Merapi volcano has shown a south-eastward migration of activity (P. Allard). We sincerely feel that this suggestion must be verified by future activity.

    We would also like to write a few words on the model proposed by Charlie Watson. At Vulcano island (southern Italy) the fumarolic vents underwent a steady increase of temperature from 300 to 700 degrees C, during the period 1988-1992. During this time no (anomalous) seismicity or ground deformation were recorded; but some scientists argued that a magma migration-injection occurred. In this case the idea of better thermal efficiency of fumarolic conduits (as here proposed by Watson) is highly possible and indeed proposed by D. Tedsco (JGR, in press). But the two cases, Merapi and Vulcano island, seem to us to be very different.

    I (D.T) think that this kind of forum is very useful and interesting. However, it seems strange to me that only very rarely do volcano observatory researchers specifically express their own idea, or "feelings". Usually discussion is initiated by individuals belonging to academic institutions or national research laboratories. I am presently the secretary of WOVO (World Organization of Volcano Observatories) and would like to push researchers working in the observatories to participate in this kind of debate and to stress their point of view. If discussion is not forthcoming the gap (already existing) between those involved with volcano modeling or volcano surveillance can only increase, to the detriment of all researchers.

    Ciao to everybody

    Dario Tedesco and Greg Bignall
    Institute for Study of the Earth's Interior
    Okayama University
    Yamada 827, Misasa, Tottori-ken
    682-01 Japan


Date: Wed, 30 Nov 1994 08:51:35 MST
From: David Stevenson
Subject: Fumarole Temperatures

    With respect to the comments of Patrick Allard, Charles Watson, and Dario Tedesco, regarding the interpretation of fumarole temperatures at Merapi, there are at least two quantitative models of fumaroles: Connor et al (1993) and Stevenson (1993). The major factors that control fumarole temperature are magma source depth, gas ascent velocity, and the temperature field surrounding the fumarole conduit. The last factor depends upon the presence or absence of a hydrothermal system, and the proximity of other gas conduits. An increase in temperature can indicate magma ascent, a higher gas flux, or a general heating of the vent surroundings. As with most volcano monitoring techniques, complimentary data from a different method is needed to pin down the actual process.

    David Stevenson

    Atmospheric Processes Research (Room 153)
    Meteorological Office
    London Road
    Berkshire RG12 2SZ

    Connor, C.B. et al (1993) Continuous monitoring of high-temperature fumaroles on an active lava dome, Volcan Colima, Mexico: Evidence of mass flow variation in response to atmospheric forcing.
    J Geophys. Res. 98:19713-19722

    Stevenson, D.S. (1993) Physical models of fumarolic flow.
    J Volcanol. Geotherm. Res. 57:139-156 (Reprints available from me)

Patrick ALLARD

Date: Fri, 2 Dec 1994 08:38:39 MST
From: Patrick Allard 85.42
Subject: Merapi eruption

    My "short comment" about Merapi eruption has stimulated a discussion (C. Watson, D. Tedesco and D. Stevenson mails) that can only be theoretical at present, given our lack of detailed information upon the actual sequence of events and changes at Merapi summit (bad weather conditions and volcanic risks having yet prevented new field investigations). My comment itself was speculative and just intended to suggest that the present destruction of the southern slopes of Merapi by pyroclastic flows and glowing surges, for the first time over decades, might announce a S-SE shift of the summit eruption site, the potential threat of which had been emphasized in previous works (listed references). Before going further, we do need more information from our Indonesian collegues of the VSI (a 28/11 VSI report indicates that the pyroclastic flows would have resulted from partial collapse of the active lava dome. Whether a new vent has appeared or not is not known yet).
    Nevertheless, I'd like to clear some points of my comment, which apparently led to misinterpretation:

    a. First, I never spoke of magma movement, but actually of "migration of the eruption site". This is different in the sense that magma is already intruding and extruding at the summit of Merapi and, thus, can easily erupt from another vent without substantial magma transfer (and seismic signals) being required. This is a common way Merapi has been working over the past centuries (see the abundant Dutch and Indonesian litereature). The problem is that, because extrusion occurs at the top of the volcano, even a rather small shift of the vent can strongly modify the flank distribution of related hazards.

