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Tofua
Tofua Caldera, in Tonga, is the summit caldera of a steep-sided composite cone that forms Tofua Island. Tofua Island is in Tonga's Ha'apai island group. Pre-caldera activity is recorded by a sequence of pyroclastic deposits and lavas constituting the older cone, followed on the northern part of the island by froth lavas or welded and unwelded ignimbrite. Following caldera collapse, lavas were erupted from the northern part of the island and the caldera-rim fissure zone, scoria and lavas from the caldera-wall fissure zones, pyroclastics and lavas from intracaldera cones, and recent pyroclastic fall deposits on the outer cone. Eruptive products are mainly basaltic andesites and andesites, plus occasional dacite flows within the older cone. A postcaldera cone with fumarolic activity (Lofia) is in the northern part of the caldera; a crater lake with depth occupies most of the remainder.
Most historical eruptions have been small explosions from Lofia cone along the northern caldera rim. The eruptions of 1958-59 caused most of the islanders to evacuate for a year or more.
==Population==
Tofua is visited by fifty men from Kotu Island for 2 weeks each year. They are there primarily to grow kava (''Piper methysticum'') for export to Tongatapu. This gives the island an average yearly population of 2 ().
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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