Geography of Samoa

Map of the Samoan archipelago
Topography of Samoa.
South east coast of Savai'i island.

The Samoan archipelago is a chain of 16 islands and numerous seamounts covering 3,123 km2 (1,206 sq mi) in the central South Pacific, south of the equator, about halfway between Hawaii and New Zealand, forming part of Polynesia and of the wider region of Oceania. The islands are Savaiʻi, Upolu, Tutuila, ’Uvea, Taʻū, Ofu, Olosega, Apolima, Manono, Nuʻutele, Niulakita, Nuʻulua, Namua, Fanuatapu, Rose Atoll, Nu'ulopa, as well as the submerged Vailuluʻu, Pasco banks, and Alexa Bank.[1]

Tectonics

The Samoan archipelago has many features that are consistent with a plume-driven hotspot model, including the currently active submarine volcano Vailuluʻu that anchors the eastern extremity. However, the chain's proximity to the northern end of the Tonga trench, and the presence of voluminous young volcanism on what should be the oldest (~5 my) western island Savaiʻi has induced controversy regarding a simple plume/hotspot model.[2] The Samoan archipelago was most likely created by the Pacific Tectonic Plate traveling over a fixed hotspot. The Samoa hotspot trail is in part coincident with a large group of islands and seamounts 1,700 km (1,056 mi) long, which were probably formed by the same hotspot, but also intersect with older seamounts along the hotspot highway left by the Macdonald, Rurutu, and Rarotonga hotspots and feature substantial postshield volcanism, probably owing to tectonic phenomena triggered by the subduction of the Pacific Plate under the Australian Plate at the nearby Tonga Trench.[3][4][5][6][7]

Vailuluʻu is a volcanic seamount discovered in 1975. It rises from the sea floor to a depth of 593 m (1,946 ft) and is located between Taʻu and Rose islands at the eastern end of the Samoa hotspot chain. The basaltic seamount is considered to mark the current location of the Samoa hotspot. The summit of Vailuluʻu contains a 2,000 m (6,600 ft) wide, 400 m (1,300 ft) deep oval-shaped caldera. Two principal rift zones extend east and west from the summit, parallel to the trend of the Samoan hotspot. A third less prominent rift extends southeast of the summit.[2]

Rose Atoll and Malulu seamount are likely remnants of where the path of either the Macdonald or Rarotonga hotspots crossed the path of the Samoa hotspot.[8][9][10] Some seamounts in western Samoa ("Samoan Seamounts"[11]), which were emplaced together with Tuvalu between 63 and 42 million years ago are likely remnants of the Rurutu hotspot.[12] These are also known as the "interloper seamounts".[13] Other undated seamounts in Samoa have been linked to the Rurutu hotspot on the basis of geochemical evidence.[14]

Islands of the Samoan archipelago

Island Area Coastline Population Highest Point Last Volcanic Eruption Country/Territory
Savaiʻi 1,694 195 43,142 1,858 1911 CE[15]  Samoa
Upolu 1,125 197 143,418 1,113 Unknown[16]  Samoa
Tutuila 142.3 135 55,876 653 440 CE[17]  American Samoa
’Uvea 96 43 8,333 131 Unknown[18]  Wallis and Futuna
Taʻū 47.02 32 790 931 Unknown[19]  American Samoa
Ofu 7.215 11.47 176 491 1866 CE[20]  American Samoa
Olosega 5.163 13.38 172 629 1866 CE[20]  American Samoa
Apolima 4.1 4.19 75 165 Unknown[16]  Samoa
Manono 3 7.5 889 37 Unknown[16]  Samoa
Nuʻutele 1.15 5.04 0 180 Unknown[16]  Samoa
Niulakita 0.4 2.2 34 4.6 Cretaceous[21]  Tuvalu
Nuʻulua 0.23 2.78 0 96 Unknown[16]  Samoa
Namua 0.18 2.08 0 91 Unknown[16]  Samoa
Fanuatapu 0.06 1.81 0 31 Unknown[16]  Samoa
Rose Atoll 0.05 0.75 0 3.5 10,000 ya[22]  American Samoa
Nu'ulopa 0.01 0.45 0 37 Unknown[16]  Samoa
Total 3,126 654 252,905

Climate

Further information: Climate change in the Pacific Islands

Due to its positioning in the South Pacific Ocean, the Samoan archipelago is frequently hit by tropical cyclones between November and April. Samoa has a trade-wind tropical rainforest climate (Köppen Af), with an average annual temperature of 26.5 °C or 79.7 °F. The wettest period occurs from November to April, although heavy rain may fall in any month.[23]

