More Volcanoes Recognised In Auckland

More Volcanoes Recognised In Auckland

Twelve months after recognising a hidden volcano beneath Grafton in Auckland City, Bruce Hayward and his colleagues from Geomarine Research have done it again. This time they have identified four more, previously unknown volcanic craters in the southern part of the Auckland Volcanic Field.

Boggust Park Crater, Favona, Mangere. Photo: Bruce W Hayward

The most prominent and interesting of the newly recognised volcanoes is Boggust Park in Favona, Mangere. This 300 m diameter crater is surrounded by a semicircular rim of volcanic ash, known as a tuff ring. "This crater was originally circular," said Dr Hayward. "It is also one of the older volcanoes in Auckland. The crater appears to have been invaded by the sea 130,000 years ago, during the last interglacial warm period when sea level was 5-6 m higher than today. At that time Boggust crater would have been an intertidal lagoon, like Panmure Basin today. The tides eroded the wide open mouth that still exists between it and the nearby estuary to the east.

Boggust Park volcano is 3 km from the next nearest volcanoes, Sturges Park in Otahuhu and Mangere Mt. It sits in the middle of a large area that was previously thought to have lacked volcanic activity.

The other three newly recognised craters are in Puhinui Reserve, Wiri. Each is about 200 m across and each sits on the crest of its own low tuff cone made of erupted volcanic ash. One crater still contains a freshwater pond, and a second has filled with pond and swamp sediment over thousands of years and is now drained and used as an equestrian arena. Each has been eroded on one side by water overflow from their small crater lakes - a process that would have taken tens of thousands of years.

Dr Hayward says that these four craters have not been recognised before because they are not major landform features like many of Auckland´s volcanoes. Until recently they were less accessible and probably not visited by earlier geologists studying the volcanoes.

"Fortunately all four craters are protected within reserves and can now be cherished and managed as part of Auckland´s rich volcanic heritage - unlike many of the volcanoes that have been quarried away or buried beneath subdivisions in this part of Auckland over the last 60 years."

Bruce Hayward is lead author of the recently published book "Volcanoes of Auckland: The essential guide" Auckland University Press, 2011.

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