Scientists say the build-up to an eruption from Auckland's volcanos would be more accelerated than those for volcanos elsewhere.
GNS Science and Auckland University are conducting a seven-year study into the risk the volcanos pose.
GNS Science vulcanologist Gill Jolly says it appears magma rises quickly after forming 80 to 100 kilometres underground.
She says it then comes to the surface very rapidly and in one event.
That is different to volcanos such as Ruapehu where the magma pools below the surface before an eruption.
Dr Jolly says once there are signs of seismic activity, an Auckland volcano could erupt in days or weeks.
She says the finding was made after looking at the mineral structure of pieces of lava and working out where it formed.