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Geology

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Setting

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Position of Mauna Loa on Hawaiʻi island
Landsat mosaic; recent lava flows appear in black

Like all Hawaiian volcanoes, Mauna Loa was created as the Pacific tectonic plate moved over the Hawaii hotspot in the Earth's underlying mantle.[1] The Hawaii island volcanoes are the most recent evidence of this process that, over 70 million years, has created the 3,700 mi (6,000 km)-long Hawaiian–Emperor seamount chain.[2] The prevailing view states that the hotspot has been largely stationary within the planet's mantle for much, if not all of the Cenozoic Era.[2][3] However, while the Hawaiian mantle plume is well understood and extensively studied, the nature of hotspots themselves remains fairly enigmatic.[4]

Mauna Loa is one of five subaerial volcanoes that make up the island of Hawaiʻi.[5] The oldest volcano on the island, Kohala, is more than a million years old,[6] and Kīlauea, the youngest, is believed to be between 210,000 and 280,000 years of age.[7] Lōʻihi Seamount on the island's flank is even younger, but has yet to breach the surface of the Pacific Ocean.[8] At 1 million to 600,000 years of age,[9] Mauna Loa is the second youngest of the five volcanoes on the island, making it the third youngest volcano in the Hawaiian – Emperor seamount chain, a chain of shield volcanoes and seamounts extending from Hawaii to the Kuril–Kamchatka Trench in Russia.[10]

Mauna Loa from Hilo Bay, December 2017


Following the pattern of Hawaiian volcano formation, Mauna Loa would have started as a submarine volcano, gradually building itself up through underwater eruptions of alkali basalt before emerging from the sea through a series of surtseyan eruptions[11] about 400,000 years ago. Since then, the volcano has remained active, with a history of effusive and explosive eruptions, including 33 eruptions since the first well-documented eruption in 1843.[12] Although Mauna Loa has not erupted since 1984, the U.S. Geological Survey states that the volcano is certain to erupt again.[13]

Structure

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Mauna Loa's summit, overlaid with 100 m (328 ft) contour lines; its rift zones are visible from the air.
Mokuʻāweoweo, Mauna Loa's summit caldera, covered in snow.


Mauna Loa is the largest active volcano[14] and one of the largest volcanoes in the world.[note 1] The subaerial portion of the volcano spans a maximum width of 120 km (75 mi)[12] and, having a surface area of about 5,100 km2 (2,000 sq mi), it makes up more than half the surface area of the island of Hawaiʻi.[9] Estimates of the volcano's volume range from 74,000 to 105,000 km3 (17,800 to 25,200 cu mi); a 2013 analysis in Geosphere estimated the volcano's volume to be 83,000 km3 (19,900 cu mi).[18]

Combining the volcano's extensive submarine flanks (5,000 m (16,400 ft) to the sea floor) and 4,169 m (13,680 ft) subaerial height, Mauna Loa rises 9,170 m (30,085 ft) from the seafloor to its summit.[12][19] In addition, much of the mountain is invisible even underwater: its mass depresses the crust beneath it by another 8 km (5 mi), in the shape of an inverse mountain, meaning that the total height of Mauna Loa from its lowest point to its summit is about 17,000 m (55,800 ft).[20][21] This figure makes Mauna Loa the tallest mountain in the world when measured from base to summit,[21] significantly taller than Mount Everest's 8,848 m or 29,029 ft height from sea level to summit.[15]


Snow-covered Moku‘aweoweo caldera in 2016

Mauna Loa is a typical shield volcano in form, taking the shape of a long, broad dome extending down to the ocean floor whose slopes are about 12° at their steepest, a consequence of its extremely fluid lava. The shield-stage lavas that built the enormous main mass of the mountain are tholeiitic basalts, like those of Mauna Kea, created through the mixing of primary magma and subducted oceanic crust.[22] Mauna Loa's summit hosts three overlapping pit craters arranged northeast–southwest, the first and last roughly 1 km (0.6 mi) in diameter and the second an oblong 4.2 km × 2.5 km (2.6 mi × 1.6 mi) feature; together these three craters make up the 6.2 by 2.5 km (3.9 by 1.6 mi) summit caldera Mokuʻāweoweo,[23] so named for the Hawaiian ʻāweoweo fish (Priacanthus meeki), purportedly due to the resemblance of its eruptive fires to the coloration of the fish.[24] Mokuʻāweoweo's caldera floor lies between 170 and 50 m (558 and 164 ft) beneath its rim and it is only the latest of several calderas that have formed and reformed over the volcano's life. It was created between 1,000 and 1,500 years ago by a large eruption from Mauna Loa's northeast rift zone, which emptied out a shallow magma chamber beneath the summit and collapsed it into its present form.[23] Additionally, two smaller pit craters lie southwest of the caldera, named Lua Hou (New Pit) and Lua Hohonu (Deep Pit).[25]

