Lake Taupo lies in a caldera created by a supervolcanic eruption which occurred approximately 26,500 years ago. According to geological records, the volcano has erupted 28 times in the last 27,000 years. It has ejected mostly rhyolitic lava, although Mount Tauhara formed from dacitic lava. The initial event 26,500 years ago is known as the Oruanui eruption. It was the world's largest known eruption over the past 70,000 years, ejecting altogether 1170 cubic kilometres of material and causing several hundred square kilometres of surrounding land to collapse and form the caldera. The caldera later filled with water, eventually overflowing to cause a huge outwash flood.[3] It is possible that the Lake Taupo event contributed to starting the Last Glacial Maximum.[citation needed] Several later eruptions occurred over the millennia before the most recent major eruption, which is traditionally dated as about 180 CE from Greenland ice-core records. Tree ring data from two studies suggests a later date of 232 CE ± 5.[4] Known as the Hatepe eruption, it is believed to have ejected 100 cubic kilometres of material, of which 30 cubic kilometres was ejected in the space of a few minutes. This was one of the most violent eruptions in the last 5000 years (alongside the Tianchi eruption of Baekdu at around 1000 and the 1815 eruption of Tambora), with a Volcanic Explosivity Index rating of 7; and there appears to be a correlation, to within a few years, of a year in which the sky was red over Rome and China. The eruption devastated much of the North Island and further expanded the lake. The area was uninhabited by humans at the time of the eruption, since New Zealand was not settled by the Māori until about 1280. Possible climatic effects of the eruption would have been concentrated on the southern hemisphere due to the southerly position of Lake Taupo.[5] Taupo's last known eruption occurred around 30 years later, with lava dome extrusion forming the Horomatangi Reefs, but that eruption was much smaller than the 180 CE eruption. Underwater hydrothermal activity continues near the Horomatangi vent,[6] and nearby geothermal fields with associated hot springs are found north and south of the lake, for example at Rotokawa and Turangi. These springs are the site of occurrence of certain extremophile micro-organisms, that are capable of surviving in extremely hot environments.[7] The volcano is currently considered to be dormant rather than extinct because there has been moderate Fumarole activity and Hot springs along the shores of the lake.