Mount Ruapehu’s Crater Lake temperature heats up to 40 °C (104 °F), Alert Level remains at 1, New Zealand


Mount Ruapehu's Crater Lake (Te Wai a-Moe) heated from 24 °C (75.2 °F) to 40 °C (104 °F) in response to earthquakes beneath the volcano, according to the GeoNet bulletin issued on Wednesday, March 18, 2020. The Volcanic Alert Level remains at Level 1 — authorities recommend people do not enter the area 400 m (1 300 feet) around Crater Lake.

GeoNet confirmed that the warming was due to hot gases and hydrothermal fluids, following the tremors that were recorded in February

Volcanologists have collected water samples from Crater Lake this week to understand current activity at the volcano. These samples are being analyzed this week, with chemistry results expected by next week, GNS Science Duty Volcanologist Art Jolly said.

In GeoNet's last bulletin, the volcanologists observed an upwelling of grey sediment and sulfur slicks on the lake surface. Now, the lake is well mixed, turning to a grey color.

The continued flow of gases and hydrothermal fluids through the lake indicates that the volcano's vent underlying Crater Lake is open, Jolly said. In addition, the lake was overflowing at the outlet channel, with a remarkable decrease in the flow rate since the scientists' past two visits.

Jolly also said that the "volcanic tremor increased in response to the volcanic earthquakes, peaking in early March, then declined slowly until today."

According to the modeling, the heat energy input into the lake rose from around 200 MW to 600 MW, although this had declined already as the temperature warming slowed down.

Carbon dioxide and sulfur gases measured in the atmosphere above the volcano on February 28 are greater than that of February 7. However, Jolly noted that the present values are not unusual, and are within the ranges over the past year's measurement.

The Volcanic Alert Level remains at Level 1. The Volcanic Alert Level reflects the current level of volcanic activity and is not a forecast of future activity.

At this level, the Department of Conservation advised people to avoid entering the area 400 m (1 312 feet) around Crater Lake.

"Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest. There is no change in the Aviation Colour Code from Green."

Jolly noted that volcanologists are continuously monitoring Mount Ruapehu for further signs of activity. 

Geological summary

Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200 000 years ago.

The 110 km3 (26.4 mi3) dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 (24 mi3) ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank.

A series of subplinian eruptions took place between about 22 600 and 10 000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene.

Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3 000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys. (GVP)

Featured image credit: Sentinel-2, Acquired March 16, 2020.

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