Geochemical Journal, Vol. 27, pp. 351 to 359, 1993

Behavior of arsenic in volcanic gases

VIKANDY S. MAMBO* and MINORU YOSHIDA

Department of Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan

(Received November 20, 1992; Accepted May 11, 1993)

Arsenic contents were determined for volcanic gases, sulfur sublimates, and alteration products from Mts. Tokachi, Meakan, Tarumae, Esan, Unzen and Iwo-dake (Satsuma-Iwojima Island), in Japan. The gas sampled from > 300°C vents contain between 700 and 4000 ppb As with a positive tem perature dependence, regardless of their major compositions. However, the As contents of <300°C gases are scattered over a wide range, possibly because of contamination from or loss to sublimates and condensates. The As/S ratios in the sulfur sublimates are highly variable, without definite relations to those in the parent-gases. However, when this is coupled with the fact that only a small fraction of total sulfur is sublimated out of the gas, it is concluded that a large part of the emitted As escapes to the atmosphere. Alteration products are enriched in As relative to the fresh lava, due to the deposition of As-bear ing sublimates and/or the condensation of volcanic gases on the surrounding altered rocks; also possibly due to gas-rock interactions. This study shows that As is an essential part of magmatic emanations which underwent almost no modification during ascent from magma top to the surface. Arsenic content in volcanic gases can be a good indicator for fumarolic activity.

American volcanoes (Menyailov, 1975; Stoiber INTRODUCTION and Rose, 1970). The increase of water content Chemical composition of volcanic gases is (which results in the decrease of the other major known to depend on the outlet temperature of components) at Mt. Tokachi was interpreted by fumaroles (e.g., Matsuo, 1961; Iwasaki et al., Hirabayashi et al. (1990) as an indication of a 1962). S02i HCl, HF, and H2 contents are quiescent period, characterized by more impor generally high in high temperature gases, while tant meteoric contribution against magmatic H2S and CO2 are relatively enriched in low tem emanations. perature gases. However, reports on the correlation of trace Change in the major composition of volcanic elements with volcanic activity are relatively gases correlates with volcanic activity. Ossaka et rare. The occurrence of arsenic in volcanic gases al. (1980) noticed that an , increase in the was reported by some authors, e.g. Mikhshen S02 /1-12S ratio in fumarolic gases is accom skiy et al. (1979), Menyailov et al. (1980), Gem panied with the renewal of activity for Mt. mell (1987), Symonds et al. (1987), and Quisefit Kusatsu-Shirane. Hirabayashi et al. (1982) et al. (1989). Mambo et al., (1991) observed a found that the Cl/ S ratio in volcanic gases and positive correlation between the fumarolic tem water soluble parts of ashes increased prior to perature and arsenic content in gases from Mt. the eruption of Sakurajima . In contrast, Usu, and suggested that the highest concentra the decrease of HC1 / S02 ratio before eruption tion of As is close to the original value in the was reported at Kamchatka and Central gases discharging from the magma. Symonds et

*Present adress: Central Research Institute of Electric Power Industry , Abiko 270-11, Japan.

