. Earth Science News .
Towards A Better Understanding Of Hot Spot Volcanism

The existence of a hot spot is usually considered to be linked to the occurrence of a mantle plume, a sort of giant bubble of magma generated by the thermal convection currents circulating in the mantle. This magmatic bubble exerts an upward pressure pushing on the base of the oceanic lithosphere.
by Staff Writers
Paris, France (SPX) Feb 04, 2008
Most of the Earth's listed active volcanoes are located at the borders between two tectonic plates, where upsurge of magma from the mantle is facilitated. When these magmatic uprisings occur at a subduction zone, where one tectonic plate plunges under another, they give rise to volcanic massifs such as the Andes cordillera. Other volcanic chains are formed along oceanic ridges, submarine regions of ocean-floor extension.

However, some volcanoes are governed by a completely different mechanism: intraplate volcanism. As their name suggests, these volcanic constructions appear in the very centre of tectonic plates. Scientists now know that some of them, such as the Hawaii-Emperor archipelago or Reunion Island, result from magmatic upsurges generated at the boundary between the Earth's core and mantle situated 2 900 km deep.

Others, such as those of the central Pacific, display different characteristics. They are anomalous, in their simultaneously high number, unusually high concentration and short life-span and prompt scientists to look for hypotheses other than a deep-mantle plume to explain the causes of intraplate volcanism.

Researchers from the IRD and the University of Chile focused on a group of islands and archipelagos in the central Pacific Ocean (Samoa, Cook, Rurutu, Austral, Tahiti, Marquis, Pitcairn), each listed as resulting from hot-spot activity. These scientists aimed to find out if movements of the Pacific plate where these seven hot spots are located could be involved in their formation. They used numerical mechanical simulation models of the effect of the westward displacement of the Pacific plate on internal deformations during the past 10 million years.

This model incorporates a differential tension regime which acts on the Pacific plate, the northern part moving with greater velocity than the southern part, which undergoes a kind of braking effect exerted by the bloc of the Australian plate (see the 3D diagram). The model shows the region to be the site of an East-West shear band which superimposes on the geographical zone where the seven hot spots investigated in the study are grouped.

Another model was subsequently built up that takes into account the cooling of the tectonic plate with increased distance from the oceanic ridge that generated it. This second model also brought evidence of a shearing band, but this zone appeared more diffuse towards the east than in the first simulation.

Moreover, this more diffuse shearing zone was superimposed on an anomaly of the Earth's surface classically attributed to an upswelling of the oceanic lithosphere. This anomaly, caused by the upward pressure of the underlying mantle, appears along with an unexplained variation in the ocean floor. This second numerical model therefore indirectly allows the geographical location of the hot spots on an East/West line of weakened lithosphere to be matched with a variation in its thickness.

The existence of a hot spot is usually considered to be linked to the occurrence of a mantle plume, a sort of giant bubble of magma generated by the thermal convection currents circulating in the mantle. This magmatic bubble exerts an upward pressure pushing on the base of the oceanic lithosphere.

Then, once broken through, the latter allows the magma to erupt through the Earth's crust. Although this process effectively explains the origin of deep-seated hot spots, it does not provide satisfactory explanations for other forms of intraplate volcanism such as that which occurs in the African rift or certain more recent hot spots situated in the central part of the Pacific Ocean.

The results of this study suggest an alternative scenario which envisages the involvement of shearing strain within the tectonic plates during the formation of a certain type of hot spot volcanism. In the central Pacific, such deformation could therefore be a step towards the break-up of the Earth's largest tectonic plate into two in a timescale of around ten million years.

Furthermore, if the movements of a tectonic plate were effectively to play a role in the formation of a hot spot, that would signify that such spots would not be so static as hitherto believed. The characteristic time-scale for heat-transfer processes in the mantle is in the order of more than 100 million years whereas the movement of the plates occurs over shorter geological time-scales of around ten million years.

Certain hot spots could thus change and develop in space relatively rapidly, in line with displacements undergone by the tectonic plates.

Community
Email This Article
Comment On This Article

Related Links
Institut de Recherche Pour le Developpement
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest



Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News


First Evidence Of Under-Ice Volcanic Eruption In Antarctica
London, UK (SPX) Jan 22, 2008
The first evidence of a volcanic eruption from beneath Antarctica's most rapidly changing ice sheet is reported this week in the journal Nature Geosciences. The volcano on the West Antarctic Ice Sheet erupted 2000 years ago (325BC) and remains active. Using airborne ice-sounding radar, scientists from British Antarctic Survey (BAS) discovered a layer of ash produced by a 'subglacial' volcano. It extends across an area larger than Wales.







  • NC-Based Piedmont Triad Ambulance And Rescue Deploys Next Gen Wireless Network
  • Millions struggle for tickets as China battles weather
  • Beijing's disaster response too little, too late: travellers
  • Winter Freeze Sends Shockwaves Through China As Cash And More Run Short

  • Ancient Climate Secrets Raised From Ocean Depths
  • Microbes As Climate Engineers
  • Economists Help Climate Scientists To Improve Global Warming Forecasts
  • When Accounting For The Global Nitrogen Budget Do Not Forget Fish

  • Indonesia To Develop New EO Satellite
  • Russia To Launch Space Project To Monitor The Arctic In 2010
  • New Radar Satellite Technique Sheds Light On Ocean Current Dynamics
  • Radical New Lab Fights Disease Using Satellites

  • Analysis: China beats West in Africa
  • Analysis: Turkey embraces wind power
  • Analysis: Iraq oil deals drawing near
  • Analysis: Shell to shut again in Nigeria

  • Globe-Trotting Black Rat Genes Reveal Spread Of Humans And Diseases
  • Risk of meningitis epidemic in Burkina Faso increases
  • Analysis: NATO begins pandemic monitoring
  • China reports outbreak of bird flu in Tibet

  • Telepathic Genes
  • Cold Spring Harbor Laboratory Researchers Race Against Time To Save Tasmanian Devils
  • Rare dolphin 'beaten to death' in Bangladesh
  • Nonlinear Ecosystem Response Points To Environmental Solutions

  • New York City Uses Mobile GPS From AT and T and TeleNav To Help Keep City Clean
  • Italy pledges to honour Naples rubbish plan after EU ultimatum
  • EU threatens Italy with court action over rubbish crisis
  • Protecting The Alps From Traffic Noise And Air Pollution

  • Blue-Eyed Humans Have A Single, Common Ancestor
  • Brain Connections Strengthen During Waking Hours And Weaken During Sleep
  • Fueling And Feeding Bigfoot
  • Higher China fines for stars breaking one-child rule: state media

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2007 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement