Excerpt; The last period of volcanic activity on the peninsula began in the 10th century and continued until the 13th. Unlike typical Icelandic volcanoes, which tend to wake for a few years and then die down, when this region gets going it appears to splutter on and off for up to 300 years, producing eruptive episodes (locally known as “fires”) lasting a few decades. Long thin cracks known as fissures extend up to five miles (8km), producing fountains of lava, usually without large amounts of ash or explosive activity.