Large explosive eruptions of volcanoes pose the highest hazard to modern jet f lights, because such eruptions can eject as much as several cubic kilometers of volcanic ash and aerosol into the atmosphere during a few hours or days. The year 2016 saw eruptions on 5 of the 30 active Kamchatka volcanoes (Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Zhupanovsky) and on 3 of the 6 active volcanoes that exist on the North Kuril Islands (Alaid, Ebeko, and Chikurachki). Effusive activity was observed on Sheveluch, Klyuchevskoy, Bezymianny, and Alaid. All volcanoes showed explosive activity. The large explosive events mostly occurred from September through December (Sheveluch), a moderate ash emission accompanied the entire Klyuchevskoy eruption in March–November, and explosive activity of Karymsky, Zhupanovsky, Alaid, and Chikurachki was mostly observed in the earlie r half of the year. The ash ejected in 2016 covered a total area of 600 000 km2, with 460 000 km2 of this being due to Kamchatka volcanoes and 140 000 km2 to the eruptions of the North Kuril volcanoes. The activity of Sheveluch, Klyuchevskoy, and Zhupanovsky was dangerous to international and local f lights, because the explosions sent ash to heights of 10–12 km above sea level, while the eruptions of Bezymianny, Karymsky, Alaid, Ebeko, and Chikurachki were dangerous for local flights, since the ash did not rise higher than 5 km above sea level.