Just found a scientific paper on Nabro (can't link to it as it's through an academic account, as I'm in grad school.)
It's entitled "Large magnitude silicic volcanism in north Afar: the Nabro Volcanic Range and Ma'alalta volcano" in the Bulletin of Volcanology.
Anyway, the authors found an ignimbrite sheet associated with Nabro with a volume of 20 to 100 cubic kilometers (Tambora was 50 cubic kilometers.)
Yeah this is a bigdog...!