Research press release


Nature Geoscience

Deadly volcanic flows outsmart friction



今回Gert Lubeたちは、大規模な火山シミュレーション実験を行った。彼らは1トン以上の高温の火山物質を観測機器を設置した35メートルの溝に流し、その様子を高速ビデオで記録した。その結果、空気を多く含んだ層が火砕流の底部に生成されることが明らかになった。火砕流が地面に流れ下った時の速度変化率が大きいと、火砕流は自己組織化する。高圧により火山物質が密に充填された領域が流れの底部近傍に生成されると、ガスは地面の方向に移動して、地面とその上の高密度領域との間に空気の層が形成される。この空気の層によって、地面の上をほとんど摩擦なしで流れることが可能となる。


Pyroclastic flows, fast-moving currents of hot gas and volcanic matter, achieve great speeds and distance by traveling on a self-generated layer of air with little friction according to a study published in Nature Geoscience this week.

Volcanic eruptions can produce pyroclastic flows when part of the eruptive column collapses or as segments of a lava dome collapse. Flows can reach temperatures of up to 1000 °C and can travel many kilometres from their source. They present a deadly hazard and are responsible for an estimated 50% of volcanic fatalities globally. However, little is known about how they move so far and so fast.

Gert Lube and colleagues conducted large-scale eruption simulation experiments. They released over one tonne of hot volcanic material down a 35 m long instrumented runout section, and recorded the results on high-speed videos. The authors observed that an air-rich layer develops at the base of the pyroclastic flow. The current self-organizes when the rate of change of velocity is high as it flows over the ground. An area of high-pressure densely packed volcanic material forms close to the base of the currents. Then, gas moves towards the ground and creates a layer of air between the ground and high-density region above. The air layer allows the current to flow over the ground with little friction.

The authors suggest that these findings may help to enable more-accurate hazard assessments of future pyroclastic flow runout distances and speeds.

doi: 10.1038/s41561-019-0338-2


メールマガジンリストの「Nature 関連誌今週のハイライト」にチェックをいれていただきますと、毎週各ジャーナルからの最新の「注目のハイライト」をまとめて皆様にお届けいたします。