Activity 3 - Evacuate?

This image shows where the Volcanic Ash Cloud has been blown so far. Did you forecast this as well?

The Centre for Emergency Situations knows that Green Island's capital, FitzRoy, is safe for now. However, the settlements to the North of Fitzroy's Peak could be affected by the ash. They've decided to evacuate Alexandria Heights, but they need to decide what advice to give to East Hadley and West Hadley. This decision will depend on the concentration of the ash cloud over those towns.

Towards the centre of an ash cloud, the concentration of ash is greater than towards the edges.

The concentration, measured in 'ash units' is related to the volume of ash erupted.

• Concentration at centre of ash cloud = 'a' x volume (in millions of m3)
• Concentration at edge of ash cloud = 'b' x volume (in millions of m3)

You found the volume of the eruption in Activity 2. If the value of 'a' is 150, and the value of 'b' is 50, then what are the concentrations of the ash cloud above West Hadley and East Hadley?

The limit for evacuation is 450 ash units. Which town do you think might be evacuated? East Hadley or West Hadley? Mark the answer on your worksheet.

Last updated: 14 March 2013