Eruption column

An eruption column is the resultant of many volcanic eruptions fountain or cloud of lava and fragments of lava, magmatic gases, entrained -rock and turned mixed air. The bandwidth ranges from a few hundred meters high lava fountain up to ash clouds that reach far into the stratosphere.

Formation

An eruption column can be divided two parts. First shot out at supersonic speed from the vent by the high pressure in the magma chamber, the magma - gas mixture. This lower region is called the gas thrust region. A key mechanism is the formation, growth and bursting of gas bubbles in the upper part of the magma chamber and vent. The resulting acceleration is sufficient but only to throw up the magma up to several hundred meters.

At higher eruption columns which ambient air is drawn into the turbulent burning gas thrust region. By heating the gas volume increases thereby abruptly. The resulting mixture is lighter than the surrounding air and rises to as convective eruption column, the rock material contained is torn up with.

From the gas content, the initial acceleration in the chimney, the fragmentation in the gas thrust region as well as on the amount of magma per unit of time, it depends now whether it remains at a lava fountain or whether a convective eruption column is created and what height it reaches. In extreme cases, they achieved only in the stratosphere layers of air of equal density. In this zone, they will rise because of their speed a bit further, but then drop and thereby laterally in the direction of wind spread.

Change in the course of the eruption certain parameters, in particular the gas content, the muzzle velocity of the vent radius and the mass eruption rate, the column may collapse. The complete or partial collapse of eruption columns is one of several possible causes of pyroclastic density currents and thus a source of volcanic hazard.