Kōrero: Volcanoes

Most large cone volcanoes have a complex history of cone-building followed by collapse. The mounds in front of Mt Taranaki (Mt Egmont) are the remains of a huge landslide that occurred about 23,000 years ago when a large volcanic cone collapsed and spread debris over a huge area. The present cone built up after this avalanche. The older Pouākai volcano is at left.

Vince Neall of Massey University has studied the volcanic history of Taranaki for many years, and in the sound clip he describes the process of collapse.

Transcript

When you see these large rounded mounds in the western Taranaki landscape, it's really unbelievable at first to appreciate that these have originated from enormous large scale volcanic debris avalanches. Sometimes many cubic kilometres in volume that have originated from large andesite stratovolcanoes which periodically collapse. This is due to large failure planes that occur in andesite volcanic edifices and due to eruptions or earthquakes, the edifices destabilised and just collapses and the material flows out across the surrounding landscape, leaving these mounds behind rather like sometimes when you spill some vegetable soup on the table and you're left with the peas and carrots that represent the portions of lava flows that were in the original volcano.