351 352 V. S. Mambo and M. Yoshida

7a discharging volcanic gases continuously till pre sent. The recent explosive eruption (June 1 Satuma-Iwojima 0 2 Mt. Esan 1988 -March 1989) was of Vulcanian type ac 3 Mt. Usu o 4 Mt. Tarumae 2 companied with small-scale pyroclastic flows 5 Mt. Tokachi 6 Mt. Meakan (Katsui et al., 1990). Since gas sampling at the 7 Mt. Unzen main crater is very difficult because of its steepness, the sampling was carried out at the Q more accessible 62-1 crater, just 150 m apart. Maximum fumarolic temperature was higher than 375'C since 1984 until 1988, with a max imum of 509°C in 1986 (Hirabayashi et al., 1990). The recent eruption of Tarumae volcano 1' a (1909) was explosive at first, followed by the for ° mation of the present . The fumarolic activity seems to have remained un 0 changed with temperature of 200-325'C to (Hirabayashi, pers. commun.) since 1978, when minor eruption of ash was observed (Katsui et Fig. 1. Localities of volcanoes for the collection of volcanic gases, sublimates and rock alteration pro al., 1981). ducts. The first historically recorded activity of Meakan volcano occurred in 1955, when steam explosion ejected rock fragments. Since 1959, al., (1990) observed the same trend at Augustine small eruptions have been occasionally ob volcano and concluded that As content could be served, e.g. in January and February 1988 (M. used to detect thermal changes in shallow Kasahara, 1988). Lava and ejecta of Meakan magma chambers. Volcano are mostly andesite. In order to understand better the arsenic The last big eruption of Mt. Esan occurred in behavior in volcanic gases, it is essential to in 1846. Fumarolic activity is seen around the dome vestigate gases from several volcanoes, with composed of andesite. A maximum fumarolic different major gas compositions and geological temperature in 1960 was 196°C (Iwasaki et al., settings. In the present study, analytical data of 1962), which is close to the 1990 record of 225 °C gases, sublimates and alteration products from reported in this study. several Japanese active volcanoes are presented The highest fumarolic temperature ever ob to ascertain the behavior of arsenic in the near tained during this investigation (872°C) was surface volcanic process. measured in 1990 at Mt. Iwodake, Satsuma-Iwo jima. Although there is no historical record of GEOLOGICAL SETTINGS AND ACTIVITY any eruption of the Iwodake crater, a submarine OF THE VOLCANOES eruption occurred at ca. 2 km east of the crater in 1934 and made a small island called Showa Samples were collected from active fumarolic Iwojima; it may be considered as a parasitic cone areas of Japanese volcanoes: Mts. Tokachi, of Mt. Iwodake. The lava consists of . Meakan, Esan, Tarumae, Iwo-dake (Satsuma Geomagnetic measurements made by Yokoyama Iwojima Island), and Unzen (Fig. 1). et al. (1966) indicate that the magmatic body of The summit area of Mt. Tokachi is mainly Iwodake is of high temperature at shallow composed of andesite. The main crater ("62-2"), depth. In addition, high 8180 values was formed by the 1962 eruption and has been (+7 +9%o) of the high temperature gases in As in volcanic gases 353 dicate the equilibration with the high tempera ducts, the sulfur was oxidized and dissolved dur ture rocks (Matsuo, 1974). For all these reasons, ing the rock decomposition procedure. even present day high temperature volcanic gases are considered to be little altered magmatic ANALYTICAL RESULTS emanations. After 198 years of dormancy, Mt. Unzen The arsenic contents in volcanic gases, sulfur started erupting on 17 May 1990 and formed sublimates and alteration products are given in nine lava domes from May 1991 to Tables 1, 2 and 3 respectively. These data shows January 1993. Intermittent pyroclastic flows that 1) Japanese volcanic gases contain a few have been occurring since that time to the pre ppm As, except for some low temperature sent. High temperature (> 800°C) fumaroles are fumaroles (< 100°C), 2) Japanese volcanic observed on and around the domes. Chemical sublimates have a large variability of arsenic con composition and OD-0180 values of the gases tent though it is mostly low, and 3) alteration show that during their ascent from magma to the products are enriched in arsenic compared with surface almost no modification of the gases takes the fresh lava. place (e.g. Hirabayashi et al., 1992). In order to easily compare the arsenic con tents of all the gas samples, As content (log scale) is plotted vs. the outlet temperatures (Fig. EXPERIMENTAL 2). Most of the data are in a narrow range of 700 Arsenic was determined in volcanic gases ab to 4000 ppb As, notwithstanding the wide sorbed into an alkaline solution, because a variability in the major gas, composition (see the substantial part of As is known to be scavenged Appendix). All the data of Mt. Usu (Mambo et by the sulfur precipitates which form in the al., 1991) fall in this range. The data for high acidic condensates (Mambo et al., 1991). The temperature gases (>300'C), which we call alkaline condensates were oxidized with H202 and As was determined by hydride generating Table 1. Arsenic and Chloride Contents in Volcanic atomic absorption spectrometry (HGAAS), us Gases* ing a SHIMADZU A-640-12 Flame Emission Date of Fumarolic As Cl Location Spectrometer. collection Temp. (°C) (ppb) (ppm) Volcanic sublimates and alteration products Hokkaido were also collected around the fumaroles. Sulfur Tokachi 1990.08.29 95.2 <10 < 100 1989.08.25 328 200 2120 sublimate samples were dissolved by reaction 1988.08.23 450 1300 3350 with strong NaOH solution in a Teflon decom Asahidake 22 142 1400 960 position vessel at 105'C for several hours. The Meakan 24 143 1500 4750 1990.08.31 300 80 20380 resulting solution was oxidized with H202 and Tarumae ~~ 09.02 232 1050 2850 As was determined by HGAAS. Esan ~~ 09.05 225 2230 890 Rock alteration products were decomposed Satsuma-Iwojima by a mixture of HC1O4, HNO3 and HF; and Arayama 1988.07.22 189 1400 n.d. Kuromoe ii ii 24 105 15000 n.d. arsenic was determined by HGAAS after 1990.10.24 110 1940 17100 eliminating interferences of coexisting elements 23 216 3700 14700 such as Cu by masking with a KI solution. 24 702 4100 12300 1988.07.24 705 3700 n.d. (Terashima, 1984; partly modified by S. K. Giri Ohachi 1990.10.22 99 <10 < 100 and M. Yoshida, unpublished)*. If elemental S Ohachi-oku 24 872 2550 12800 happened to be present in the alteration pro Monogusa 25 100 12 < 100 Unzen 1992.07.21 801 1000 n.d.

