A volcano is an opening (or vent) in the surface of the earth or sea floor from which very hot melted rock (called magma) emerges.
Mt Ruapehu is one of the New Zealand's most active volcanoes
The magma material is ejected in explosive bursts of gas and debris (tephra), as flowing fountains of lava spray and froth, and as rivers of molten rock. This volcanic debris piles up or spreads out to produce many different kinds of volcanic rocks and landforms.
Many of New Zealands striking landscape features have been shaped over several million years by volcanic activity, including iconic landmarks such as Lake Taupo, Rangitoto Island and Mt Ruapehu.
The North Island is home to all of New Zealands active volcanoes today: the Auckland Volcanic Field, White Island, Ruapehu, Tongariro (Ngauruhoe), Taranaki, Taupo and Okataina (Tarawera).
The beautiful and awe inspiring cones of Ngauruhoe and Taranaki are striking examples of New Zealands volcanic nature whereas the South Islands volcanic heritage belongs to a more distant past but is still evident today at sites such as the Takitimu Mountains, Mount Tapuaenuku, Mount Somers, Oamaru, Otago Peninsula, Banks Peninsula, Timaru and Solander Island.
Tarawera and Tangiwai are names that live in the collective memory of New Zealanders as devastating examples of the threat posed to us by living in close proximity to our volcanoes. The numerous hazards that may result from a volcanic eruption depend upon which of our volcanoes is erupting and also the nature of the eruption itself. An eruption from Mt Ruapehu through the crater-lake will be different from Ngauruhoe where there is no lake. Other volcanic hazards include ash (pyroclastic falls), ballistic fall (lapilli and lava bombs), pyroclastic flows and surges, lava extrusions (flows and domes), lahars, volcanic gases, volcanic earthquakes and atmospheric effects.
Volcanic forces remain a very real threat to New Zealanders today and understanding more about how possible eruptions may impact upon us, what precautions we can take to help protect our homes and families is of vital importance if we are to live safely alongside our beautiful but potentially catastrophic volcanoes.
Dr Hamish Cambpbell talks about New Zealand's volcanoes.
Dr Jan Lindsay Audio Clip (2:10) The 3 main types of volcanoes found in New Zealand
Types of Volcanoes
The most important factor in determining the shape of the volcano is the composition of the magma.