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Dispersal index

January 01, 1970

Dispersal index is a parameter in volcanology. The dispersal index was defined by George P. L. Walker in 1973 as the surface area covered by an ash or tephra fall, where the thickness is equal or more than 1/100 of the thickness of the fall at the vent.[1] An eruption with a low dispersal index leaves most of its products close to the vent, forming a cone; an eruption with a high dispersal index forms thinner sheet-like deposits which extends to larger distances from the vent.[2] A dispersal index of 500 square kilometres (190 sq mi) or more of coarse pumice is one proposed definition of a Plinian eruption.[3] Likewise, a dispersal index of 50,000 square kilometres (19,000 sq mi) has been proposed as a cutoff for an ultraplinian eruption.[4] The definition of 1/100 of the near-vent thickness was partially dictated by the fact that most tephra deposits are not well preserved at larger distances.[5]

Originally, the dispersal index was considered a function of the height of the eruption column. Later, a role for the size of the tephra and ash particles was identified,[1] with coarser fall deposits covering smaller surfaces than finer deposits generated by a column of the same height.[3] For example, a deposit with a dispersal index of 500 square kilometres (190 sq mi) can be formed by a column with heights of 14–18 square kilometres (5.4–6.9 sq mi).[6] Thus, Walker's idea of the column height alone separating a cone forming eruption and an eruption generating a sheet-like deposit was later considered oversimplified.[7] An additional complicating factor is that fine particles are prone to aggregating and thus falling out more quickly from the column.[8] Further problems arise when the maximum thickness has to be determined.[9]

The height of the eruption column, the presence and behaviour of water, the speed and direction of the wind as well as the sizes of the various tephra particles influence the fallout patterns of an ash cloud.[10]

The dispersal index for volcanic eruptions ranges from <1 square kilometre (0.39 sq mi) and 1–1,000 square kilometres (0.39–386.10 sq mi).[3] A number of basaltic phreatomagmatic deposits, frequently associated with tuff rings, have a dispersal index of less than 50 square kilometres (19 sq mi).[11]

Volcano Eruption Age Dispersal index Source
Taupō Hatepe eruption 1820 BP 100,000 square kilometres (39,000 sq mi) [3]
Taupō Oruanui eruption ~20000 BP >100,000 square kilometres (39,000 sq mi) [11]
Taupō Hinemaiaia tephra 4500 years ago 40,000 square kilometres (15,000 sq mi) [12]
Kelut 1990 2,000 square kilometres (770 sq mi) [13]
Rinjani 1257 Samalas eruption, P1 phase 1257 7,500 square kilometres (2,900 sq mi) [14]
Rinjani 1257 Samalas eruption, P3 phase 1257 110,500 square kilometres (42,700 sq mi) [14]
Mount Pelée P1 eruption 650 BP 900 square kilometres (350 sq mi) [15]
Mount Pelée P2 eruption 1670 BP 800 square kilometres (310 sq mi) [15]
Mount Pelée P3 eruption 2010 BP 1,000 square kilometres (390 sq mi) [15]
Rabaul Vulcan 1937 40 square kilometres (15 sq mi) [16]
Okataina Volcanic Complex Whakatane tephra ~ 5500 BP ~200,000 square kilometres (77,000 sq mi) [17]
Agua de Pau Fogo A 5000 BP 1,500 square kilometres (580 sq mi) [18]
Hekla 1991 460 square kilometres (180 sq mi) [19]
Sakurajima Taisho 1914 539 square kilometres (208 sq mi) [20]
Mono Craters 4th century AD 1,800 square kilometres (690 sq mi) [21]

A related measure is the thickness half-distance ,[10] which defines the distance over which the thickness of a deposit halves.[22] These values are related with each other over for circular deposits.

