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The thermal signature of Aso Volcano (Nakadake) during unrest episodes has been analyzed by combining the MODIS-MIROVA data set (2000–2017) with high-resolution images (LANDSAT 8 OLI and Sentinel 2) and ground-based thermal observations (2013–2017). The site of major activity (crater 1) is located at the summit of the volcano and is composed by a fumarole field (located in the South Area) and an acidic lake (replaced by a Central Pit during Strombolian phases). The volcanic radiative power (VRP) obtained by nighttime satellite data during the reference period was mainly below 3 MW. This thermal threshold marks the transition from high fumarole activity (HFA) to Strombolian eruptions (SE). However, periods characterized by sporadic phreatic eruptions (PE, eventually bearing phreatomagmatic episodes), which is the prevalent phase during unrest episodes, exhibit very low VRP values, being around 0.5 MW, or below. The statistical analysis of satellite data shows that the transition from HFA to Strombolian activity (which started on August 2014 and ceased in May 2015) occurs when VRP values are above the cited 3 MW threshold. In particular during marked Strombolian phases (November–December 2014), the radiative power was higher than 4 MW, reaching peak values up to 15.6 MW (on December 7, 2014, i.e., 10 days after the major Strombolian explosion of November 27). Conversely, ground-based measurements show that heat fluxes recorded by FLIR T440 Thermo-camera on the fumarole field of the South Area has been relatively stable around 2 MW until February 2015. Their apparent temperatures were fluctuating around 490–575 °C before the major Strombolian explosive event, whereas those recorded at the active vent, named Central Pit, reached their maxima slightly above 600 °C; then both exhibited a decreasing trend in the following days. During the Strombolian activity, the crater lake dried out and was then replenished by early July, 2016. Then, volcanic activity shifted back to phreatic–phreatomagmatic and the eruptive cycle was completed. During this period, the MIROVA system detected very few thermal alerts and the ground-based measurements were fluctuating around 1 MW. The most violent explosion occurred on October 8, 2016, and within the following weeks measured VRP were moderately above 2 MW. This is coeval with a thermal increase at the fumarole field of the South Area, with temperatures well above 300 °C. Thermal monitoring at Aso Volcano is an additional tool in volcano surveillance that may contribute to near-real-time hazard assessment.

Soil CO2 flux measurement is a key method that can be used to monitor the hazards in an active volcanic area. In order to determine accurately the variations of the CO2 soil emission we propose an approach based on the radiocarbon (14C) deficiency recorded in the plants grown in and around the Solfatara (Naples, Italy). We twice sampled selected poaceae plants in 17 defined sites around the Solfatara volcano. 14C measurements by liquid scintillation counting (LSC) were achieved on the grass samples. The 14C deficiency determined in the sampled plants, compared to the atmosphere 14C activity, ranged from 6.6 to 51.6%. We then compared the proportion of magmatic CO2 inferred to the instantaneous measurements of CO2 fluxes from soil performed by the accumulation chamber CO2 degassing measurement at the moment of the sampling at each site. The results show a clear correlation (r=0.88) between soil CO2 fluxes and 14C activity. The determination of the plants 14C deficiency provides an estimate of the CO2 rate within a few square meters, integrating CO2 soil degassing variations and meteorological incidences over a few months. It can therefore become an efficient bio-sensor and can be used as a proxy to cartography of the soil CO2 and to determine its variations through time

Torishima is an active volcanic island located on the Izu Arc, 570 km south of Tokyo at Honshu island. The eruptive activity is divided into two stages; the stratovolcano stage, and the central cone stage. The eruption during the historic period in Torishima volcano has occurred in 1902, 1939, and 2002. We conducted landing observation ofTorishima in May, 2004. Temperatures of the fumes and ground and compositions (CO_2, S0_2, H_2S) of volcanic gases were measured. The current activity of Torishima volcano is as follows: The highest temperature region showing approximately I00 ℃ is distributed along the narrow band inside the westside rim of Torishima caldera. The fume and ground temperatures at the north side in Io-yama, which is the central major cone of Torishima volcano are nearly constant at l00 ℃ from 1957 to present. CO_2 concentrations in volcanic gases from the fumaroles of the north side in Io-yama is in levels that have almost unchanged from 1965 to the present. A remarkable change of the fumarolic activity resulting from the eruption in 2002 was not detected in this observation.

1995年10月に九重火山で生じた水蒸気爆発以後, 我々は繰り返し光波辺長測量とGPS測量を行ってきた。最も大きく変化したSGM・HSS測線(1.1km)では, 約6年間で70cm以上も収縮し, 多くの測線でほぼ直線的な辺長の変化が現在も継続している。茂木モデルの減圧源が硫黄鉱山のあった硫黄山の噴気地帯直下600mの位置に求まった。これらの地殻変動と噴気による放出エネルギーの時間変化との間に相関関係がみられることから, これらの継続的な地殻変動は噴気活動に伴う地熱貯留層の減圧に起因していると考えられる。, A phreatic eruption occurred at Kuju volcano in October 1995.We deployed EDM and GPS networks around the active craters of the volcano just after the eruption.Slope distances of the survey lines in the northern network have tended to contract, whereas those in the southern one tended to extend.The maximum contraction observed in the northern network was 70 cm over 6 years. A spherical volume decrease just beneath the fumarolic area is a plausible model for these changes in slope distances.A noteworthy feature is that over 6 years after the phreatic eruption ended, the deflation rate is still approximately linear.We also estimated the thermal energy discharge by fumaroles in the new craters.Temporal variation of the energy discharge is well correlated with the observed deflation rate.It is strongly suggested that the ground deformation around Iwoyama is caused by the deflation volume of a geothermal reservoir.

