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Eruption Columns. Jon Peterson, Taylor Witcher , Casey Duncan. Basic Features of an Eruption Column. Divided into three parts: Gas thrust region Convective region Umbrella region. Gas Thrust Region. Cooler atmospheric air is mixed into the column the air is heated and expands
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Eruption Columns Jon Peterson, Taylor Witcher, Casey Duncan
Basic Features of an Eruption Column Divided into three parts: • Gas thrust region • Convective region • Umbrella region
Gas Thrust Region • Cooler atmospheric air is mixed into the column • the air is heated and expands • The gas thrust region is the initial acceleration of the erupted pyroclastic material and gas expansion • The nozzle velocity Eyjafjallajokull, Iceland Mount St. Helens, Washington
Convective Region • Density of the column is less dense than the surrounding air then the eruptive column rises • The level of neutral buoyancy Mt. Redoubt, Alaska
Umbrella Region • At the level of neutral buoyancy • the column spreads out laterally forming the umbrella region • The degree of lateral expansion is determined by various factors Santa Maria, Guatemala
Ash Dispersal • Max column height of 10 km • Main wind direction at 5 km over crater in a southeast to east direction. • Average wind speed was 20 m/s
Ash Fallout • Bulk ash fallout volume for first 3 days of eruption compared to the whole eruption • 0.05-.075 km3 first 3 days • 0.2-0.35 km3 accumulation for whole eruption in Mainland Europe • Total airborne tephra produced: 270 x 106 m3
Eyjafjallajokull Eruption Column • Eruption column heights varied. • Three distinct phases of eruptive style and column height.
April 14th-17th • Mainly phreatic eruptions. • Column reached maximum height of ~8-10 km.
April 18th-May 4th • Magmatically driven eruptions. • Column heights varied between <1 km to ~6 km. • Coarser ash during this period.
May 5th-18th • Explosive activity increased in this period. • Column height reached between 4-6 km, and as high as 8-9 km.