References edit

  1. ^ a b Pyle 1989, p. 10.
  2. ^ Fierstein et al. 1997, p. 215.
  3. ^ a b c d Walker 1980, p. 88.
  4. ^ Walker 1980, p. 91.
  5. ^ Bonadonna, C.; Ernst, G.G.J.; Sparks, R.S.J. (May 1998). "Thickness variations and volume estimates of tephra fall deposits: the importance of particle Reynolds number". Journal of Volcanology and Geothermal Research. 81 (3–4): 181. Bibcode:1998JVGR...81..173B. CiteSeerX 10.1.1.519.5180. doi:10.1016/S0377-0273(98)00007-9.
  6. ^ Sparks et al. 1992, p. 690.
  7. ^ Pyle 1989, p. 11.
  8. ^ Sparks et al. 1992, p. 694.
  9. ^ Hildreth, Wes; Drake, Robert E (January 1992). "Volcan Quizapu, Chilean Andes". Bulletin of Volcanology. 54 (2): 111. doi:10.1007/BF00278002. S2CID 128972435.
  10. ^ a b Sparks et al. 1992, p. 685.
  11. ^ a b Self, S.; Sparks, R. S. J. (September 1978). "Characteristics of widespread pyroclastic deposits formed by the interaction of silicic magma and water". Bulletin Volcanologique. 41 (3): 209–210. Bibcode:1978BVol...41..196S. doi:10.1007/BF02597223. S2CID 130066909.
  12. ^ Lowe, David J. (January 1986). "Revision of the age and stratigraphic relationships of Hinemaiaia Tephra and Whakatane Ash, North Island, New Zealand, using distal occurrences in organic deposits". New Zealand Journal of Geology and Geophysics. 29 (1): 71. doi:10.1080/00288306.1986.10427523. hdl:10289/5345.
  13. ^ Bourdier, Jean-Louis; Pratomo, Indyo; Thouret, Jean-Claude; Georges Boudon; Vincent, Pierre M (December 1997). "Observations, stratigraphy and eruptive processes of the 1990 eruption of Kelut volcano, Indonesia". Journal of Volcanology and Geothermal Research. 79 (3–4): 200. Bibcode:1997JVGR...79..181B. doi:10.1016/S0377-0273(97)00031-0.
  14. ^ a b Vidal, Céline M.; Komorowski, Jean-Christophe; Métrich, Nicole; Pratomo, Indyo; Kartadinata, Nugraha; Prambada, Oktory; Michel, Agnès; Carazzo, Guillaume; Lavigne, Franck; Rodysill, Jessica; Fontijn, Karen; Surono (8 August 2015). "Dynamics of the major plinian eruption of Samalas in 1257 A.D. (Lombok, Indonesia)". Bulletin of Volcanology. 77 (9): 20. Bibcode:2015BVol...77...73V. doi:10.1007/s00445-015-0960-9. S2CID 127929333.
  15. ^ a b c Traineau, Hervé; Westercamp, Denis; Bardintzeff, Jacques-Marie; Miskovsky, Jean-Claude (August 1989). "The recent pumice eruptions of Mt. Pelée volcano, Martinique. Part I: Depositional sequences, description of pumiceous deposits". Journal of Volcanology and Geothermal Research. 38 (1–2): 25. Bibcode:1989JVGR...38...17T. doi:10.1016/0377-0273(89)90027-9.
  16. ^ Mckee, C.O.; Johnson, R.W.; Lowenstein, P.L.; Riley, S.J.; Blong, R.J.; De Saint Ours, P.; Talai, B. (February 1985). "Rabaul Caldera, Papua New Guinea: Volcanic hazards, surveillance, and eruption contingency planning". Journal of Volcanology and Geothermal Research. 23 (3–4): 201. Bibcode:1985JVGR...23..195M. doi:10.1016/0377-0273(85)90035-6.
  17. ^ Holt, Katherine A.; Lowe, David J.; Hogg, Alan G.; Wallace, R. Clel (December 2011). "Distal occurrence of mid-Holocene Whakatane Tephra on the Chatham Islands, New Zealand, and potential for cryptotephra studies". Quaternary International. 246 (1–2): 348. Bibcode:2011QuInt.246..344H. doi:10.1016/j.quaint.2011.06.026. hdl:10289/5454.
  18. ^ Bursik, M I; Sparks, R S J; Gilbert, J S; Carey, S N (April 1992). "Sedimentation of tephra by volcanic plumes: I. Theory and its comparison with a study of the Fogo A plinian deposit, Sao Miguel (Azores)". Bulletin of Volcanology. 54 (4): 330. Bibcode:1992BVol...54..329B. doi:10.1007/BF00301486. S2CID 128420221.
  19. ^ Larsen, Gudrun; Houghton, Bruce F.; Thordarson, Thor; Gudnason, Jonas (1 May 2017). "The opening subplinian phase of the Hekla 1991 eruption: properties of the tephra fall deposit". Bulletin of Volcanology. 79 (5): 11. Bibcode:2017BVol...79...34G. doi:10.1007/s00445-017-1118-8. ISSN 1432-0819. S2CID 132867922.
  20. ^ Todde, A.; Cioni, R.; Pistolesi, M.; Geshi, N.; Bonadonna, C. (26 September 2017). "The 1914 Taisho eruption of Sakurajima volcano: stratigraphy and dynamics of the largest explosive event in Japan during the twentieth century". Bulletin of Volcanology. 79 (10): 7. Bibcode:2017BVol...79...72T. doi:10.1007/s00445-017-1154-4. hdl:2158/1095306. S2CID 55692912.
  21. ^ Yang, Qingyuan; Bursik, Marcus (7 September 2016). "A new interpolation method to model thickness, isopachs, extent, and volume of tephra fall deposits". Bulletin of Volcanology. 78 (10): 3. Bibcode:2016BVol...78...68Y. doi:10.1007/s00445-016-1061-0. S2CID 132693559.
  22. ^ Pyle 1989, p. 2.

