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A plume of ash rises from a volcano under the Eyjafjallajokull glacier near Hvolsvollur, Iceland, last Wednesday. ((Brynjar Gauti/Associated Press))

Another massive cloud of volcanic ash from Iceland forced transatlantic flights to change routes and carry extra fuel Saturday in case they had to be delayed.

Forecasters said the cloud measured about 2,000 kilometres in length, stretching from southern Greenland to the northwest tip of Spain.

About half of the flights between Europe and North America were being delayed or rerouted.

Spain shut 19 airports, including those in Santiago, Vigo and Bilbao. Spain's main international airports of Madrid and Barcelona reported flight cancellations but were expected to remain open.

More than 100 flights into and out of Portugal were cancelled Saturday morning, affecting mainly Faro, Lisbon and Porto. There were also flight disruptions to the Azores and Madeira Islands in the Atlantic

Because of strong winds, passengers in southern France were warned they could expect to see their travel plans disrupted.

A new wave of dense volcanic ash from Iceland had snarled air traffic on Wednesday in Ireland and Scotland, stranding tens of thousands of people.

The eruption of the glacier-capped volcano near Hvolsvollur in Iceland has shown no signs of stopping since it began belching ash April 13.

Last month, the ash cloud forced airlines to ground more than 100,000 flights and left as many as 10 million passengers stranded for days.

Volcanic ash can stall jet engines. The heat of the engine melts the ash, which forms a glassy deposit on the turbine blades, corrodes the metal and clogs the fuel system.

With files from The Associated Press