A cloud of dense ash from the volcano in Iceland resumed its havoc-making disruptions on European air travel early Monday, forcing the temporary closing of important airports in the British Isles including London Heathrow, Europe's busiest. The airspace over Heathrow was ordered closed from 1 a.m. until 7 a.m. London time, the British National Air Traffic Control Services, or NATS, said in a statement posted on its website Sunday night. The restrictions also included Gatwick and London City airports and all airfields in Northern Ireland and parts of Scotland. Later, Dutch authorities announced the closing of airports in Amsterdam and Rotterdam from 6 a.m. until at least 2 p.m. The drifting ash, which can stall jet engines with potentially catastrophic results, also forced the closing of Dublin's international airport Sunday night, until at least noon Monday. Met, the United Kingdom's national weather service, estimated that the ash spewing from the volcano now towered around 25,000 feet. The weather service expected that southwesterly winds Monday would blow the ash cloud away from Britain by Tuesday. Pilots reported that in many areas, the cloud, which can potentially damage engines through clogging and abrasion, was visible to the naked eye and was described as 'a gray-black layer.' 