Sources edit

  • Fierstein, J.; Houghton, B.F.; Wilson, C.J.N.; Hildreth, W. (April 1997). "Complexities of plinian fall deposition at vent: an example from the 1912 Novarupta eruption (Alaska)". Journal of Volcanology and Geothermal Research. 76 (3–4): 215–227. Bibcode:1997JVGR...76..215F. doi:10.1016/S0377-0273(96)00081-9.
  • Sparks, R S J; Bursik, M I; Ablay, G J; Thomas, R M E; Carey, S N (October 1992). "Sedimentation of tephra by volcanic plumes. Part 2: controls on thickness and grain-size variations of tephra fall deposits". Bulletin of Volcanology. 54 (8): 685–695. Bibcode:1992BVol...54..685S. doi:10.1007/BF00430779. S2CID 128546539.
  • Walker, G.P.L. (August 1980). "The Taupo pumice: Product of the most powerful known (ultraplinian) eruption?". Journal of Volcanology and Geothermal Research. 8 (1): 69–94. Bibcode:1980JVGR....8...69W. doi:10.1016/0377-0273(80)90008-6.
  • Pyle, David M. (January 1989). "The thickness, volume and grainsize of tephra fall deposits". Bulletin of Volcanology. 51 (1): 1–15. Bibcode:1989BVol...51....1P. doi:10.1007/BF01086757. S2CID 140635312.

