Askja is an enormous caldera and central volcano in the Dyngjufjöll mountains, north of Vatnajökull glacier. The caldera is a bedrock subsidence located above a massive magma chamber, and is still ‘in the making’. Askja was not explored until the nineteenth century, but a series of eruptions in 1874-1875, especially a very powerful explosive eruption in March 1875, caught the attention of the local people as well as scientists. In the massive eruption in 1875, the volcano erupted approximately 2 billion cubic meters of ash and pumice, and a new caldera was formed inside the older one. In the following decades the new caldera was filled with water, and now contains the 11km² Lake Öskjuvatn, which is also one of the deepest lakes in Iceland (220m). The Askja volcano erupted a few times in the 1920s, but the latest eruption was in the autumn of 1961.