Have a lava-hot, burning question about Auckland volcanoes? Comment below or send a note to me at the email address on my profile page (see ‘Contact Details’ on right sidebar).
Q. What is a volcanic field?
A. A volcanic field is just an area with a lot of volcanoes. In a monogenetic volcanic field, it is thought that the amount of magma created in the mantle underneath these fields is too small to keep one route to the surface open, hot, and flexible. So, each individual batch of magma has to find a new way to the surface, and erupts in a different location every time. This means that instead of building up one LARGE volcano, like at Ruapehu or White Island, you get many small volcanoes that erupt once and then never again. Between eruptions, the field remains dormant while the individual volcanoes within it are extinct.
The next eruption in Auckland is therefore likely to be in a new place in the field, rather than at an existing volcano. The one exception could be Rangitoto–researchers are studying this volcano thoroughly to figure out why.
Q. Is Auckland an active volcano?
A. The Auckland Volcanic Field is considered dormant, while the individual volcanoes within it are considered extinct.
Q. Is Auckland a supervolcano?
A. No. Our volcanoes and eruptions are some of the tiniest in the entire world, while supervolcanoes are the largest. As an example, compare the size of Panmure Basin, a volcanic explosion crater, to Lake Taupo, which formed in the caldera created by supervolcano eruptions: Panmure Basin is just 1 kilometer across, while Lake Taupo is 46 kilometers across. We aren’t even close.
Q: How many volcanoes are in the Auckland Volcanic Field?
A: Tricky question. At least 50, and as many as 55. I can name 53.
Q. Why is the number of volcanoes in Auckland a tricky question?
A. Because it depends on what you consider a volcano and how you count them. Read more here.
Q. Are the individual eruptions in Auckland moving in a certain direction with time?
A. No. We do not see any definitive patterns in eruption location with time within Auckland. Interestingly, however, there is a chain of volcanic fields spanning the region from Raglan to Auckland, and the location of these volcanic fields seems to move north with time, seemingly unrelated to the movement of the Australian tectonic plate on which we are located (which is also moving north with time). The next-youngest volcanic field, called the South Auckland Volcanic Field, stopped erupting about 500,000 years ago. After a brief 300,000 year break, the eruptions then shifted from South Auckland to Auckland proper. Again, we’re not sure why, but investigations into the tectonic setting and mantle geochemistry underneath Auckland are ongoing to shed more light on these possible influences.
Q: How old is the Auckland Volcanic Field?
A: Our latest results date the earliest eruption at Pupuke to about 200,000 years ago. We are not sure what happened to kick off magmatism in Auckland as a whole, though.
Q. When was the last eruption in Auckland?
A: Rangitoto Volcano was the last to erupt, about 600 years ago. For more about Rangitoto, see here.
Q. Will there be another eruption in Auckland?
A: All our information says yes, there will be another eruption. We have no reason to think that the field is extinct–the last eruption was only 600 years ago, which is very short in geologic time! Also, there is a low-velocity seismic zone at a depth of about 80 km under Auckland–we think this correlates to a zone where rock is partially molten. This molten rock would create and feed our next volcano if it rose to the surface.
Q: When is the next eruption in Auckland?
A: It could as easily be next month as in 1,000 years. We don’t have the capability of forecasting eruptions in Auckland, and are unlikely to ever be able to do that with any certainty. Scientists need indications of volcanic unrest (gas emissions, earthquakes from rising magma, changes in the shape of the land) before we can start to figure that out.
Q. Where will the next volcano in Auckland erupt?
A. We do not know and cannot forecast this. We have studied the timing and location of past eruptions, and there are no patterns that we can identify with certainty. Our best guess is that the next eruption will occur somewhere within the current boundaries of the volcanic field, which forms a rough ellipse around all of the volcanoes. The entire city of Auckland is within that ellipse.
Q: What kind of warning will we get before future eruptions?
A: The first signs of an eruption will probably be earthquakes as the magma breaks up the Earth’s crust on its way to the surface. We could also see ground swelling or deformation and gas emissions, all of which are monitored in the AVF.
Q. How long will we have after we feel the first earthquakes from rising magma in Auckland?
A. I am working on this problem as a part of my PhD! Current warning time estimates vary from a half-day to 40 days, but from all of our evidence, magma is likely to ascend very quickly. This is why it is really important to always be prepared! Check out Civil Defence for tips.
Elaine R. Smid 