Geophysical expedition to the Namib completed Without any major complications we successfully completed our 21 days geophysical survey at the Roter Kamm impact crater and the Aurus clay pan on 15 March. The survey took us deep into the Sperrgebiet of the Namib desert, required us to shuttle food and water supplies regularly from the mining town Roshpinah located two hours off-road driving distance. With great support from the local community and the Sperrgebiet rangers we had our camp set up close to the Aurus mountains. Two existing metal rondavels protected our kitchen facilities and geophysical equipment from animals, extreme winds and dust storms, even sometimes from rain. 12 sleeping tents were set up around the camp site. A close by borehole with rather minor water quality provided us with sufficient usage water for washing and showering.

Besides beautiful night skies, magnificent desert sceneries with a variety of color spectacles we met plenty desert inhabitants - from small spiders, scorpions and snakes to many ostriches, herds of oryx antilopes, few springboks and the mostly night active hyenas and jackals. Every morning we could see the traces of hyenas and jackals around our equipment, which we left in the field overnight. Several seismic trigger cables and electromagnetic sensor lines suffered from curious and hungry mouths. For the past 100 years the Sperrgebiet remained untouched and the beautiful nature preserved. Ongoing negotiations will probably result in an opening of the Sperrgebiet as a national park for tourists. For this reason the park rangers allowed us only a few driving tracks and prohibited driving into the Roter Kamm. Consequently all geophysical measurements inside the crater had to be done with man power.

On the geophysical side - the Aurus clay pan could efficiently be covered by two long seismic and electromagnetic transects at extremely high resolution. Preliminary results show that the clay pan is larger than expected and visible from satellite images, since the periphery is covered by younger fluvial deposits. Clear seismic refraction traces with high p-wave velocities and electromagnetic data indicate bedrock already at depths of roughly 15-20 meters. The clay sediment record, recovered with a simple coring device down to four meters, will provide important information concerning past pluvial periods. Although access was difficult, we surveyed two electromagnetic transects across the Roter Kamm, of which one transect extended 10 km over the crater rim towards the Aurus mountains. First results are extremely convincing and showed a bowl shape basement resistor with a maximum depth of 350 meters at the crater center. But also some interesting internal layering is imaged within the upper 150 meters that need further analysis and an integration of seismics, magnetics and geological background for a concise understanding. Halftime of our survey we hosted 20 UNAM students for one night in our camp and gave an half day introductory tutorial to the project including a short geophysical field practice on EM and seismic methods.

All our team efforts and long term preparations were totally worth it - we return home with plenty of good data and rich experiences. A big thanks goes out to the complete team and all involved people.

In March 2022, a mixed group of scientists from all CRC1211 projects, covering biology, geology, geography, conducted a 10-day introduction field excursion guided by Prof. Tibor Dunai, Prof. Dietmar Quandt, Dr. Benedikt Ritter and Dr. Damian Lopez to the Atacama Desert. For many scientists working in the CRC1211, this was the first time in the Atacama Desert. Earlier plans were unfortunately prevented by the pandemic.

The group with the majority being young researchers (PhDs and PostDocs) visited all three major focus sites of the CRC and experienced the gradual change of aridity through several transects. The itinerary of the excursion allowed participants to experience changes in landscape, soils and biology in relation to altitude and increasing aridity. The intertwining interaction of all scientific branches of the CRC1211 led to lively discussions in the field and close collaborations of all fields within an interdisciplinary approach. The participants experienced first-hand how hyperaridity feels, and what it means for life and of geological processes in the Atacama Desert.

Author: B.Ritter

After taking the samples to the shipping agency in Antofagasta, our last days in the Paranal claypan were dedicated to packing and organizing all our gear. It was also time to gradually tear down the “small village” in which we lived for the past six weeks and have all the drilling equipment prepared for new work in another location.  The rotary drill and some of the trucks left the site on Friday February 18^th and we finally said goodbye to this unique place in the desert the following day.

Although the drilling operation was officially finalized, the work was far from being over. After returning to Antofagasta, we spent two full days at the “Bodega” in the UCN cleaning the camping gear and all our tools so they could be in proper conditions for future projects. It is incredible how much dust was collected by our equipment during the length of our operation!

On Wednesday February 23^rd, we returned to the Paranal site for a last time to conduct a down-hole logging in the three drilled holes. The analyses were performed by Chilean specialists of the company Comprobe Ltda. using four probes. These were lowered into the open holes to measure different geophysical parameters such as resistivity, conductivity, spectral gamma radiation and magnetic susceptibility. Fortunately, the holes had only collapsed slightly after removing the casing from the drilling and we were able to measure down to 24 m (Hole 1A), 134 m (Hole 1B) and 94 m (Hole 1C) respectively. These data will provide the first important information on the recovered sediments, even before the cores arrive in Germany. It will also allow us to make an initial correlation of the holes and, subsequently, the down-hole logging records will be used to calibrate the estimates of the geophysical surveys conducted in 2018 and 2019. We also took advantage of our last visit to the claypan to install a set of homemade dust samplers that will remain in place for the next few months.

These activities marked the final point of our challenging operation. Now we are all looking forward to having a few days of rest before returning home!