The Rise, Fall, and Revival of the Moai on Rapa Nui: An Engineering Journey

When I visited Rapa Nui in 2023, I found the community to be mostly made up of the descendants of the original Rapa Nui people. The local guides are very knowledgeable and excited to teach students about ancient engineering practices like the methods used to carve and transport the Moai statues. They also share information about current efforts to preserve and protect the island’s archaeological sites.

Easter Island, also known as Rapa Nui by its indigenous people, is a small and remote island in the southeastern Pacific Ocean. Rapa Nui is famous for its gigantic stone statues called Moai. This triangular-shaped island measures only about 163 square kilometers (63 square miles). It is located over 3,700 kilometers (2,300 miles) from the coast of Chile and 2,075 kilometers (1,289 miles) from the nearest inhabited land, Pitcairn Island. It was first settled around 1200 CE by Polynesians who sailed there in canoes from other parts of Polynesia. Its first known European visitor was Dutch explorer Jacob Roggeveen. He named the island after he landed there on Easter Sunday in 1722 CE.

The geology of Rapa Nui is volcanic. Rapa Nui began to form about three million years ago after a series of volcanic eruptions from three now-extinct volcanoes: Poike, Rano Kau, and Terevaka.

The geology of Rapa Nui is volcanic. Rapa Nui began to form about three million years ago after a series of volcanic eruptions from three now-extinct volcanoes: Poike, Rano Kau, and Terevaka.

Poike

Poike is the oldest of the three main volcanoes on Rapa Nui. It started forming from the Easter Island hotspot around 3 million years ago. Located on the easternmost part of the island, it rises about 370 meters (1,214 feet) above sea level.

Rano Kau

Rano Kau is the second oldest of the three main volcanoes that formed Rapa Nui. Its volcanic activity dates back to around 2.5 million years ago. Rano Kau is located at the southwestern tip of the island and rises to an elevation of approximately 324 meters (1,063 feet) above sea level. It has a large caldera with a diameter of about 1.6 kilometers (1 mile) and a freshwater lake at its base. The ceremonial village of Orongo, where the famous Birdman cult rituals were performed, is situated on the southwestern rim of Rano Kau. These rituals involved a competition to retrieve the first sooty tern egg of the year from the nearby islet of Motu Nui.

Terevaka

Terevaka is the youngest and tallest of the three main volcanoes on Rapa Nui. The volcanic activity that formed Terevaka began around 370,000 years ago, with its last eruptions occurring between 110,000 and 220,000 years ago. Terevaka is 507 meters (1,663 feet) above sea level and occupies the central and northern parts of the island.

The volcanic activity from these three volcanoes is linked to the Easter hotspot, which is located near the junction of the Nazca and Pacific tectonic plates. This hotspot is a plume of molten rock (magma) that rose from deep within the Earth’s mantle and created the island as the tectonic plates moved over it.

Diagram of a hotspot by Warren Volles

HOTspot:

A hotspot refers to a region in the Earth's mantle where a plume of hot magma rises to the surface, causing volcanic activity. Unlike the volcanic activity at tectonic plate boundaries, such as along the Mid-Atlantic Ridge, hotspots occur in the middle of tectonic plates. This phenomenon can create volcanic islands and seamount chains as the tectonic plate moves over the stationary hotspot. Rapa Nui is situated over the Easter hotspot, which explains its formation and rugged landscape. Similarly, the Hawaiian Islands were formed by volcanic activity as the Pacific Plate moved over the Hawaiian hotspot. The study of hotspots helps scientists understand the dynamic processes within the Earth’s mantle.

The volcanic activity on Rapa Nui created the volcanic tuff that was used to create approximately 1,000 Moai statues. Recent archeological evidence suggests that the Rapa Nui people carved most of the Moai at the height of their civilization between 1400 and 1650 CE. Scientists believe that they were constructed to honor chieftains or other important ancestors. Although the Moai vary in size, most are around 4 to 10 meters (13 to 33 feet) tall and weigh about 12 to 20 tons.

