Hekla (ˈhɛhkla), or Hecla, is an active stratovolcano in the south of Iceland with a height of . Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since the year 1210. During the Middle Ages, the Icelandic Norse called the volcano the "Gateway to Hell" and the idea spread over much of Europe.
Hekla is part of a volcanic ridge, long. The most active part of this ridge, a fissure about long named Heklugjá ˈhɛhklʏˌcauː, is considered to be within Hekla proper. Hekla looks rather like an overturned boat, with its keel being a series of craters, two of which are generally the most active.
The volcano's frequent large eruptions have covered much of Iceland with tephra, and these layers can be used to date eruptions of Iceland's other volcanoes. Approximately 10% of the tephra created in Iceland in the last thousand years has come from Hekla, amounting to 5 km3. Cumulatively, the volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around 8 km3.
In Icelandic Hekla is the word for a short hooded cloak, which may relate to the frequent cloud cover on the summit. An early Latin source refers to the mountain as Mons Casule.
After the eruption of 1104, stories, probably spread deliberately through Europe by Cistercian monks, told that Hekla was the gateway to Hell. The Cistercian monk Herbert of Clairvaux wrote in his De Miraculis (without naming Hekla): The renowned fiery cauldron of Sicily, which men call Hell's chimney ... that cauldron is affirmed to be like a small furnace compared to this enormous inferno. A poem by the monk Benedeit from circa 1120 about the voyages of Saint Brendan mentions Hekla as the prison of Judas.
In the Flatey Book Annal it was recorded that during the 1341 eruption, people saw large and small birds flying in the mountain's fire which were taken to be souls.
In the 16th century Caspar Peucer wrote that the Gates of Hell could be found in "the bottomless abyss of Hekla Fell".