Mauna Loa's summit is also the focal point for its two prominent rift zones, marked on the surface by well-preserved, relatively recent lava flows (easily seen in satellite imagery) and linearly arranged fracture lines intersected by cinder and splatter cones.[26] These rift zones are deeply set structures, driven by dike intrusions along a decollement fault that is believed to reach down all the way to the volcano's base, 12 to 14 km (7 to 9 mi) deep.[27] The first is a 60 km (37 mi) rift trending southwest from the caldera to the sea and a further 40 km (25 mi) underwater, with a prominent 40° directional change along its length; this rift zone is historically active across most of its length. The second, northeastern rift zone extends towards Hilo and is historically active across only the first 20 km (12 mi) of its length, with a nearly straight and, in its latter sections, poorly defined trend.[26] The northeastern rift zone takes the form of a succession of cinder cones, the most prominent of which the 60 m (197 ft) high Puu Ulaula, or Red Hill. There is also a less definite northward rift zone that extends towards the Humuula Saddle marking the intersection of Mauna Loa and Mauna Kea.[25]

Simplified geophysical models of Mauna Loa's magma chamber have been constructed, using interferometric synthetic aperture radar measures of ground deformation due to the slow buildup of lava under the volcano's surface. These models predict a 1.1 km (1 mi) wide magma chamber located at a depth of about 4.7 km (3 mi), 0.5 km (0 mi) below sea level, near the southeastern margin of Mokuʻāweoweo. This shallow magma chamber is significantly higher-placed than Mauna Loa's rift zones, suggesting magma intrusions into the deeper parts and occasional dike injections into the shallower parts of the rift zone drive rift activity; a similar mechanism has been proposed for neighboring Kīlauea.[27] Earlier models based on Mauna Loa's two most recent eruptions made a similar prediction, placing the chamber at 3 km (1.9 mi) deep in roughly the same geographic position.[28]


Mauna Loa has complex interactions with its neighbors, Hualālai to the northwest, Mauna Kea to the northeast, and particularly Kīlauea to the east. Lavas from Mauna Kea intersect with Mauna Loa's basal flows as a consequence of Kea's older age,[29] and Mauna Kea's original rift zones were buried beneath post-shield volcanic rocks of Mauna Loa;[30] additionally, Mauna Kea shares Mauna Loa's gravity well, depressing the ocean crust beneath it by 6 km (4 mi).[29] There are also a series of normal faults on Mauna Loa's northern and western slopes, between its two major rift zones, that are believed to be the result of combined circumferential tension from the two rift zones and from added pressure due to the westward growth of neighboring Kīlauea.[31]


Because Kīlauea lacks a topographical prominence and appears as a bulge on the southeastern flank of Mauna Loa, it was historically interpreted by both native Hawaiians and early geologists to be an active satellite of Mauna Loa. However, analysis of the chemical composition of lavas from the two volcanoes show that they have separate magma chambers, and are thus distinct. Nonetheless, their proximity has led to a historical trend in which high activity at one volcano roughly coincides with low activity at the other. When Kīlauea lay dormant between 1934 and 1952, Mauna Loa became active, and when the latter remained quiet from 1952 to 1974, the reverse was true. This is not always the case; the 1984 eruption of Mauna Loa started during an eruption at Kīlauea, but had no discernible effect on the Kīlauea eruption, and the ongoing inflation of Mauna Loa's summit, indicative of a future eruption, began the same day as new lava flows at Kīlauea's Puʻu ʻŌʻō crater. Geologists have suggested that "pulses" of magma entering Mauna Loa's deeper magma system may have increased pressure inside Kīlauea and triggered the concurrent eruptions.[32]

Mauna Loa is slumping eastward along its southwestern rift zone, leveraging its mass into Kīlauea and driving the latter eastward at a rate of about 10 cm (4 in) per year; the interaction between the two volcanoes in this manner has generated a number of large earthquakes in the past, and has resulted in a significant area of debris off Kīlauea's seaward flank known as the Hilina Slump. A system of older faults exists on the southeastern side of Mauna Loa that likely formed before Kilauea became large enough to impede Mauna Loa's slump, the lowest and northernmost of which, the Kaoiki fault, remains an active earthquake center today. The west side of Mauna Loa, meanwhile, is unimpeded in movement, and indeed is believed to have undergone a massive slump collapse between 100,000 and 200,000 years ago, the residue from which, consisting of a scattering of debris up to several kilometers wide and up to 50 km (31 mi) distant, is still visible today. The damage was so extensive that the headwall of the damage likely intersected its southwestern rift zone. There is very little movement there today, a consequence of the volcano's geometry.[33]

A view of Mauna Loa taken from a hill near The Onizuka Center for International Astronomy Visitor Information Station at the 9,300 ft. level of Mauna Kea.

