Volcanic hazards from Bezymianny- and Bandai-type eruptions

摘要: Major slope failures are a significant degradational process at volcanoes. Slope and associated explosive eruptions have resulted in more than 20 000 fatalities the past 400 years; historic record provides evidence for least six of these events century. Several debris avalanches exceed 1 km3 volume. Holocene an order magnitude larger traveled 50–100 km from source volcano affected areas 500–1500 km2. Historic with major include those magmatic component (Bezymianny type) solely phreatic (Bandai type). The gravitational remove segments volcanoes, creating massive horseshoe-shaped depressions commonly caldera size. paroxysmal phase Bezymianny-type eruption may powerful lateral explosions pumiceous pyroclastic flows; it is often followed by construction lava dome or cone new crater. Bandai-type begin end phase, during which failure removes portion edifice. Massive volcanic landslides can also occur without related eruptions, as Unzen 1792. main potential hazards derive blasts, avalanche itself, avalanche-induced tsunamis. Lateral blasts produced sudden decompression hydrothermal and/or systems devastate excess 500km2 velocities exceeding 100 m s−1. ratio area covered to distance Mount St. Helens Bezymianny exceeds that many flows surges comparable large-scale likely location magma time appears highest when has intruded into upper edifice, Bezymianny. Debris move faster ms−1 travel tens kilometers. When not confined valley walls, affect wide beyond volcano's flanks. Tsunamis coastal volcanoes caused themselves eruptions. probable (L) be estimated considering vertical drop (H). Data catalog around 200 indicates H/L rations volumes 0.1–1 average 0.13 range 0.09–0.18; km3, ratios 0.09 0.5–0.13. Large-scale deformation edefice intense local seismicity precede indicate direction orientation blasts. nature duration precursory activity vary widely, timing faliure greatly affects type eruption. particularly difficult anticipate because they typically climax suddenly preceded only short periods seismicity.