Complex sentence: They were soon joined by drummer Þorvaldur Gröndal, replaced in 2001 by Arnar Geir Ómarsson, drummer of the legendary Icelandic rock band HAM.
Split into simpler sentences: They were soon joined by drummer Þorvaldur Gröndal. When Þorvaldur left the band in 2001 he was replaced by Arnar Geir Ómarsson, drummer of the legendary Icelandic rock band HAM.