Presentation on theme: "Ages and Life-cycle of Hawaiian volcanoes MBARI’s high-resolution bathymetry of Hawaii first revealed the presence of numerous flat-topped volcanoes on."— Presentation transcript:
The mantle source generating the Hawaiian Islands is chemically heterogeneous from volcano to volcano as is well documented in numerous studies. Moreover, growing evidence suggests that the source also varies over time within a single volcano
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.
Magma rises into reservoir beneath volcano Rising magma and volcanic gases exert pressure High pressure causes rocks to break, 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
Hotspots Lowman accepts the orthodox view that oceanic islands and seamounts in the Pacific are the result of the Pacific plate moving over hotspots. This should give rise to a systematic age progression along hotspot trails, but good age progressions are very rare, and a large majority show little or no age progression. The Cook-Austral and Marquesas chains, for example, are marked by gross violations of a simple age-distance relationship and by extreme variations of isotopic signature, inconsistent with a single volcanic source. The Hawaiian chain provides a more consistent age sequence, but the recent renewed volcanism in the Island after a gap of a million years does not support the ‘hotspot hypothesis’. There is no systematic variation of heat flow across the Hawaiian swell, contradicting the simple hotspot model (Keith, 1993). There is no smoking gun that is puffing up the islands, contradicting the ‘hotspot hypothesis’ origin of the Hawaiian Island chain.
Hotspots are commonly attributed to "mantle plumes" rising from the core-mantle boundary. Sheth (1999) showed that plume explanations are ad hoc, artificial, and inadequate, and that plumes are not required by any geological evidence. A mantle plume from a deep hotspot would broaden upward as a result of drag forces, and would attain a surface width of several hundred kilometres, far beyond oceanic island dimensions. It is therefore claimed that hotspot tracks are produced by plume tails – but the problem of what has happened to ancient and modern plume heads remains unsolved. It is significant that many ocean island chains are found along fracture zones, and flood basalt provinces are at orthogonal intersections of the fracture zones (Smoot, 1997). A credible alternative explanation is that hotspot tracks are produced by propagating rifts, and delineate the stress field, not the displacement field, of the lithosphere (Sheth, 1999). In surge tectonics, linear volcanic chains are believed to be produced by magma surge channels in the lithosphere (Meyerhoff et al., 1996). There is a major controversy among plate tectonicists as to how fast hotspots move relative to one another; one group believes that hotspots move at 3 mm/yr or less, whereas the other believes that hotspots move at 10-20 mm/yr or more. These differences are partly the result of "plate reconstruction" uncertainties (Gordon, 1995; Baksi, 1999
Giant blocks in the South Kona Landslide, Hawaii James G. Moore, Wilfred B. Bryan, Melvin H. Beeson, and William R. Normark U. S. Geological Survey, Menlo Park, CA, United States Geology; February 1995; v. 23; no. 2; p. 125-128 A large field of blocky sea-floor hills, up to 10 km long and 500 m high, are gigantic slide blocks derived from the west flank of Mauna Loa volcano on the island of Hawaii. These megablocks are embedded in the toe of the South Kona landslide, which extends approximately 80 km seaward from the present coastline to depths of nearly 5 km. A 10- 15-km-wide belt of numerous, smaller, 1-3-km-long slide blocks separates the area of giant blocks from two submarine benches at depths of 2600 and 3700 m depth that terminate seaward 20 to 30 km from the shoreline