The Volcano

Þríhnúkar (Three Peaks) formed in three separate volcanic eruptions. The peaks line up within a few hundred meters of each other so they can be clearly distinguished from afar, hence the name. The three peaks reach an elevation of about 550 meters and are of nearly the same height.

The most northeasterly one, Þríhnúkagígur is the youngest and is considered the most important volcano speleological phenomenon on Earth. The name applies to both the outside and the inside of the 35m high cinder cone, which formed in an eruption about 4.500 years ago. There is a funnel shaped opening on top of the cone leading into the almost 200 m deep open vertical volcanic conduit, the plumbing system of the volcano. The bottom originates from around the time that modern humans first walked the planet, about 30–40.000 years ago. The crater walls tell the story of all the local geological processes that have taken place since then. The unexpectedly diverse microbial life offers clues about the development of life on Earth, and even on other planets. The crater is not only the third largest in the world, but also the deepest formation of its kind.

The middle peak, a scoria cone, is located 200 m west of Þríhnúkagígur. It stems from an older Þríhnúkar eruption, which took place about 500 years earlier. It is a part of an elongated shield volcano crater, which is now half-filled with the younger Þríhnúkar lava. The tidal level of the absolutely flat secondary lava pond can be seen around most of the circumference of the rim.

The third peak, furthest to the west, consists of hyaloclastite, a rock typical of having been quenched in contact with ice and water. It formed in a subglacial eruption, deep within the glacier, more than 50.000 years ago. At the time, most of Iceland was covered with a thick ice cap. We are talking about ice age here!

On a bright winter day in 1974 the cave explorer Árni B. Stefánsson became the first human being to enter Þríhnúkagígur. He was lowered in by a few of his friends in an adventurous exploration of the phenomenon.

It wasn't until 1991 that his brother Einar and Einar's friend; Björn Ólafsson, started to explore the cave, making several expeditions with Árni, where they made daring attempts to map out the gigantic cavern inside the volcano. For years they went down, in ropes, hanging in their harnesses with headlamps, slings and belay devices. Slowly the idea came up to make it accessible to the public and in 2004 Árni presented the first idea of making a tunnel into the chamber.

In year 2010 an expedition from National Geographic came for filming inside the volcano. It was a big operation that needed different approach than to use climbing ropes to get in and out. The founders started to devise how to lower people and equipment into the volcano. The solution was to use a heavily modified window cleaning lift. It worked like a charm and since 2012 people are now able to go inside the volcano to experience mother nature in all its magnificent grace.

The peak you will enter 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 entrance of a huge 120 m (400 ft) deep, bottle-shaped volcanic vault. The bottom measures 50×70 m (160×220 ft). Volcanic passages continues down to the southwest, to a total depth of about 200 m (700 ft).

The beauty of the crater mostly consists in the various coloration 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 a full sized Statue of Liberty into the chamber. So make no mistake – it’s huge!