Islands of Life, Part II

In satellite images, this region of Salar de Navidad appeared to contain sinkholes, the origin of which scientists hoped to understand by taking a closer look at them. Credit: ©2011 Inav/Geosistemas SRL, DMapas; Image ©2011 GeoEye

Astrobiology Magazine Field Research Editor Henry Bortman recently accompanied a group of researchers to the Atacama Desert in northern Chile, the driest place in the world. Here, in an environment that resembles Mars in the ancient past, even bacteria have a hard time surviving. In this second in a series of reports, Bortman recounts a day of research activities at Salar de Navidad.

Salar de Navidad, Atacama Desert, Chile
May 9, 2011

On Monday, we headed over the coastal mountains, up out of Antofagasta, in a pair of rented pickup trucks. Our ultimate goal was the Yungay Desert Research Station, located in an unnamed salar (salt flat), “home base” for much of the astrobiology research that takes place in the Atacama. Thanks to mining roads – mining roads are everywhere in the Atacama – you can drive to Yungay from Antofagasta in about an hour. No need even to go off-road. But before going to Yungay to set up camp, we drove first to another nearby salar, Salar de Navidad.

As an example of the pervasive mining activity, when we turned onto the road that would take us in the direction of Salar de Navidad, I asked Alfonso Davila where the road went. “To the Escondida copper mine,” he said. “And then where?” I asked. “Just the copper mine.” It was the best-maintained road we traveled on during the whole expedition.

Formations thought initially to be sinkholes turned out upon closer inspection to be dunes. Credit: Henry Bortman

Salar de Navidad had been pegged as an interesting spot to explore by studying Google Earth satellite images of the region. About four or five kilometers long and perhaps three km wide, like the salar at Yungay it is covered in places by vast fields of small, knobby salt rocks, some of which are colonized by microbes. “The salt deposits mark the bottom of some kind of lacustrine system,” Davila told me, maybe “a massive lake,” maybe shallow salty water, ”and once it evaporates it leaves the salt behind.”

The halite formations in Salar de Navidad were smaller than those at Yungay, most of them only two or three inches tall. The salar was mined – bulldozed flat, actually – by a commercial salt operation about 20 years ago, so all the formations we saw there had formed within the past two decades.

Two features in the satellite images that drew the attention of researchers were, in one spot, circular depressions that looked like sinkholes; and in another, rows of salt formations that appeared from space as straight lines.

Some of the halite rocks in Salar de Navidad have formed uncharacteristically in straight lines, perhaps as a remnant of salt-mining activity that took place here 20 years ago. Credit: Henry Bortman

What appeared to be sinkholes from orbit, however, turned out on closer inspection to be sand dunes with depressions between them. Beautiful, but not particularly interesting from a scientific point of view.

Up close the straight lines still looked like straight lines, but their origin remained a mystery. In most places the salt knobs form in a seemingly random pattern. (More on this in a future post.) Except in Salar de Navidad. There the salt formations line up in rows so straight it looks as if they’re marching across the desert. Davila wasn’t sure why, but he speculated that it might be an artifact that resulted from the bulldozing of the salar.

I don’t know about the scientists, but from my perspective, Salar de Navidad was a big hit, great for photography. In places it reminded me a lot of images of Mars. One of the most beautiful features was a wide channel that cut through it. “From satellite images, these large channels look like the classic channel that flows into the lake,” Davila said. But there hasn’t been a lake there for millions of years. “Now we see the whole thing dried up.”

Expedition leader Jacek Wierzchos examines a halite rock for evidence of bacterial colonization. For reasons not yet completely understood, fewer of the halite formations in Salar de Navidad are colonized than are similar rocks in other nearby salars. Credit: Henry Bortman

Although some of the halite knobs in Salar de Navidad are colonized by bacteria, the extent of colonization there is much lower than in Yungay and in other similar ultra-dry salars. That’s another mystery. One possibility is that because the knobs are so young, having just turned 20, they haven’t had time to become extensively colonized. Another is that because Salar de Navidad is so windy – it’s very windy – and because wind has a desiccating effect, the salt knobs there may have a harder time holding on to their moisture than they do in other places. It’s the moisture retained by the salt that makes the halite rocks habitable.

For those interested, panoramic images of Salar de Navidad can be explored here and here. They were taken with a GigaPan Epic, an automated system that uses small digital cameras to produce large, detailed panoramas. GigaPan technology is based on the panoramic cameras used on NASA’s Spirit and Endurance rovers.

Once we were done at Salar de Navidad, we headed for Yungay to set up camp. Accommodations there were far from luxurious. Although there is an old building there that was used by the University of Antofagasta when it was an active research station, the building is now abandoned. There is no available water or electricity. But there are a few trees. One of the main activities of the research station was an experiment to see whether various plants, including corn and other vegetables, could grow in the poor soil.

All that remains from that experiment are a couple of bone-dry, empty furrowed fields, and perhaps 20 trees, 10-15 feet tall, planted in two rows spaced a few yards apart. The trees’ leaves look like long, thin, gray-green pine needles and are rimed with salt. The trees absorb salt from the soil, then sweat it out through their leaves. They have survived because at Yungay the water table is relatively close to the surface, close enough for the trees’ root systems to reach it. But even the trees are dying. Nearby mining activity consumes tremendous amounts of water and the water table has been dropping steadily for many years.

Having finally arrived at their campsite in Yungay, expedition team members engaged in a traditional post-fieldwork ritual: drinking beer. (Note trees in the background.) From left to right: Jocelyne DiRuggiero, Petr Vitek, Octavio Artieda, Alfonso Davila, Sergio Valea and Jacek Wierzchos. Credit: Henry Bortman