*Details of the analytical procedures can be obtained *: expressed as concentrations in condensed waters . from either of the authors. n.d.: not determined. 354 V. S. Mambo and M. Yoshida

Table 2. Arsenic content in volcanic sulfur sub A Iwojima limates Q Mt.Usu * Mt.Tokachi • OthersinHokkaido Location Type Date As (As/ S)*gas (ppm) x 10-6 B Q Mt.Unzen 1 89 0 Tokachi sulfur .08.25 194 4.7 10000 A tt molten sulfur a tt ft 34 4.7 '90 sulfur .08.29 87 g tt tt tt <2 A Q Q A tt tt tt tt tt 15 1000 '88 Meakan sulfur .08.24 5.9 75 080° '89 As(ppb) t tt .08.29 3.7 '90 molten sulfur .08.31 8.5 '90 molten sulfur .08.31 8.5 100 G '90 sulfur .08.31 24 0.5 '88 Asahi-dake sulfur .08.22 215 300 74 j C '89 Tarumae tt .08.24 8.2 '90 1990u.' ~/ .09.02 115 93 10 200 300 400 500 600 700 800 t '90 .09.02 11360 '90 Esan .09.05 7700 86 T(C) tt tt tt tt 4800 86 Iwojima Fig. 2. Arsenic content in volcanic gases vs '88 Arayama sulfur (yellow) .07.22 44 fumarolic temperature. Group A: active high tempera tt sulfur (red) tt tt tt 16 ture gases representing almost non modified direct '90 Ohashi-oku molten sulfur .10.20 64 150 magmatic emanations. Groups B: low temperature Ohashi sulfur 185 gases with As contamination from As-bearing S Kuromoe sulfur (red) 23 9.3 220 sublimates and condensed waters. Group C: low tem tt sulfur (yellow) <2 220 perature gases with As depletion by nearly complete sulfur 88 220 trapping into S-sublimates and condensed waters. The *The As/S weight ratio in the gas is calculated by using the dotted line shows a drastic As depletion at Mt. HC1, SO2, and H2S contents given in the appendix. The Tokachi which corresponds to the decline of volcanic calculation was done only for sublimates whose corre activity from 1988 to 1990. sponding gas data were available.

Table 3. Arsenic content in alteration products cussed separately.

