Complex sentence: The ash cloud from the eruption rose to, and is so far 10 times larger than the 2004 eruption, and the strongest in Grímsvötn in the last 100 years.
Split into simpler sentences: The ash cloud from the eruption rose to. The eruption was 10 times larger than the 2004 eruption, and the strongest at Grímsvötn in the last 100 years.