Friday, November 2, 2012

A Visit to the Bex Salt Mines, Oct 30th

One of the places that I have wanted to visit since we have been living in Switzerland is the Bex Salt Mine.  The weather on Tuesday was sunny and warm so I decided  to make the trip.

Here is the train station in Bex (pronounced Bay).  It is about a 30 minute train ride east of Vevey.

Bex is similar to many of the small towns in the area surrounding Vevey.  It is located in the Rhone Valley and it is ringed by the Swiss Alps.  Following are pictures of the Alps that surround  the town.

Last night Paula and I were talking about living in Switzerland and how we never get tired of seeing the  mountains as they change with the seasons.

On the way to the "Mines de Sel de Bex" - The Salt Mines of Bex, I passed this car that was used to haul salt rock from the mine.

A view of the mountains where the salt mine is located.

About a mile from the Bex train station I followed this path all the way to the mine.  It was about a 2 1/2 mile trek.  I followed this same route when I returned to the train station.

I have arrived at the mine.  I am scheduled for the 11:15am tour.

A little history about the mine:

Between 200 to 60 million years ago, the present Rhone Valley was a shallow sea. When the sea evaporated, as the climate warmed up, the Bex salt deposits were formed.

All through the Middle Ages Switzerland had to rely on importing salt, mainly from Franche-Comte (the region around Burgundy, France), an expensive business, not least because of the transportation costs. 

Then, in the mid fifteenth century, legend has it that a shepherd pasturing his flocks above Bex noticed that the animals preferred drinking from two particular springs. Tasting the water himself, he discovered that it was salty. Out of curiosity he tasted the water, and finding it salty, took a full cauldron and boiled it. When the water had evaporated, he discovered that salt crystals had formed.
This led to further investigation, principally by the Bernese authorities, who began to mine the hills around Bex. 

In 1554 a large deposit of salt was discovered. They used natural evaporation to produce the salt.  Starting in the 16th Century, they began to replace natural evaporation with boiling to speed up salt production. The first underground tunnels were dug in 1684 to find new salt sources.

The first steps for the recuperation of salt were limited to tapping it at the spring. It then became necessary to proceed by digging deeper in order to reach the water, at a lower levels, by means of stairs. By 1684 the springs had diminished and huge caverns had to be dug to reach the immense reservoirs of saltwater in the mountain. A labyrinth of shafts, stairs and caverns were excavated over more than a century. This gigantic piece of work was carried out at first with hammer and chisel and later on with blasting powder.

The saline rock, that was mined, was cut up in the underground quarries. These blocks were then grouped by twos or threes and transported into the caverns, the desalination sites. It is here that the salt was liquefied by washing the blocks. The brine was then pumped, to the salt works of Bex, through pipes made of trunks of larch trees. This was an expensive form of exploitation, requiring a large workforce.

Around 1877, the wood-burning stoves, used to evaporate the water, were abandoned and replaced by a new technique: salination by thermo-compression with the Piccard apparatus (named after the inventor who was at the time manager of the salt works at Bex). This system, steadily improved with time, is still in use worldwide today. It works on the same principle as the heat pump. Brine is brought to boil in evaporators using live steam generated in boilers. Then the steam is compressed, increasing its temperature, before conveying it to the evaporator, where it serves as a heating agent. All this happens in a closed circuit.  At the end of the process, salt is produced.

In recuperating the heat contained in the steam, this new technique saved a considerable amount of energy. From 1867 to 1913, the two largest caverns "Coulat" and "Bouillet" furnished 164,486 tons of salt. Within a century, thanks to the various processes used, production at the salt works increased tenfold, whereas energy consumption was reduced to less than a tenth of what it used to be.  Thus, the cost of producing salt was greatly reduced.

In the 1920's, with the invention of the pneumatic drill, it allowed the miners to more quickly reach the veins of salt, thus, again lowering costs.

