Pumice stone in Waikato – My surprising volcanic rock reunion

Pumice. Many of you know it. You’ve used it, seen it, or at least heard about it at some point.

I’ve known pumice for as long as I can remember. Growing up, we called it itiat because it looked and felt like a rough stone. Unlike the heavy stones we’d find outside, this one was light in the hand, full of tiny holes, almost like a stone-shaped sponge. We used it during at-home pedicures to exfoliate tough skin, mostly on the soles of our feet.

As a child, I often wondered why it was so much lighter than other stones. But, like most childhood curiosities, the question floated away unanswered… until one road trip changed that.

It was just after we’d started to shake off the COVID era. Two friends and I went on a road trip to Waikato to see the famous glow worms. Not the typical one you know, this was the Twilight glow worm kayak tour by Riverside Adventure in Pairere, Waikato region. After kayaking for what felt like hours, we stopped at the base of a rock for a snack break (this was the half way point of the tour). That’s when I saw it… pumice, scattered casually around the ground as if it had just been dropped there by nature

Read more about my first glow worm experience (coming soon!)

Our tour guide, a cheerful man with a knack for random trivia, picked one up and asked, “Do you know what this is?” The name was right at the tip of my tongue but slipped away before I could answer. Thankfully, Abi, my kayak partner, stepped in with confidence: “Pumice.”, he responded.

The guide smiled and explained that pumice is actually born from volcanic eruptions. My inner engineer instantly perked up. Back then, AI wasn’t the go-to source it is today, so I whipped out my phone and Googled it (well, I can’t recall if this was after the Kayak or while we were at the spot, but there definitely was some googling). Sure enough, he was right.

Pumice, a lightweight volcanic rock, is often linked with its use in personal care, particularly for exfoliating skin and smoothing calluses.

Here’s the science: pumice forms when lava cools rapidly during an eruption. The sponge-like appearance comes from a network of gas bubbles trapped between fragile volcanic glass and minerals. Volcanic gases dissolve into molten magma, and during an eruption, these gases expand rapidly, creating a foamy texture in the lava. When the lava cools and solidifies around the gas bubbles, the gases escape, leaving behind those signature pores.

As for how that pumice ended up in Waikato? I have my theories. The most likely? It was carried there by water, floating along until it found a home at the base of that rock where we stopped.

From an old childhood bathroom essential to an unexpected geology lesson in the middle of a kayaking trip, pumice and I have met in the most unexpected ways.