Complex sentence: The eruption, in May 2011, at Grímsvötn under the Vatnajökull glacier sent thousands of tonnes of ash into the sky in a few days, raising concerns of a repeat of the travel chaos seen across northern Europe.
Split into simpler sentences: The eruption, in May 2011, at Grímsvötn under the Vatnajökull glacier. Grímsvötn volcano sent thousands of tonnes of ash into the sky in few days, raising concerns of a repeat of the travel chaos seen across northern Europe.