Volcanoes!

Volcanes

Iceland has a high concentration of active volcanoes due to its location on the mid-Atlantic Ridge, a divergent tectonic plate boundary, and also due to its location over a hot spot. The island has 30 active volcanic systems, of which 13 have erupted since the settlement of Iceland in AD 874.^[1]

Of these 30 active 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.

The most fatal volcanic eruption of Iceland's history was the so-called Skaftáreldar (fires of Skaftá) in 1783-84. The eruption was in the crater row Lakagígar(craters of Laki) southwest of Vatnajökull glacier. The craters are a part of a larger volcanic system with the subglacial Grímsvötn as a central volcano. 

Roughly a quarter of the Icelandic nation died because of the eruption. Most died not because of the lava flow or other direct effects of the eruption, but from indirect effects, including changes in climate and illnesses in livestock in the following years caused by the ash and poisonous gases from the eruption. The 1783 eruption in Lakagígar is thought to have erupted the largest quantity of lava from a single eruption in historic times.

The eruption under Eyjafjallajökull ("glacier of Eyjafjöll") in 2010 was notable because the volcanic ash plume disrupted air travel in northern Europe for several weeks; however this volcano is minor in Icelandic terms. In the past, eruptions of Eyjafjallajökull have been followed by eruption of the larger volcano Katla, but after the 2010 eruption no signs of an imminent eruption of Katla were seen.