Report on Raoul Island (New Zealand) — 26 April-2 May 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 April-2 May 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Raoul Island (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 26 April-2 May 2006. Smithsonian Institution and US Geological Survey.
29.27°S, 177.92°W; summit elev. 516 m
All times are local (unless otherwise noted)
Hydrothermal activity at Raoul Island's Green Lake crater had declined significantly as of 28 April and the lake water level continued to fall. The Alert Level at Raoul Island was reduced from 2 to 1 (some signs of volcano unrest), on a scale of 0-5.
Geologic Background. Anvil-shaped Raoul Island is the largest and northernmost of the Kermadec Islands. During the past several thousand years volcanism has been dominated by dacitic explosive eruptions. Two Holocene calderas exist, the older of which cuts the center the island and is about 2.5 x 3.5 km wide. Denham caldera, formed during a major dacitic explosive eruption about 2200 years ago, truncated the W side of the island and is 6.5 x 4 km wide. Its long axis is parallel to the tectonic fabric of the Havre Trough that lies W of the volcanic arc. Historical eruptions during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. An unnamed submarine cone, one of several located along a fissure on the lower NNE flank, has also erupted during historical time, and satellitic vents are concentrated along two parallel NNE-trending lineaments.