Increased Activity, Ruapehu Volcano

Volcanic earthquake activity at Mt. Ruapehu has increased since Sunday’s lahar, indicating that there may be a consequent increase in activity within the crater lake over the next few days to weeks.

Prior to Sunday’s lahar, caused by the collapse of the tephra dam blocking the crater lake’s outlet, the temperature of Mt. Ruapehu’s crater lake had risen to 28º C early in March having risen 12º C since the minor eruption in October 2006.

Since the lahar, GNS Science has recorded an increase in the number of small volcanic earthquakes, some up to magnitude 1. It is thought that these earthquakes indicate changes in the volcano’s hydrothermal system as it adjusts to rapid lowering of the warm lake by 6 metres.

Experience has shown that rapid removal of water from the top of a hydrothermal system can lead to instability, resulting in small-scale steam eruptions as the lake continues heating. The larger of these events could generate waves within the lake, presenting a danger at the lake’s shore and resulting in overflows at the lake’s outlet.

GNS Science have not raised the alert level for Mt. Ruapehu but their alert bulletin released late yesterday serves as a reminder that the volcano needs to adjust to the rapid change caused by Sunday’s lahar, and some risk exists nearby as it does so.

Three volcanos in the North Island are undergoing change at this time, In addition to Mt. Ruapehu, White Island’s crater lake is still sitting at a record temperature of 74º C and minor volcanic tremor continues. No eruptions have occurred, but steam plumes have been seen over the island in recent times.

The small volcanic earthquakes being recorded underneath the northern flank of Mt. Ngauruhoe continue at the rate of up to 20 per day.

[Compiled from data supplied by GNS Science and Hazardwatch.]

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