Complex sentence: The earliest recorded eruption of Hekla took place in 1104, since then there have been between twenty and thirty considerable eruptions, with the mountain sometimes remaining active for periods of six years with little pause.
Split into simpler sentences: The earliest recorded eruption of Hekla took place in 1104. Since then there have been between twenty and thirty considerable eruptions, with the mountain sometimes remaining active for periods of six years with little pause.