Maui Nui
Maui Nui ( Hawaiian Great Maui ) was an island that comprised the land mass of the present-day Hawaiian islands of Maui , Molokaʻi , Lānaʻi , Kahoʻolawe and Penguin Bank . The island was formed about two million years ago from the activity of seven shield volcanoes that contributed to the formation of the massif. The volcanoes now all form their own islands, with the exception of the Penguin Bank, which formerly sank by over 1600 m from 500 m above sea level and is now a coral reef below sea level.
history
Geological foundations
The great Hawaiian Islands are the southeasternmost section of the Hawaii-Emperor Ridge , a chain of oceanic shield volcanoes formed by a hot spot across which the Pacific Plate moved to the northwest. The heating of the lithosphere above the hot spot raises it and the partial melting of the lithospheric material forms magmas that penetrate to the sea floor, where it emerges as lava and cools. This causes the volcano to grow in height, eventually reaching the surface of the sea and becoming an island. If the resulting island wanders further due to the plate movement and thereby moves away from the hot spot, volcanic activity subsides, the island's growth stops and the cooling lithosphere, additionally laden with the weight of the volcano, sinks back into the mantle . In addition, since the island is no longer growing, it is being eroded by weathering and erosion .
Development and decline
In the case of Maui Nui, seven volcanoes were responsible for the formation of the island: Penguin Bank , West Molokaʻi , East Molokaʻi , Lānaʻi, West Maui , Haleakalā and Kahoʻolawe. The age of the volcanoes steadily decreases from northwest to southeast and is between 2.2 (Penguin Bank) and 1.2 million years (Kahoʻolawe and Haleakalā). The Penguin Bank Volcano was originally connected to the island of Oahu northwest of Molokaʻi until about 1.9 million years ago , the same is probably also true for West Molokaʻi. This "Oahu Nui" predecessor island of Maui Nui reached a maximum extent of around 7000 km².
About 1.8 million years ago the connection to Oahu was finally interrupted, at the same time East Molokaʻi had completely completed its growth, which means that for the first time one can speak of an island of its own, Maui Nui. West Maui and Lānaʻi were in an early phase of shield formation at this time, East Molokaʻi had lost part of its area due to a landslide , but the area of Maui Nui was already about 5,000 km² at that time, East Molokaʻi was the highest elevation with 3,000 m. While Lānaʻi, West Maui, Haleakalā and Kahoʻolawe continued to grow, the older northwestern volcanoes sank again. With the end of the growth of Haleakalā 1.2 million years ago, Maui Nui reached its greatest extent, around 14,000 km²; about one and a half times the size of the island of Hawaii today.
As a result, the area of the island decreased significantly, at the same time the islands separated from each other. However, the size was subject to strong fluctuations caused by the growth and melting of the global glacier mass. The connection between Penguin Bank and the rest of the island was broken for the first time a million years ago; the area between East Molokaʻi and West Maui was flooded around 700,000 years ago, but they remained connected via Lānaʻi. 600,000 years ago the connection between East Molokaʻi and Lānaʻi broke, but at times re-emerged; the same thing happened 200,000 years later with West Maui. The isthmus between the eastern and western parts of Maui, however, was apparently never interrupted because it is too high above sea level and only sinks slowly. However, at 70 m, it is now lower than ever before. The Haleakalā-Kahoʻolawe saddle disappeared around 200,000 years ago. While it may reappear 150,000 years ago, it had sunk too low during the last glacial high about 20,000 years ago. At that time, the total area of the islands was around 5,900 km², about twice the area today. Over the past 1.2 million years, the four islands of Maui Nuis were connected for 75% of the time.
Topography, ecology and climate
Maui Nui differed topographically from today's Hawaii through great heterogeneity: 77% of the area was below 1000 m, which resulted in strong contrasts to the few altitudes between 2000 and 3700 m. This probably resulted in a different climate than in Hawaii: The large proportion of lowland resulted in higher temperatures, rainforest could only develop irregularly due to the less pronounced slopes towards the coast, as the rain did not follow a specific pattern. Nevertheless, Maui Nui should have had the necessary size to cause incline rain .
Maui Nui's development played an important role in the biogeography of the Hawaiian Islands. Initially, the land bridges to Oahu enabled plants and flightless birds to spread to Penguin Bank and West Molokaʻi. From there they spread to all of Maui Nui, only to be isolated again on the individual islands and to form new species. The genus Tetramolopium from the Asteraceae family alone formed eleven species on Maui Nui, while the extinct Maui Nui ibises ( Apteribis ) lost their ability to fly here. Maui Nui was also closer to the other Hawaiian islands than it is today; 500,000 years ago the distance to Hawaii was only 15 km (50 km today); a fact that also made it possible to colonize Hawaii. Maui Nui thus played a key role in the high biodiversity on the surrounding islands. At the same time, the formerly connected islands also show a higher biodiversity than the rest of the archipelago.
research
The thesis of a coherent large land mass at the location of today's islands was first postulated in 1942 by Harold Stearns and Gordon MacDonald , but they could not make any statements about the age or duration of this formation. This hypothesis could only be proven from the 1970s, when bathymetric studies showed an undersea massif around Maui. After it had been established that parts of this massif had sunk by up to 2000 m in the past, the thesis was formulated in the mid-1990s that Maui Nui was only connected to Oʻahu before it reached an area of over 10,000 km² as an independent island and finally disintegrated into individual islands due to rising sea levels and the subsidence of the volcanoes. This was finally confirmed in 2004 by paleoclimatic and geological analyzes.
swell
literature
- Jonathan Paul Price & Deborah Elliott-Fisk: Topographic History of the Maui Nui Complex, Hawaiʻi, and Its Implications for Biogeography. In: Pacific Science 58 (1), January 2004. pp. 27-45. (Online as PDF )
- Alan C. Ziegler: Hawaiian Natural History, Ecology, and Evolution. University of Hawaii Press, Honolulu 2002. ISBN 0824821904 .
Web links
Individual evidence
- ^ A b c Jonathan Paul Price & Deborah Elliott-Fisk: Topographic History of the Maui Nui Complex, Hawaiʻi, and Its Implications for Biogeography. In: Pacific Science 58 (1), January 2004. pp. 37-39.
- ^ Price & Elliot Fisk 2004, p. 40.
- ↑ Price & Elliot-Fisk 2004, pp. 41-43.
- ^ Alan C. Ziegler: Hawaiian Natural History, Ecology, and Evolution. University of Hawaii Press, Honolulu 2002. ISBN 0824821904 , p. 254.
- ↑ Price & Elliot-Fisk 2004, p. 28.
Coordinates: 21 ° 8 ′ N , 157 ° 13 ′ W