Harrat Rahat, Saudi Arabia's largest lava field, covers 20,000 km2 and extends for 300 km S of Madinah (Medina). Four coalescing lava fields erupted from offset NNW-trending vent systems comprise the field, which has an average width of 60 km. Lava flows extend as far as 100 km W of the axis of the field. Basaltic scoria cones dominate, but the volcanic field has also produced silicic trachy-basaltic to trachytic rocks. Small shield volcanoes and lava domes with associated pyroclastic flow and surge deposits are also present. Activity has migrated to the north over time, resulting in eruptions near Madinah. The best-known eruption took place in 1256 CE, when a 0.5 km3 lava flow erupted from six aligned scoria cones and traveled 23 km to within 4 km of Madinah.