    b. High temperatures in Woro and Gendol fumarole fields: I acknowledge the comment of C. Watson that very high fumarole temperatures are not a unique indicator of magma approach and may simply be related to increased aperture of volcanic fractures/conduits or/and lower buffering of magmatic gases by a hydrothermal system. The examples of Momotombo in the eighties and Poas in 1979-1980, where fumarole temperatures reached 900 or even 1000C without any magma eruption, are good illustrations. At Merapi, however, the persistency of very high gas temperatures in Gendol and Woro areas is closely connected with almost continuous nearby (=BE 100m) magma extrusion and with shallow lateral extension of the magma column beneath this sector, as revealed by electrical measurements (M. Halbwachs, in Forecasting Volcanic Events, Elsevier, figure p. 516, 1983). That means, magma has been emplaced for many years at subsurface level beneath this sector. Such conditions have favoured the development of numerous proximal gas conduits (marked by flames at night) and extensive heating of the conduits surroundings (important factors, as recalled by D. Stevenson). This in turn has led to extensive fumarolic alteration of the host rocks in this sector of the edifice (reduced to powder or crust in many parts), weakening its mechanical resistance.

    c. D. Tedesco mentionned that gas temperature in Gendol "reached more than 900C in August". Such an increase (900C had never been yet recorded at Gendol) strengthens the idea of an increased gas pressure in the magma column prior to the eruption (suggested by reported testimonies of a 25 mn early phase of pressurized gas steaming, preceeding the first pyroclastic flows; note that this observation would discard a simple gravitational collapse of the lava dome as the cause of the events). Higher temperature (i.e. higher gas flow) in Gendol during the pre-eruptive period is consistent with increasing leak of magmatic gas in this area, facilitated by blockage of the vent by the huge 1992-1994 lava dome. Such a pattern was observed before several other eruptions of Merapi: once the lava dome has become stabilized and voluminous, the lava extrusion rate decreases and gas pressure progressively builds up, leading to either dome destruction and/or opening of another vent (e.g. Hartman, 1931-1932; Van Bemmelen, 1949). Finally, note that the high fumarole temperature of 849C reported by D.Tedesco is equivalent to the highest temperature measured in pressurized gases sampled directly in contact with the lava dome in 1978 (Allard and Tazieff, 1979; Allard, 1980b).

    I think such a discussion has nothing to do with any so-called "eternal controversy between geophysicists and geochemists" (D. Tedesco), whereas I entirely share the opinion (also D. Tedesco) that it could strongly benefit from the contribution of volcano observatory researchers. Last, I'd like to outline that our IAVCEI Commission on the Chemistry of Volcanic Gases, whose the Fifth Workshop in Indonesia included gas sampling of Merapi summit fumaroles (Gendol-Woro) during the last days of July, has been very lucky: given the very tenuous warning signals of the recent eruption (reported by a VSI team just working on top), it would have been more than a delicate situation to be faced with urgent running down of the quite numerous participants! In that sense, geochemists are particularly exposed to volcanic risks.

    All the best,

    Patrick ALLARD
    Centre des Faibles Radioactivités, CNRS-CEA
    91190 Gif/Yvette, France
    Tel. 33-1-69088542; fax: 33-1-69087716;


Date: Thu, 8 Dec 1994 14:36:43 MST
From: Dario Tedesco and Greg Bignall
Subject: Re: Merapi eruption

