Rediscovery of the 8th Natural Wonder of the World: The Pink and White Terraces' survival of the 1886 Tarawera Rift eruption
Abstract
On June 10, 1886, Mt. Tarawera in the rhyolitic Okataina Volcanic Centre of the central North Island, New Zealand, erupted in spectacular fashion. Basaltic eruptions at Tarawera produced tall eruption columns, while hydrothermal and phreatomagmatic eruptions at Rotomahana excavated the pre-1886 Lake Rotomahana site, which later filled to form a new lake up to 125 m deep and ~5 x larger than its predecessor. The Pink and White Terraces, which were the world's largest silica aprons and buttresses, had formed as a result of discharging thermal waters and deposition of silica on the margins of the pre-1886 lake, and were believed destroyed during the 1886 eruption. The post-eruption landscape was scarred by eruption craters with the largest marking the foci of the phreatomagmatic eruption, which blanketed the area with 10s of m of mud. A combined ~250 line km survey of Lake Rotomahana was conducted using two REMUS 100 AUVs simultaneously mapping with multibeam and sidescan sonar. Also fitted were a magnetometer, minature plume recorders (LSS, Eh, temperature, depth) and pH sensors. Surface vessels conducted magnetic surveys (110 line km), CO2 flux measurements (420 sites), deployed a CTD and Niksin bottles for water properties and sampling (14 stations), and a camera over sites (12) of known venting and/or where the sidescan showed evidence for the terraces. New bathymetric data clearly shows the en-echelon rift of 1886 in the center of the lake and identifies some pre-1886 shoreline. When combined with sidescan sonar images, several of the basal layers of the Pink Terraces were found very near their original, pre-eruption locations. Underwater photographs reveal buttresses of several tiers. Magnetic data show a pronounced positive anomaly in the southern part of the lake, associated with older lavas, and a distinct negative anomaly associated with the Pink Terraces, marking the boundaries of the pre-1886 geothermal field. Bubble plumes recorded during the magnetic survey and also seen on sidescan sonar images show modern hydrothermal activity occurs within the Pink Terraces area, to a lesser degree the White Terraces area, and in two new (post-1886) locations, namely; along the southern boundary of the newly formed rift and an area further eastwards. CTD casts and water column measurements made by the AUVs confirm these areas as primary discharge zones, establishing continuation of hydrothermal activity in the Terraces area and corroborating the existence of a new geothermal system in the southern part of the lake. Maximum helium concentrations show the main discharge source is at a depth of ~40 m and when combined with CO2 flux for the lake, suggests degassing of a sub-lake floor magmatic system.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP51B0839D
- Keywords:
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- 3080 MARINE GEOLOGY AND GEOPHYSICS / Submergence instruments: ROV;
- AUV;
- submersibles