Volcanic Avalanche Investigated in New Zealand

When a volcano erupts, the lava itself is not the only hazard you have to worry about. Depending on the size and type of volcano, avalanches resulting from the eruption might actually prove a more immediate danger than the eruption itself.

Researchers in New Zealand are now studying the devastation of volcanic debris avalanches, paying special attention to the results of an eruption that occurred on the Taranaki peninsula about 25,000 years ago.

According to a study published in the Geological Society of America (GSA) Bulletin, the eruption on the Taranaki peninsula was the largest and most catastrophic "slope failure" ever known, where the sides of a particularly steep Stratovolcano collapsed violently.

Known as the Pungarehu debris avalanche deposit (DAD), the initial collapse resulted in some highly irregular topography - a dismantled puzzle that researchers are only now putting back together.

A close examination of geological grain size, sedimentary structures and microscopic particle attributes of the ancient avalanche has already revealed part of the story.

Twenty-five thousand years ago, the massive Stratovolcano known as the "proto-Taranaki volcano" experienced volcanic activity so violent that it collapsed.

Even as fiery debris flew through the scorched and sooty air, an avalanche of solid rock rumbled towards the edges of the Taranaki peninsula, crashing through snow, ice-cover and substantial pools of groundwater that spotted the region.

Collapsing and sliding large blocks that once made up the face of the mountain, called "megaclasts," fractured into smaller pieces under the forces of their tumbling fall, leaving large and jagged "jigsaw pieces" that would remain for centuries to come. Water and drainage systems in the region were also dramatically altered by this cataclysmic event.

According to the authors of this study, mapping out exactly what happened during such a volcanic avalanche will help them better understand the formation of irregular topography across the globe, as well as better predict the long-term impacts of some erruptions and their hazards in the future.

The study was published in the GSA Bulletin on June 30.

Additonal information from the GSA.