During the 2012-2013 we have measured SO2 on Kamchatka volcanoes (Gorely, Mutnovsky, Kizimen, Tolbachik, Karymsky, Avachinsky) using DOAS (differential optical absorption spectroscopy). Mobile-DOAS, on a base of USB2000+, has been used as an instrument. The goal of this work was to estimate SO2 emission by Kamchatka volcanoes with the different types of activity. Mutnovsky and Avachinsky during the measurements period passively degassed with SO2 emission ~ 480 t/d and 210 t/d, respectively. Gorely volcano was very active, with intensive vapor-gas activity with gas discharge rate 800-1200 t/d. During the measurements at Karymsky volcano there were relatively weak explosive events (ash plum rose up to 0.5 km above the crater) with 5-10 minutes periodicity. For this time, SO2 discharge rate was ~350-400 t/d. Due to the remoteness and difficulties for accessibility of Kizimen volcano, the measurements were done only once – on October 15th, 2012. 5 traverses have been done above the gas plume. SO2 emission was ~ 700 t/d. On Tolbachik fissure eruption we have measured SO2 emission repeatedly from January until August 2013. The intensive effusion of the lava flows (basaltic andesite by composition) and frequent explosions in the crater of the cinder cone were characteristic features of this eruption. The measured gas emission was from ~1500-2200 t/d in January until 600-800 t/d in August 2013. All measurements were made not permanently, but to the extent possible. Therefore, it is difficult to make detailed conclusions on the SO2 emission on these volcanoes. Nevertheless, this research may become a starting point for the development of the system of the constant monitoring of volcanic gases emission by the active volcanoes of Kamchatka.

Estimation of the sulfur dioxide emission by Kamchatka volcanoes using differential optical absorption spectroscopy.

Fissure eruption on the slope of Plosky Tolbachik volcano continued from November 27th, 2012 until September
2013. It was named as The Institute of Volcanology and Seismology 50th Anniversary Fissure Tolbachik Eruption.
The eruption started from the 5 km-long fissure opening and continued with the intensive lava effusion from it.
During the first two days of eruption the length of the lava flows was 9 km, and lava covered the area of 14.4
km2 (Gordeev et al., 2013). Lava discharge rate at this period was about 400 m3/sec. Two eruptive centers were
formed on the fissure – upper (Menyailov vent) and lower (Naboko vent), and lava gushed from them to the height
up to 200-300 meters. On December 1st, the Menyailov vent activity ceased, and the eruption concentrated at the
Naboko vent. Cinder cone was formed here, and lava flows effused from the base of the cone. Lava erupted from
the Menyailov vent, is different from the Naboko vent lava by higher silica content (SiO2 55.35 wt.% vs. 52.5
wt.%, respectively). That may be caused by the discharge of two levels of the magma chamber, fractionated to
a different extent. Morphologically, lava flows from the beginning of eruption until April 2013 were dominantly
aa-lava type, and from April until September 2013 pahoehoe type dominated.
For distinguishing of the dynamic of the lava flows the following methods were applied. As remote sensing methods
we used different satellite data – for specification of the area covered by lava flows, their length, temperature we
used Landsat 7 ETM+, Landsat 8, ASTER, EO-1 ALI and HYPERION. For time averaged discharge rate (TADR)
and lava flow area determination we used AVHRR data. We detected that in December 2013 lava discharge rate
varied from 120 to 40 m3/sec, and then it gradually decreased to average values 5-15 m3/sec and remained on this
level until the end of eruption. These data are confirmed by the ground-based observations, which were conducted
during the entire period of eruption. At the end of eruption in September 2013, lava flows area was about 36 km2, the maximum length of the lava flow – 15 km.

Concentrations and emission rates of major gas species were measured in August 2015 at Ebeko volcano, a quiescently degassing andesitic volcano on Paramushir Island, Northern Kuriles. Using mobile and scanning DOAS measurements we estimated SO 2 emission from the active crater of the volcano at 100 +36/-15 t/d. Based on the comparison of plume areas of individual fumaroles, ca. 90% of the total gas emission from Ebeko in 2015 was provided by a single powerful vent (" Active Funnel " fumarole) and the rest was shared among low-temperature fumaroles. At the time of measurements, gases from the main fumarole had temperature from 420 to 490 °C and composition close to the average arc gas [1], as shown in Table. Gas species CO2 SO2 H2S HCl H2O T, °C mmol/mol Main fumarole 27.9 23.5 6.1 5.6 936 420 Low-temp. jets 92.2 2.62 0.68 1.6 902 <120 Low-temperature fumaroles (<120 °C) emitted gas enriched in CO 2 (up to 28 mol%, 9.2 mol% on average). Such CO 2 enrichment together with depletion in HCl and sulfur species can be explained by scrubbing of soluble gas species by a well-developed hydrothermal system which discharges ultra-acid SO 4-Cl waters [2]. A weighted-average estimate of the total gas+vapor emission from the Ebeko summit provided 1470 t/d, which includes ~ 101 t/d SO2, ~ 110 t/d CO2, ~ 14 t/d H2S and HCl, and 1230 t/d of water vapour with > 50% of the magmatic component. The gas fluxes measured in August 2015 using DOAS fall into the range of previous measurements made from 1960 to 2012 that used direct methods [2] and correspond to the moderate degassing rate of the volcano.

