Re: Why are there more volcanos in New Zealand than in Australia?

Volcanoes form where there is a thin spot in the Earth's crust, and very hot rock 
is closer to the surface than in other places.
The Earth's crust is made up of a number of large solid sections or "plates" that 
"float" on top of the mantle, which is molten rock in the form of a rather 
viscous liquid. The plates move relative to one another, and often there are hot 
spots made where their edges bump into one another, or slide past one another, or 
lap over one another. This is where volcanoes and large earthquakes tend to 
happen.

You can follow the boundary of the very large Pacific Plate from New Zealand up 
through Vanuatu, the Philippines, Japan, Kamchatka peninsula in Siberia, Aleutian 
Islands, Rocky Mountains, California, Western Mexico, Central America, Andes 
Mountains. That path is known as "the fiery ring of the Pacific", and includes 
about half of the Earth's active volcanoes and major earthquake zones. Some other 
similar zones, also associated with plate boundaries, occur in the Indonesian 
Islands, the Eastern Mediterranean and Middle East, the Caribbean, and the mid-
Atlantic ocean.

Unlike New Zealand, which is situated on and near a plate boundary, Australia is 
located on a single relatively stable plate of its own.

Not all hot spots are associated with plate boundaries. The hot spot that 
generated the Hawaiian Islands, and still feeds the active volcano there is the 
prime example.

There is lots of useful information about volcanoes at Volcano World.

You might be surprised to know that in the Southern part of Australia, there are 
lots of volcanoes. In the Western part of Victoria and South-Eastern corner of 
South Australia volcanoes were active in very recent times, geologically 
speaking. There have been numerous eruptions in the last 20000 years, with the 
most recent only about 5000 years ago. Volcanic eruptions are certainly part of 
the oral tradition of the aboriginal peoples of this region.

But unlike in New Zealand, there is no current volcanic activity of any kind in 
mainland Australia/Tasmania. We do not even have steam vents or hot springs.