January 01, 1970
dispersal, index, parameter, volcanology, dispersal, index, displaystyle, defined, george, walker, 1973, surface, area, covered, tephra, fall, where, thickness, equal, more, than, thickness, fall, vent, eruption, with, dispersal, index, leaves, most, products,. Dispersal index is a parameter in volcanology The dispersal index D displaystyle D was defined by George P L Walker in 1973 as the surface area covered by an ash or tephra fall where the thickness is equal or more than 1 100 of the thickness of the fall at the vent 1 An eruption with a low dispersal index leaves most of its products close to the vent forming a cone an eruption with a high dispersal index forms thinner sheet like deposits which extends to larger distances from the vent 2 A dispersal index of 500 square kilometres 190 sq mi or more of coarse pumice is one proposed definition of a Plinian eruption 3 Likewise a dispersal index of 50 000 square kilometres 19 000 sq mi has been proposed as a cutoff for an ultraplinian eruption 4 The definition of 1 100 of the near vent thickness was partially dictated by the fact that most tephra deposits are not well preserved at larger distances 5 Originally the dispersal index was considered a function of the height of the eruption column Later a role for the size of the tephra and ash particles was identified 1 with coarser fall deposits covering smaller surfaces than finer deposits generated by a column of the same height 3 For example a deposit with a dispersal index of 500 square kilometres 190 sq mi can be formed by a column with heights of 14 18 square kilometres 5 4 6 9 sq mi 6 Thus Walker s idea of the column height alone separating a cone forming eruption and an eruption generating a sheet like deposit was later considered oversimplified 7 An additional complicating factor is that fine particles are prone to aggregating and thus falling out more quickly from the column 8 Further problems arise when the maximum thickness has to be determined 9 The height of the eruption column the presence and behaviour of water the speed and direction of the wind as well as the sizes of the various tephra particles influence the fallout patterns of an ash cloud 10 The dispersal index for volcanic eruptions ranges from lt 1 square kilometre 0 39 sq mi and 1 1 000 square kilometres 0 39 386 10 sq mi 3 A number of basaltic phreatomagmatic deposits frequently associated with tuff rings have a dispersal index of less than 50 square kilometres 19 sq mi 11 Volcano Eruption Age Dispersal index Source Taupō Hatepe eruption 1820 BP 100 000 square kilometres 39 000 sq mi 3 Taupō Oruanui eruption 20000 BP gt 100 000 square kilometres 39 000 sq mi 11 Taupō Hinemaiaia tephra 4500 years ago 40 000 square kilometres 15 000 sq mi 12 Kelut 1990 2 000 square kilometres 770 sq mi 13 Rinjani 1257 Samalas eruption P1 phase 1257 7 500 square kilometres 2 900 sq mi 14 Rinjani 1257 Samalas eruption P3 phase 1257 110 500 square kilometres 42 700 sq mi 14 Mount Pelee P1 eruption 650 BP 900 square kilometres 350 sq mi 15 Mount Pelee P2 eruption 1670 BP 800 square kilometres 310 sq mi 15 Mount Pelee P3 eruption 2010 BP 1 000 square kilometres 390 sq mi 15 Rabaul Vulcan 1937 40 square kilometres 15 sq mi 16 Okataina Volcanic Complex Whakatane tephra 5500 BP 200 000 square kilometres 77 000 sq mi 17 Agua de Pau Fogo A 5000 BP 1 500 square kilometres 580 sq mi 18 Hekla 1991 460 square kilometres 180 sq mi 19 Sakurajima Taisho 1914 539 square kilometres 208 sq mi 20 Mono Craters 4th century AD 1 800 square kilometres 690 sq mi 21 A related measure is the thickness half distance b t displaystyle b t 10 which defines the distance over which the thickness of a deposit halves 22 These values are related with each other over D p b t 2 l n 0 01 2 l n 0 5 2 textstyle D frac pi b t 2 ln 0 01 2 ln 0 5 2 for circular deposits References edit a b Pyle 1989 p 10 Fierstein et al 1997 p 215 a b c d Walker 1980 p 88 Walker 1980 p 91 Bonadonna C Ernst G G J Sparks R S J May 1998 Thickness variations and volume estimates of tephra fall deposits the importance of particle Reynolds number Journal of Volcanology and Geothermal Research 81 3 4 181 Bibcode 1998JVGR 81 173B CiteSeerX 10 1 1 519 5180 doi 10 1016 S0377 0273 98 00007 9 Sparks et al 1992 p 690 Pyle 1989 p 11 Sparks et al 1992 p 694 Hildreth Wes Drake Robert E January 1992 Volcan Quizapu Chilean Andes Bulletin of Volcanology 54 2 111 doi 10 1007 BF00278002 S2CID 128972435 a b Sparks et al 1992 p 685 a