Arc magmatism is a product of subduction factory, involving thermal and chemical interactions
between a subducted slab as a material input and mantle wedge as a processing factory. In turn, the
compositions of arc magma provide invaluable information concerning the material input and the
interactions. The northeast Kamchatka Peninsula is an ideal field to examine such interactions and
relationships, being characterized by (1) subduction of the Emperor Seamount Chain (Davaille and
Lees, 2004), and (2) possible material and thermal interaction among the subducted slab, the
overlying mantle wedge and the sub-slab mantle via the edge of subducted Pacific slab (Portnyagin
and Manea, 2008). Within this area, a monogenetic volcanic group occurs along the east coast,
including high-Mg andesitic rocks and relatively primitive basalts (East Cones, EC (Fedorenko,
1969)). We have conducted geochemical studies of the EC lavas, with bulk rock major and trace
elements, and K-Ar and Ar-Ar ages, based on which a possible contribution of subducted seamounts
and its relation to the tectonic setting are discussed.
The elemental compositions indicate that the lavas from individual cones have distinct mantle
sources with different amounts and/or compositions of slab-derived fluids. Based on mass balance,
water content and melting phase relations, we estimate the melting P-T conditions to bet ~1200 ℃
at 1.5 GPa, while the slab surface temperature is 620 –730 ℃ (at 50-80 km depth). Compared with
the southern part of Kamchatka, the slab surface temperature beneath EC seems to be high due to the
thinner Pacific slab associated with the seamount chain and/or the plate rejuvenation from a mantle
plume impact (Davaille and Lees, 2004; Manea and Manea, 2007).
The K-Ar and Ar-Ar ages of the Middle Pleistocene are consistent with the tephrochronological
study (Uspensky and Shapiro, 1984) and the present tectonic setting after 2 Ma (Lander and Shapiro,
2007). The high-Mg andesite with the highest SiO2 content in the EC lavas shows the oldest age
(0.73 ±0.06 Ma) within not only EC but also the northeast part of Kamchatka (e.g., Churikova et
al., 2015, IAVCEI). On the other hand, the rest of EC lava samples show relatively younger ages to
0.18 ±0.07 Ma. These results suggest that the EC lavas including high-Mg andesite and basalt were
generated by mantle flux-melting induced by dehydration of a subducted seamount inheriting a local
thermal anomaly (Nishizawa et al., 2014, JpGU; 2015, JpGU).

島弧火成活動はサブダクションファクトリーの産物で, それは沈み込んだスラブ（物質のインプット）－マン
トルウェッジ（加工工場）間の熱的・物質的相互作用を含む. 島弧マグマの組成は, その物質インプットと相
互作用について非常に貴重な情報をもたらす. カムチャツカ半島北東部はそのような相互作用と関係性を調べ
るうえで理想的な場所である, それは次のような特徴を有する為だ（1）天皇海山列の沈み込み（Davaille and
Lees, 2004）（2）沈み込んだスラブ, マントルウェッジと太平洋スラブエッジにかけてのサブスラブマントル
との物質的・熱的相互作用の可能性（Portnyagin and Manea, 2008）. この地域の東海岸沿いに, 高-Mg安山岩
と比較的初生的な玄武岩を産出する単成火山群が確認されている（East Cones, EC（Fedorenko, 1969））.
我々はこのEC溶岩について全岩主要-微量元素組成分析とK-Ar, Ar-Ar年代測定を含む地球化学的研究を行い,
沈み込んだ海山からの寄与の可能性とテクトニックセッティングとの関係について議論する.
EC溶岩の組成は, 火山ごとに独立したソースに由来しており, そのソースの違いはスラブ起源流体の量および
またはその組成の違いによることを示す. マスバランス, 含水量, 相関係に基づき, 我々は溶融温度－圧力条
件を推定した, 溶融温度・圧力～1200℃, 1.5 GPa, スラブ表面温度 620－730℃（深度50-80 km）. カム
チャツカ南部に沈み込むスラブ表面温度と比較すると, EC直下のスラブ表面温度は高く, これは天皇海山列に
沿ったプレートの薄化およびまたは沈み込む直前のプルームからの熱的効果による若返り効果によるものと考
えられる（Davaille and Lees, 2004; Manea and Manea, 2007）.
K-Ar, Ar-Ar年代測定値は中期更新世で, これはテフラ層序学からの推定年代と一致し（Uspensky and
Shapiro, 1984）, 2Ma以降現在のテクトニックセッティングに変化したこととも矛盾しない（Lander and
Shapiro, 2007）. 最もSiO2含有量が高い高Mg安山岩は最古の年代を示し（0.73 ±0.06 Ma）, これはECのみな
らずカムチャツカ北東部においても最も古いとみられる（e.g., Churikova et al., 2015, IAVCEI）. 一方他
のECはより若い年代を示す（～0.18 ±0.07 Ma）. これらの結果は以下のことを示す： 高Mg安山岩, 玄武岩を
含むEC溶岩は沈み込んだ海山による局所的な温度異常がスラブ起源流体の脱水を強めそれによって生じたフ
ラックス溶融によりもたらされた（西澤他, 2014, JpGU; 2015, JpGU）.