There is a good article about how Bárðarbunga volcano collapsed during it’s six month long eruption in Holuhraun. The most recent data (the work on Bárðarbunga volcano is far from over even there is no eruption taking place currently) show that Bárðarbunga volcano did in fact collapse. This collapse was not marked by a big explosion, but rather slow subsidence of Bárðarbunga volcano over a large area. Holuhraun eruption is the largest eruption in Iceland for the past 230 years, both in magma and size of the eruption.
More details can be found here.
Iceland’s Bárðarbunga-Holuhraun: a remarkable volcanic eruption (blogs.egu.eu)