Backgrounder: The harm volcanic ashes can do to air planes

LONDON, April 18 (Xinhua) -- Volcanic ashes from Iceland, carried by winds, have spread across the skies of Europe in the past few days, forcing grounding of most civil aviation flights and closing-down of airspaces.

The ashes, feared to be harmful to plane jet engines and body frames, are formed from an interaction between scorching magma and icy water.

When the Icelandic volcano Eyjafjallajokull erupted on April 14, the magma gushed up right beneath the ice cap near the summit of the volcano.

The interaction, known as phreatomagmatic activities in geophysics, forms glassy granules -- armored lapilli -- in the volcanic ash. Rather abrasive, the particles can clog jet engines to stop them from working mid-air.

The Jakarta incident was the earliest reported mid-air engine stalling as a British Airways Boeing 747-236B had all four engines stalled after having flown through a volcanic ash cloud over Indonesia in 1982.

A KLM Boeing 747-400 ran into a nearly identical incident seven years later when it dashed into a volcanic ash cloud over Alaska.

In both cases, the crew managed to re-start the engines after their planes were out of the ash clouds.

Civil aviation authorities across Europe have to resort to extreme measures as closing down airspaces and grounding nearly all civil flights because the prevailing winds in the past few days have been blowing from the west to spread volcanic ashes all over.

The British Geological Survey has also explained that volcanoes in Iceland are the type of volcanoes that tend to produce plumes of harmful ashes, in that the country's volcanoes are often covered by glaciers.

Iceland is a country which is formed by volcanoes which erupted when the tectonic plates of Eurasia and North America moved apart to allow magma well up to create rising sea floors.

The underwater volcanism interacts with a mantle plume which brings magma up from deep within the Earth. The result is the formation of the volcanic country.

There are now more than 100 active volcanic mountains in Iceland.