薩摩硫黄島は, 島の東部にある硫黄岳の山頂火口において活発な噴気活動を続けている.京都大学, 地質調査所, 福岡管区気象台により行なわれている地震観測, GPSの繰り返し測定および火口内の地形, 噴気の調査結果から, 1995年-1998年の薩摩硫黄島の活動は次のようにまとめられる.(1)薩摩硫黄島においても桜島火山と類似した種類の火山性地震A型, B型およびC型(モノクロマティック微動)が発生している.(2)1995年から1998年のA型地震の発生頻度には, 顕著な変化はみられず, 1975年-1978年における発生頻度と比較しても大きな変化はない.また, 正断層型のメカニズムをもつA型地震が火口の西側に震源決定されたが, その震源位置は1975年-1978年における発生位置と同様である.(3)1996年6月8日に発生したM=2.9の有感地震は, それ以外のA型地震と比べて規模が大きい.硫黄岳山頂火口近傍の測量基準点は, 1995年6月から1997年4月の間に6cm北東に変位した.また, 火口の南東側周辺に割れ目が形成された.この地震の発生は火口周辺の地盤変動および火口の南東における割れ目の形成と関連があるのかもしれない.(4)B型地震は, 山頂火口直下の浅い場所において発生している.その発生頻度は, 1998年7-8月には1日に15回程度であったが, 10月以降は, 1日150回程度に増加した.B型地震は体積膨張型のメカニズムをもち, 火山ガスの膨張と関連している可能性が高い., Fumarolic activity has continued at the summit crater of Satsuma-Iwojima volcano located south off Kyushu, Japan. Sakurajima Volcanological Observatory (SVO), DPRI, Kyoto University has conducted seismic observation at a permanent station 1.5 km west of the summit crater since June 1995. Fukuoka Meteorological Observatory installed 4 stations at the volcano since September 1997. Geological Survey of Japan has repeated visual, geochemical, topographical survey at the crater. SVO and GSJ have cooperated in GPS measurement since June 1995. Volcanic activity of Satsuma-Iwojima is summarized as follows; (1)Volcanic earthquakes are classified into A-type (high frequency), B-type (low frequency) and C-type (monochromatic tremor). (2) A-type earthquakes occurred at the west of the summit crater at a depth of 1km. The focal mechanism of the A-type earthquakes is normal fault type. (3) B-type earthquakes are located at very shallow depth beneath the summit crater. B-type earthquakes are generated by expansive volumetric source, maybe expansion of gas pocket. (4) The seismicity of A-type earthquakes during 1995-1998 is the same as that in 1975-1978, except the earthquakes at 21:06 on June 8, 1996. (5) A crack with length of lOOm was formed southeast of the summit crater before October 1996. The benchmark near the crack moved eastward by 6 cm during the period from June 1995 to April 1997. The earthquakes on June 8, 1996 may be related with topographic change and ground deformation around the crater.

A phreatic eruption occurred at Kuju volcano in October 1995.We deployed EDM and GPS networks around the active craters of the volcano just after the eruption.Slope distances of the survey lines in the northern network have tended to contract, whereas those in the southern one tended to extend.The maximum contraction observed in the northern network was 70 cm over 6 years. A spherical volume decrease just beneath the fumarolic area is a plausible model for these changes in slope distances.A noteworthy feature is that over 6 years after the phreatic eruption ended, the deflation rate is still approximately linear.We also estimated the thermal energy discharge by fumaroles in the new craters.Temporal variation of the energy discharge is well correlated with the observed deflation rate.It is strongly suggested that the ground deformation around Iwoyama is caused by the deflation volume of a geothermal reservoir.

Fumarolic activity has continued at the summit crater of Satsuma-Iwojima volcano located south off Kyushu, Japan. Sakurajima Volcanological Observatory (SVO), DPRI, Kyoto University has conducted seismic observation at a permanent station 1.5 km west of the summit crater since June 1995. Fukuoka Meteorological Observatory installed 4 stations at the volcano since September 1997. Geological Survey of Japan has repeated visual, geochemical, topographical survey at the crater. SVO and GSJ have cooperated in GPS measurement since June 1995. Volcanic activity of Satsuma-Iwojima is summarized as follows; (1)Volcanic earthquakes are classified into A-type (high frequency), B-type (low frequency) and C-type (monochromatic tremor). (2) A-type earthquakes occurred at the west of the summit crater at a depth of 1km. The focal mechanism of the A-type earthquakes is normal fault type. (3) B-type earthquakes are located at very shallow depth beneath the summit crater. B-type earthquakes are generated by expansive volumetric source, maybe expansion of gas pocket. (4) The seismicity of A-type earthquakes during 1995-1998 is the same as that in 1975-1978, except the earthquakes at 21:06 on June 8, 1996. (5) A crack with length of lOOm was formed southeast of the summit crater before October 1996. The benchmark near the crack moved eastward by 6 cm during the period from June 1995 to April 1997. The earthquakes on June 8, 1996 may be related with topographic change and ground deformation around the crater.