Climate data for Apia, Upolu
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Mean daily maximum °C (°F) 30.4
(86.7) 		30.6
(87.1) 		30.6
(87.1) 		30.7
(87.3) 		30.4
(86.7) 		30.0
(86.0) 		29.5
(85.1) 		29.6
(85.3) 		29.9
(85.8) 		30.1
(86.2) 		30.3
(86.5) 		30.5
(86.9) 		30.2
(86.4)
Mean daily minimum °C (°F) 23.9
(75.0) 		24.2
(75.6) 		24.0
(75.2) 		23.8
(74.8) 		23.4
(74.1) 		23.2
(73.8) 		22.6
(72.7) 		22.8
(73.0) 		23.1
(73.6) 		23.4
(74.1) 		23.6
(74.5) 		23.8
(74.8) 		23.5
(74.3)
Average rainfall mm (inches) 489.0
(19.25) 		368.0
(14.49) 		352.1
(13.86) 		211.2
(8.31) 		192.6
(7.58) 		120.8
(4.76) 		120.7
(4.75) 		113.2
(4.46) 		153.9
(6.06) 		224.3
(8.83) 		261.7
(10.30) 		357.5
(14.07) 		2,965
(116.72)
Source: World Meteorological Organization (UN)[24]

Terrain

Detailed map of Samoa

The terrain of the larger islands consists of a narrow coastal plains with volcanic, rocky, rugged mountains in the interior. The Natural resources include hardwood forests, fish, and hydropower. The smaller islands are remnants of eroded volcanic tuff rings, some are just a coral reef atop the eroded cone of a defunct volcano.[25]

Rose Atoll is the easternmost point of the archipelago and the southernmost point of the United States.[26] American Samoa is home to the National Park of American Samoa.

The highest mountains are: Mt Silisili (Savaiʻi) at 1,858 m (6,096 ft), Mount Fito (Upolu) at 1,113 m (3,652 ft), Lata Mountain (Taʻū), 3,170 ft (970 m); Matafao Peak (Tutuila) at 2,141 ft (653 m), Piumafua (Olosega) at 2,095 ft (639 m), and Tumutumu (Ofu) at 1,621 ft (494 m). Mount Pioa (Tutuila), nicknamed the Rainmaker, is 1,718 ft (524 m).[27] : 3  American Samoa is also home to some of the world's highest sea cliffs at 3,000 ft (910 m).[28]

