Wednesday, August 03, 2022

Descending Into the Throat of a Young Iceland Cinder Cone

Screen capture the new fissure eruption taken August 3, 5:58 PM local Iceland time

With news this morning of renewed fissure eruptions in Geldingadalir Iceland, I thought it would be fun and instructive to share photos and descriptions of a unique trip I recently completed in Iceland. On the trip from July 7-17 I served as a geologic lecturer and interpreter for Smithsonian Journey's. Imagine my disappointment at missing this new activity by only a little more that two weeks. (I may go back). A live feed of the new eruption can be viewed here.

The Ericsjökull ice cap on the Ring Road to Reykjavik

After touring the island with our Smithsonian guests for nine days, I had a free day while in the capital city of Reykjavik. A chance opportunity to go on a local tour known as "Inside the Volcano" popped up for me. I jumped on it! This is an excursion a short drive out of Reykjavik where visitors descend about 150 meters through a narrow vent into an extinct cinder cone. Of course, I said yes to the opportunity.

Preparing for the short walk

After the 45-minute drive out of the city and toward an upland area, visitors are brought to a waiting room where they receive instructions and rain gear. 

Cross-section of the volcanic neck (depths in meters) with the Statue of Liberty for scale

I was impressed with the signage inside the waiting room, which graphically explained the age, composition, and eruptive history of the volcano. A great resource for folks to understand the deeper story of the "thrill descent."

The trail to Ᵽrínúkagígur, two miles one way 

The cone is called Ᵽrínúkagígur (Ᵽrínúka Crater) and it was formed about 4,500 years ago in a post-glacial eruption. Iceland classifies its younger volcanoes as glacial or post-glacial. Ᵽrínúkagígur is one of three closely-spaced scoria cones (also called cinder or tephra cones) erupted along part of Iceland's southwest rift, part of the Brennisteinsfjöll (Sulphur Mountain) rift.

The opening at the top of the cone

Finally, we arrived at the opening to the volcano. The site was discovered and initially explored only about 20 years ago. Numerous studies were made to determine the advisability and safety of developing the site for visitors. The main concern was that in most scoria cone eruptions, the removal of magma in the terminal phase of an eruption causes the crest of the newly formed cone to collapse into a crater. It was determined that this cone did not collapse due to its relatively small size. The cavity that we would descend is bell-shaped.

Looking down after entering the cable car

The descent takes about seven minutes. The cable car has rubber "runners" on its sides as it comes quite close to the walls. There is just enough room.

On the floor of the volcano looking up to the surface opening 

On the way down we viewed multiple dikes that were feeding the surface lava eruptions. In the photo above, note the linear dike trending upwards toward the opening and a subsidiary dike above the person with with the purple jacket.

Another party descending to the floor of the volcano

The feature is well-visited and is well-organized for visitors. Three separate parties of about seven people each are rotated through the inside the volcano and cable car at any one time. 

The trail marking the path on the volcano floor

A loop trail over very coarse rubble can be made. This is not for the faint of heart - the lighting is low, the trail very rough and water constantly drips down from the roof making things slippery.

Note the person in white for scale

The temperature is quite cold at about 38º F and many people found gloves useful on the trip. After 4500 years, the inside of the volcano has cooled sufficiently.

Dike swarm in the walls of the volcano 

The colors are due to the various states of oxidation adjacent to the dikes in the walls.

Lavacicles form on the walls 

This was a very unique trip. It is somewhat expensive being about $300 US per person. But it does include excellent and geologically literate guides, a bowl of hot, Icelandic meat soup in their kitchen near the volcano, hot tea and coffee, and heaps of fresh Icelandic air (and likely rain). See their website for more information here.

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