Modelling And Predicting The Movement In Pyroclastic Flows

When most people think of volcanoes they think of lava, molten rock flowing across the surface of the Earth like a river. The truth is, in most situations, someone could outrun lava as it moves quite slowly unless the angle is steep and there already a channel grooved into the landscape for it to follow (in this case just get out of the way). The real danger is from pyroclastic flows. There is very little chance of outrunning one of these, as instead of viscous lava, it is a cloud of hot ash, dust and gas. Being denser then air this cloud rolls down the side of the volcano reaching speeds of 700 km/h. The chances of outrunning one is slim. The dust in the cloud gathers static and so lightning can be seen ripping through the flow, just to add more awe to the spectacle. Some humans that have been hit by pyroclastic flows can still be seen, the heat of 1000 °C turning them into carbon statues, and on occasion ash ones.

To investigate how pyroclastic flows form and move, the kinematics of the cloud are studied. It was believed that was a turbulent ash cloud resting on top of a much more ordered underflow. A recent study has proven this theory but has added some new nuance to it. The smooth flow bed and rough dust cloud are separated by an intermediary zone which is a mix between the two. It is not a continuous change the layers are discrete but they are also dynamically linked, so that any change on one zone would have a definite effect on another. Being able to forecast the movement of these more destructive elements of a volcano leads to better hazard models and a greater chance to save people in an emergency.

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