Crater Lakes

When volcanic craters cool down after major eruptions, they often fill with water to form crater lakes. Some are cool, just filled by rain water, while others are warm or hot and remain connected to the volcanic plumbing. The colour of crater lakes varies markedly according to the temperature and chemistry of the water, and the type and concentration of particles suspended within it.

Frying Pan Lake, Waimangu.

Inferno Crater Lake, Waimangu.

Measuring lake temperature.

Ruapehu Crater Lake.

White Island Crater Lake.

Why Monitor Crater Lakes?

Crater lakes occupy volcanic craters and any reactivation or change in status of an active volcano is often reflected in the lake. This may be a chemical change, a temperature increase or water level variation. Many factors can influence a crater lake.

Crater lakes come in many forms and sizes, ranging from a few tens of metres across like Frying Pan and Inferno Craters at Waimangu, to the larger lakes in craters like at Ruapehu, Raoul Island and Tongariro, to the very large caldera lakes like Rotorua and Taupo.

Crater Lake Changes

Ruapehu Crater Lake

At Ruapehu we monitor the lake temperature, water level and overflow along with the chemistry. The lake temperature varies from about 10 to 50 °C; unfortunately this is not always a measure of activity as eruptions have occurred from both hot and cold lakes. The Mg (magnesium) values increase if new/fresh rock is in contact with the crater lake waters, while the Cl (chloride) changes with steam input.

Raoul Island

The water level of Green Lake (at Raoul Island) rose more than six metres before the 1964 eruption started. In 1993 it rose 1.2 m following an earthquake swarm, but no eruption followed. However in 2006 it didn’t change before the March eruption.

Waimangu

Within the Okataina Volcanic Centre, heat flow from the large crater lakes at Waimangu has been monitored. Inferno Crater lake shows large water level variations (10 m) while the overflow of Frying Pan lake varies between 120 and 100 litres/sec.

White Island

In February 2003 a large pool of water started to collect on the floor of the 1978/90 Crater Complex, drowning the vent that was active during the July 2000 eruptions. In 2005, the lake filled to within one metre of overtopping, before falling over 25 m. When full, the lake has an area of 74,850 m², whereas when low it only covers 24,800 m². When (if?) the lake reaches overflow level the volume of the water in the crater will be about 1.8 million m³. The primary source of water filling the lake was, and in future is likely to be, condensing steam and gas from fumaroles now beneath the lake and runoff from the surrounding crater walls.

The establishment of a semi-permanent Crater Lake at White Island has changed the range and likely impacts of the hazards to visitors on the island.