A steaming stream in Rotorua.

I spent the weekend in Rotorua at GeyserCon, the national science fiction and fantasy convention.  I had a great time hanging out with other writers and learning new things about writing, but being a science geek at heart, the one thing I can’t stop thinking about is a presentation by Peter Brownbridge, the Rotorua Lakes Council Geothermal Inspector.

For those unfamiliar with New Zealand, Rotorua is a town on the North Island known for its extensive geothermal activity. And when I say extensive, I mean extensive. The whole town bubbles and steams and smells of sulphur. There are geysers, boiling mud, hot pools, and hot springs all within the township. In some places, the footpaths are broken, gently steaming, and crusted with mineral deposits.

As you might guess, Rotorua sits inside a volcanic crater. The volcano’s last major eruption happened about 240,000 years ago, and molten rock still lurks below, heating rocks and the aquifers above them. 

It makes for some unique urban planning and maintenance issues.

Peter spoke about the ongoing need to monitor existing and new hot springs and geysers. He spoke about how the layers of ash and sediment overlaying the old magma dome are prone to erosion by hot gassy water, leading to huge underground holes that need to be filled before they become giant sinkholes. He talked about the challenges of repairing ageing geothermal bores when the pressure in them can be as high as 200psi. He mentioned the need to use alternate materials for underground pipes to avoid damage by corrosive gas. He talked about having to evacuate homes and schools due to poisonous gases belched out by hot springs. He described a median strip in the middle of town that spontaneously catches fire every summer because of highly flammable gas oozing from the ground there.

But what I found most remarkable was, after Peter described all the crazy things the city has to do to maintain services, he said, “Yeah, we’ve pretty much got it under control. The only thing we struggle with is delivering cold water to some homes.”

Think about that for a moment. Let it sink in.

I’ve been to Rotorua several times, and have visited stunning hot pools and geysers, but that one little fact has given me an entirely new appreciation for the nature of the earth beneath the town.