The Auckland Volcanic Field is a basaltic volcanic field containing many small eruption cones and craters.
Researchers call this a distributed volcanic field. In volcanic fields, small eruptions occur over a wide geographic area and are spaced over long periods of time (i.e. thousands of years). Each eruption builds a single new volcano, which typically only erupt once. However, those eruptions can last from days to years.
In Auckland, this happens because the field sits above a part of the mantle, deep under the surface, where the rocks are slightly more molten and which sometimes releases a batch of magma that may rise and erupt anywhere within the field at any time.
Because the Auckland Volcanic Field sits above this zone of partial melting in the mantle, the magma in each of its 53 volcanic eruptions comes from the same region in the mantle deep within the Earth. This is true from Pupuke Moana / Lake Pupuke and Rangitoto Island in the north to Matukutururu / Wiri Mountain in the south, and from Te Ahi-kā-a-Rakataura / Ōwairaka / Mt Albert in the west to Ōhuiarangi / Pigeon Mountain in the east.
This animation shows how the Auckland Volcanic Field evolved over time, including its boundaries.
At only 190,000 years old, the Auckland Volcanic Field is young for a distributed volcanic field. In fact, it is the youngest and only active part of a chain of now extinct distributed volcanic fields stretching from Port Waikato (Okete, Ngatutura), through to South Auckland. The next youngest field, South Auckland Volcanic Field, erupted around 82 times over about a million-year timespan, from ~500,000 to 1.6 million years ago. There are also two older, unrelated distributed volcanic fields in Northland that are still potentially active.
Resources
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More about this topic
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Our geology
Explaining the geological history of the Auckland Volcanic Field
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Volcanic landforms and eruption deposits
Why Tāmaki Makaurau’s landscape looks the way it does
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Frequency of eruptions
The chance of a future eruption is roughly 10% over the next 50 years, based on a gap of about 500 years between eruptions over the last 60,000 years.
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Human geography
The impact of humans on Tāmaki Makaurau Auckland
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Hochstetter's map
The 1859 map of the Auckland isthmus and its volcanoes, and who really drew it