Grasse’s only natural lake and a ‘Year without Summer’

There is a small lake, located just off a scruffy industrial road rather romantically called Chemin du Lac, in Le Plan de Grasse. Named Lac de Saint-Joseph, it’s nearly circular and only about 50 metres wide. It looks rather odd, almost as if it might be man-made, perhaps by mineral extraction or for water storage.

Lac St-Joseph from Google Earth with (inset) its position relative to Grasse. Chemin du Lac, which runs alongside the Mourachonne stream, is the road across the upper right corner of the main image. Access to the lake is via a footpath starting from the centre-top of the picture, through the trees.

In reality, it’s Grasse’s only natural lake (though maybe we’d call it a pond in English) and recently the town has made it more accessible and provided some signage.

And there’s more to this little feature than meets the eye.

Rivers, falls and lakes or ponds are often ephemeral in areas like Grasse which, geologically speaking, are limestone dominated. Many streams and some rivers can disappear completely in summer when rainfall is low, although they are usually still flowing underground, while cascades (such as the one in Les Ribes) appear only after heavy rains. Because rain water, which is mildly acidic, slowly dissolves limestone, there are many channels, holes and caves below the surface which we cannot see. Lac St-Joseph was originally one of these caves, into which the surface has at some time collapsed. But sediment and run-off subsequently filled up the hole beneath the cave and the lake was formed above this natural plug.

Lac Saint-Joseph from its viewing platform

A disappearing lake

Lakes like St-Joseph can abruptly disappear if the plug is in some way disturbed. The most common cause is heavy rain creating high water pressure which loosens the plug, causing the lake to drain rapidly through the bedrock like an unplugged bath. And in 1816 this is what seems to have happened to Lac St-Joseph.

A local historian named Paul Sénequier, writing in 1892*, says that “in 1816, [the lake] suddenly drained: this was quite an event. Every Sunday, a large crowd of onlookers would gather at the site to contemplate the dried-up lake; vendors of nougat and scalded pastries would set up shop there, and for a while, a sort of country fair took place on the banks of the vanished water”.

Although I can find nothing in the records about it, the sudden draining of the lake was almost certainly caused by the unprecedented weather of that year.

The weather in 1816

On 5th April 1815, a volcano named Tambora on the island of Sumbawa in what is now Indonesia exploded. It is believed to have been the most powerful volcanic eruption in recorded human history, five times larger than that of Krakatoa in 1883; it is estimated that the explosion threw around 160 cubic kilometres of material into the atmosphere. To put that into perspective, that’s enough to cover the whole land area of France to a depth of around 20 cm. To make things worse, there had been several smaller eruptions around the globe in the previous four years which had already built up atmospheric dust.

The residual caldera (the main vent) of Mount Tambora is over 7km wide. Some 4,000 feet of the original volcano was blown into the atmosphere. (Photo: US Geological Survey)

The result in 1816 was a so-called ‘Year without a Summer’ all around the world. Depressed temperatures (Paris hardly exceeded 15°C), exceptional rainfall and unseasonal frosts had catastrophic effects on harvests everywhere. In an era dominated economically by agricultural production, this meant food shortages which, because of the lack of seed grain for 1817, extended for 2 or 3 years.

The price of wheat in Europe rose by half in 1816 and doubled by 1817. There was unrest across a continent still recovering from the Napoleonic wars, with food riots taking place in many cities and towns. Typhus epidemics of the time were probably exacerbated by the weather. Flooding affected navigation of major rivers like the Rhine and Rhone, also affecting the distribution of food. In France, efforts to maintain the affordability of bread in Paris created shortages of grain elsewhere in the country, resulting in riots and unrest in the provinces where scarcity was made even worse.

Two masterpieces owe their origin to the Year without Summer: (above) JMW Turner's 'Sunset' (1816), whose orange theme clearly derives from the year's freak weather, is recognisably related to later works such as 'The Fighting Temeraire'; while (below) Mary Shelley's Frankenstein was created as a result of a weather-blighted summer house party in 1816 on Lake Geneva when Percy Shelley, Lord Byron and Mary challenged each other to write a ghost story. This is part of the original manuscript.

1816 in Grasse

In Grasse, unprecedented frosts in May almost destroyed the ‘rose de mai’ harvest and killed many orange trees used for neroli production, while the lack of summer heat drastically cut the jasmine harvest later in the summer.

The accounting records, in the archives and the Musée International de la Parfumerie, of perfumeries such as Chiris and Galimard demonstrate the impact, showing their paying at least five times the price for local flowers compared to previous years. Poor Anselme Chiris took over the business from his father Antoine in 1816: he must have walked straight into a major crisis. Even animal fats (for cold enfleurage) and firewood for the stills soared in price because of weather conditions.

One longer term impact was that these companies began to import materials such as musk, ambergris and civet. Later in the century, when the advent of steam distillation meant that Grasse’s fields could no longer supply enough raw material for them, the likes of Chiris and Roure were already familiar with sources abroad.

The ephemeral lake

It seems unlikely that the draining of Lac St Joseph in 1816 was a coincidence: exceptional and unseasonal rainfall is the most plausible reason. But the people of Grasse, whether peasants in the fields or perfumers and merchants in the town, certainly had more to worry about than an unexpected loss of a pond in 1816. So perhaps the fairs mentioned by Sénequier started when summers returned in 1817 and 1818 rather than in 1816.

Sénequier goes on to say that “since then, the….sinkhole, almost completely dry in summer, partially fills with rainwater in winter”. He appears to mean that during the nineteenth century the lake was seasonally ephemeral. If so, at some stage the plug must have become more permanent, since today the lake does not disappear during the summer.

Lac St Joseph today

The lake is close to the Mourachonne stream and certainly links into its watercourse below ground. But whereas the streambed is dry in summer (the water normally continues to flow below it), the lake remains almost full.

Grasse has recently opened up a footpath through trees to a viewing platform by the lake and added a small number of signboards about the local flora and fauna. The entrance to the footpath is for some reason unmarked, but it will make a nice five minute walk once our hot, dry summer is over and the vegetation looks green again.

Clockwise from top left. The Mourachonne stream nearby, dry during summer; the entrance to the footpath is marked by plastic posts but otherwise is for some reason unsigned; the edge of the lake, with water plants typical of static water; one of the signs, in this case explaining the relationship between the local flora and small fauna.

It’s certainly unusual to find a permanent lake like this one in a narrow flood plain such as that of the Mourachonne. It’s good to see its environment being recognised and looked after by the town.

* Grasse. Notes à la suite de l’inventaire des archives communales, Paul Sénequier, 1892