Volcanic Tuff

Volcanic tuff is a relatively soft rock formed from volcanic ash that was ejected during volcanic eruptions. The ash consists of tiny rock and mineral fragments that settle, compact over time, and cement together by heat and pressure to create a lightweight rock. Tuff can vary in color and composition, depending on the materials present during the eruption. Rapa Nui’s volcanic origins provide an abundant source of tuff, which the Rapa Nui people used to create their Moai statues.

Moai statues

The giant stone statues found on Rapa Nui are called Moai. A typical Moai has a large, elongated head that is about one-third of the statue’s height. They have prominent facial features, including deep eye sockets, a long nose, and a heavy brow. Their bodies are often less detailed, with arms carved along the sides and hands resting at the hips or lower abdomen.

Most of the Moai were carved at the Rano Raraku quarry in the southeastern part of the island. This quarry had an abundant supply of a special form of volcanic tuff, called lapilli tuff, that was useful for making Moai. The Rapa Nui people used basalt stone tools called toki to carve a statue’s shape directly into the rock face. They gradually detached the statues from the bedrock using a series of deep grooves. Details on the front of the Moai, such as facial features, were often carved while the statues were still partially embedded in the rock. Once separated from the quarry rock, the Moai were slid into pits where they could be supported while standing upright. These pits enabled the carvers to add details to the backs of the statues.

Rano Raraku

Rano Raraku is a volcanic crater that was formed about 300,000 years ago. The crater has a diameter of about 700 meters (2,300 feet). It is approximately 160 meters (525 feet) tall and contains a freshwater lake at its base. Since Rano Raraku has an abundance of volcanic lapilli tuff, it served as the main quarry for the Moai statues. Over 400 unfinished Moai remain attached to the bedrock or partially buried nearby. Recently, an unfinished Moai was found in the lakebed of Rano Raraku on March 13, 2023.

Lapilli Tuff

Toki are traditional Polynesian tools used for carving and shaping wood and stone. On Rapa Nui, the term “toki” refers to the basalt or obsidian tools used by the Rapa Nui people to carve the Moai statues from volcanic tuff. Basalt tools were used to carve the Moai from the relatively softer volcanic tuff in the quarry. The hardness and strength of basalt made it an ideal material for shaping massive stone figures. Obsidian is a naturally occurring volcanic glass. Due to its sharpness, obsidian tools were used for the detailed work required to create the intricate designs on the Moai.

Toki

Other Moai were removed from the pits and transported across the island to their final place on a ceremonial platform called an ahu. Constructing an ahu involved stacking large, flat stones to create a stable base for the statues. Ahu are typically located along the coast of the island, facing inland. This positioning allowed the Moai to look over and protect the communities. Some ahu are found further inland, indicating their use in different contexts and ceremonies. Notable examples of ahu on Rapa Nui include Ahu Tongariki in the southeast, Ahu Akivi in the west, Ahu Te Pito Kura in the northeast, and Ahu Nau Nau in the north.

ahu

An ahu is a stone platform found on Rapa Nui that served as a base for the Moai statues. Many ahu are elongated and rectangular, with a raised platform where the Moai were placed. These stones were fitted together without mortar. Some ahu have additional structures, such as ramps, terraces, or small stone walls.

Ahu Tongariki

Ahu Tongariki is the largest ceremonial platform and one of the most photographed sites on Rapa Nui. Located on the southeastern coast of the island, the platform has a row of 15 massive Moai statues. The Moai vary in height, with the tallest one standing about 9 meters (30 feet). The Ko Te Riku Moai has a red pukao (topknot) and well-preserved eye sockets. Ahu Tongariki was extensively restored in the 1990s after being toppled by a tsunami in 1960.

ahu akivi

The Ahu Akivi platform is located inland on the western side of the island. It is notable for its seven Moai statues that face the ocean, unlike most other Moai, which face inland. The Moai at Ahu Akivi are thought to represent the seven explorers sent by the Polynesian king Hotu Matu’a to discover the island. These statues stand about 4.5 meters (15 feet). Ahu Akivi is also significant for its precise astronomical alignment since the statues are positioned to face the sunset during the equinoxes. Ahu Akivi was restored in the 1960s by archaeologists William Mulloy and Gonzalo Figueroa.

