The girl from Sahel

We were lost. Lost in the sandy Sahel of northern Mali. The Toyota 4x4 managed the terrain well, but we couldn’t track our position on the map. The Sahel stretched out endlessly in all directions, and today the landscape was partly masked by the sandy veil lifted by the strong winds. What to do now? Should we try to follow the tracks back to M’Bouna, the village we came from? We chose to continue. The guides told us that we might get lucky and still find the localities we were looking for: Areas with a red oxidized soil or sediment layers that were apparently formed from the heat emanating from shallow volcanic intrusions. 

We continued and came across a small valley with some trees and a water well. A few guys rose among the animals (picture 1) and came to meet us.

(Picture 1)

They gave us new directions and we moved on. After a while we drove through a small settlement with Tuareg nomads (picture 2). We stopped, and the guides got out of the cars and talked to the locals. I stayed in the car.  

(Picture 2)

Kids came running to see what all the fuss was about. I pulled down the window and took a few pictures. The kids didn’t seem to mind. On the contrary. They boys wanted their pictures taken, and to see the results on the camera screen. They all got very exited. Then a girl, somewhat older that the boys, pushed them aside and pointed at the camera before she closed her eyes. I took her picture. She had a look at it and smiled. We left the settlement, and continued our search. 

(Picture 3)

Later that day we found the red rocks, and took some samples. The landscape seemed endless. Sand-polished rocks with thick weathering crusts were silent witnesses of the passage of time and climates. I took a picture before we headed back to M’Bouna.

 (Picture 4)

 

What hit Tunguska in 1908?

In 2004, I visited East Siberia for the first time. Together with colleagues from Oslo and Russia, we targeted the enormous sedimentary basin called the Tunguska Basin. The basin is cut by large rivers such as the Stony Tunguska and the Lower Tunguska – names that are familiar for those interested in Earth mysteries. Because in late June 1908, something exploded in Siberia that created shock waves that knocked down 2000 square kilometers of the surrounding Taiga and was recorded all the way to central Europe. It’s known as the Tunguska event. But what happened? 

Most scientists believe it was caused by a meteorite or asteroid impact, whereas others put the blame on sub-surface explosions. The problem is that the evidence is missing. There is apparently nothing out there, not even a small crater that can verify that the event was due to an impact.

We went there by helicopter in late August 2004, and camped in the middle of the estimated epicenter of the blast (Picture 1). We put up the tents on the permafrost ground, and went searching for volcanic rocks. Yes, volcanic rocks. Our target was not to study the impact site per se, but to investigate the geology in the area. We knew from Russian maps that the surrounding hills were composed of volcanic sill intrusions, and the idea was to sample those hills, and look for structures associated with volcanic gas release. One of the few outcrops of volcanic rocks is shown in picture 2. Fieldwork in the Taiga is a challenge… 

Picture 1: The epicentre of the Tunguska 1908 event.

 Picture 2: Outcrop of a dolerite sill.

The next day we moved camp to the shore of Lake Cheko, where met the park ranger. In picture 3 you see our helicopter, the kitchen, and the southern part of the lake.       

Picture 3.

The problems started the following day, after we came back from a trip looking at the geology of the south-western part of the area. We saw the trees that fell in 1908, which still dominated the landscape (picture 4). We sampled some interesting volcanic rocks that were deposited in water, most likely shallow lake water.

When we returned to Lake Cheko, the police had arrived and gave us a hard time due to visa-related issues. Guns were pulled, a policeman got wet, and we had to answer questions about why and what, where and how.

We left the lake and the Tunguska site a couple of days later. The question about what happened there still lingers.

Epilogue: An Italian research group in Bologna has visited Lake Cheko several times, and they claim that the lake occupies the crater formed in 1908. But they are not entirely sure: “Up to now, it is not clear whether the great explosion was due to a comet or an asteroid or something else. We are searching for an answer.” (http://www-th.bo.infn.it/tunguska).

 Picture 4. 

 Picture 5. 

Muddy encounters

Nothing compares with action geology, when you are out in the field and can observe geological processes occurring on a timescale that compares with the lifetime of your favourite sandwich. For me, working with mud volcanoes has been enlightening in that respect, despite the muddy nature of the subject. 

The pictures of this week are from Azerbaijan – the country where most of the spectacular onshore mud volcanoes are located. Many of them have frequent eruptions (every 10-15 years or so) and are characterized by dormant periods in between which in fact are far from dormant or boring. Constant seepage of gases, mud, and water take place in the volcano centres, producing landscapes and morphologies on the surreal side of the spectrum. I have been to these volcanoes two times and wonder when I will be back...

The Bahar mud volcano field. One of the biggest mud cones is constantly active and is composed and build from countless small flows.

 A field of gryphons, characterized by their relatively small size (up to 2-3 meters tall) and clustered occurrence.

 Bursting of a bubble in a gryphon.

 The Caspian Sea as seen from the shore along the Bahar mud volcano. The poles are part of the infrastructure that used to belong to offshore oil platforms. Oil fields are commonly associated with the mud volcanoes.

 

For more information about these volcanoes, check out this paper.