Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Algoman orogeny wikipedia , lookup
Geological history of Earth wikipedia , lookup
Geology of Great Britain wikipedia , lookup
Izu-Bonin-Mariana Arc wikipedia , lookup
Plate tectonics wikipedia , lookup
Ring of Fire wikipedia , lookup
Mantle plume wikipedia , lookup
Geology of the Pacific Northwest wikipedia , lookup
Subduction crack on the Pacific Ocean crust Magma is created at the subduction wedge Volcanoes are thought to form in three settings: where tectonic plates are diverging (for instance at mid-ocean ridges); where tectonic plates are converging (in island arcs, for example); and in "hotpots" (a generic term for volcanic activity that cannot be attributed to plate tectonic movements. Hotspots are generally thought to be formed by hot, buoyant plumes rising rapidly from the boundary between Earth's core and the mantle. The "new" volcanoes, which are actually between one and eight million years old, are not at plate boundaries. But neither were they formed by deep plumes. The team thinks the minivolcanoes were created when cracks formed in the Earth's crust during the elastic bending of the northwestern Pacific plate, which is diving under the Kuril and Japan trenches. They think partially melted material from the upper mantle squeezed out of the cracks, to form the volcanoes. Origin of Intra-Plate Volcanism Hawaiian Islands on the Pacific Oceanic Plate Hot Spot Model Fixed Plume coming from Core-Mantle Boundary, ~ 3000 km (1800 miles) deep down under in the interior of Earth There is lack of strong geothermal, geophysical, and gravity, geomagnetic radioactivity evidences that suggest that the magma is ascending from the Core-mantle boundary. Composition of Hawaiian volcanic basaltic rocks is very similar to that of the sea floor oceanic basalts. There is a lack of super heavy elements, radioactive minerals, and even absence of Potassium ‘S’ Seismic waves pass minerals which are normally under the suggestive of deep Islands. ‘S’ wave do not rooted magma. travel through molten material A new type of volcano has been discovered in the western Pacific Ocean. The findings may reduce the strength of a popular theory of “hotspot” volcanism, researchers say. http://volcano.und.nodak.edu/dn9629.html Naoto Hirano at the Tokyo Institute of Technology, Japan, and colleagues have discovered miniature volcanoes – between 0.005 cubic kilometres and 1 km3 in size – near the underwater Japan Trench. These volcanoes, dubbed “petit spot” because of their size, cannot be accounted for by any of the conventional theories of volcanism. The team thinks the mini-volcanoes were created when cracks formed in the Earth's crust during the elastic bending of the northwestern Pacific plate, which is diving under the Kuril and Japan trenches. They think partially melted material from the upper mantle squeezed out of the cracks, to form the volcanoes. “I was unbelievably excited to discover this volcanism,” Hirano says. “The possibility had been proposed in the past, but had never been adequately documented.” Buoyant plumes Volcanoes are thought to form in three settings: where tectonic plates are diverging (for instance at mid-ocean ridges); where tectonic plates are converging (in island arcs, for example); and in “hotpots” (a generic term for volcanic activity that cannot be attributed to plate tectonic movements. Hotspots are generally thought to be formed by hot, buoyant plumes rising rapidly from the boundary between Earth’s core and the mantle. The "new" volcanoes, which are actually between one and eight million years old, are not at plate boundaries. But neither were they formed by deep plumes. When Hirano’s team analysed the trace element geochemistry and compositions of noble gas isotopes in their volcanic flows, they concluded that the material originated in the asthenosphere – a layer of the mantle directly under Earth’s crust. Samples of the flows were collected by Universal explanations “These findings are probably the best evidence to date that not all chains of mid-plate volcanoes are formed by plumes,” says Marcia McNutt of the Monterey Bay Aquarium Research Institute in Moss Landing, California, US, who wrote a commentary on the paper published in Science. “These findings do not mean that plumes don’t exist at all – there may be some volcanic chains that are caused by plumes, but they are no longer a universal explanation.” The question remains whether this new type of volcanism could explain other volcanic hotspots. There are lava fields near Samoa and in Hawaii for which a flexing of the tectonic plate had been suggested as a cause. But these suggestions had not been documented well, and the studies were largely discounted by other researchers, according to Hirano. Now, in the light of the new research, scientists will go back to observations for other volcano chains with a more critical eye, McNutt believes. “They’ll look to see what observations were ignored or swept under the rug because they couldn’t explain the finding in the context of plume theory.” Journal reference: Science (DOI: 10.1126/science.1128235 and 10.1126/science.1131298) There are geochemical differences between shield volcanoes and lavas from the two parallel trends, Kea and Loa, defined by young Hawaiian volcanoes. Lanai There is lack of geothermal, geophysical, and geomagnetic evidences that suggest that the magma is ascending from the Coremantle boundary. Composition of Hawaiian volcanic basaltic rocks is very similar to that of the oceanic basalts. There is a lack of super heavy elements, radioactivity, and even absence of Potassium minerals which are suggestive of deep rooted magma. Kaholawai Hawaiian Islands Volcanic Islands and Volcanic Fields Pacific Ocean Map shows the North and South Arch lava fields in red, in relation to the Hawaiian Isles. The axes of the trough and arch are encircling the isles. Older volcanoes and eruptions are mixed in with younger ones in no