Report on Ruapehu (New Zealand) — July 1994
Bulletin of the Global Volcanism Network, vol. 19, no. 7 (July 1994)
Managing Editor: Richard Wunderman.
Ruapehu (New Zealand) Relatively stable with water cooling of Crater Lake
Please cite this report as:
Global Volcanism Program, 1994. Report on Ruapehu (New Zealand). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 19:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199407-241100.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
When visited on 8 June, Crater Lake appeared a very pale, almost yellowish, gray. On 4 July, as was more typical for the recent past, the crater lake was a uniform battleship-gray with no evidence of convection or slicks. Temperature at Outlet, 22°C, was slightly higher than for June-July in past years. The lake is currently cooling following a minor heating event in early June that followed strong acoustic signals, minor earthquakes, and volcanic tremor 10-15 days earlier. These two recent visits revealed no evidence of eruptive activity.
On 4 July, unusually thick accumulations of snow prevented deformation surveys and emphasized the need to install tiltmeters in key locations to improve the continuity of monitoring. Snow and ice were removed from the ARGOS satellite installation, but the solar panel could not be located under deep snow and battery and transmission power steadily declined.
A working party coordinated by the Ministry of Civil Defence has considered developing a contingency plan for volcanic hazards. They also may adopt a system using "Volcanic Alert Levels" graded from 1 (low level) to 5 (highest level, hazardous eruption in progress).
Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.
Information Contacts: P. Otway, B. Scott, and A. Hurst, IGNS Wairakei.