London ( CNN ) -- Icelandic volcano ash is affecting flights in European airspace , but authorities say it is unlikely to cause the same levels of disruption triggered by a similar eruption last year . So what are the main differences between the two volcanic ash clouds and to what extent will travel plans be hit ? Who has been affected so far ? Icelandic airspace was closed over the weekend . By early Tuesday , several hundreds flights from England , Scotland and Northern Ireland had been canceled with British Airways , easyJet , Ryanair , Aer Lingus , Loganair , Flybe and KLM among operators grounding jets . Meteorologist have warned prevailing winds are blowing the ash cloud towards London 's Heathrow airport , potentially closing airspace above Europe 's busiest air hub . Officials say there is a strong possibility some Scandinavian airports may also be affected . Send travel report to Twitter . Among those changing travel plans have been U.S. President Barack Obama , who flew into London a day ahead of schedule , and Barcelona 's soccer team , which is traveling to the UK capital early ahead of Saturday 's Champion 's League final clash against Manchester United . How will the disruption differ from last year 's ? Ash from the eruption of Iceland 's Eyjafjallajokull volcano in April 2010 prompted the closure of airspace across Europe , stranding millions of passengers and costing the airline industry more than $ 2 billion . Authorities say there is uncertainty over how long the latest ash cloud , generated by Grimsvotn -- Iceland 's most active volcano -- is likely to last , and how it will be affected by atmospheric changes . However , weather patterns indicate most mainland European airports will not be hit and airspace will remain open . Changes in flight safety regulations also mean fewer flights will be affected . What are the safety regulation changes ? Most significantly , aviation authorities have raised the threshold on what density of ash cloud is considered safe to fly through . Last year , 200 micrograms of ash per cubic meter was seen as the maximum , this year it has been raised to 4,000 micrograms per cubic meter . Ash density is also being classified in terms of low , medium or high density . In theory , airlines can make a case to fly through all three provided they can prove they are taking adequate safety precautions . Irish carrier Ryanair has , however , condemned these limited restrictions as pointless . It said it has successfully piloted a test flight into an area of high ash density , with no adverse affects . What other differences are there ? Scientists and airlines say the type of ash produced by Grimsvotn is potentially less harmful to aircraft engines than that thrown up by Eyjafjallajokull . According to a study by the Institute of Earth Sciences at the University of Iceland , ash particles from Eyjafjallajokull were unusually fine and angular due to the higher silica content of the magma produced in the eruption . This `` stickier '' magma caused a powerful explosion when it hit the volcano 's ice cap , resulting in smaller and sharper ash particles capable of traveling further and remaining airborne longer . The larger particles produced by Grimsvotn , though still capable of traveling far , are more likely to fall out of the sky sooner . Jeremy Phillips of Bristol University 's Earth Sciences department told CNN that Grimsvotn 's eruptions are typically shorter than the Eyjafjallajokull event of 2010 , lasting only a few days . What rights do affected passengers have ? Last year 's eruption left tens of thousands of passengers scrambling to make alternative travel plans via road , rail and sea amid debate over who was liable to compensate them for inconveniences faced . This year , the situation is far clearer , following court rulings over what is covered by travel insurance in the event of ash cloud disruption and clarified airline policy . According to UK consumer watchdog Which ? delayed travelers are entitled to accommodation , food and phone calls . Those whose flights are canceled can expect refunds and re-routing to final destination .
Ash cloud , cancellation of number of flights , . Authorities have raised the threshold for flying in ash cloud . They say ash particles emitted by Grimsvotn glacier are less hazardous than those from Eyjafjallajokull .