FQ 2. What are the processes that produce a volcanic eruption?

Mt Tarawera Eruption 1886

Step 1:
Convection currents move magma around under the Pacific and Indo-Australian Plates.

Step 2:
The Pacific Plate subducts under the Indo-Australian Plate.

Step 3:
- Magma rises through weaknesses in the Indo-Australian Plate in the North Island.
- On the 10th June 1886, shortly after midnight, earthquakes are felt in Te Wairoa and Rotorua.
- Around 1.30am there is a violent earthquake followed by the sound of an explosion.

Step 4:
Pressure builds up in the magma chamber when sulphur dioxide and chlorine combine with steam.

Step 5:
- Mt Tarawera’s Wahanga dome exploded.
- At 2am there was a second explosion as the Ruawahia Peak and then finally the Tarawera Peak erupted.
- The contents of the crater lake blew out and the contents of the lake and terraces spread ash and mud over the surrounding landscape. It was estimated that 2 billion cubic yards of ash were scattered over an area of more than 6000 square miles.


Mt Ruapehu Eruption 1995

Step 1:
Convection currents move magma around under the Pacific and Indo-Australian Plates.

Step 2:
The Pacific Plate subducts under the Indo-Australian Plate.

Step 3:
- Magma rises through weaknesses in the Indo-Australian Plate in the North Island.
- On the 10th June 1886, shortly after midnight, earthquakes are felt in Te Wairoa and Rotorua.
- Around 1.30am there is a violent earthquake followed by the sound of an explosion.

Step 4:
Pressure builds up in the magma chamber when sulphur dioxide and chlorine combine with steam.

Step 5:
- Mt Tarawera’s Wahanga dome exploded.
- At 2am there was a second explosion as the Ruawahia Peak and then finally the Tarawera Peak erupted.
- The contents of the crater lake blew out and the contents of the lake and terraces spread ash and mud over the surrounding landscape. It was estimated that 2 billion cubic yards of ash were scattered over an area of more than 6000 square miles.



See Mrs O'Hagan for diagrams.