A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent.[1] Believed to be primarily caused by internal and gravitational stresses generated by magma emplacement within and across various regions of the volcano, rift zones allow the intrusion of magmatic dykes into the slopes of the volcano itself. The addition of these magmatic materials usually contributes to the further rifting of the slope, in addition to generating fissure eruptions from those dykes that reach the surface. It is the grouping of these fissures, and the dykes that feed them, that serves to delineate where and whether a rift zone is to be defined.[2] The accumulated lava of repeated eruptions from rift zones along with the endogenous growth created by magma intrusions causes these volcanoes to have an elongated shape.[3] Perhaps the best example of this is Mauna Loa, which in Hawaiian means "long mountain",[4] and which features two very well defined rift zones extending tens of kilometers outward from the central vent.
Rift zones are characterized by the close grouping of intrusive dykes and extrusive fissures extending outward along a relatively narrow band from the area of a central vent. The internal extensional forces and isostatic loading generated by intruding magma volumes (either associated with the magma chamber or subsequent dyke and sill formation extending outward from that chamber), in conjunction with accumulation of erupted materials, contribute to the mass and slope of the forming edifice. It is the weight of the edifice exceeding its material strength, with the additional stresses of the magma inflating the internal regions of the edifice, that can generate the initial cracking around a developing volcanic summit.[2] Additionally, tectonic activity such as normal faulting is also commonly associated with formation of rifts along volcanic flanks.[2][5] Following the path of least resistance, subsequent magmatic dykes form along and within these initial cracks, causing additional stresses to be imparted to the local materials of the edifice, which in turn generate new rifts for the magma to flow towards.[1][6] In this way, established rift zones can potentially be self-sustaining geologic features along the flanks of the given volcanic vent. The orientation of this rifting is largely dependent on the gravitational and tectonic stresses at play.[7] Basaltic shield volcanoes typically feature two main rift zones, situated with angles of 120° between in ideal situations.[1][3] On shield volcanoes forming from level seafloor without neighboring vents, flank rifting occurs more evenly distributed around the vent.[1] However, where the flanks of a volcano may be supported on one side by the presence of a pre-existing feature, or burdened with various planes of weakness, rift zone formation promulgates according to down-slope pull of gravity.
Structureedit
The infill of magmas in the form of dykes helps to define the shape of a volcano. A higher frequency of intrusive events along rift zones leads to elongated topographies of the affected edifices.[6] Mathematical models show how the presence of rift zones contributes to a central horizontal bulge or ridge parallel to the orientation of the rifts.[3] This same modelling shows how this central bulge is dependent on the ratio between rift zone length and depth of the magma sources, with longer fissures over shallower sources being more positively associated with very elongated topographies of the associated flanks.[3] Occasionally, fissure eruptions associated with rift zones can actually evolve into new vents along the volcanic edifice, generating lava flows lasting for months or longer.[1] These lava flows add surface materials to the slopes of the volcano, extending the slopes outward in a general flattening of the morphology of the flank.[6] The extensional character of these events can contribute to flank instability and mass wasting events where whole sections of the volcanic edifice can collapse along rift zone boundaries.[5] These mass wasting events can affect the dyke formations and orientations as the mass of the edifice shifts, which can have profound impacts on the structural development of the edifice,[5] while also potentially creating many volcanic hazards, such as tsunamis and dramatic shifts in directions of lava flows, to unsuspecting communities.
Volcanologist George P.L. Walker stated that rift zones were common in most volcanoes around the world, regardless of their type and formation.[2] Walker put forward the idea that, absent any obvious signs of rifting on the surface, the presence of other volcanic features that are also associated with dyke intrusions (such as elongated cinder cones and linearly-aligned fissure vents) should also be taken to represent the presence of a rift zone-like processes in the given region.[2] Therefore, rift zones of various lengths and widths can be tentatively identified on many stratovolcanoes and monogenetic lava fields in addition to classic Hawaiian shield volcanoes.
Examplesedit
Hawaii: Most Hawaiian volcanoes have two or sometimes three rift zones.
^ abcdeW., Hazlett, Richard (2010-05-17). Volcanoes : global perspectives. Wiley-Blackwell. ISBN9781405162500. OCLC 892899076.{{cite book}}: CS1 maint: multiple names: authors list (link)
^ abcdeWalker, George P. L. (1999-12-01). "Volcanic rift zones and their intrusion swarms". Journal of Volcanology and Geothermal Research. 94 (1–4): 21–34. Bibcode:1999JVGR...94...21W. doi:10.1016/S0377-0273(99)00096-7.