Mauna Loa is tall enough to have experienced glaciation during the last ice age, 25,000 to 15,000 years ago.[1] Unlike Mauna Kea, on which extensive evidence of glaciation remains even today,[34] Mauna Loa was at the time and has remained active, having grown an additional 150 to 300 m (492 to 984 ft) in height since then and covering any glacial deposits beneath new flows; strata of that age don't occur until at least 2,000 m (6,562 ft) down from the volcano's summit, too low for glacial growth. Mauna Loa also lacks its neighbor's summit permafrost region, although sporadic ice persists in places. It is speculated that extensive phreatomagmatic activity occurred during this time, contributing extensively to ash deposits on the summit.[1]

Removed sources, may be used elsewhere in article

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Notes

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  1. ^ Some sources describe Mauna Loa as either the largest mountain on earth[15] or the largest volcano in the world.[16] However, in 2020, a group of researchers proposed that Gardner Pinnacles, another shield volcano created by the Hawaiian hotspot, is larger than Mauna Loa.[17]

References

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  1. ^ a b c David R. Sherrod; John M. Sinton; Sarah E. Watkins & Kelly M. Brunt (2007). "Geologic Map of the State of Hawai'i" (PDF). Open-File Report 2007–1089. United States Geological Survey. pp. 50–51. Retrieved 9 December 2012.
  2. ^ a b Watson, Jim (May 5, 1999). "The long trail of the Hawaiian hotspot". United States Geological Survey. Retrieved August 26, 2010.
  3. ^ Foulger, G.R; Anderson, Don L. (March 11, 2006). "The Emperor and Hawaiian Volcanic Chains: How well do they fit the plume hypothesis?". MantlePlumes.org. Retrieved April 1, 2009.
  4. ^ Clague, David A.; Dalrymple, G. Brent (1987). "The Hawaiian-Emperor Volcanic Chain – Geological Evolution" (PDF). Volcanism in Hawaii: papers to commemorate the 75th anniversary of the founding of the Hawaii Volcano Observatory. Professional Paper 1350. Vol. 1. United States Geological Survey. p. 32.
  5. ^ Juvik, Sonia P.; Juvik, James O., eds. (1998). Atlas of Hawaiʻi (3rd ed.). University of Hawaiʻi Press. p. 44. ISBN 0-8248-2125-4. Hawaiʻi Island. Hawaiʻi consists of five coalescent, subaerial (above sea level) volcanoes...
  6. ^ Sherrod, David R.; Sinton, James M.; Watkins, Sarah E.; Brunt, Kelly M. (2007). "Geologic Map of the State of Hawaiʻi" (PDF). Reston, Virginia: United States Geological Survey. p. 41.
  7. ^ "Kīlauea: Geology and History". U.S. Geological Survey. Retrieved December 25, 2021.
  8. ^ David A. Clague; David R. Sherrod (2014). "Growth and degradation of Hawaiian volcanoes". In Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M. (eds.). Characteristics of Hawaiian volcanoes, Professional Paper 1801 (PDF). Reston, VA: U.S. Geological Survey. p. 104.
  9. ^ a b "Mauna Loa: Earth's Largest Volcano". Hawaiian Volcano Observatory – United States Geological Service. Retrieved January 29, 2022.
  10. ^ W. J. Kious & R. I. Tilling (1996). "Hotspots": Mantle thermal plumes (1.14 ed.). United States Geological Survey. ISBN 978-0-16-048220-5. Retrieved 9 December 2012.
  11. ^ "Evolution of Hawaiian Volcanoes". Hawaiian Volcano Observatory – United States Geological Survey. March 26, 1998. Retrieved January 29, 2022.
  12. ^ a b c "Mauna Loa". US Geological Survey. Retrieved January 29, 2022.
  13. ^ "Mauna Loa". US Geological Survey, Hawaiian Volcano Observatory. Retrieved December 26, 2021.
  14. ^ "Where is the largest active volcano in the world?". US Geological Survey. Retrieved May 25, 2022.
  15. ^ a b "How big are the Hawaiian volcanoes?". US Geological Survey. Retrieved May 27, 2022.
  16. ^ Letzter, Rafi (July 9, 2019). "Geoscientists Were Wrong About the 'World's Largest Volcano'". Live Science.
