Steve Connor: Larger ash particles will mean less chaos

Although it is the biggest volcanic eruption in Iceland for 50 years – bigger than the one that caused air travel chaos this time last year – experts believe the Grímsvötn disturbance is unlikely to cause the widespread closure of airports.

The most notable difference between Grimsvotn and Eyjafjallajokull is in the type of ash plume. Grimsvotn is producing ash composed of relatively large particles that should in theory fall out of the sky closer to the volcano than the much finer particles of ash produced by Eyjafjallajokull last year.

How much fine ash there is in a volcanic plume depends on several factors, including the type of magma and whether it has interacted with water. The magma of Eyjafjallajokull exploded through a glacier, which meant that 90 per cent of the resulting ash was composed of particles less than 1mm across. Grimsvotn's basalt magma is not usually explosive, except when it interacts with meltwater, which means the fragmentation is less efficient than Eyjafjallajokull's eruption, resulting in coarser ash particles.

The plume produced by Eyjafjallajokull rose to about 9km and the plume from Grimsvotn initially reached 17km. However, experts believe the height will not be as important as the particle size of the ash cloud.

Weather conditions are also different this time, with strong westerlies tending to blow the Grimsvotn plume away from Britain. Grimsvotn is also unlikely to cause the same problems as last year because the airlines are now more relaxed about the rules governing flights near clouds of volcanic ash.