Ahu te pito kura

The Ahu Te Pito Kura platform is located on the northeastern coast. It is known for once holding the largest Moai ever successfully placed on a platform. The massive statue, known as Paro, is about 10 meters (33 feet) tall and weighs approximately 82 tons. Paro was toppled and now lies on the ground near the platform. Ahu Te Pito Kura is also famous for a large stone that is located nearby. This stone, called “Te Pito O Te Henua” or “The Navel of the World,” is spherical and smooth. It is believed to hold magnetic and supernatural energy known as mana. Due to its high iron content, it heats more than other stones and causes compasses to act erratically.

Ahu nau nau

The Ahu Nau Nau platform is located on the northern coast at Anakena Beach. This ahu features seven well-preserved Moai statues. Some of them have topknots (pukao) and intricate carvings. The site’s location at Anakena Beach is believed to be the landing place of the island’s first settlers led by the legendary Polynesian king Hotu Matu’a. Archaeologist Sergio Rapu restored Ahu Nau Nau in the 1970s.

Once the Moai were placed on their ahu, they were given a pukao (topknot) to make them look more impressive. According to scientists, the pukao were first carved and shaped at the Puna Pau quarry, where there was a large supply of red scoria. The pukao were transported from the quarry to the Moai sites by rolling them along paths. Their cylindrical shape made them easier to roll across the land by teams of workers using ropes. Once the pukao were transported to the Moai sites, they were moved up ramps built next to the ahu. These ramps allowed the workers to gradually elevate the heavy pukao to the height of the Moai heads. After rolling the pukao up the ramps, the workers may have used levers, ropes, and wooden frameworks to position the pukao on the heads of the Moai.

Pukao

A pukao is a cylindrical stone topknot that was placed on the heads of some of the Moai statues on Rapa Nui. It is believed that they may represent hair or headdresses worn by the Rapa Nui people. Pukao were carved in the Puna Pau quarry from red scoria, a type of volcanic rock that is lighter and more porous than the tuff used for the Moai. Pukao vary in size but are generally large and cylindrical, often with a flat base and a slightly rounded top. The largest pukao is located at Ahu Te Pito Kura. It weighs almost 12 metric tons (13 tons) and has a diameter of over two meters (6.5 feet). The pukao were placed on top of the Moai using a combination of ramps, levers, and ropes.

Puna Pau

Puna Pau is a quarry located in a volcanic crater in the southwest part of Rapa Nui. The crater is relatively small, with a diameter of approximately 150 meters (492 feet). It was formed by volcanic eruptions during the island’s second phase of volcanic activity between 200,000 and 300,000 years ago. These eruptions were due to basaltic magma, which had low viscosity and a high amount of dissolved gas. As the magma rose and reached the surface, the gases expanded rapidly, causing explosive eruptions. These explosions created the crater and shattered the magma into small fragments, which rapidly cooled and solidified into red scoria.

Red scoria

Red Scoria is a lightweight and porous volcanic rock characterized by its reddish color due to its high iron content. Formed from volcanic eruptions, red scoria has a rough and bubbly texture created by gas bubbles trapped in the rock as it cooled and solidified. On Rapa Nui, red scoria from the Puna Pau quarry was used to create the pukao, the cylindrical topknots placed on the heads of many Moai statues.

About 400 of the Moai were only partially carved and remained at the quarry where they were created. These statues were in various stages of completion, with some still partially embedded in the rock, like Te Tokanga. Others were slid into pits at the quarry site so their backs could be carved. If not moved from the quarry, these statues became partially buried in the soil over, leaving only the Moai heads visible above ground. The presence of these unfinished Moai provides valuable insights into the carving techniques and transportation processes used by the Rapa Nui people.

te tokanga

The statue Te Tokanga, also known as El Gigante, is the largest known Moai on Rapa Nui. This huge Moai is lying in the Rano Raraku quarry, still embedded in the volcanic tuff from which it was partially carved. It is approximately 21 meters (69 feet) long and is estimated to weigh 270 tons. El Gigante demonstrates the ambition of the Rapa Nui carvers and their ability to work with immense stone blocks using primitive tools.

