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 .
Ash cloud prompts cancellation of dozens of flights , . Authorities have raised safety threshold for flying in ash cloud . Scientists say ash particles produced by Grimsvotn volcano are less hazardous than those from Eyjafjallajokull .