The eruption frequency, calculated from tephra layer frequency in soil profiles around Vatnajökull, reveals Grímsvötn as the most active volcanic system followed by Bárdarbunga, but Kverkfjöll show episodic activity with repose periods of more than 1000 years.
Grímsvötn eru virkust bæði á sögulegum og forsögulegum tíma, næst kemur Bárðarbunga en Kverkfjöll reka lestina, en virknin þar einkennist af löngum goshléum (allt upp í 1200 ár).