^ abcdAnnen, C.; Lénat, J. -F.; Provost, A. (2001-03-01). "The long-term growth of volcanic edifices: numerical modelling of the role of dyke intrusion and lava-flow emplacement". Journal of Volcanology and Geothermal Research. 105 (4): 263–289. Bibcode:2001JVGR..105..263A. doi:10.1016/S0377-0273(00)00257-2.
^""Mauna Loa: Earth's Largest Volcano". USGS. 2 February 2006. Retrieved 21 October 2015".
^ abcWalter, T. R.; Troll, V. R.; Cailleau, B.; Belousov, A.; Schmincke, H.-U.; Amelung, F.; Bogaard, P. v d (2005-04-01). "Rift zone reorganization through flank instability in ocean island volcanoes: an example from Tenerife, Canary Islands" (PDF). Bulletin of Volcanology. 67 (4): 281–291. Bibcode:2005BVol...67..281W. doi:10.1007/s00445-004-0352-z. ISSN 0258-8900. S2CID 130290027.
^ abcMichon, Laurent; Cayol, Valérie; Letourneur, Ludovic; Peltier, Aline; Villeneuve, Nicolas; Staudacher, Thomas (2009-07-01). "Edifice growth, deformation and rift zone development in basaltic setting: Insights from Piton de la Fournaise shield volcano (Réunion Island)" (PDF). Journal of Volcanology and Geothermal Research. Recent advances on the geodynamics of Piton de la Fournaise volcano. 184 (1–2): 14–30. Bibcode:2009JVGR..184...14M. doi:10.1016/j.jvolgeores.2008.11.002.
^Walter, Thomas R.; Troll, Valentin R. (September 2003). "Experiments on rift zone evolution in unstable volcanic edifices". Journal of Volcanology and Geothermal Research. 127 (1–2): 107–120. Bibcode:2003JVGR..127..107W. doi:10.1016/S0377-0273(03)00181-1.
External linksedit
Rift Zones | Volcano World | Oregon State University
April 14, 2024
rift, zone, confused, with, rift, rift, valley, rift, zone, feature, some, volcanoes, especially, shield, volcanoes, which, linear, cracks, rifts, develops, volcanic, edifice, typically, forming, into, three, well, defined, regions, along, flanks, vent, believ. Not to be confused with rift or rift valley A rift zone is a feature of some volcanoes especially shield volcanoes in which a set of linear cracks or rifts develops in a volcanic edifice typically forming into two or three well defined regions along the flanks of the vent 1 Believed to be primarily caused by internal and gravitational stresses generated by magma emplacement within and across various regions of the volcano rift zones allow the intrusion of magmatic dykes into the slopes of the volcano itself The addition of these magmatic materials usually contributes to the further rifting of the slope in addition to generating fissure eruptions from those dykes that reach the surface It is the grouping of these fissures and the dykes that feed them that serves to delineate where and whether a rift zone is to be defined 2 The accumulated lava of repeated eruptions from rift zones along with the endogenous growth created by magma intrusions causes these volcanoes to have an elongated shape 3 Perhaps the best example of this is Mauna Loa which in Hawaiian means long mountain 4 and which features two very well defined rift zones extending tens of kilometers outward from the central vent East Rift Zone on Kilauea Hawaiʻi Contents 1 Formation 2 Structure 3 Examples 4 See also 5 References 6 External linksFormation editRift zones are characterized by the close grouping of intrusive dykes and extrusive fissures extending outward along a relatively narrow band from the area of a central vent The internal extensional forces and isostatic loading generated by intruding magma volumes either associated with the magma chamber or subsequent dyke and sill formation extending outward from that chamber in conjunction with accumulation of erupted materials contribute to the mass and slope of the forming edifice It is the weight of the edifice exceeding its material strength with the additional stresses of the magma inflating the internal regions of the edifice that can generate the initial cracking around a developing volcanic summit 2 Additionally tectonic activity such as normal faulting is also commonly associated with formation of rifts along volcanic flanks 2 5 Following the path of least resistance subsequent magmatic dykes form along and within these initial cracks causing additional stresses to be imparted to the local materials of the edifice which in turn generate new rifts for the magma to flow towards 1 6 In this way established rift zones can potentially be self sustaining geologic features along the flanks of the given volcanic vent The orientation of this rifting is largely dependent on the gravitational and tectonic stresses at play 7 Basaltic shield volcanoes typically feature two main rift zones situated with angles of 120 between in ideal situations 1 3 On shield volcanoes forming from level seafloor without neighboring