Alteration products Fresh lava

As As DISCUSSION Location Location (ppm) (ppm) Sulfur sublimates Usu, sandy 50 Usu, 3.2 The As content in sulfur sublimates is mostly Usu, reddish block 850 Usu, bomb 2.9 low (Table 2). However, under some cir Esan, yellowish block 17200 Esan, dome 6.6 cumstances, arsenic concentrates in sulfur Meakan, sandy 51 Meakan, lava 3.2 sublimates, reaching from hundreds to Iwajima, sandy 15 Iwodake, lava 3.7 thousands ppm (e.g., at Tarumae and Esan) . Iwojima, block 88 Showa iwojima, lava 3.7 Powder X-ray diffraction was carried out for Iwojima, brittle 5.5 these samples after the dissolution of sulfur in carbon disulfide. No known arsenic mineral could be identified, indicating that arsenic incor "Group A" gases , are plotted in the narrow porates in sulfur sublimates mostly in an amor range, whereas those for low temperature gases phous state. show large scatter. The < 300°C gases are sub Sulfur sublimates are known to form at tem divided into "Group B" and "Group C" for the peratures below 200°C by the following reaction reasons to be explained later, and will be dis (e.g., Matsuo, 1962): As in volcanic gases 355

of a large fumarole of Tarumae where gas sampl 2H2S+SO2=3S+2H2O. (1) ing is practically impossible. The gases were so To relate the sulfur sublimates to their parent diluted with air that their cooling rate was very gases, we calculate the As / S ratios in the gases high; this may have promoted the condensation (Table 2). Arsenic is a chalcophile element and of water and then favored effective incorpora usually thought to behave in intimate relation tion of As into the sulfur sublimate. with sulfur. Also, Mambo et al. (1991) found The study of volcanic sublimates by silica that As is coprecipitated with elemental sulfur in tube method (Bernard, 1985) revealed that the acid condensate. Furthermore, As-bearing native sulfur is deposited as one of the last sulfosalt has been observed in volcanic phases at temperatures lower than 150°C. In sublimates collected on silica tubes (Quisefit et some cases, the sulfur collected from the silica al., 1989). Therefore, it seems natural to con tubes was found to contain up to a few % of As, sider that sulfur sublimates would be somehow though no arsenic-bearing mineral could be iden enriched in As. The As / S ratios in the gases tified (Bernard, 1985). This agrees well with the (Table 2) are in the range from two orders of present results on natural sulfur sublimates. magnitude lower to one order of magnitude Other studies of sublimates on silica tubes higher than the arsenic content in sulfur (Symonds et al., 1987; Quisefit et al., 1989) sublimates, indicating that the incorporation of report some As deposition at higher tempera As in the sulfur sublimates is not always an tures as well, with gradual increase in As content enrichment process. Since only a small part of from ca. 30 to 970 ppm as the temperature the total S is deposited out of SO2 and H2S in decreases from 767 to 530°C (Symonds et al. volcanic gases, it is clear that a great amount of 1987). In contrast with As, sulfur content in the As emitted by volcanoes escapes to the at these high temperature sublimates is nearly con mosphere. This conclusion was also obtained by stant and very low, ca. 5 ppm, with no relation Menyailov et al. (1982) and Symonds et al. to arsenic (Symonds et al. 1987). Quisefit et al. (1987) by studying high temperature gases from (1989) found 1.5% As in a sulfosalt phase at tem volcanoes in Kamchatka and Merapi volcano re perature between 360 and 240°C, in which they spectively. In addition, Greenland and identified dufrenoysite (PbAs2S5). Between 250 Aruscavage (1986) also found that most of As in and 200°C they found amorphous As, with As volcanic plumes is in the gas phase, while most content representing up to 98% of the whole of the Se and Te exist as particulates in eruptive deposit with small amounts of sulfur and heavy plumes of Kilauea volcano. Se and Te were also metals; they concluded that the amorphous As found to be four to six times more concentrated was the residue of liquid aerosols that had dried than As in sulfur sublimates of Iwojima (K. up. Below 200°C, As-enriched crystalline native Yamaya, private communication). sulfur was observed. It can be concluded from The deposition of sulfur in the acidic raw con these studies that As deposition in sublimates is densates results in the enrichment of As in the less effective at high temperature (>400°C), and solid sulfur relative to the condensed water, with it becomes more important at low temperature. the Assulf./ Asc°nd. concentration ratio = 2 7 x Volcanic sublimates at low temperature consist 103(Mambo et al., 1991). Since sulfur precipitates mostly of sulfur. As we stated earlier, arsenic is immediately in the acid volcanic condensate, the likely to be concentrated in the sulfur precipitate formation of the high As sulfur sublimate (e.g. in the presence of liquid water. Since sulfur is a from Tarumae and Esan) could be explained by major element in volcanic gases, further deposi the partial condensation of water vapor near the tion of sulfur from gases, which already deposit outlet. As, will dilute the average As concentration in The sulfur sublimates with the highest As con the sulfur precipitate. This may explain the high tents (11360 ppm) were collected from the wall variability of As/S ratios observed in sulfur 356 V. S. Mambo and M. Yoshida sublimate. high As. For these reasons, the present authors The Esan sulfur sublimates contain very high conclude that the Esan alteration product might As contents (4800 and 7700 ppm) despite the low have been formed by the mixing of altered rock As / S ratio (86x 10-6) in the corresponding with arsenic-bearing sulfur sublimate. gases (Table 2). According to reaction (1), elemental sulfur is formed from gases with the High temperature "Group A" Volcanic gases H2S/SO2 molar ratio of 2. However, the The range of 700 4000 ppb As is characteris H2S/ SO2 ratio in Esan gas is ca. 26, showing that tic for > 300°C Japanese volcanic gases (Fig. 2), the maximum deposited S is only 1 / 9 of the total irrespective of the wide variability in the major S in the gas. The high As/S ratio in Esan sulfur composition (Appendix). The high As content sublimate samples may be due to the small and its narrow range reflects little modified amount of sulfur precipitate. magmatic emanation. A positive correlation be Naturally occurring sassolite (boric acid tween As content and temperature is found in sublimate) was collected in Usu and Iwojima, that range with a correlation coefficient of 0.635; and its arsenic content is only 2 and 3.1 ppm re the linear relationship is significant at the 1% spectively, showing that the formation of level. The deposition of As-bearing