Volcano Observation - Kazankansoku

Japanese: 火山観測 - かざんかんそく

Observation to understand volcanic activity. In addition to observing the height of volcanic gas and smoke from a fixed point, various observation equipment is used to observe seismic activity, crustal movement, the Earth's electromagnetic field, temperature, and other changes. Seismic observation is the most common method, and volcanic earthquakes and volcanic tremors are measured using seismometers placed on the volcano and its surroundings. Leveling and light wave surveys are regularly conducted to observe the deformation of the volcanic body, and expansion and contraction are detected by continuous observations using tiltmeters, extensometers, and volumetric strainmeters installed on the volcanic body. Space technologies such as the Global Positioning System (GPS) and Interferometric SAR (→Synthetic Aperture Radar) are also used. Other effective methods include observing the composition of volcanic gases and groundwater, and observing geomagnetic and electrical resistivity to detect changes in rock magnetism. In recent years, a small measuring device called DOAS (Differential Optical Absorption Spectroscopy) has been used to observe the amount of sulfur dioxide gas emitted.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

火山作用（火山活動）を把握するための観測。火山の噴気や噴煙の高さなどを定まった地点から遠望観測するほか，さまざまな観測機器を用いて，地震活動，地殻変動，地球電磁場，温度などの変化を観測する。地震観測は最も一般的な手法で，火山やその周辺に配置した地震計によって，火山性地震や火山性微動をはかる。火山体の変形の観測には水準測量や光波測量を定期的に行なうほか，火山体に設置した傾斜計，伸縮計，体積ひずみ計の連続観測によって膨張や収縮などをとらえる。人工衛星による全地球測位システム GPSや干渉SAR（→合成開口レーダ）などの宇宙技術も使われる。また火山ガスや地下水の成分観測，岩石磁気の変化をとらえる地磁気や電気抵抗の観測も有力な手法である。近年，二酸化硫黄ガスの放出量の観測には DOAS（Differential Optical Absorption Spectroscopy）という小型計測器が使われる。

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