from the jungle into the desert
After the first three days of the StRATEGy field school 2016 I want to recapitulate my first impressions. In general, we are driving with two busses through NW Argentina starting from Tucumán through several intermontane basins and the Puna plateau to Salta. In between we stop quite often and release the geologists for “rock hunting”. Here, I don’t want to focus that much on the geology because I guess Wera will describe everything in her blog more in detail and much better, as she understands everything much better than me due to her different education. 😉
The fieldschool started with a nice get together of the StRATEGy PhD group, as some people were already in the field and the rest arrived from Germany. Unfortunately, Leo and Maryam couldn’t join the trip due to visa issues on short notice. Argentineans in general and the guys in the Ambassy are quite relaxed, but getting things done in short time is nearly impossible. All the others arrived fine and some other students from Argentina, Colombia and Canada joined us. In the first stage we headed towards the mountains and higher altitude. Towards the mountain front we could observe the increase of the yearly amount of rainfall from 700 mm (quite comparable to Berlin and Potsdam) to more than 2000 mm directly at the mountain front. This results obviously into a lot of moisture and a highly densed vegetation cover as you can see in the pictures. The reason for that are the high mountain ranges in this place. The Sierra Aconquija rises up to more than 5 km and therefore builds a huge orographic barrier for all the moisture laden clouds of the basin with around 500m in elevation. Hence, if the moisture want to cross the mountain range (and yes it want to do this) it rises in altitude, cool down and loose the capability of keeping moisture which results in precipitation. This effect well known also in other places on earth (e.g. Harz, Germany), but it is very strong in this area (further reading: Strecker et al. 2007, ‘Tectonics and Climate of the Southern Central Andes’). All along the Andes you find this cloud forest with a jungle like vegetation and a lot of clouds which appears as fog in the pictures. The vegetation is even much denser as we’ve seen in the Candelaria Range some days before and all the trees are vegetated with parasite plants. Much more interesting is the change of the landscape when you cross the orographic barrier. The pass we took is around 2000m high between the Sierra Aconquija and the Cumbres Calchaquís and within only a few hundred meter (!!!!!) the vegetation change from dark green to more shady, yellowish green and is then completely removed by grassland with shrubs and bushes. This rapid change illustrates the drop of mean annual rainfall from over 2000 mm to 200-300 mm and the transition from humid and subtropical to semi-arid climate settings. Also the clouds were completely gone at this point.
The actual pass into the Santa Maria basin was at 3000m altitude. But driving around with a group of geoscientists don’t allow you to just cross a mountain pass and driving from A to B. Instead every few kilometer they want to stop and discuss what they are seeing there. But the difference of Geologists and Seismologist I will describe in another post. In fact, roads providing the best outcrops to analyze the stratigraphy because their construction lead to undercutting of the slopes and reveal the bedrock quite easily. That’s why we need a whole day to drive around 200 km.
The next days, we discussed the stratigraphical evolution of the Santa María basin and what kind of features we can observe in the landscape: old dunes, landslides, landslide dammed former lakes and the surrounding mountain ranges. The best place to see the evolution of the stratigraphy is the Quebrada de las Conchas from Salta to Cafayate, also a breathtaking beautiful valley. Cafayate is one of the highest vineyard areas in the world. And yes we drunk a lot of wine there. Another thing that I learned here is the high UV insolation in that area. It’s so strong, in an elevation of around 1000m one to two hours of sunny weather is enough to completely sunburn your skin. I was coming from the european winter and my skin was white as chalk. Normally I don’t use suncream, only in very high altitude in the alps sometimes. But here you have to start with 50+ sun protection factor. Even my my factor 30 cream was not enough to protect my skin and I got more sunburned. Wera mentioned with a factor 30 in europe you would stay completely white, but here you need a lot more.