  17. ^ Garcia, Michael O.; Tree, Jonathan P.; Wessel, Paul; Smith, John R. (July 15, 2020). "Pūhāhonu: Earth's biggest and hottest shield volcano". Earth and Planetary Science Letters. 542 (116296): 4. doi:10.1016/j.epsl.2020.116296. The new volume calculation shows that Puhahonu is substantially larger than any other Hawaiian volcano including Mauna Loa, which was presumed to be the largest volcano on Earth.
  18. ^ Lipman, Peter W.; Calvert, Andrew T. (October 1, 2013). "Modeling volcano growth on the Island of Hawaii: Deep-water perspectives". Geosphere. 9 (5): 1364–1365. doi:10.1130/GES00935.1.
  19. ^ Rubin, Ken; Minicola, Rochelle (20 March 2009). "Mauna Loa Volcano". Hawaiian Volcano Observatory – United States Geological Survey. Retrieved 12 December 2012.
  20. ^ J.G. Moore (1987). "Subsidence of the Hawaiian Ridge". Volcanism in Hawaii: Geological Survey Professional Paper. 1350 (1).
  21. ^ a b "How High is Mauna Loa?". Hawaiian Volcano Observatory – United States Geological Survey. August 20, 1998. Retrieved May 27, 2022.
  22. ^ Claude Herzberg (30 November 2006). "Petrology and thermal structure of the Hawaiian plume from Mauna Kea volcano". Nature. 444 (7119). Nature Publishing Group: 605–09. Bibcode:2006Natur.444..605H. doi:10.1038/nature05254. PMID 17136091. S2CID 4366221.
  23. ^ a b "When did Moku'aweoweo (the summit caldera of Mauna Loa) form?". Hawaiian Volcano Observatory – United States Geological Survey. 28 March 2001. Retrieved 25 September 2022.
  24. ^ "Place Names of Hawaii – Moku-ʻāweoweo". Ulukau – Hawaiian Electronic Library. Archived from the original on 28 December 2012. Retrieved 11 December 2012.
  25. ^ a b c G. Macdonald & D. Hubbard (24 March 2006) [1951, 7th ed. revision December, 1974]. "Mauna Loa, Fiery Colossus of the Pacific". National Park Service. Retrieved 9 December 2012.
  26. ^ a b Peter W. Lipman (1980). "The Southwestern Rift Zone of Mauna Kea: Implications for Structural Evolution of Hawaiian Volcanoes". American Journal of Science. 280-A. American Journal of Science: 752–76.
  27. ^ a b Cite error: The named reference science-stress was invoked but never defined (see the help page).
  28. ^ "What's up with Mauna Loa?". Hawaiian Volcano Observatory – United States Geological Survey. 23 October 2001. Retrieved 16 December 2012.
  29. ^ a b E. W. Wolfe; W. S. Wise; G. B. Dalrymple (1997). The geology and petrology of Mauna Kea volcano, Hawaii : a study of postshield volcanism. Professional Paper 1557. United States Geological Survey. Retrieved 12 December 2012.
  30. ^ E. C. Cannon & R. R. Bürgmann (26 October 2009). "Complete Report for Mauna Kea Volcano (Class B) No. 2601". United States Geological Survey. Archived from the original on 16 February 2012. Retrieved 12 December 2012.
  31. ^ "Rift Zones". Oregon State University. Retrieved 13 December 2012.
  32. ^ "Inflation of Mauna Loa Volcano slows". Volcano Watch. Hawaiian Volcano Observatory – United States Geological Survey. 28 January 2003. Retrieved 30 January 2012.
  33. ^ Ken Hon. "Giant Landslides: Kilauea and Mauna Loa: GEOL 205: Lecture Notes". University of Hawaii at Hilo. Retrieved 16 December 2012.
  34. ^ "Glaciers on Mauna Kea? You crazy? In the middle of the Pacific? YES!". Hawaiian Volcano Observatory – United States Geological Survey. 22 October 2007. Retrieved 16 December 2012.

Notes to consider

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  • See Wikipedia:Reliable sources/Noticeboard/Archive 327#mantleplumes.org re: Mantleplumes.org as a reliable source
  • GIIP 117, re: evidence of explosive activity, paged 26, 34
  • Find USGS image of night view of lava flow from Hilo, 1984, by David Little (page 52)
  • Relationship with Kilauea (more) - PP 1806, page 208-214
  • Hawaii Volcano Watch: A Pictorial History, 1779-1991, Thomas L. Wright, Taeko Jane Takahashi, J.D. Griggs, University of Hawaii Press, 1992 (mostly for historical/eruptions)
  • Note to self - see PP1801, re: radial vents

Stuff

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