The Gravity Expedition

By: Miriam Jackson

This is part two, a follow up from the entry Preparing for gravity.

Now we are here to do the work in earnest. A group of five people are now living in the tunnel for a week to measure positions to place gravimeters, and perform measuremets with both absolute and relative instruments. Christian Gerlach and Siri Eikerol are back and together with them student Alexander Helland and PhD student Vegard Ophaug from the Norwegian University of Life Sciences. Miriam Jackson is here to guide us through the tunnel system.

With us we brought “tons” of equipment, and had to fly up to the tunnel entrance with a helicopter. Three flights were made to bring up all we needed for the week. A clear blue sky and no wind made the trip an amazing experience and gave us spectacular views of the glacier! Is there a better way to arrive?! It was another story getting all the equipment into the tunnel and placed where it was needed. The FG5 absolute gravity instrument alone weighs about 350 kg and had to be transported all the way up to the laboratory cabin, the exact metres in height difference can be calculated after the levelling is done.

To get an exact position of the FG5 station, a complete tunnel survey is needed. Because of the poor geometry through the entrance tunnel a small network was measured outside the tunnel before we started inside.  Another day with a clear sky, but windy at times and probably a bit colder than what we had in mind. The clothing we had brought with us was mainly aimed at stable tunnel “weather” conditions of about 4-5 degrees and not necessarily ideal for windy far-below-zero conditions outside. The view from the outside stations, however, is unforgettably beautiful. The next day the weather was completely different, and since we weren't finished with the outside survey, helping hands to hold tripods in place were needed. Challenging conditions!

Since the last visit the pillar we built in September was now dry and ready for the FG5. The instrument is now in place and measuring absolute gravity below the glacier. When the land survey is completed, a selection of stations will be measured with a relative gravimeter. Data processing will be done under the sun safely back in Ås.

Summing up, the first days in the tunnel have been long days of hard work and it will probably continue like this for the whole stay, but exciting helicopter flights and successful gravity measurements - probably the first gravity measurements ever from a tunnel below a glacier - surely make up for it!
As Norwegians say: “So went now the days”. Peace out.

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