Hekla is a stratovolcano in the south of Iceland with a height of 1,491 m (4,892 ft). Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since 874. During the Middle Ages, Europeans called the volcano the "Gateway to Hell".

An eruption occurred from 17 January 1991 to 11 March 1991, producing 0.15 km³ of lava and 2×107 m³ of tephra. The eruption, which was preceded by sulphurous smells and earthquakes, started as a Plinian eruption (similar to the eruption of Mount Vesuvius in 79 AD), producing an ash cloud reaching an altitude of 11.5 km within 10 minutes which had travelled over 200 km north-northeast to the coast within 3 hours. The eruption then began producing andesitic lava, the flows eventually covering an area of 23 km² to an average depth of 6–7 m. Initially, part of the Heklugja fissure and other fissures erupted with lava fountains reaching 300 m in height.

By the second day, the activity stopped in all but one fissure where the main crater formed. During these 2 days, 800 m³/s of lava were produced, slowing to between 1 m³/s and 14 m³/s for most of the eruption. This low viscosity lava had a Silicon dioxide content of approximately 54%.

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