The largest island of French Polynesia, Tahiti, is filled with many spectacular features. Once you look past the crystal clear waters and lush rain forests, you can see the beauty of the geography.
Tahiti Nui (on the right) and Tahiti Iti (on the left)
Image borrowed from: http://www.welt-atlas.de/map_of_tahiti_3-190
Tahiti is comprised of two shield volcanos, Tahiti Nui and Tahiti Iti. They were both created by the same hot spot, magma rising from the mantle, under the Pacific plate. They are no longer active because the Pacific plate has moved west. Tahiti Nui is by far the most fascinating of the two shield volcanoes. The topography of the island is quite steep and does not show the gradual ascent for a normal shield volcano. The steepness is attributed to the many years of erosion from intense rainfall.
Summit of Mount Orohena
Image borrowed from: http://travel.webshots.com/photo/1042692240012119764WpzSMl
The highest point is Mount Orohena (7,353 feet) which was the center of volcanic activity on the island. Common for shield volcanos, there was also lava flow in other places on the island. Dikes, magma flowing through vertical fissures, aided in carrying lava out from the center of the volcano. The erosion of the island lets us observe the dikes protruding the landscape. These intrusive volcanic land forms can be easily recognized by their steep linear structure.
Example of Dike on Tahiti Nui
Image borrowed from: http://photos.igougo.com/pictures-photos-p370657-Tahitian_Mountains.html
In the northeastern section of Tahiti Nui you can see lava tubes. These lava tubes are the remnants of lava that cooled on the outer edges while liquid lava still flowed through the inside. The tubes are now a great location for tourist explorations.
Lava Tube
Image borrowed from: http://www.cerclesmarinetoulon.com/outremer/index.php?option=com_content&view=article&id=20:tahiti-club-decouverte-sorties-&catid=1
Around the periphery of the island there are pahoehoe accumulations, smooth "ropey" basalt lava flows, that merge with the black sandy beaches. The black sand comes from the break down of volcanic rock and gets its color from the mafic composition of the basalt lava. Basalt lava is dark in color because of magnesium and iron in the rock.
Black Sand Beach on Tahiti Nui
Image borrowed from: http://www.flickr.com/photos/kalevkevad/3336817775/
References:
Hildenbrand, A., Gillot, P., & Le Roy, I. (2004). Volcano-tectonic and geochemical evolution of an oceanic intra-plate volcano: Tahiti nui (french polynesia). Earth and Planetary Science Letters,217(3-4), 349-365. Retrieved from http://0-www.sciencedirect.com.skyline.ucdenver.edu/science/article/pii/ S0012821X03005995
Allen, C. (n.d.). Geog 1202: Introduction to physical geography. Retrieved from http://clasfaculty.ucdenver.edu/callen/1202/
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