Jurassic Joy

The Jurassic (as in “Jurassic Park”) is a geological era that lasted from roughly 200 million years ago to 145 million years ago. This period falls right in the middle of the “age of dinosaurs”. The name Jurassic actually derives from the Jura, a mountain range stretching across parts of France and Switzerland, the basis of which was formed during that period. This range is just north of the larger and taller Alps, and is considered part of the “Alpine foreland”. Because of its mostly limestone makeup, it features many beautiful gorges, cliffs, and caves, eroded by wind and water over eons of time.

A view over the Jura from the top of Mont Tendre, at 1679m altitude the highest point in the Swiss part of these mountains.

The Jura mountains form an arc along the Franco-Swiss border of roughly 370km in length, with a maximum width of 75km. During the Jurassic period this area was mostly covered by sea, and marine sediments were deposited on the sea floor. In some areas this sediment layer reached a thickness of between 1.5 and 3km.

The formation of the actual mountain range began in the Cenozoic era (the past 65 million years) as part of the same uplifts that formed the Alps, due to the collision of the Adriatic and Eurasian tectonic plates. Because of its relative softness, the limestone layer, now well above sea level, began eroding away, giving rise to many beautifully sculpted rock formations.

The thick limestone layer exposed at the Creux du Van.

Limestone is very porous, which means water can easily penetrate the rock and erode it from the inside out. This has given rise to many caves in the Jura mountains.

The view from inside one of the many caves in the Jura.

The Grottes de Vallorbe (“Vallorbe Caves”) in the Jura were first discovered and explored in the 1960s. In the 1970s they were opened to the public, and since then the accessible area has been expanded and improved over the years. This system of caves contains many spectacular stalactites and stalagmites, and even an underground river!

Stalactites and stalagmites form when water enters the porous limestone rock from above and dissolves some of it as calcium carbonate. When this water reaches the ceiling of a cave, it drips down while leaving a tiny calcium carbonate deposit on the ceiling. Each subsequent drop deposits another bit of calcium carbonate. Eventually, these deposits will form a narrow and hollow tube. When these tubes (or “straws”) become filled with debris, the water will start flowing along the outside, depositing even more calcium carbonate and forming a more solid stalactite. The water drops that fall down from a stalactite also deposit some calcium carbonate on the cave floor. Over time, this gives rise to a stalagmite. This process can take thousands or even millions of years, as the average growth rate of a stalactite is less than one millimeter per year.

Inside the Grottes de Vallorbe.

With several rivers flowing through, the Jura mountains also contain spectacular gorges worn out by these flowing waters. In some places these gorges are only a few meters wide, and are only accessible on foot.

A narrow part of the Gorge de l’Areuse.
A small waterfall in the Gorge de Poëta-Raisse.

All these beautiful formations make for a wonderful playground, sculpted over millions of years by the forces of nature. And thanks to modern science, we can understand and reconstruct the processes by which they formed. The beauty and science of nature, combining to making for some Jurassic joy…

The river Le Doubs flowing through the Jura mountains.

All photographs © Wim Hordijk

This article is part of the Beauty and Science of Nature series.