References

  1. ^ "Demographic Yearbook—Table 3: Population by sex, rate of population increase, surface area and density" (PDF). United Nations Statistics Division. 2010.
  2. ^ a b Hart, S.R.; Coetzee, M; Workman, R; Blusztajn, Jerzy (2004). "Genesis of the Western Samoa seamount province: Age, geochemical fingerprint and tectonics". Earth and Planetary Science Letters. p. 38.
  3. ^ Price, Allison A.; Jackson, Matthew G.; Blichert-Toft, Janne; Kurz, Mark D.; Gill, Jim; Blusztajn, Jerzy; Jenner, Frances; Brens, Raul; Arculus, Richard (March 2017). "Geodynamic implications for zonal and meridional isotopic patterns across the northern Lau and North Fiji Basins" (PDF). Geochemistry, Geophysics, Geosystems. 18 (3): 23. Bibcode:2017GGG....18.1013P. doi:10.1002/2016gc006651. hdl:1912/8979. ISSN 1525-2027.
  4. ^ Smith-Vaniz, William F. (1987). "The Saber-Toothed Blennies, Tribe Nemophini (Pisces: Blenniidae): An Update". Proceedings of the Academy of Natural Sciences of Philadelphia. 139 (1): 5. JSTOR 4064893.
  5. ^ Russell, Jamie A. "Hotspot Lesson: Samoan Hotspot". Enduring Resources Earth Science Education. Retrieved 2 December 2009.
  6. ^ "Samoan Hotspot Trail". Archived from the original on December 23, 2010. Retrieved 2009-12-01.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  7. ^ Bird 2003, Tonga Plate (TO), Kermadec Plate (KE), and Niuafo’ou Plate (NI), p. 28
  8. ^ Jackson, Matthew G.; Hart, Stanley R.; Konter, Jasper G.; Koppers, Anthony A. P.; Staudigel, Hubert; Kurz, Mark D.; Blusztajn, Jerzy; Sinton, John M. (December 2010). "Samoan hot spot track on a "hot spot highway": Implications for mantle plumes and a deep Samoan mantle source". Geochemistry, Geophysics, Geosystems. 11 (12): 19. Bibcode:2010GGG....1112009J. doi:10.1029/2010GC003232. S2CID 131425199.
  9. ^ Koppers, Anthony A. P.; Russell, Jamie A.; Roberts, Jed; Jackson, Matthew G.; Konter, Jasper G.; Wright, Dawn J.; Staudigel, Hubert; Hart, Stanley R. (July 2011). "Age systematics of two young en echelon Samoan volcanic trails". Geochemistry, Geophysics, Geosystems. 12 (7): 5. Bibcode:2011GGG....12.7025K. doi:10.1029/2010GC003438. hdl:1912/4769. S2CID 54947952.
  10. ^ Price, Allison A.; Jackson, Matthew G.; Blichert-Toft, Janne; Blusztajn, Jerzy; Conatser, Christopher S.; Konter, Jasper G.; Koppers, Anthony A.P.; Kurz, Mark D. (May 2016). "Geochemical evidence in the northeast Lau Basin for subduction of the Cook-Austral volcanic chain in the Tonga Trench". Geochemistry, Geophysics, Geosystems. 17 (5): 1694–1724. Bibcode:2016GGG....17.1694P. doi:10.1002/2015GC006237. hdl:1912/8238.
  11. ^ Koppers, A. A.; Konter, J. G.; Jackson, M. G. (2013-12-01). "Insights Into the Origin of the Longest-lived Hotspot in the Pacific: Clues from the Tuvalus". AGU Fall Meeting Abstracts. 13: V13F–2668. Bibcode:2013AGUFM.V13F2668K.
  12. ^ Finlayson, V.; Konter, J. G.; Konrad, K.; Price, A. A.; Koppers, A. A. P.; Jackson, M. G. (2016-12-01). "Identification of a Hawaiian-Emperor Style Bend in the Tuvalu Segment of the Rurutu Hotspot". AGU Fall Meeting Abstracts. 52: DI52A–05. Bibcode:2016AGUFMDI52A..05F.
  13. ^ Finlayson, V.; Konter, J. G.; Konrad, K.; Koppers, A.A.P.; Jackson, M.G.; Rooney, T.O. (October 2018). "Sr–Pb–Nd–Hf isotopes and 40Ar/39Ar ages reveal a Hawaii–Emperor-style bend in the Rurutu hotspot"". Earth and Planetary Science Letters. 500: 168–179. Bibcode:2018E&PSL.500..168F. doi:10.1016/j.epsl.2018.08.020. ISSN 0012-821X. S2CID 135064417.
  14. ^ Jackson, Matthew G.; Konter, Jasper G.; Steinberger, Bernhard; Koppers, Anthony A. P.; Konrad, Kevin (2018-02-27). "On the relative motions of long-lived Pacific mantle plumes". Nature Communications. 9 (1): 854. Bibcode:2018NatCo...9..854K. doi:10.1038/s41467-018-03277-x. ISSN 2041-1723. PMC 5829163. PMID 29487287.
  15. ^ "Global Volcanism Program: Savai'i". Smithsonian Institution.
  16. ^ a b c d e f g h "Global Volcanism Program: Upolu". Smithsonian Institution.
  17. ^ "Global Volcanism Program: Tutuila". Smithsonian Institution.
  18. ^ "Global Volcanism Program: Wallis Islands". Smithsonian Institution.
  19. ^ "Global Volcanism Program: Ta'u". Smithsonian Institution.
  20. ^ a b "Global Volcanism Program: Ofu-Olosega". Smithsonian Institution.
  21. ^ Duncan, R.A. (1985). Brocher, T.M. (ed.). Radiometric ages from volcanic rocks along the New Hebrides-Samoa lineament. Investigations of the nonhern Melanesian borderland. Vol. Series 3. Circum-Pacific Councilfdr Energy and Mineral Resources Earth Science. pp. 67–76.
  22. ^ "Global Volcanism Program: Rose Island". Smithsonian Institution.
  23. ^ "Samoa: Climate". Encyclopædia Britannica. Retrieved 26 November 2007.
  24. ^ World Weather Information Service – Apia, World Meteorological Organization. Retrieved 15 October 2012.
  25. ^ [1] Restoration of Nu'utele and Nu'ulua Islands, Samoa by David J. Butler, April 2005, SPREP. Retrieved 25 October 2009
  26. ^ "Rose Atoll Marine National Monument". July 2022.
  27. ^ Sunia, Fofo I.F. (2009). A History of American Samoa. Amerika Samoa Humanities Council. Page 355. ISBN 9781573062992.
  28. ^ Harris, Ann G. and Esther Tuttle (2004). Geology of National Parks. Kendall Hunt. p. 603. ISBN 978-0787299705.

Sources

See also

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