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Increased hydrothermal activity possible at Crater Lake - 19/03/2007

Volcanologists today said it was possible there could be increased volcanic activity at Mount Ruapehu following Sunday’s partial emptying of the crater lake to the former overflow level.

Brad Scott, Volcano Surveillance Co-ordinator at GNS Science, said there had been an increase in volcanic earthquakes at the summit of Mt Ruapehu since Sunday’s lahar.

“The rapid removal of water from above a hydrothermal system can destabilise that hydrothermal system, resulting in small-scale eruptions,” Mr Scott said.

Lowering of the lake could lead to increased heating and steam-driven eruptions.

“ If a small eruption occurred under the lake it could generate waves large enough to overtop the hard rock rim of the lake, resulting in a small lahar.”

Mr Scott said since the dam failed on Sunday, GNS Science had recorded an increased number of small volcanic earthquakes up to magnitude 1.

“This phenomenon is common after volcanic lakes empty and is an indication of changes to the hydrothermal system under the crater lake.

“ Based on visual and instrumental observations, we believe there could be elevated hydrothermal activity at the crater lake over the next few days to weeks as the hydrothermal system adjusts to the reduced weight of the new lake level.”