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Flooding is one of the greatest disasters that produces strong effects on the ecosystem and livelihoods of the local population. Flood frequency is expected to increase globally making its risk assessment an urgent issue. In spring-summer 2017, an extreme flooding occurred in the Indigirka River lowland of Northeastern Siberia that inundated a large area. In this study, the extent and climatic drivers of the flooding were determined using the results of field observations, satellite images, and climate reanalysis dataset, and its possible effects on the ecosystem were discussed. In 2017, a significant lowland area of around 16,016 km 2 was covered with water even in July, which was 5,217 km 2 (around 4% of the total area) greater than the water-covered area in 2015 when usual hydrological condition in the area was observed. The hydrographic signature obtained for the Indigirka River water level in 2017 was unusual. Although the water level rose sharply at the end of May (which was typical for the Arctic region), it did not fall afterwards and even increased again to an annual daily maximum value in the middle of July. The climate reanalysis dataset obtained for the temporal-spatial variations of snow water equivalent, snowmelt, and runoff over the lowland revealed that a large amount of snowmelt runoff in June and July 2017 produced a large water-covered area and unusually high river water levels that lasted until summer. Snow depth from winter to spring was largest in 2017 over the period from 2009 to 2017, and the surface of the lower reach of the lowland was partially covered with snow even in the end of June due to the extreme snowfall that occurred in October 2016. Such unusual hydrological conditions waterlogged most trees over the lowland, which caused serious ecosystem devastation and changes in the material cycle.

Minor seismicity may occur at volcanoes with hydrothermal system before a steam eruption. To forecast any steam eruption, it is indispensable to detect and understand the nature of this shallow seismicity. As the fumarolic gas resides in the hydrothermal system, it may provide insights for elucidating the nature of any seismicity and thus forecast steam eruptions. At Kusatsu-Shirane volcano Japan, intense seismic activity took place in 2014 and 2018. To investigate the relationship between the seismicity and gas chemistry, five fumarolic gas discharges have been repeatedly analyzed. Since July 2014 to November 2017 a monotonic decrease in CO 2 /H 2 O, He/H 2 O and N 2 /H 2 O ratios was recorded in the fumarolic gasses located north of the summit of volcano, suggesting the decline of the magmatic component. On the contrary the CH 4 /H 2 O ratio significantly increased during the seismically quiet period, indicating that reduced conditions developed in the hydrothermal system, favoring the formation of CH 4. The high N 2 /He ratio in the quiet period indicates the addition of N 2 , likely deriving from the crustal rocks hosting hydrothermal reservoir. The N 2 /He ratio in 2018 was significantly lower than those recorded in 2014, indicating the evolution of magma with the progress of degassing. The δD(H 2 O) and δ 18 O(H 2 O) values and the CO 2 /H 2 O ratios of fumarolic gas discharges were modeled with the following processes: generation of vapor phase after the mixing between magmatic gas and a cold groundwater with meteoric origin, addition of vapor phase with meteoric origin, and partial condensation of water vapor near surface. Only a single magmatic gas is necessary for the above modeling. These data suggest that at Kusatsu-Shirane volcano the activation of seismicity was synchronized with the increase of the magmatic component in the fumarolic gas. It is postulated that the injection of magmatic gas increased the fluid pressure in the reservoir, which triggered seismicity. The injection would have been triggered by a break of the sealing zone surrounding the degassing magma. The injection of magmatic gas can be detected by monitoring the composition of the fumarolic gas, thus giving the possibility to forecast any future seismicity.

Taiga-tundra boundary ecosystems are affected by climate change. Methane (CH 4) emissions in taiga-tundra boundary ecosystems have sparsely been evaluated from local to regional scales. We linked in situ CH 4 fluxes (2009-2016) with vegetation cover, and scaled these findings to estimate CH 4 emissions at a local scale (10 Â 10 km) using high-resolution satellite images in an ecosystem on permafrost (Indigirka lowland, northeastern Siberia). We defined nine vegetation classes, containing 71 species, of which 16 were dominant. Distribution patterns were affected by microtopographic height, thaw depth and soil moisture. The Indigirka lowland was covered by willow-dominated dense shrubland and cotton-sedge-dominated wetlands with sparse larch forests. In situ CH 4 emissions were high in wetlands. Lakes and rivers were CH 4 sources, while forest floors were mostly neutral in terms of CH 4 emission. Estimated local CH 4 emissions (37 mg m À2 d À1) were higher than those reported in similar studies. Our results indicate that: (i) sedge and emergent wetland ecosystems act as hot spots for CH 4 emissions, and (ii) sparse tree coverage does not regulate local CH 4 emissions and balance. Thus, larch growth and distribution, which are expected to change with climate, do not contribute to decreasing local CH 4 emissions.

