Volcano Circuit in Freedom - Lake Bouchet

Depart from the town of Cayres, latitude 44.9099000 (N 44° 54’ 36”), longitude 3.7980600 (E 3° 47’ 53”)

• A remnant of a volcano

• The summit of Mount Maillon offers a relaxing break before descending quietly to the Goat Cross. You have just climbed a volcano older than the crater that contains Lake Bouchet. You have mainly walked on reddish slag (projected volcanic rocks with very irregular shapes). Eventually your gaze saw oval and smooth shapes: volcanic bombs.
• The summit of Mount Maillon dominates the large basin occupied by the lake hidden by spruce plantations. However, below, you will have no trouble seeing a small open cavity in the dark red slag. It is an old quarry where men came to detach slags of slag in regular layers using the natural structure of the rock.
• You will also see the different layers of the ancient volcano, stacked very regularly.
• It's a remnant of a crack volcano, without a crater. The volcano was partly located at the site of the present lake. The tremendous explosions that opened the Bouchet crater largely destroyed the ancient volcano of Mount Bee.

• Volcanoes can be explosive

• The size of the crater is imposing with a diameter of between 700 and 800 m. It is not totally round. It is extended deep by a large funnel (path) that descends to nearly 100 m. It is a volcano born of underground eruptions when the rising magma met one or more water bodies. Very strong explosions linked to the release of tremendous amounts of water vapour and rock dust gave rise to very large plumes that could rise several km high.
• Several hundred eruptions followed until the vast crater was filled by water in the water of the water in a second phase.
• The lake's vases, which are more than 100 km away, have retained a level of volcanic ash from the Sancy massif (Puy-de-Dôme) which bears witness to the last eruptions of this great volcano (275,000 years old).
• A gigantic eruption that must have frightened the first men for a long time!

• Projections of the explosive volcano

• You'll just have to follow the lines that separate the layers of volcanic fallout. To the left, they take you to the crater that existed before the lake.
• Each violent eruption at the crater level immediately resulted in the installation of a layer of very fine projections from the violent explosions.
• Large blocks of old rocks interrupt the regular arrangement of the layers. From the crater, they were thrown violently and pushed into the large clouds of dust, before falling back and breaking the layers already deposited.
• This embankment is one of the few places where it is possible to observe closely the deposits resulting from the eruptions that created the crater. The forest hides the other layers under deep soil.

• The lake that witnesses changes in climate

• Between 1980 and 1990, the lake's vases were dug to a depth of 50 m. The oldest date back more than 300,000 years. That means the crater is even older.
• A drill had to be installed from a boat to reach such a depth. The aim was to reassemble mud cylinders, the carrots, in order to find the pollen grains accumulated during geological times.
• Pollen studied in the laboratory has allowed us to discover successive vegetation and thus to inform us about the evolution of the climate. Thus the lake of Bouchet and the marsh of Landos, very close, allowed the scientists of Marseille to show that five glacial periods with shaved vegetation (cold steppe) followed, followed by five episodes of warming marked this time by the presence of hardwoods. All over a period of 450,000 years.

• A lake whose level has varied

• It is hard to imagine that the lake as you see it today has not always been at the same level.
• It was geologists who discovered above the sides of the crater the traces left by an ancient lake with sand and pebbles that testify to a very high level, up to the edge of the crater and in the middle. The lake would be at its current level (the lowest) in 120,000 years.
• Its level varies very little during the year (50cm) and its diet remains a mystery. Despite efforts to search for deep sources, divers have not found enough to satisfy human curiosity.
• It was a scientist from The Puy in 1790 who, in winter on the deeply frozen lake, brought down a large stone through a hole in the ice at the end of a large rope. It was the first time that there was nearly 28 metres of water in the centre of the lake.