Thrihnukagigur volcano is dormant – it last erupted over 4,000 years ago. There are no indications of it erupting again in the near future. The volcano’s name, mostly unpronounceable for anyone other than locals, would be directly translated as ‘Three Peaks Crater’. The name comes from Árni B. Stefánsson, who was the first to explore the vault and who has pleaded the case for making it accessible for years. The three craters (one of which you will be descending into) are prominent landmarks, standing against the sky on the highland edge, about 20 km (13 miles) southeast of the capital area, within the protected area of Bláfjöll Country Park (see map and how to get there).
Simply put, Iceland is one giant geological hotspot. The country is one of the most active volcanic regions in the world, with eruptions occurring every 3–4 years on average. But why is Iceland so active? It´s mostly due to its location on the Mid-Atlantic Ridge, where the Eurasian and North American plates are moving apart – and therefore literally opening the earth’s crust. In the center of this ridge sits Thrihnukagigur volcano.The most north-easterly of the three peaks is a small cinder cone, standing about 35 m/100 ft higher than its surroundings. At the top of this cone is a funnel-shaped opening, about 4×4 m/12×12 ft wide, the entrance of a huge 120 m/400 ft deep, bottle-shaped volcanic vault, measuring 50×70 m/160×220 ft at the bottom. Volcanic passages continue down to the southwest, to a total depth of about 200 m/700 ft.
The beauty of the crater mostly consists in the various colourations found inside it and its enormous – and to some extent intimidating – size. To put it in context, the ground space is equivalent to almost three full-sized basketball courts planted next to each other and the height is such that it would easily fit full sized Statue of Liberty into the chamber. So make no mistake – it’s huge!
One of a kind magma chamber
The magma chamber is often referred to as the heart of a volcano. It’s there that the liquid rock waits to find a way through to the surface, causing a volcanic eruption. In most cases, the crater is usually closed after the eruption by cold, hard lava.
Thrihnukagigur volcano is a rare exception to this, because the magma in the chamber seems to have disappeared. It’s believed that the magma solidified in the walls or quite simply retreated to the depths of the earth. Haraldur Sigurdsson, volcanoist, explaines it like this:
“Thrihnukagigur is unique (…) It’s like somebody came and pulled the plug and all the magma ran down out of it.