sublimate, is sassolite may have only little effect on the frac likely to be the most probable reason for the tionation of As. positive correlation between fumarolic tempera ture and arsenic content in high temperature Products of rock alteration volcanic gases. This mechanism is consistent Arsenic is enriched in alteration products in with the observation of As-bearing sublimates in fumarolic areas, compared with the fresh lava silica tubes over a wide range of temperature which contains usually less than 10 ppm of (Symonds et al. 1987, Quisefit et al. 1989). arsenic (Table 3). As we mentioned earlier, the deposition of As in sublimates out of volcanic Low temperature volcanic gases gases does occur even at high temperatures Massive deposition of As-bearing sulfur though it is most effective at lower temperatures. sublimates was observed in low-temperature The arsenic addition to alteration products (< 300°C) fumarolic fields. Therefore, arsenic results probably from the deposition of As-bear content in low temperature volcanic gases will be ing sublimate. Although no arsenic mineral has seriously influenced by the sulfur deposition. been so far reported in these fumarolic areas, the However, contamination of As-bearing S deposition of small amounts of arsenic minerals sublimates will also modify the As content in the (below the detection limit of X-ray powder volcanic gases. Therefore, the low temperature diffraction), cannot be ruled out. The partial con volcanic gases can be divided into two groups: densation of water vapor with the resulting reac the one of high As content due to As-bearing tion with wall rocks may also play an important sulfur contamination, and the other of low As role in the As-addition to altered rocks at temper content without any As contamination. The atures of < 100°C, similarly to the case of former occurs at temperatures between 300 and chlorine addition as was concluded by Yoshida 100°C-we call this "Group B" gases-, and the lat (1975; 1990). ter occurs mostly at < 100°C-we call this Strikingly high As content was found in the "Group C" gases-, (Fig . 2). Esan rock alteration product (1.72% As). The "Group B" gases high ignition loss (6.6%) of this sample not . These gases are characteriz withstanding its compactness, together with its ed by widely variable As contents (80 15000 yellowish color may indicate that it contains ppb As) that may result from contamination of substantial amount of sulfur. Moreover, the As-bearing sublimates or condensates (Fig. 2, B). Esan sulfur sublimates (Table 2) contains very The effect of contamination is most clearly As in volcanic gases 357 shown by the case of the abnormally high As temperature gases without a secondary supply of (15000 ppb) found in one sample collected from arsenic. As it was discussed before, the decrease a 105°C vent in Iwojima. Although the gas sam of As content with decreasing temperature is ple is from a low temperature vent, it is close to believed to be due to the deposition of As-bear that of 705°C gases with 3700 ppb As (Table 1). ing sublimates. This is illustrated by the 300°C Similar results were obtained by Ozawa et al., sample from Meakan and the 328'C sample (1974); they found 11900 ppb As (and abnormal from Tokachi (Fig. 2). Mambo et al., (1991) ly high content of other heavy metals such as showed that practically all the As in volcanic Hg) in gases emitted from a 109°C vent that was gases is trapped in the acid condensed water dur close to a 835°C vent with a lower As content of ing sampling, with the half of it being scavenged 1180 ppb. High temperature vents in Iwojima by the sulfur precipitates formed in the conden field move around from year to year. Ozawa et sate. In that respect, the condensation of water al. (1974) observed only low temperature 100°C is an important controlling factor of As fumaroles at the same place six months before in gases, (Fig. 2). their collection of the 835'C gases. Although we do not have any direct observation showing Mts. Tokachi and Unzen when the high temperature vents were formed, Volcanic activity at Mt. Tokachi has gradual we believe that the temperature recently increas ly declined after the explosive eruption in 1988. ed because we noticed the presence of molten The highest temperature fumarole in the 62-1 sulfur, or that of dehydrated silica sublimate; crater was 450°C in August 1988; this is four both are believed to result from secondary months before the last eruption at the 62-2 heating of low temperature sublimates around crater. It decreased to 328°C in August 1989, these high temperature areas. Low temperature and was only 95'C in August 1990. Over this fumaroles around high temperature ones may period, the H20 concentrations of the gases in emit gases that have come from the high tempera creased, while the halogen contents decreased ture source and have effused through a layer of dramatically; these trends are in harmony with debris of sublimates, alteration products and the declining activity of Mt. Tokachi sulfur deposits. Arsenic and other metals which (Hirabayashi et al., 1990; see also the Appendix). had accumulated in such debris might be A strong positive correlation was observed be volatilized into the gas phase. We believe that it tween the As content in the gas and the fumarole must be ephemeral feature. temperature at Mt. Tokachi (Fig. 2, dotted line), When fumarolic temperature decreases, As with a more drastic change in As content than bearing sublimates and then condensates are the one discussed before for high temperature formed out of the gases, and this will results in a gases. Therefore, in addition to monitoring gradual depletion of As in the gases. Any arsenic halogens and sulfur compounds in volcanic increase in low temperature gases is most likely gases as it is usually done in the geochemical due to contamination by sublimates and conden surveillance of volcanic activity, a drastic change sates. Therefore, we suggest that the relatively in As content can also provide valuable informa high As content in Group B gases (Fig. 2, B) is tion on the fumarolic activity. mostly due to the volatilization of As-containing In contrast with Mt. Tokachi, Mt. Unzen has sublimate and/or the boiling of condensates at recently become active, awakening from a quies shallow depth. cent to active state. Unfortunately, there was no fumarolic activity on Mt. Unzen during the Group C gases. Arsenic content of gases in this quiescence preceding the 1990 activity. Never group decreases from 1000 ppb at ca. 350°C to theless, the high As content of the gases collected less than 10 ppb (which is the detection limit) at in July 1992 is in harmony with the ongoing erup 100°C (Fig. 2). The group includes any low tion (Table 1, and Fig. 2). 358 V. S. Mambo and M. Yoshida

