Inside a volcano

There are about 1,500 volcanoes on land — and even more underwater — but only one that you can truly climb inside.

It’s called Thrihnukagigur, a name that even some Icelandic locals have difficulty pronouncing. The name means “Three Peaks Crater,” and one of the three peaks is a gateway into the volcano’s magma chamber, the heart of a volcano. It’s the only known magma chamber in the world that’s possible to climb inside.

When Thrihnukagigur last erupted more than 4,000 years ago, it did something unusual for a volcano: It erupted, but it didn’t really explode or collapse. When we typically think of a volcanic eruption, we imagine vast amounts of ash, rock, and lava being ejected from a volcano’s cone. In this case, the eruption was much, much less violent.

There was plenty of magma, molten lava, inside. But instead of building tremendous pressure and blasting out the top, most of magma appeared to just drain back into the earth. And since there was no major explosion, the magma chamber itself is essentially intact to this day.

The magma chamber itself is like an upside-down funnel that’s 400 feet (120 meters) tall. There’s more than enough room for the Statue of Liberty. The bottom is more than 200 feet wide in places.

Some Icelanders have been exploring this chamber for years, and a couple of years ago they made it a bit more accessible, at least on a temporary basis. For the past two summers, a company has erected scaffolding across the top of the cone, providing people who aren’t experienced cavers a means of exploring the chamber. That means involves being lowered in a window-washer basket.

Just below the scaffolding, the cone is so narrow they’ve attached wheels on the side of the basket so that it can roll across some of the especially tight spots. As we descend at a slow, but steady pace, a minute later, the magma chamber comes into view.

The first thing that struck me was the colors. There are so many different colors.

As we neared the top of the chamber, we crept past a lava chimney, a small vertical vein that transported some lava higher into the cone. The center of the vein was fire engine red, its walls were deep purple, and it was surrounded by gold.

The astounding variety of color continued throughout the chamber. Scrambling across the bottom, I was struck by one wall where a deep purple hourglass shape appeared on an otherwise golden wall. Another wall was solid gold.

The colors come from the different types of minerals in the rock. Some rust faster than others.

Travel in the magma chamber is slow going. The bottom was likely uneven to begin with. And 4,000 years of erosion peeled large boulders off the inside of the cone, scattering them on the floor as well.

The photography was even slower. Even with the temporary lights installed in the chamber, it was dim. Most of the images I made there required exposure times of more than 10 seconds.

The amateur geologist in me appreciated how remarkable it was that I got to explore a place that you typically only get to read about in textbooks. The photographer in me was drawn to the colors and patterns.

Thrihnukagigur delivered for both.

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