Mount Ruapehu Crater Lake

VOLCANIC FORM: Andesitic Stratovolcano
 
 

RECENT ACTIVITY:

• 1945 - Brief disappearance of Crater Lake during a period of magmatic extrusion

• Major phreatic and phreatomagmatic eruptions in 1966, 1968, 1969, 1971, 1975, 1977, 1978, 1982, 1988

At present, the lake is an oval shaped body of water with a maximum depth of about 134 m. A single outlet flows from the southern end of the lake, and feeds Whangaehu Stream.  Two hydrothermal vents are present at the lake bottom - a more active vent located in the center of the lake, and a less active vent located in the north-central part of the lake.

The most obvious sign of fluctuations in the hydrothermal activity of Crater Lake is the change in lake color.  During times of high activity and convection, sediments become suspended in the water column and color the water grey.  However, during more quiescent periods, the sediments begin to settle and reveal the blueish-green color of the lake water.

Fluctuations in the hydrothermal activity of Crater Lake have caused extreme changes in the bathymetry of the lake.  Since 1965, the maximum depth of Crater Lake has varied between 80 m and greater than 300m!  In 1965, the bathymetric profile of the lake was likened to a champagne glass, with the central vent forming a neck more than 300 m deep.  By 1970 magmatic inflows and sedimentation had reduced the lake depth to about 80 m.  Eruptive activity between 1970 and 1982 cleared the vent to a depth of 180 m, and subsequent in-filling resulted in a lake depth of about 134 m by 1991.

Changes in the chemistry of Crater Lake also reflect the cyclic activity of Mt. Ruapehu.  Abrupt increases in magnesium (Mg) and chloride (Cl) are correlated with periods of eruptive activity.  Except for the 1988 eruption, spikes in temperature of the lake water show increased heat flow to the lake prior to eruptive events (Figure 1).
(Source: Christenson and Wood, 1993)

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1. Title: Surveillance of Ruapehu Crater Lake, New Zealand, by aqueous polythionates
Authors: Takano, B.; Ohsawa, S.; Glover, R.B.
Source: Journal of Volcanology and Geothermal Research
Volume: 60
Year: 1994

2. Title: Evolution of a vent-hosted hydrothermal system beneath Ruapehu Crater Lake, New Zealand.
Authors: B.W.Christenson and C.P. Wood
Source: Bulletin of Volcanology
Volume: 55
Year: 1993

3. Title: The heat source of Ruapehu Crater Lake; deductions from the energy and mass balances.
Authors: Hurst, A.W; Bibby, H.M; Scott, B.J; McGuinness, M.J.
Source: Journal of Volcanology and Geothermal Research
Volume: 46
Year: 1991

4. Title: The chemistry of Crater Lake, Mt Ruapehu (New Zealand) during and after teh 1971 active period.
Authors: W. Giggenbach
Source: New Zealand Journal of Science
Volume: 17
Year: 1974