Greenland, L. P. and Aruscavage, P. (1986) Volcanic CONCLUSION emissions of Se, Te, As from Kilauea Volcano, Analyses of As in gases, sublimates and Hawaii. J. Volcanol. Geotherm. Res. 27, 195-201. altered rocks from fumaroles at active Japanese Hirabayashi, J., Ossaka, J. and Ozawa, T. (1982) Relationship between volcanic activity and chemical volcanoes show that: composition of volcanic gases.-A case study on 1.-Irrespective of their major composition, the Sakurajima volcano. Geochem. J. 16, 11-21. > 300°C volcanic gases have increasing As con Hirabayashi, J., Yoshida, M. and Ossaka, J. (1990) tents between 700 and 4000 ppb with tempera Chemistry of volcanic gases from the 62-1 Crater of ture. For 100 to 300°C gases, As contents vary Mt. Tokachi, Hokkaido, Japan. Bull. volcanol. widely due to the combined effects of As scaveng Soc. Japan, Ser. 2, 35, 205-215. Hirabayashi, J., Ohba, T., Yoshida, M., Kusakabe, ing by sulfur sublimates and the volatilization of M. and Scott, G. L. (1992) Chemical composition As-bearing native S. In < 100°C gases, nearly all of volcanic gases and discharge rate of SO2 from the As is trapped in the sublimates and in the con Unzen Volcano. Read at the 1992 Fall Meeting of densed water. the Volcanological Society of Japan (Japanese). 2.-The arsenic in high temperature gases is Iwasaki, I., Ozawa, T., Yoshida, M., Katsura, T., Iwasaki, B., Kamada, M. and Hirayama, M. (1962) believed to be of little modified, direct magmatic Volcanic gases in Japan. Bull. Tokyo Inst. Technol. origin, whereas the As in low-temperature gases 47, 1-54. may come entirely or partially from a secondary Kasahara, M. (1988) Commentary on photogravures emanation, such as volatilization of sublimates on small eruptions of Meakandake Volcano in the or boiling of As-bearing waters. Eastern part of Hokkaido, Japan (January 3.-A comparison between the As/S ratios in February, 1988). Bull. Volcanol. Soc. Japan 33, 379-381 (Japanese). sulfur sublimates with those in their parent gases Katsui, Y., Yokoyama, I. and Murozumi, M. (1981) indicates that some of As in volcanic gases incor Tarumae Volcano. Field excursion guide to Usu porates in sulfur sublimates, though most of As and Tarumae Volcanoes and Noboribetsu Spa (Y. escapes to the atmosphere. Alteration products Katsui, ed.), The Volcanological Society of Japan, are enriched in As by the deposition of As-bear pp 39-54. Mambo, V. S., Yoshida, M. and Matsuo, S. (1991) ing sublimate and/or the condensation and reac Partition of arsenic and phosphorus between tion of the acid volcanic gases. volcanic gases and rock. Part I: analytical results and magmatic conditions of Mt. Usu, Japan. J. Acknowledgments-Most of this work is a part of Volcanol. Geotherm. Res. 46, 37-47. V.S.M.'s PhD dissertation at Tokyo Institute of Matsuo, S. (1961) On the chemical nature of volcanic Technology, which was initiated by the Late Prof. S. gases of volcano Showashinzan, Hokkaido, Japan. Matsuo; we are very grateful to him. We thank Prof. J. Earth Sci. Nagoya Univ. 9, 80-100. J. Hirabayashi and Mr. K. Nogami for allowing us to Matsuo, S. (1962) Establishment of chemical use their major gas data. We also thank Drs. R. B. equilibrium in the obtained from the Symonds, T. Abiko and H. Shinohara for very con lava lake of Kilauea, Hawaii. Bull. Volcano!. 24, structive reviews. 59-71. Matsuo, S., Suzuoki, T., Kusakabe, M., Wada, H. and Suzuki, M. (1974) Isotopic and chemical com REFERENCES positions of volcanic gases from Satsuma-Iwojima, Japan. Geochem. J. 8, 165-173. Bernard, A. (1985) Les mecanismes de condensation Menyailov, I. A. (1975) Prediction of eruptions using des gaz volcaniques: chimie, mineralogie, equilibre changes in composition of volcanic gases. Bull. des phases condensees majeures et mineures. Ph. D. Volcanol. 39, 112-125. Thesis, Universite Libre de Bruxelles (Belgium), 402 Menyailov, I. A., Nikitina, L. P., Shapar, V. N. and pp Miklishanky A. Z. (1982) The role of active Gemmel, J. B. (1987) Geochemistry of metallic trace volcanism in enrichment of the atmosphere in elements in fumarolic condensates from chalcophile elements. J. Geophys. Res. 87, 11113 Nicaraguan and Costa Rican volcanoes. J. 11118. Volcanol. Geotherm. Res. 33, 161-181. Mikhshenskiy, A. Z., Yakovlev, Y. V., Menyailov, I. As in volcanic gases 359

