Lac de Derborence

Lac de Derborence is a mountain lake in the municipality of Conthey, in the Swiss canton of Valais. It lies beside the hamlet of Derborence on the northern slope of the Rhône valley, above the village of Ardon. No glacier carved this lake: a disaster made it, when fallen rock closed off a river.

How did Lac de Derborence form?

The first major rockfall came on 24 September 1714. A second one, on 23 June 1749, was larger still. An estimated 50 million cubic metres of rock came down the mountainside and blocked the Derbonne river. Water built up behind the barrier and the lake appeared. Swiss sources describe it as the largest historically recorded rockfall in the country, with a vertical drop of around 1,900 metres. The 1749 debris followed the right flank of the earlier 1714 deposit.

What will you see there?

The Derborence valley is now a nature reserve, protected since 1961. The old forest growing on the debris mounds is the most valued part, and it is described as one of the last primaeval mountain forests in the Alps. The terrain is lumpy and uneven, with boulders, hummocks and trees rooted in the old rockfall, which gives a clear sense of the scale of what happened more than two centuries ago. The Vaud Alps rise around the valley, and their rock walls reflect in the lake.

How do you get to Derborence?

A narrow road leads up to the valley from Conthey. The drive is part of the experience: the road climbs out of the Rhône valley towards the reserve and calls for careful driving. Check current road conditions and access on the Valais tourism website before you set out, since mountain conditions change with the season. Walking routes pass nearby, including the Sanetsch–Muveran trail.

When should you go?

The easiest time is the snow-free season, when the road is open and the paths through the debris and forest are walkable. Bring shoes with a solid sole and a warm layer, because mountain weather turns quickly. The area is protected, so stay on marked paths and take your litter with you.

Who is it for?

Anyone who wants to see something in the Alps beyond the classic summit view: the mark of a natural disaster that the forest has since reclaimed. A calm walk around the lake and nearby paths fills half a day. Photographers, nature lovers and geology fans will find plenty to look at.

Frequently asked questions

How did Lac de Derborence form?

Through the rockfalls of 1714 and 1749. The 1749 debris blocked the Derbonne river and the water formed the lake.

Is Derborence a nature reserve?

Yes. The valley has been protected since 1961, and its old forest is among its most important natural features.

Which municipality is the lake in?

Conthey, in the canton of Valais, Switzerland.

Is the drive difficult?

The road from Conthey is narrow and steep, so it needs attention. Check current access information before you go.