7. FROM THE FIELD: Ancient and contemporary stone mining on Rapa Nui

Scientific Concepts and Discoveries

• Geological Formation of Rapa Nui:
  • The island was formed through approximately 12 volcanic events over 700,000 years.
  • These events created multiple lava flows of varying thickness and viscosity, forming distinct layers ("cake layer model").
  • Key volcanic centers include Tangaroa, Puno Pao, and Vaio Hao in the northern part of the island.
  • The volcanic rocks include types such as hawaiianite and olivine basalt, common in the Pacific region.
• Contemporary and Ancient Stone Quarrying:
  • The south coast of Rapa Nui hosts both contemporary quarries and ancient mining sites.
  • Contemporary quarries supply stone for modern construction (roads, houses, foundations).
  • Ancient Rapa Nui people also mined stones in similar locations, demonstrating advanced geological knowledge.
  • Archaeological evidence shows at least 21 mining sites nearby, indicating systematic extraction of high-quality stone.
• Types of Stone and Their Uses:
  • Kehoe (fine-grained, thin stone): Ideal for making stone tools such as fish hooks, adzes, and knives due to its thin profile.
  • Chia (red mineral pigment): Rich in iron and magnesium, used for painting moai statues, body painting (tacona), and coloring artifacts.
  • Poro stones (beach-worn boulders): Used as hammer stones for reducing larger stones and as foundation stones in construction.
• Mining and Natural Processes:
  • Natural erosion by waves and wind breaks down larger boulders into smaller usable pieces.
  • Some caves, like Queho cave, have been expanded over time by both natural processes and human extraction.
  • Mining debris (debitage) accumulates around extraction sites, indicating stone tool production activities.
• Archaeological and Geological Methodology:
  • Field documentation and mapping of mining sites (21 sites documented for PhD research).
  • Use of stratigraphic observation (layers of volcanic flows) to understand island formation.
  • Comparative study of ancient and contemporary quarrying techniques and stone use.

Key Points / Methodology

• Examine volcanic layers to understand geological history.
• Identify and classify stone types by texture and composition.
• Document quarry sites and analyze spatial relationships between ancient and modern mining.
• Observe natural erosion and its role in stone availability.
• Study mining debris to infer tool production processes.
• Connect archaeological evidence with geological data to interpret prehistoric resource use.

Researchers / Sources Featured

• Dr. Dale Simpson (PhD researcher and field archaeologist/geologist on Rapa Nui)