b Self S Sparks R S J September 1978 Characteristics of widespread pyroclastic deposits formed by the interaction of silicic magma and water Bulletin Volcanologique 41 3 209 210 Bibcode 1978BVol 41 196S doi 10 1007 BF02597223 S2CID 130066909 Lowe David J January 1986 Revision of the age and stratigraphic relationships of Hinemaiaia Tephra and Whakatane Ash North Island New Zealand using distal occurrences in organic deposits New Zealand Journal of Geology and Geophysics 29 1 71 doi 10 1080 00288306 1986 10427523 hdl 10289 5345 Bourdier Jean Louis Pratomo Indyo Thouret Jean Claude Georges Boudon Vincent Pierre M December 1997 Observations stratigraphy and eruptive processes of the 1990 eruption of Kelut volcano Indonesia Journal of Volcanology and Geothermal Research 79 3 4 200 Bibcode 1997JVGR 79 181B doi 10 1016 S0377 0273 97 00031 0 a b Vidal Celine M Komorowski Jean Christophe Metrich Nicole Pratomo Indyo Kartadinata Nugraha Prambada Oktory Michel Agnes Carazzo Guillaume Lavigne Franck Rodysill Jessica Fontijn Karen Surono 8 August 2015 Dynamics of the major plinian eruption of Samalas in 1257 A D Lombok Indonesia Bulletin of Volcanology 77 9 20 Bibcode 2015BVol 77 73V doi 10 1007 s00445 015 0960 9 S2CID 127929333 a b c Traineau Herve Westercamp Denis Bardintzeff Jacques Marie Miskovsky Jean Claude August 1989 The recent pumice eruptions of Mt Pelee volcano Martinique Part I Depositional sequences description of pumiceous deposits Journal of Volcanology and Geothermal Research 38 1 2 25 Bibcode 1989JVGR 38 17T doi 10 1016 0377 0273 89 90027 9 Mckee C O Johnson R W Lowenstein P L Riley S J Blong R J De Saint Ours P Talai B February 1985 Rabaul Caldera Papua New Guinea Volcanic hazards surveillance and eruption contingency planning Journal of Volcanology and Geothermal Research 23 3 4 201 Bibcode 1985JVGR 23 195M doi 10 1016 0377 0273 85 90035 6 Holt Katherine A Lowe David J Hogg Alan G Wallace R Clel December 2011 Distal occurrence of mid Holocene Whakatane Tephra on the Chatham Islands New Zealand and potential for cryptotephra studies Quaternary International 246 1 2 348 Bibcode 2011QuInt 246 344H doi 10 1016 j quaint 2011 06 026 hdl 10289 5454 Bursik M I Sparks R S J Gilbert J S Carey S N April 1992 Sedimentation of tephra by volcanic plumes I Theory and its comparison with a study of the Fogo A plinian deposit Sao Miguel Azores Bulletin of Volcanology 54 4 330 Bibcode 1992BVol 54 329B doi 10 1007 BF00301486 S2CID 128420221 Larsen Gudrun Houghton Bruce F Thordarson Thor Gudnason Jonas 1 May 2017 The opening subplinian phase of the Hekla 1991 eruption properties of the tephra fall deposit Bulletin of Volcanology 79 5 11 Bibcode 2017BVol 79 34G doi 10 1007 s00445 017 1118 8 ISSN 1432 0819 S2CID 132867922 Todde A Cioni R Pistolesi M Geshi N Bonadonna C 26 September 2017 The 1914 Taisho eruption of Sakurajima volcano stratigraphy and dynamics of the largest explosive event in Japan during the twentieth century Bulletin of Volcanology 79 10 7 Bibcode 2017BVol 79 72T doi 10 1007 s00445 017 1154 4 hdl 2158 1095306 S2CID 55692912 Yang Qingyuan Bursik Marcus 7 September 2016 A new interpolation method to model thickness isopachs extent and volume of tephra fall deposits Bulletin of Volcanology 78 10 3 Bibcode 2016BVol 78 68Y doi 10 1007 s00445 016 1061 0 S2CID 132693559 Pyle 1989 p 2 Sources edit Fierstein J Houghton B F Wilson C J N Hildreth W April 1997 Complexities of plinian fall deposition at vent an example from the 1912 Novarupta eruption Alaska Journal of Volcanology and Geothermal Research 76 3 4 215 227 Bibcode 1997JVGR 76 215F doi 10 1016 S0377 0273 96 00081 9 Sparks R S J Bursik M I Ablay G J Thomas R M E Carey S N October 1992 Sedimentation of tephra by volcanic plumes Part 2 controls on thickness and grain size variations of tephra fall deposits Bulletin of Volcanology 54 8 685 695 Bibcode 1992BVol 54 685S doi 10 1007 BF00430779 S2CID 128546539 Walker G P L August 1980 The Taupo pumice Product of the most powerful known ultraplinian eruption Journal of Volcanology and Geothermal Research 8 1 69 94 Bibcode 1980JVGR 8 69W doi 10 1016 0377 0273 80 90008 6 Pyle David M January 1989 The thickness volume and grainsize of tephra fall deposits Bulletin of Volcanology 51 1 1 15 Bibcode 1989BVol 51 1P doi 10 1007 BF01086757 S2CID 140635312 Retrieved from https en wikipedia org w index php title Dispersal index amp oldid 1193540816, wikipedia, wiki, book, books, library,

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