A volcanic foundation
Maungakiekie / One Tree Hill is a complex scoria cone that rises 182 meters (597 feet) above sea level. It is a member of the Auckland Volcanic Field, a collection of approximately 53 volcanoes. The volcano erupted around 67,000 years ago, creating three distinct craters and extensive lava flows. Two of the craters were breached, releasing basaltic lava that covered 20 square kilometers (7.7 sq mi), making it the second-largest lava flow in the Auckland field by area.
The eruptions here were explosive, fountaining scoria, a type of volcanic rock full of gas bubbles, to build the central cone. This was followed by the effusion of fluid basaltic lava that flowed across the surrounding landscape. Geologically, the volcano is capped with up to three meters of ash from the more recent eruption of Te Tātua-a-Riukiuta / Big King, which occurred over 28,500 years ago. This layering of volcanic material created a landform with steep, defensible slopes and highly fertile soil, a combination that proved ideal for human settlement.
Engineering an earthwork fortress
The geological features of Maungakiekie made it one of the most extensively developed pre-European fortified settlements (pā) in New Zealand. At its peak, the pā housed as many as 5,000 people. The inhabitants engineered the volcanic slopes into a massive fortress, constructing terraces, ditches, and banks. These terraces, known as whare moe, provided flat areas for sleeping houses. The steep scoria cone slopes offered a natural defense, which was augmented with heavy wooden palisades.
Archaeological evidence shows a complex settlement. The fertile volcanic soil was used for extensive gardens, particularly for cultivating kūmara (sweet potato). Food was stored in hundreds of rua, which are roofed storage pits dug into the earth. The entire complex was a feat of landscape engineering, with radiating stone walls defining over 1,000 hectares of fields. Archaeological finds on the mountain include stone adzes (toki) and implements for grinding red ochre (papa-kokowai), revealing details about the daily life and technology of the people who lived there. The pā was a major political and economic center for the Waiohua confederation of tribes during the 17th and 18th centuries.