A., Nikitina, L. P. and Savel'yev, B. V. (1980) Symonds, R. B., Rose, W. I., Gerlach, T. M., Briggs, Geochemical significance of element transport with P. H. and Harmon, R. S. (1990) Evaluation of volatiles in active volcanism. Geochem. Int. 16, 33 gases, condensates, and SO2 emissions from 40. Augustine volcano, Alaska: the degassing of a Cl Ozawa, T., Yoshida, M. and Juwadi, P. (1974) Minor rich volcanic system. Bull. Volcanol. 52, 355-374. composition of volcanic gases from Satsuma-Iwo Terashima, S. (1984) Determination of arsenic and an jima. Part I: content of alkali metals, iron and timony in geological materials by automated arsenic. Paper read at the Annual Meeting of the hydride generation and electrothermal atomic ab Geochemical Society of Japan, Gakushuin Univer sorption spectrometry. Bunseki Kagaku 33, 561 sity, Tokyo. 563 (in Japanese with English abstract). Quisefit, J. P., Toutain, J. P., Bergametti, G., Javoy, Yokoyama, I., Seino, M., Motoya, Y., Iizuka, S., M., Cheynet, B. and Person, A. (1989) Evolution Maki, T. and Aota, M. (1966) Geophysical in versus cooling of gaseous volcanic emissions from vestigation of Iwo-island on the southern sea of Momotombo Volcano, Nicaragua: Ther Kyushu. Geophys. Bull. Hokkaido Univ. 16, 33. mochemical model and observations. Geochim. Yoshida, M. (1975) An experimental study for the Cosmochim. Acta 53, 2591-2608. fractionation of fluorine and chlorine in volcanic Stoiber, R. E. and Rose, W. I. (1970) The gases through the reaction of them with volcanic geochemistry of Central American volcanic gases rocks. J. Chem. Soc. Japan 3, 449-454 (in condensates. Bull. Geol. Soc. Amer. 81, 2891-2912. Japanese, with English abstract). Symonds, R. B., Rose, W. I., Reed, M. H., Lichte, F. Yoshida, M. (1990) Fractionation of fluorine and E. and Finnegan, D. L. (1987) Volatilization, chlorine through the volcanic process. transport and sublimation of metallic and non Geochemistry of Gaseous elements and com metallic elements in high-temperature gases at pounds. (E. M. Durrance et al., eds.) 163-184, Merapi Volcano, Indonesia. Geochim. Theophrastus Publications, SA. Athens. Cosmochim. Acta 51, 2083-2101.

