A boiling mud pool that erupted in suburban Rotorua had previously been filled in illegally, a Rotorua District Council inspector says.   Because of fears the earth-filled hole could erupt, the matter had been referred to the regional council, but it appeared no action had been taken to fix the problem, geothermal inspector Peter Brownbridge said yesterday. 

The problem pool was reported to the Whakatane-based Environment Bay of Plenty, which manages Rotorua's geothermal field.   "We pointed it out to the regional council at the time and we voiced our concerns that this very thing would happen if we allowed it to remain covered," Mr Brownbridge said.   But the regional council's regulation and monitoring director, Paul Dell, said he was not aware if it had been told the Tarewa Road pool had been tampered with. 

Even if it had, any infill would not have been removed by the regional council.   Mr Dell said the regional council took action if it caught people interfering with geothermal features, but once the damage was done, and the council did not know who was responsible, it would not act.   "We just have to leave Mother Nature to take her course," Mr Dell said.

Mr Brownbridge said the mud pool had "popped and cleared its throat".   The eruption sent boiling mud 13m into the air, coating nearby grass with thick, sticky geothermal mud and demolishing a fence around the pool.   Steam from the explosion could be seen over Rotorua.