The Pacific Ocean evolved from the Panthalassic Ocean that was first formed ca 750 Ma with the rifting apart of Rodinia. By 160 Ma, the first ocean floor ascribed to the current Pacific plate was produced to the west of a spreading centre in the central Pacific, ultimately growing to become the largest oceanic plate on the Earth. The current Nazca, Cocos and Juan de Fuca (Gorda) plates were initially one plate, produced to the east of the original spreading centre before becoming split into three. The islands of the Pacific have originated as: linear chains of volcanic islands on the above plates either by mantle plume or propagating fracture origin, atolls, uplifted coralline reefs, fragments of continental crust, obducted portions of adjoining lithospheric plates and islands resulting from subduction along convergent plate margins. Out of the 11 linear volcanic chains identified, each is briefly described and its history summarized. The geology of 10 exemplar archipelagos ( Japan, Izu-Bonin, Palau, Solomons, Fiji, New Caledonia, New Zealand, Society, Galápagos and Hawaii) is then discussed in detail.

A stratigraphy and chronology of andesitic tephras erupted from Mt Ruapehu, and other volcanoes of Tongariro Volcanic Centre, is constructed from the tephra record preserved on the southeastern Mt Ruapehu ring plain. Here, tephras of late Quaternary age (c. 22,500 years B.P. to present) are found interbedded with local laharic and fluvial deposits, and with distal rhyolitic tephras from Taupo and Okataina Volcanic Centres. Tephras are identified from their field characteristics and stratigraphic positions relative to dated rhyolitic tephra marker beds. The radiocarbon ages of these rhyolitic tephras provide a chronology for the andesitic tephras, dating back to 22,500 years B.P. All tephras erupted from Tongariro Volcanic Centre are grouped into two subgroups: the Tongariro Subgroup (redefined) and the newly defined Tukino Subgroup. Tephras identified on the southeastern Mt Ruapehu ring plain are grouped into seven formations on the basis of lithology: Ngauruhoe Formation [dated c.

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Mt. Egmont/Taranaki in western North Island, New Zealand, has been inactive during historic time and thus its pattern of eruptive history must be reconstructed by inference from the stratigraphy and chronology of associated volcanic and pyroclastic deposits. The most complete record of eruptive activity from Egmont Volcano is found on the surrounding ring plain rather than on the volcanic cone, where surficial deposits are readily removed by erosion or deeply buried by the products of more recent eruptions. In this study, a comprehensive post-28 ka record of the volcano's eruptive history is presented, and the relationship of andesitic tephra beds to andic soil material, Egmontsourced volcaniclastic detritus, and two silicic tephra beds from Taupo Volcano are discussed, along with implications for inter-regional correlation.The post-28 ka tephra succession is recorded in sixteen andesitic tephra formations. These formations and their approximate ages are as follows: Manganui tephra (4 beds;

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Ten newly named formations and members of ash and lapilli, erupted from Mt Egmont and the Pouakai Range, comprise the principal tephras mantling the western Taranaki landscape. They are overlain by nine restricted younger eruptives, previously described by Druce, which are also summarised in this paper. The Newall Ash and Lapilli are considered to have been deposited by nU(~es ardentes between 1500-1550 A.D., in contrast with the Burrell Lapilli, an airfall deposit of 1655 A.D.The newly named tephras include the "Egmont Shower", here split into two separate formations, qne considered to be less than (NZl144) 6,970 ± 76 yr B.P., and the other between (NZ1l44) and (NZ942) 16,100 ± 220 yr B.P. The underlying Saunders Ash is considered to be a nuee ardente deposit preserved between much thicker tephras, it contains charcoal dated (NZ942) at 16,100 ± 220 yr B.P. The other newly named tephras are richly allophanic, stratigraphically overlie the Rapanui Formation near New Plymouth and are thought to have been erupted from Mt Egmont. They overlie, with major dis conformity, the oldest tephras described: the New Plymouth Ashes and Buried Soils, which form massive halloysite bearing deposits and were probably erupted from the Pouakai Range volcano.

The Murimotu Formation comprises three facies, distinguished on the basis of surface morphology and abundance of debris-avalanche blocks: masses of loosely consolidated debris transported nearly intact from the source area Facies 1 and 2 are debris-avalanche deposits. Facies 1 occupies the axial part of the deposit, contains over 50% debris-avalanche blocks (to 36 m in length), and is characterised by large (to 10 m high) hummocks. Lithologic layering in facies 1 preserves the original stratigraphy of the volcano. Facies 2 surrounds facies 1, contains less than 30% debris-avalanche blocks « 1.0 m in length), and has low (to 1.5 m) hummocks. Facies 3 was deposited by lahars. Facies 3 either overlies facies 1 and 2 or occurs around the margins of facies 2. Facies 3 is matrix supported, ungraded, and has planar upper surfaces.The Murimotu event was triggered by gravitational collapse probably due to inbUSion of dikes into hydrothermally weakened Te Herenga Formation. Facies relationships suggest t1mt the collapse occurred neru-the headwaters of the Whakapapanui Stream. Facies 1 was confined to the Whakapapanui valley while on the volcano and spreadlateraUy over a small distance when flow became unconfmed on the ring plain. Greater mobility of facies 2 allowed it to overtop drainage divides on the volcano and spread laterally over -larger areas on the ring plain than did facies 1. Lahars postdated emplacement of the debris avalanche. They resulted from subsequent failures in the area of the initial collapse or from the surface of the debris-avalanche deposit

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