Further Eruptions May Occur at Raoul Island

Following last Friday’s eruption at Raoul volcano, GNS Science has issued a bulletin based on an aerial inspection from an RNZAF Orion on March 21st.

It states that Green Lake has risen by 6 to 8 metres and drowned most of the formerly active vents, while some of the craters dating from the 1964 eruption have reactivated. A fumarole at Bubbling Bay is now a crater 20 to 30 meters across and there are new craters inside the volcano.

Raoul Island volcano has erupted 15 times in the last 3600 years, most recently in 1814, 1870 and 1964. All but the 1964 eruption were magmatic – eruptions of molten rock (magma) from below the surface. The 1964 eruption (and now last Friday’s) were hydrothermal – eruptions caused by underground water suddenly escaping to the surface. The trigger for Friday’s eruption could have been an earthquake weakening the structure holding the pressurised water underground, or possibly a sudden welling up of magma underneath the island.

Vulcanologists have been studying what they believe to be a sizeable body of boiling hydrothermal brine at some depth under Raoul Island. Since Friday’s eruption, it seems that the level of this body of boiling salty water has risen considerably, causing Green Lake to rise by 6 to 8 metres within the Raoul caldera (volcanic vent) and seepage to occur from under the beach along Denham Bay caldera, another active vent on the coast of the island. The seepage at the bay is causing a milky discolouration of the sea as seawater and hydrothermal brine are mixing.

Scientists now have to wait while the hydrothermal system at the island adjusts to the increased fluid pressure according to GeoHazards Duty Officer Steve Sherburn. Further eruptions remain possible while this occurs.

If the activity declines to its pre-Friday level, then this particular eruptive episode may be finished. However, if activity continues at an increased level and fluid continues to rise it could indicate that magma is rising underneath the island.

Leave a Reply