Physical and chemical characteristics of volcanic ash are primarily controlled by the style of volcanic eruption . Volcanoes display a range of eruption styles which are controlled by magma chemistry , crystal content , temperature and dissolved gases of the erupting magma and can be classified using the volcanic explosivity index ( VEI ) . Effusive eruptions ( VEI 1 ) of basaltic composition produce 5 m3 of ejecta , whereas extremely explosive eruptions ( VEI 5 ) of rhyolitic and dacitic composition can inject large quantities ( > 109 m3 ) of ejecta into the atmosphere . Another parameter controlling the amount of ash produced is the duration of the eruption : the longer the eruption is sustained , the more ash will be produced . For example , the second phase of the 2010 eruptions of Eyjafjallajökull was classified as VEI 4 despite a modest 8 km high eruption column , but the eruption continued for a month , which allowed a large volume of ash to be ejected into the atmosphere
2010 eruptions of Eyjafjallajökull
2010 eruptions of Eyjafjallajökull
Volcanic ash