There have been no “significant changes” at Mt Ruapehu after a swarm of earthquakes east of the volcano, volcanologists say.

More than 90 small and relatively deep earthquakes were recorded beneath Mt Ruapehu’s north-eastern flank early on July 8.

GNS Science said the quakes were about six to seven minutes apart.

Duty volcanologist Geoff Kilgour said on Monday no significant changes to the volcano had been observed after the earthquakes.

The temperature of Te Wai ā-moe (Ruapehu Crater Lake) remained stable at about 12C.

“We continue to record emissions of volcanic gas, indicating heat and gas flow from depth is occurring.”

Kilgour said the temperature of Te Wai ā-moe had declined from 17C to 12C since May.

“Observations from a visit on June 8 confirmed the presence of sulphur slicks on the lake surface, usually related to hot fluids entering the lake floor, melting sulphur.

“The lake was also observed overflowing, indicating that there continues to be inflow of hydrothermal fluids into the lake,” Kilgour said.

Sulphur dioxide emissions were at a continuous but low level.

Kilgour said despite the recent swarm of earthquakes, a lack of other observable changes at Ruapehu showed that the volcano continued to exhibit “typical background activity”.

“When weather permits, we will be conducting further gas flights and sampling Crater Lake fluids to monitor any changes closely.”

GNS Science duty volcanologist Yannik Behr said last week swarms were not unusual in the central North Island, where volcanic fluids interacted with pre-existing faults.

“The current sequence of earthquakes is possibly related to fluid movement at depth.”

The last eruption at Mt Ruapehu was in 2007.

The mountain is currently at Volcanic Alert Level 1, which indicated minor volcanic unrest.

Behr said Mt Ruapehu was an active volcano and had the potential to erupt with little or no warning when in a state of minor volcanic unrest.

The last time it erupted was on September 25, 2007, which caused a seven-minute earthquake, two lahars and flying rocks - one that landed on Dome Shelter near the crater, crushing the leg of primary school teacher William Pike.

The volcano also exhibited noticeable activity in 1995 and 1996, most notably on June 17, 1996 when a large eruption produced giant clouds of smoke and ash.

Eruptions continued for weeks and damaged crops and killed livestock. The resulting ash cloud disrupted flights and caused delays across the country.