Geologists say the crater lake on White Island has jumped to a record temperature of 74degC and the water level has plunged 6m - possibly signalling an eruption on the island.

The drop in water level "may cause instability in the geothermal system that could result in minor eruptive activity," said GNS Science volcanic surveillance co-ordinator Brad Scott.

White Island in the Bay of Plenty has not erupted since 2000 but the water level has risen 30m in the past six years.

The water temperature in its crater lake has jumped from 45degC last August to over 60degC in January and was now 74degC. The lake water was also very acidic "like scalding hot battery acid", Mr Scott said.

"Over the past few months, increased heat and gas flow into the volcano has caused both a rapid evaporation of the lake and more gas being released into the atmosphere."

The drop in water level is equivalent to a 10 per cent fall in the volume of the lake, and some prominent hot pools and streams on the island are drying up because water has stopped leaking out of the crater.

Sulphur dioxide gas being released into the atmosphere has jumped from 300 tonnes a day to 500 tonnes over the past eight months, and the amount of carbon dioxide being pumped out has risen from 1000 tonnes a day to 1400 tonnes.

"The increase in gas through the lake might cause some discomfort to visitors to the island when they are close to the lake," Mr Scott said.
About 20,000 tourists visit White Island each year, most of them ferried in boats from Whakatane, 48km away on the Bay of Plenty coast. Four helicopter operators - three from Rotorua and one from Whakatane also take people to the island.

A dozen sulphur miners sleeping on the island were killed in a landslide from the collapsing crater. Mining of sulphur resumed in the 1920s and the remains of buildings from that era are a tourist attraction.

About 70 per cent of the White Island volcano is underwater: though only 321m rises above the sea surface, it is the biggest volcanic structure in New Zealand, and is about 6km in circumference at sea level.

Normally the transition zone in which volcanic heat is transferred to geothermal systems is 3km to 4km underground, but at White Island it is within a few hundred metres of the surface.

According to GNS Science volcanic hazards at the island range from isolated eruptions after quiet periods, to another crater collapse, ashfall, steam eruptions and occasional explosions throwing ballistic blocks.

Explosive eruptions can pose a risk to visitors on the island, nearby boats and aircraft passing close to the island, but there are no reliable warning signs of large explosive eruptions. This is partly because many are triggered by the collapse of part of the volcano wall, which temporarily "blocks the plumbing", making an explosion almost inevitable.

According to GNS Science, particularly large and violent steam explosions occur when groundwater-saturated crater floor material collapses into the eruption conduit, and on to the top of the hot column of molten rock (magma) under the island.

Such steam explosions produced eruption columns 5km high in 1977.
In 2000 the volcano blasted a new crater 150m across in five hours and blew out ash, rock, debris and pumice in blocks up to 1.5m wide, which were hitting the ground in a semi-molten state.

A GNS "volcanocam" recording regular images of the crater can be seen on the Internet at