"Using basalt stone picks, the Easter Island Moai were carved from the solidified volcanic ash of Rano Raraku volcano. They are all monolithic, the carvings are created in one piece [with] an average weight of 20 tons and measuring 20 feet tall or more." Source: "Sentinels in Stone: The Rise and Fall of Easter Island," Bradshaw Foundation.
How were these gigantic statues moved into position? Various methods have been suggested, including the ingenious "walking heads" theory, but it seems more likely that the Rapa Nui simply dragged the heads down from the quarry, breaking some of them in the process. That's just an assumption, though. Ancient peoples all over the world were adept at moving extremely heavy blocks of stone, but however it was done on Easter Island, it must have been a difficult job.
When asked how the moai were moved into postion, the Easter Islanders themselves say that the statues "walked," according to this 2012 National Geographic story. "In the Rapanui oral tradition, the moai were animated by mana [see 2nd sense of the word], a spiritual force transmitted by powerful ancestors."
"In Polynesian culture, mana is a spiritual quality considered to have supernatural origin—a sacred impersonal force existing in the universe. Therefore to have mana is to have influence and authority, and efficacy—the power to perform in a given situation. This essential quality of mana is not limited to persons—peoples, governments, places and inanimate objects can possess mana." Source: Wikipedia.
Related News: Easter Island is currently having some serious problems. According to the BBC (April 2014), these include "dengue fever, the lack of a decent hospital, a steady accumulation of garbage, over-fishing, the arrival of thousands of tourists each year and damage to the moai, the giant stone statues that have made the island famous across the world." The statues are being damaged both by environmental conditions and by tourists, which isn't surprising since Rapa Nui National Park is basically a wildlife area and an open-air archaeological museum.