Iceland - Viti crater

A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not made. Crater lakes covering active (fumarolic) volcanic vents are sometimes known as volcanic lakes, and the water within them is often acidic, saturated with volcanic gases, and cloudy with a strong greenish color. Lakes located in dormant or extinct volcanoes tend to have fresh water, and the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment.

Askja (Icelandic pronunciation: [ˈascja]) is a stratovolcano situated in a remote part of the central highlands of Iceland. The name Askja refers to a complex of nested calderas within the surrounding Dyngjufjöll mountains, which rise to 1,510 m (4,954 ft), askja meaning box or caldera in Icelandic

This is a list of active and extinct volcanoes in Iceland. Iceland has about 130 volcanic mountains, of which 18 have erupted since the settlement of Iceland, circa 900 CE.

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.

The most fatal volcanic eruption of Iceland's history was the so called Skaftáreldar (fires of Skaftá) in 1783, lasting until 1784. The eruption was in the crater row Lakagígar (craters of Laki) southeast 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 did not die 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 coming 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 in Eyjafjallajökull (glacier of Eyjafjöll) in 2010 was notable because the volcanic ash plume disrupted air travel in northern Europe for several weeks; however, Eyjafjallajökull is a minor volcano in Icelandic terms. In the past, eruptions of Eyjafjallajökull have been followed by eruption of the larger volcano Katla, but following the 2010 eruption no signs of an imminent eruption of Katla were seen.