【英语时差8,16】火山灰与飞机-上（在线收听）

After six days of being grounded aeroplanes have been given the all-clear to fly in British airspace again. The UK has effectively been a no-fly zone since last Thursday when a huge cloud of volcanic ash was thrown up into the atmosphere by a volcano in Iceland. The eruption beneath an Icelandic glacier created an ash cloud that forced airspace closures across northern Europe, stranding many thousands of air travellers. The ash cloud posed a risk to jet planes because it rose to around 30,000ft which is the normal cruising altitude for passenger planes. Volcanic ash can clog up and damage jet engines while the tiny particles of glass in the ash can also melt and block the ventilation holes which can cause the engines to overheat and stop working.