Easter Island: Origin, Volcanoes, And Climate Change
Rapa Nui, otherwise known as Easter Island, is a small, remote landmass off the west coast of Chile in South America in the southeastern Pacific Ocean. Along with other small neighboring islands, it lies on top of Nazca oceanic plate, coming in contact with the South American plate in a subduction zone.
Easter Island is situated in the Sala y Gomez Ridge, a high topographic region measuring 2,900 km, trending eastward from the East Pacific Rise. The island sits on top of a series of underwater volcanoes called the Easter Seamount Chain, stretching 2,500 km. The chain’s formation is the result of the relative plate movement of the Nazca and Pacific plates traveling at a rate of 150 mm per year (seafloor spreading). In contrast to the Hawaiian hotspot track, where islands get older as they drift further away from the hotspot, there is an unclear age progression of the islands on the Easter Seamount Chain, with newly formed volcanoes spawning over distances longer than the overall span of the chain itself.
The explanation for the island’s triangular shape is associated with the three inactive neighboring shield volcanoes: Terevaka, Poike, and Rano Kau. Each one is made up of tuff, a rock compiled from volcanic fragments, as well as tholeiitic and alkali basaltic rocks. While the Poike and Rano Kau formed during the Pleistocene era, Terevaka formed in the Pliocene era, making it the youngest of the three.
The oldest volcano among the group, Poike (0.78-0.41 Ma) is found on the eastern end of the island, emerging from the ocean floor about 3 million years ago and spanning a height of 370 m. Poike was its own separate peninsula before unifying with Easter Island, as lava flows from the Terevaka and Rano volcanoes pushed them together.
Forming after Poike, Rano Kau (0.78-0.46 Ma) spans a height of 324 m and reaches about 300 m above sea level. It possesses a circular-shaped crater (caldera) filled with fresh water, one of three main sources found on the island. Its formation is the result of numerous basaltic lava flows. The acidity of the lava from those eruptions led way to the formation of secondary cones, whose eroded lava fields would leave behind mineral deposits of obsidian and trachyte.
Spanning a height of 511 m, Terevaka (77 Ma) is found on the northern end of the island. In contrast to the previous two volcanoes, this one does not have a main crater, for its formation is the result of eruptions from a series of small volcanic centers chiefly oriented north-south. By 0.24 Ma, new eruptive fissures from the southern and southeastern flanks released flows of basalt, alkali basalt, hawaiite, mugearite, and benmoreite. The eruptions from the Terevaka volcano allowed for the formation of the island’s main body, merging the other two volcanoes and giving rise to the island’s shape recognized today.
Another important volcanic crater is the Rano Raraku tuff cone (0.21 Ma), the source of over 1,000 Moai statues populating the land mass. The ash’s light weight and durability “not only enabled the artisans to carve the enormous statues, but also made it more practical to transport them across the island.” Red volcanic rock called scoria, acquired from the Puna Pau quarry, was used for the hats (pukao) adorning the heads. One argument holds that the reason production on the statues seized in the 17th century was due to the deforestation degrading the soil and stimulating ecological turmoil. Other arguments suggest overexploitation of forests, invasive species, overpopulation, and natural climate change via fluctuating temperatures impacted resource depletion.
There is no doubt that Easter Island is falling victim to the effects of climate change, as studies show that the water temperature is getting colder, “suggesting that unlike other parts of the planet, this part of the Pacific Ocean will cool at a rate close to 0.15 degree Celsius (0.27 degree F) per decade.” Additionally, little rainfall in 2017 set a record for the driest year, resulting in the depletion of the water level in the Raraku lagoon. Floating plastic waste from the “South Pacific Gyre” trash heap continues to threaten the biodiversity of turtles, fish, and bird species sacred to Easter Island’s culture, such as the Manutara bird and the nanue “rudderfish.” To reduce the amount of human activity contributing to environmental pollution, Easter Island looks toward promoting sustainability tourism groups to collaborate on seeking effective solutions to preserve the rich local environment and tourist attractions.