Appendix: Major gas composition

Temp. H20 Dry gases* (V%) Location Date of collection (°C) (V%) HF HC1 S02 H2S CO2 R**

Hokkaido Tokachi '90 .08.29 95.2 98.3 31.2 2.1 66.3 0.4 '89 r .08.25 328 96.3 0.1 2.3 37.9 13.6 45.8 0.3 '88 .08.23 450 95.3 0.3 2.7 36.9 19.5 40.2 0.4 Asahidake rr rr rr 142 98.3 0.01 3.2 5.2 12.2 76.4 3.0 Meakan rr rr 24 143 96.6 0.02 8.3 20.7 18.0 51.2 1.8 '90 .08.31 300 91.7 0.07 3.0 12.9 9.7 70.9 3.4 Tarumae ri 09 .02 232 98.0 0.25 7.9 13.3 20.5 53.9 4.2 Esan ri ri 04 225 98.0 0.06 0.5 0.6 15.7 79.6 3.5 Satsuma-Iwojima '90 Kuromoe .10.24 110 97.6 6.8 29.6 31.5 18.2 11.6 2.2 r 23 216 97.8 2.9 35.7 22.6 23.3 9.1 6.4 24 702 97.4 6.4 25.7 34.3 9.5 14.0 10.0 '90 Ohachi .10.22 99 98.9 67.3 8.8 19.0 4.9 Ohachioku rr rr 24 872 97.8 2.8 27.1 30.3 10.1 11.3 18.5 Monogusa rr rr 25 100 98.8 55.9 0.04 39.3 1.0 Unzen '92 .07.21 801 96.8 0.4 7.8 14.1 6.5 47.3 23.9

*Dry gases refer to the recalculated composition excluding H20 . **R stands for residual gases. It includes all the incondensable gases (He, H2, N2, CH, CO & Ar).