First, the good news: the odds are that a volcanic eruption wont occur in Auckland during your lifetime.
Look at the maths: there have been 48 eruptions over almost 250,000 years one every 5,000 years on average. But, we dont yet know when many of these occurred. Current research aims to show whether eruptions have clustered in time and trend to more or less frequent activity.
An eruption may or may not happen soon, but it will almost certainly happen. Its not a case of if, but when.
There is no way of knowing when it will happen.
The last eruption (Rangitoto) was by far the biggest.
If all that is not enough, consider this: Aucklands volcanoes are powered by runny basaltic magma, which rises through the crust quickly, at several kilometres per hour. So when the next eruption happens, whether its tomorrow or in 5000 years time, we wont get much warning.
Its not just our local volcanic field we have to worry about. Auckland could be affected by a volcano erupting outside the city, such as Taranaki or Ruapehu, just as easily as a local eruption. The chance of ash from one of these volcanoes coating Auckland in the next 50 years is between 15 and 60 percent.
Herne Bay Seismogram Drum
You read a seismogram like you are reading these words; the earliest time is at the top left and then goes along the line to the end and then starts at the left of the next line. The top-left is therefore the oldest data and the bottom-right the most recent. All the seismograms shown here cover a 24-hour period.
Just in case youre panicking, lets end with some more good news: scientists carefully monitor all of New Zealands volcanic activity, and the Auckland Regional Council has detailed contingency plans for any volcanic disaster.
Brad Scott discusses volcanic surveillance in New Zealand
Click for an overview of current volcanic activity in New Zealand.
Brad Scott Audio Clip (1:43) Brad explains the activity that shows on the seismogram.