Geothermal eruption leaves 50m crater

When his cows started stampeding up the hill, farmer Phil Morgan knew something wasn't quite right.

But he couldn't have imagined the huge geothermal eruption which was taking place just behind him -- throwing huge stones into the air and leaving a crater more than 50m wide.

Yesterday morning's eruption on Department of Conservation land at Reporoa about 42km southeast of Rotorua is believed to be one of the biggest in New Zealand in 50 years.

Mr Morgan said he turned around after the cows started stampeding and saw "a massive cloud heading up into the heavens".

He added: "It hurled some big rocks a fair distance so it must have had a bit of grunt."

Geologist Ashley Cody was called to the farm after the eruption and was stunned by the extent of it.

The crater the eruption left is about three times the size of the 2001 Kuirau Park eruption.

Mr Cody said rocks thrown out of the crater were up to 60cm in diameter and more than a hectare of land had been destroyed.

The land within 20-30m of the crater was covered with ash and mud more than four metres thick. About a hectare of land has been left barren.

Mr Cody said it was both unusual and exciting to see such an event as they often happened when nobody was around.

While the major eruption came about 10.30am the area was still erupting at 3.30pm yesterday with stones being shot about 15m into the air and the steam column rising almost 50m.

Mr Cody said geologists would be keeping an eye on the eruption and it was likely it would weaken as it lost its energy. This could take hours or even days.

Mr Cody said it was possible that had someone been within 20m of the eruption, they "may have come to grief".

Before the eruption, head-high blackberry covered the land but now there was "not a skerrick of vegetation" left.

The eruption has blocked the neighbouring stream which is expected to "run muddy" for days.

Mr Cody said while the area was not really thought of as a place for eruptions, it had been heating up over the past year, with trees dying and new springs breaking out. An almost identical eruption happened in the area in 1948.

There had been no obvious triggers for the eruption, such as earthquakes, heavy rain or changes in air pressure.

"Almost every geothermal field does this from time to time."

- DAILY POST (ROTORUA)