vents flank rifting occurs more evenly distributed around the vent 1 However where the flanks of a volcano may be supported on one side by the presence of a pre existing feature or burdened with various planes of weakness rift zone formation promulgates according to down slope pull of gravity Structure editThe infill of magmas in the form of dykes helps to define the shape of a volcano A higher frequency of intrusive events along rift zones leads to elongated topographies of the affected edifices 6 Mathematical models show how the presence of rift zones contributes to a central horizontal bulge or ridge parallel to the orientation of the rifts 3 This same modelling shows how this central bulge is dependent on the ratio between rift zone length and depth of the magma sources with longer fissures over shallower sources being more positively associated with very elongated topographies of the associated flanks 3 Occasionally fissure eruptions associated with rift zones can actually evolve into new vents along the volcanic edifice generating lava flows lasting for months or longer 1 These lava flows add surface materials to the slopes of the volcano extending the slopes outward in a general flattening of the morphology of the flank 6 The extensional character of these events can contribute to flank instability and mass wasting events where whole sections of the volcanic edifice can collapse along rift zone boundaries 5 These mass wasting events can affect the dyke formations and orientations as the mass of the edifice shifts which can have profound impacts on the structural development of the edifice 5 while also potentially creating many volcanic hazards such as tsunamis and dramatic shifts in directions of lava flows to unsuspecting communities Volcanologist George P L Walker stated that rift zones were common in most volcanoes around the world regardless of their type and formation 2 Walker put forward the idea that absent any obvious signs of rifting on the surface the presence of other volcanic features that are also associated with dyke intrusions such as elongated cinder cones and linearly aligned fissure vents should also be taken to represent the presence of a rift zone like processes in the given region 2 Therefore rift zones of various lengths and widths can be tentatively identified on many stratovolcanoes and monogenetic lava fields in addition to classic Hawaiian shield volcanoes Examples editHawaii Most Hawaiian volcanoes have two or sometimes three rift zones Mahukona Mauna Loa Hualalai Kilauea Galapagos Islands Canary Islands La Palma El Hierro Newberry Volcano Oregon Craters of the Moon IdahoSee also editFracture geology Lateral eruptionReferences edit a b c d e W Hazlett Richard 2010 05 17 Volcanoes global perspectives Wiley Blackwell ISBN 9781405162500 OCLC 892899076 a href Template Cite book html title Template Cite book cite book a CS1 maint multiple names authors list link a b c d e Walker George P L 1999 12 01 Volcanic rift zones and their intrusion swarms Journal of Volcanology and Geothermal Research 94 1 4 21 34 Bibcode 1999JVGR 94 21W doi 10 1016 S0377 0273 99 00096 7 a b c d Annen C Lenat J F Provost A 2001 03 01 The long term growth of volcanic edifices numerical modelling of the role of dyke intrusion and lava flow emplacement Journal of Volcanology and Geothermal Research 105 4 263 289 Bibcode 2001JVGR 105 263A doi 10 1016 S0377 0273 00 00257 2 Mauna Loa Earth s Largest Volcano USGS 2 February 2006 Retrieved 21 October 2015 a b c Walter T R Troll V R Cailleau B Belousov A Schmincke H U Amelung F Bogaard P v d 2005 04 01 Rift zone reorganization through flank instability in ocean island volcanoes an example from Tenerife Canary Islands PDF Bulletin of Volcanology 67 4 281 291 Bibcode 2005BVol 67 281W doi 10 1007 s00445 004 0352 z ISSN 0258 8900 S2CID 130290027 a b c Michon Laurent Cayol Valerie Letourneur Ludovic Peltier Aline Villeneuve Nicolas Staudacher Thomas 2009 07 01 Edifice growth deformation and rift zone development in basaltic setting Insights from Piton de la Fournaise shield volcano Reunion Island PDF Journal of Volcanology and Geothermal Research Recent advances on the geodynamics of Piton de la Fournaise volcano 184 1 2 14 30 Bibcode 2009JVGR 184 14M doi 10 1016 j jvolgeores 2008 11 002 Walter Thomas R Troll Valentin R September 2003 Experiments on rift zone evolution in unstable volcanic edifices Journal of Volcanology and Geothermal Research 127 1 2 107 120 Bibcode 2003JVGR 127 107W doi 10 1016 S0377 0273 03 00181 1 External links editRift Zones Volcano World Oregon State University Retrieved from https en wikipedia org w index php title Rift zone amp oldid 1204737003, wikipedia, wiki, book, books, library,