Moai Heads

Many Moai heads are visible near the quarry sites at Rano Raraku. They are actually complete statues that are partially buried. While only the heads are visible, these Moai have bodies that extend deep into the ground. Their eyes were left unfinished, and no pukao were placed on their heads.

how were the moai transported across the island?

How these massive statues were transported up to 18 kilometers (11 miles) from the quarry without heavy machinery, large animals, or even wheels is one of the most debated subjects in the island’s history. Early theories suggested that the Moai were moved using wooden sleds and logs. According to these theories, the Moai were placed on sleds, which were then dragged over logs. The logs acted as rollers beneath the sleds to reduce friction and allow the heavy statues to be transported over the rugged terrain. This method would have required hundreds of workers and might have contributed to the deforestation of Rapa Nui since large quantities of wood from the native palm trees would have been needed for both sleds and rollers.

A more recent theory by Terry Hunt and Carl Lipo, known as “walking” the Moai, proposes that the Rapa Nui people might have used ropes to rock the statues from side to side to mimic a walking motion. According to this theory, teams of people pulled on ropes tied around the statue’s head and base, carefully coordinating the movement to tilt and rotate the Moai forward in a controlled fashion. This method required fewer trees since it primarily used human labor and ropes.

The walking method was partially demonstrated in experiments that show it is a viable way to move giant statues. In addition, the upright transport of the Moai aligns with the stories of the Rapa Nui people, who say that the statues “walked” to their locations.

Scientists demonstrate how Easter Island's statues may have been moved using a walking method
National Geographic. (2012, June 21). Scientists make Easter Island statue walk [Video].

This walking theory is based on observations that Moai in or near the quarry often have larger bellies than those positioned on the ahu platforms. This difference in design suggests that the larger bellies served a functional purpose by shifting a statue's center of gravity more forward. This design would facilitate the rocking and walking motion using ropes since the balance required to sway the Moai from side to side would be more manageable with the altered center of gravity.

Sketch of Shifting Center of Gravity While "Walking"

by Warren Volles

center of Gravity

Center of gravity is the average location of the weight distribution of an object. It refers to the point where the entire weight acts in a body or system. The center of gravity coincides with the geometric center for simple, uniform objects. However, the center of gravity might be located at a different point for irregular shapes or objects, such as Moai, with non-uniform density. Understanding the center of gravity is essential for ensuring stability and balance in structures, vehicles, and even during human activities. By analyzing the center of gravity, engineers can predict how objects will behave under different conditions, such as when subjected to forces or when tilted. One application of the center of gravity is seen in the theories about how the ancient Moai statues of Rapa Nui were transported. Some researchers suggest that the statues, which weigh several tons, were moved using a “walking” method. By tilting the statues forward, their center of gravity would shift forward. The shifting center of gravity allows workers to rock them back and forth in a controlled manner without the need for complex machinery.

Additional Insights

Unfortunately, the Rapa Nui civilization eventually declined, and many of the Moai were toppled by the mid-19th century. Historically, this decline has been attributed to overpopulation and the unsustainable use of natural resources, such as the palm trees, which led to deforestation. The toppling of the Moai was linked to fights among rival Rapa Nui tribes as resources became scarce. However, newer studies suggest that the arrival of foreigners was responsible for the decline in the Rapa Nui civilization. Europeans brought diseases to which the Rapa Nui had no immunity, leading to a drastic decrease in population. Peruvian slave traders raided the island in the 1860s further decimating the population since many islanders were either forcibly removed or killed. In addition, earthquakes may have caused the toppling of the statues since they occur frequently in that area. Furthermore, the deforestation was likely exacerbated by Polynesian rats, which ate the seeds of the palm trees, preventing regrowth after sections were cut down.

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