Direct sampling and analysis of fumarolic gas was conducted at Ebinokogen Ioyama volcano, Japan, between December 2015 and July 2020. Notable changes in the chemical composition of gases related to volcanic activity included a sharp increase in SO2 and H2 concentrations in May 2017 and March 2018. The analyses in March 2018 immediately preceded the April 2018 eruption at Ioyama volcano. The isotopic ratios of H2O in fumarolic gas revealed the process of formation. Up to 49% high-enthalpy magmatic vapor mixed with 51% of cold local meteoric water to generate coexisting vapor and liquid phases at 100–160 °C. Portions of the vapor and liquid phases were discharged as fumarolic gases and hot spring water, respectively. The CO2/SO2 ratio of the fumarolic gas was higher than that estimated for magmatic vapor due to SO2 hydrolysis during the formation of the vapor phase. When the flux of the magmatic vapor was high, effects of hydrolysis were small resulting in low CO2/SO2 ratios in fumarolic gases. The high apparent equilibrium temperature defined for reactions involving SO2, H2S, H2 and H2O, together with low CO2/SO2 and H2S /SO2 ratios were regarded to be precursor signals to the phreatic eruption at Ioyama volcano. The apparent equilibrium temperature increased rapidly in May 2017 and March 2018 suggesting an increased flux of magmatic vapor. Between September 2017 and January 2018, the apparent equilibrium temperature was low suggesting the suppression of magmatic vapor flux. During this period, magmatic eruptions took place at Shinmoedake volcano 5 km away from Ioyama volcano. We conclude that magma sealing and transport to Shinmoedake volcano occurred simultaneously in the magma chamber beneath Ioyama volcano.

Abstract. The response of CH4 emission from natural wetlands due to meteorological conditions is important because of its strong greenhouse effect. To understand the relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, as well as the concentration, δ13C, and δD of dissolved CH4 during the summer from 2009 to 2013 at the taiga–tundra boundary in the vicinity of Chokurdakh (70∘37′ N, 147∘55′ E), located on the lowlands of the Indigirka River in northeastern Siberia. We also conducted soil incubation experiments to interpret δ13C and δD of dissolved CH4 and to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variations in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m−2 day−1 emitted). Increased CH4 emission was recorded in the summer of 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 emission remained relatively high in 2012, and increased further in 2013. Thaw depth became deeper from 2011 to 2013, which may partly explain the increase in CH4 emission. Moreover, dissolved CH4 concentration rose sharply by 1 order of magnitude from 2011 to 2012, and increased further from 2012 to 2013. Large variations in δ13C and δD of dissolved CH4 were observed in 2011, and smaller variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and less significance of CH4 oxidation relative to the larger pool of dissolved CH4. These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years following the wetting. Delayed activation of acetoclastic methanogenesis following soil reduction could also have contributed to the enhancement of CH4 production. These processes suggest that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in the permafrost ecosystem.

An extreme flooding event occurred from June to July 2017 in the Indigirka River lowland of northeastern Siberia. We used Landsat 8 satellite surface reflectance data to detect the flood inundation area and extract water color for delineating different water sources. We also took direct samples of dissolved methane concentrations in the river water. Relatively high concentrations of dissolved methane (0.7-1.1 μmol l -1 , or µM) were observed in four tributary areas in 2017 during the flood's recession, while the values remained low in the main channel (0.2-0.3 µM). In contrast, the concentrations of dissolved methane were low in both the main channel and tributaries during the non-flood period of 2016 (0.1-0.2 μM). We then used 2017 satellite reflectance data with an empirical model to estimate the spatial differences of dissolved methane concentration for water sources contributing to the methane-poor main channel and methane-rich tributaries and applied the results to the calculation of riverine methane in the study region (approx. 200 × 300 km). This approach to estimating dissolved methane 17 concentrations using satellite reflectance can provide a new tool for environmental monitoring 18 of flood events in remote areas.