Grabrok crater, Iceland
Iceland has a high concentration of active volcanoes due to the unique geological conditions of its location on the mid-Atlantic Ridge, a divergent tectonic plate boundary. The island has 30 active volcanic systems, of which 13 have erupted since the settlement of Iceland in 874 AD.
Of these 30 volcanic systems, the most active/volatile is Grímsvötn. Over the past 500 years, Iceland's volcanoes have erupted a third of the total global lava output.