particular order on the ocean floor and on the islands. This seems to contradict the idea that a hotspot created this chain of islands. Oahu Maui Nui Hawaii is not fixed Magma is created at the Mantle wedge Cracks on the Pacific Ocean crust Oahu Maui Nui Hawaii Cracks on the Pacific Ocean crust is not fixed Intra-Plate Volcanism on the Pacific Oceanic Plate Magma is created at the subduction zone wedge Origin of Intra-Plate Volcanism on the Pacific Oceanic Plate Hawaiian Islands – Plate Tectonics Rifting Model, showing the flexing of the tectonic plate. Two principal types of basalt in the ocean basins Tholeiitic Basalt and Alkaline Basalt Mauna Loa Kilauea Kilauea Caldera 18481982 Halema’uma’u Crater Height of Eruption Column and Degree of Explosivity -Whereas the height of the eruption column can be measured directly in observed eruptions, it can also be estimated in ancient eruptions by measuring the geographic dispersal of the airfall tephra. The degree to which this tephra is fragmented provides a means to measure the explosiveness of the eruption. The diagram here demonstrates how these parameters will vary with eruption type. For more detailed information on these parameters, click on image. Note that hydrovolcanic eruptions (above dashed line) are generally the most explosive, but do not necessarily generate the highest eruption columns. Lava flows behave in many ways like flowing water - they seek the lowest elevation, driven by the force of gravity. Here pahoehoe lava which flowed down a crevice in an earlier flow. Mahukona There are geochemical differences between shield lavas from the two parallel trends, Kea and Loa, defined by young Hawaiian volcanoes. Kilauea Slump: On Nov. 8, 2000, the motion suddenly accelerated by factor of several hundred, with some parts of the slope moving as much as half an inch over the course of one day. Their computer models indicate that a 9-mile-by-3-mile slab located about 2 1/2 miles underground slipped about 3 1/2 inches, pulling along the ground above it. The event was equivalent to a magnitude 5.7 earthquake. a flank collapse would unleash with up to 1,200 cubic miles of rock sliding at speeds of up to 100 miles an hour for 20 to 40 miles The Honolulu Series of Volcanic Eruptions is Recent, 100, 000 years old with 15 Tuff Cones in northeast and southwest perpendicular to 3 million year old KoolausVolcanoc Series. If the Hotspot has been active over 500,000 years under the Big Island, 300 km away from Oahu. Other younger volcanoes are present on Molokai and Maui. Did the Hotspot wander to Oahu and other Islands at the same time? NO FIXED HOTSPOT, it is migrating along with the Pacific Plate. Shallow oceanic crust is recycled by Plate Subduction to make Younger volcanoes such as Diamond Head on the older Isles. Any satisfactory theory for Hawaiian volcanism must explain (or rationalize) the: change in migration direction of the melting locus at the bend, association of the great bend with the Mendocino fracture zone, change in migration rate at the bend, apparent commencement of the volcanic chain near a ridge, absence of a “plume head”, large variations in magmatic production, and a current magmatic rate about 3 times greater than the next most productive hotspots, absence of a significant heat flow anomaly, absence of lithospheric thinning, absence of a strong high-temperature signal in the erupted basalts, production of very large volumes of magma even though the depth to the top of the melting column is exceptionally large compared with MORs, spatial and temporal variation in the composition of erupted lavas on a variety of scales, remote location of Hawaii, near the center of a very large plate, location of the oldest end of the chain with respect to the “Pacific pocket”, unique rift zones, paired Loa and Kea trends, seismic whole-mantle mantle structure that is apparently normal compared with the Pacific ocean elsewhere, and occurrence of a bathymetric swell (a moat and “arch”) along the eastern two-thirds of the Hawaiian chain and wrapping around its southeastern end, with alkalic basaltic volcanism occurring at some places along it. In conclusion, Hawaii is not fully explained by any current hypothesis. It is impressive that a region of the Earth so extensively studied for so many years, by so many Earth scientists with so many techniques could remain so intransigent to full understanding. Many of the numerous features that are not yet fully understood, and the parameters of alternative hypotheses, are not currently being studied, but they offer exciting research opportunities. Rising magma and Magma rises into High pressure causes volcanic gases exert reservoir beneath rocks to break, pressure volcano triggering earthquakes Earthquake activity beneath a volcano almost always increases before an eruption because magma and volcanic gas must first force their way up through shallow underground fractures and passageways. Pacific Ocean: The Pacific Ocean is the largest of the world's five oceans Location: the body of water between the Southern Ocean, Asia, Australia and the western hemisphere Area: 155.6 million square km, or about 15 times the size of the US. The Pacific Ocean covers about 28 per cent of the global surface - larger than the total land area of the world Terrain: the ocean floor in the eastern Pacific is dominated by the East Pacific Rise, while the western Pacific is dissected by deep trenches, including the Mariana Trench, which is the world's deepest place Deepest point: Challenger Deep in the Mariana Trench - 11,022m The hybrid remotely operated vehicle, or HROV, will be able to operate in two modes: as an autonomous, or free-swimming, vehicle for wide area surveys, and as a tethered, or cabled, vehicle for close-up sampling and other tasks. (Image: ©Jack Cook, WHOI) Ocean Intraplate Volcanism Ocean islands and seamounts, Commonly associated with hot spots Figure 14-1. After Crough (1983) Ann. Rev. Earth Planet. Sci., 11, 165-193.