In the 1960's they started using hydraulic mining. This method involves using a 4-inch drill bit, which enables them to drill between 35 to 50 ft. per day to extract core samples.  The core samples, once extracted, must contain a minimum salinity of 30% to justify exploiting the borehole.  If this is the case, a double pipe is inserted into the borehole.  Spring water is then injected at high pressure.  The water spreads out into the salty rock and starts dissolving the salt up to 1,300 ft. around the borehole.  Once saturated with salt at 30%, the salty water, called brine, is pumped up to the surface through the second pipe and is stored in their brine reservoir.  Currently, approximately 50 boreholes, containing 22 miles of steel pipe, are placed in the saliferous rock.  Without this modern technology, exploiting these salt deposits, economically, would not be possible.

At the refinery, the water is evaporated from the brine, leaving grains of salt. These grains are placed in revolving cylinders, into which hot air is forced to speed the drying of the salt. The dried grains are then graded for purity, grain size, and their final use. 

According to our guide there are over 14,000 different uses for salt.

The Visitor Log Book in the Marie-Louise Reservoir.
The tour of the mine started with a film presentation and exhibition relating the fascinating story of salt mining from 1684 to the present.  The presentation is in an old reservoir that was dug in 1826 to hold the salt water that was produced in the mine.  The reservoir is known as the "Marie-Louise Reservoir" (named for Empress Marie-Louise, the wife of  Napoleon). The film shows the immense amount of effort that went into searching for salt sources underground, the digging of the mine shafts and the breaking up of the rock to extract the salt, which was, at the time, worth its weight in gold, thus it was known as White Gold. 
Two of the most famous visitors were:
Alexandre Dumas (1802 -1870), see picture above.
He was thirty years old when he visited the Bex salt mines.
Fleeing Paris, which was in the throes of a cholera epidemic, the young writer, who had travelled by stagecoach, finally reaches the foothills of the Dents du Midi, (French for "The Teeth of the South") which is a mountain composed of seven distinct summits, which is the location of the mine.
A miner leads him into the bowels of the earth, this frizzy-haired giant proved less intrepid than his “Three Musketeers”.
With great humor, Dumas recalls his adventure in the mines, scuttling down ladders “like a beetle down a blade of grass”, asking his guide if “this foolishness” was nearly at an end, and dropping his lamp which his eyes followed “until finally a dull thump could be heard as it made contact with the water, signalling to me that it had arrived at our final destination before we had”.

Empress Marie-Louise (1791 - 1847).
She visited the Bex salt mine on July 15, 1814.
Gathering her blond hair under a black hood, Empress Marie-Louise entered the Bex salt mines ...
Walking in front of her, torch in hand, the miner took her on a journey through a subterranean underworld...
Around the corner from a deep well, the young woman discovered a vast room of columns covered in gypsum crystals, the reflection of which could be seen in a salt lake.
According to our guide, she admired the boldness of this feat of human engineering and all thoughts of her husband Napoleon, exiled on the island of Elba, vanished that day.

After the film, this train took us 4,921 ft. into the very heart of the mountain.  When we departed the train, for the tour, we were 1,476 ft. under ground.

One of the many caverns that have been excavated.  The air temperature remains a stable 17 degrees Celsius (62.6 degrees Fahrenheit) year around.  The mine is ventilated naturally by shafts crossing the upper and lower floors.  The ambient humidity is 80%.  The oxygen level is 19% (it is 21% outside the mine).

One of the many tunnels that we went through during the tour.

The rock in the mine tunnels is anhydrite (or dehydrated gypsum).  It absorbs humidity and by doing so it produces heat.  Without this beneficial side effect, the temperature here would not exceed 12 degrees Celsius (53.6 degrees Fahrenheit).

This is one of the old salt water lakes.  The wooden paddle wheel, which is setting in the brine solution, was turned by water and the brine was piped, by wooden tubes, to the salt works to be turned into salt.

The brine solution is saturated to 30% which is 10 times saltier than seawater.  The lake of saturated brine has a density of 1.2 which is comparable to the Dead Sea.  It is impossible to drown in it, because you would float like a piece of wood.  The temperature of the solution is 17 degrees Celsius (62.6 degrees Fahrenheit), too cold to swim in.

A picture of a pneumatic drill, no longer in use.

Here we are coming out of the mine at the end of the tour.

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