    The comments made by P. Allard, views we share, signal the end to this interesting discussion on Merapi.
    Patrick started, probably unintentionally, a new theme that we feel is very important. He said that geochemists working on Merapi during the 5th International Workshop om Volcanic Gases (August) were very lucky. This is true!! But what should we say about the V.S.I. team, working on the summit on the same day of the eruption? They were unbelievebly lucky, and it was only by chance (probably a "miracle", ... Allah is great ...!!) that they were on the other side of the dome and not close to the two fumarolic fields at Woro and Gendol. Does this mean that despite the sophisticated geophysical network, no premonitory signals were recorded? We suppose so, since the team was clearly in the danger area. Did the team receive any warning by radio? This is difficult to say, we should wait for some answers from the Indonesian scientists.
    It is true that geochemists, and all scientists, working on active volcanoes, are exposed to risk. In 1993 (the black year for volcanologists) three different accidents occurred on active volcanoes resulting in 15 deaths...
    In two different occasions, once in the WOVO Newsletter column (no longer published, due to a shortage of funds) and once at the International Conference on Volcanoes (May, 1993. Accademia dei Lincei, Rome, Italy) we have tried to introduce a new discussion, not only on the safety measures* that scientists must follow when working on active volcanoes, but more on the possibility of forecasting small scale eruptions (explosions). A large eruption can usually be forecast, sometime long enough in advance to dispatch a warning and to avoid casualties. There is a long list of well documented eruptions which have been forecast. However the weak point of active volcanology and particularly of monitoring observatories is that our present knowledge doesn't allow us to recognize the small scale eruption-explosion, large enough to kill scientists, tourists or those curious and too close to the volcano or crater.
    Is there any team working on this subject? Is there any news from obsertory geophysicists, geochemists or others about this kind of activity? In our opinion, all volcanological conferences should devote time to this subject. If it is true that small scale explosions (often phreatic in origin) are largely responsible for most casualties on volcanoes, we think we should try to understand and to forecast this kind of activity. Difficult we know, but still ...
    We recommend to all observatories and scientists interested in this field to express their feelings and to make proposals. Possibly, a small scale conference can be organized. Also IAVCEI, sensitive to the problems of safety [*a subcommission of IAVCEI (S. Aramaki, F. Barberi and S. McNutt) last year, produced for the first time, a memorandum for scientists working on active volcanoes, the first version of which was published in the WOVO Newsletter n. 4) should participate.

    Just to finish, the idea of a program helping to develop observatories, in Indonesia or elsewhere. The idea to supply observatories with e-mail system (hardware and software) has been proposed (informally) this year to the United Nations and to interested scientists. The eruptions at Merapi dramatically highlights this problem. Any idea to how obtain sponsors, funds and materials?

    Ciao Dario and Greg

    Dario Tedesco and Greg Bignall are at ISEI, Okayama University, Japan e-mail fttcj147 at jpnoucc.Bitnet


Date: Sun, 11 Dec 1994 22:01:04 MST
From: Graeme Wheller
Subject: Re: Merapi eruption

    Just a small comment to the following paragraph from Dario Tedesco and Greg Bignall:

    " Just to finish, the idea of a program helping to develop observatories, in Indonesia or elsewhere. The idea to supply observatories with e-mail system (hardware and software) has been proposed (informally) this year to the United Nations and to interested scientists. The eruptions at Merapi dramatically highlights this problem. Any idea to how obtain sponsors, funds and materials? "

    Having conducted volcanological research in Indonesia and worked for two years with the Fiji Mineral Resources Department (another developing country), in my view the installation of e-mail facilities should very much be secondary to the development of a country-wide, well-equipped monitoring program with trained staff and comprehensive emergency contingency plans. The VSI has a very large job to do, with over 120 active or fumarolic volcanoes to deal with, many of them lying within some of the most densely populated areas on earth. However, in general, their equipment is extremely basic and very thinly distributed. The level of monitoring of Merapi is probably an exception in Indonesia, to a large extent because it has attracted international researchers.

    I believe the international volcanological community should be giving greater emphasis to government-to-government development programs in the area of volcanic risk mitigation in developing countries. This requires lobbying by volcanologists in both developed and developing countries to their respective governments. This is the only way that sufficiently large amounts of money will be made available for the development of adequate monitoring programs.

    It is therefore distressing to hear that the WOVO Newsletter has died through lack of funds. Is this indicative of a lack of interest in volcano monitoring? I doubt it, but if there is to be any chance of increasing government funding for monitoring programs then publicity is the key, and resurrecting and expanding the distribution of the WOVO Newsletter seems like a good starting point....

    Graeme Wheller (Dr)
    Consultant Geologist
    Volcanex International Pty Ltd
    Post: 521 Tinderbox Rd, Blackmans Bay, TAS, 7052, Australia
    Voice/Fax: domestic (002) 298057, international +61 02 298057

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