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Healy (volcano)
James Healy Seamount (former names Healy Seamount, Healy Volcano) is a submarine volcano located among the South Kermadec Ridge Seamounts south of New Zealand's Kermadec Islands. It consists of a volcanic cone that reaches a depth of below sea level, two and wide calderas and a parasitic cone that reaches a depth of below sea level. The flanks of the volcano are covered with pumice and volcanic rocks, and hydrothermal venting occurs inside the caldera. The caldera appears to have formed in one large explosive eruption that may have generated a pumice raft. Parts of the "Loisels Pumice" in New Zealand are suspected to have originated in this eruption, which took place 590±80 years before present (1950). Healy is also suspected to be the source of a tsunami that impacted Maori communities during the 15th century, and may be a continuing tsunami hazard. Geography and geology Regional The seafloor northeast of New Zealand is dominated by four structures, from east to wes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kermadec Islands
The Kermadec Islands ( mi, Rangitāhua) are a subtropical island arc in the South Pacific Ocean northeast of New Zealand's North Island, and a similar distance southwest of Tonga. The islands are part of New Zealand. They are in total area and uninhabited, except for the permanently manned Raoul Island Station, the northernmost outpost of New Zealand. The islands are listed with the New Zealand outlying islands. The islands are an immediate part of New Zealand, but not part of any region or district, but instead an ''Area Outside Territorial Authority''. Toponymy The islands were named after the Breton captain Jean-Michel Huon de Kermadec, who visited the islands as part of the d'Entrecasteaux expedition in the 1790s. The topographic particle "Kermadec" is of Breton origin and is a lieu-dit in Pencran in Finistère where '' ker'' means village, residence and madec a proper name derived from '' mad'' (which means 'good') with the suffix '' -ec'', used to form adjectives in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Izanagi Plates. The Pacific Plate subsequently grew to where it underlies most of the Pacific Ocean basin. This reduced the Farallon Plate to a few remnants along the west coast of North America and the Phoenix Plate to a small remnant near the Drake Passage, and destroyed the Izanagi Plate by subduction under Asia. The Pacific Plate contains an interior hot spot forming the Hawaiian Islands. Boundaries The north-eastern side is a divergent boundary with the Explorer Plate, the Juan de Fuca Plate and the Gorda Plate forming respectively the Explorer Ridge, the Juan de Fuca Ridge and the Gorda Ridge. In the middle of the eastern side is a transform boundary with the North American Plate along the San Andreas Fault, and a boundary with the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pillow Lava
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one meter in diameter. They form the upper part of Layer 2 of normal oceanic crust. Composition Pillow lavas are commonly of basaltic composition, although pillows formed of komatiite, picrite, boninite, basaltic andesite, andesite, dacite or even rhyolite are known. In general, the more felsic the composition (richer in silica - resulting in an Intermediate composition), the larger the pillows, due to the increase in viscosity of the erupting lava. Occurrence They occur wherever lava is extruded underwater, such as along marine hotspot volcano chains and the constructive plate boundaries of mid-ocean ridges. As new oceanic crust is formed, thick sequences of pillow lavas are erupted at the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lava Flow
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from . The volcanic rock resulting from subsequent cooling is also often called ''lava''. A lava flow is an outpouring of lava during an effusive eruption. (An explosive eruption, by contrast, produces a mixture of volcanic ash and other fragments called tephra, not lava flows.) The viscosity of most lava is about that of ketchup, roughly 10,000 to 100,000 times that of water. Even so, lava can flow great distances before cooling causes it to solidify, because lava exposed to air quickly develops a solid crust that insulates the remaining liquid lava, helping to keep it hot and inviscid enough to continue flowing. The word ''lava'' comes from Italian and is probably derived from the Latin word ''labes'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. Andesite is the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is andesitic. Along with basalts, andesites are a component of the Martian crust. The name ''andesite'' is derived from the Andes mountain range, where this rock type is found in abundance. It was first applied by Christian Leopold von Buch in 1826. Description Andesite is an aphanitic (fine-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhyolite
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent to granite. Rhyolitic magma is extremely viscous, due to its high silica content. This favors explosive eruptions over effusive eruptions, so this type of magma is more often erupted as pyroclastic rock than as lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been extensively used for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive, in concrete, and as a soil amendment. Description Rhyolite i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dacite
Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz. Dacite is relatively common, occurring in many tectonic settings. It is associated with andesite and rhyolite as part of the subalkaline volcanic rock, subalkaline tholeiite, tholeiitic and calc-alkaline magma series. Composition Dacite consists mostly of plagioclase feldspar and quartz with biotite, hornblende, and pyroxene (augite or enstatite). The quartz appears as rounded, corroded phenocrysts, or as an element of the ground-mass. The plagioclase in dacite ranges from oligoclase to andesine and labradorite. Sanidine occurs, although in small proportions, in some dacites, and when abundant gives rise to rocks that form rhyodacite, transitions to the rhyolites. The rel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial planet, rocky planet or natural satellite, moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of volcanism on Venus, Venus, which cover ~80% of the surface, are basaltic; the lunar mare, lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tonga
Tonga (, ; ), officially the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about , scattered over in the southern Pacific Ocean. As of 2021, according to Johnson's Tribune, Tonga has a population of 104,494, 70% of whom reside on the main island, Tongatapu. The country stretches approximately north-south. It is surrounded by Fiji and Wallis and Futuna (France) to the northwest; Samoa to the northeast; New Caledonia (France) and Vanuatu to the west; Niue (the nearest foreign territory) to the east; and Kermadec (New Zealand) to the southwest. Tonga is about from New Zealand's North Island. First inhabited roughly 2,500 years ago by the Lapita civilization, Tonga's Polynesian settlers gradually evolved a distinct and strong ethnic identity, language, and culture as the Tongan people. They were quick to establish a powerful footing acr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tofua
Tofua is a volcanic island in Tonga. Located in the Haʻapai island group, it is a steep-sided composite cone with a summit caldera. It is part of the highly active Kermadec-Tonga subduction zone and its associated volcanic arc, which extends from New Zealand north-northeast to Fiji, and is formed by the subduction of the Pacific Plate under the Indo-Australian Plate. It lies about above a very active seismic zone.Ewart, A.; Bryan, W.B.; and Gill, J.B. "Mineralogy and Geochemistry of the Younger Volcanic Islands of Tonga, S.W. Pacific." ''Journal of Petrology.'' 14:3 (1973). It is connected to the nearby island of Kao by a submarine ridge. The island is a national park. Geography and geology The island is oval, measuring approximately 80 square kilometers. Its sides rise steeply to the rim of the caldera, which is partially filled by a volcanic crater lake with a depth of . The caldera was formed by a major eruption around 1,000 years BP, which left deposits up to thick on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Backarc
The back-arc region is the area behind a volcanic arc. In island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal depths, which may be separated by remnant arcs, similar to island arcs. In continental arcs, the back-arc region is part of continental platform, either dry land ( subaerial) or forming shallow marine basins. Formation Back-arc deformation is a product of subduction at convergent plate tectonic boundaries. It initiates and evolves behind the volcanic arc on the overriding plate of a subduction zone. The stresses responsible for the deformation in this region of a subduction zone result from a combination of processes. The absolute motion of the upper plate as it moves towards or away from the trench strongly contributes to deformation in the back-arc region. Since the downgoing slab is partly anchored in the viscous layers of the mantle, and therefore its lateral movement is significantly slower than the surface plate, then any motion of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
