I can vouch for the decision to suspend flights - volcanic ash can be very dangerous to aircraft... it's dense and hot and if it gets into aircraft engines, it can melt on fuel nozzles and turbine blades, causing engine failure. Also, the ash contains sulphur dioxide which can have corrosive effects on the aircraft, When I was doing my masters we did a course on Natural Hazards and our professor was telling us of an incident in the late '80s where a commercial plane flew into an ash cloud over Alaska (KLM flight 867) and lost power to all four engines. It descended 14,000 ft before the pilot got the engines started again and caused $80 million of damage to the plane (we even heard the black box recording of it happening... not fun to listen to). Thankfully it managed to land safely and no one was hurt.