How Coal Waste Mountains in Northern France Became a UNESCO Heritage Site
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In brief
The twin slag heaps of Loos-en-Gohelle, built from decades of coal-mining waste and left standing instead of demolished, developed a warm microclimate that now supports around 190 plant and 159 animal species. In 2012 UNESCO listed the wider Nord-Pas-de-Calais Mining Basin, including these heaps, as a World Heritage Site.
From Waste Rock to Twin Peaks
In Loos-en-Gohelle, a small town in the Pas-de-Calais department near Lens in northern France, two cone-shaped mounds of coal-mining waste rise above the flat farmland. Known as the twin terrils of the former Fosse 11-19 mining pit, they reach about 186 meters above sea level — roughly 150 meters above the surrounding land — making them among the tallest mining-waste piles in Europe, according to Spanish outlet Xataka and the Pas-de-Calais regional tourism board.
According to the tourism board, most of the roughly 24 million cubic meters of waste rock spread across 90 hectares was deposited mainly between 1960 and 1970, with a connecting flat-topped mound added in 1970. Xataka reports that dumping at this particular site ended by 1986, when the pit was abandoned.
Rather than leveling the heaps, as happened elsewhere, the town's mayor at the time, Marcel Caron, who led Loos-en-Gohelle from 1977 to 2001, chose to leave them standing, Xataka reports. National Geographic notes that authorities elsewhere in the mining basin had tried aerial seeding to force vegetation onto similar slopes before abandoning that method in favor of letting the terrils recover on their own.
A Mediterranean Microclimate in Northern France
The heaps are made largely of dark slate and shale, which absorb solar radiation and create warmer, drier conditions than the surrounding farmland, Xataka reports. Those conditions allowed Mediterranean-type vegetation to take hold far north of its usual range, including wild orchids, alongside various insects and reptiles. Xataka counts 190 plant species and 159 animal species on the 11/19 terrils and describes the site as a stopover point for migratory birds.
National Geographic reports that the terrils also host species such as the European nightjar and the natterjack toad, a species more commonly associated with coastal habitats. The Pas-de-Calais tourism board adds that plants not usually found in the region, including horned poppies, have established themselves on the slopes.
A separate, more recent survey covering the whole commune of Loos-en-Gohelle, not only the 11/19 terrils, recorded 460 plant species, 117 bird species and 27 mammal species by the end of 2023, according to the municipality, which cites a biodiversity assessment carried out by the CPIE Chaîne des Terrils association. The municipality lists a neglected-orchid variety and the cornelian cherry among protected species found locally, describes red squirrels and hedgehogs as common, and flags the spread of invasive Japanese knotweed as an emerging concern.
Biodiversity figures reported for Loos-en-Gohelle
Survey scope
Plant species
Animal species
Source
Terrils 11/19 (twin heaps)
190
159 (birds, reptiles, insects, etc.)
Xataka
Whole commune, end of 2023
460
117 bird species + 27 mammal species
Loos-en-Gohelle municipality / CPIE Chaîne des Terrils
UNESCO World Heritage Listing
On 30 June 2012, UNESCO inscribed the Nord-Pas-de-Calais Mining Basin on its World Heritage List, citing the site's continuing cultural significance as a reflection of Europe's industrial past, according to the Pas-de-Calais tourism board and National Geographic. The listing covers mining infrastructure across the wider basin, not just the Loos-en-Gohelle terrils.
National Geographic reports that the basin as a whole produced nearly 2.4 billion tons of coal between 1720 and 1990, supplying roughly half of France's coal output between 1940 and 1960 and contributing to the country's post-war reconstruction; the last mine in the basin closed in 1990.
Public access to the Loos-en-Gohelle terrils remains restricted. The Pas-de-Calais tourism board says one of the two cones is fully protected and closed to visitors, while the second can be reached via two marked viewpoints overlooking landmarks including the Bollaert-Delelis football stadium and the Louvre-Lens museum.
Tourism and Economic Recovery
The Louvre-Lens museum opened in 2012 on the site of a former coal mine in nearby Lens and includes a garden built on a flattened slag heap, according to National Geographic. The 11/19 site in Loos-en-Gohelle has itself become a visitor hub offering guided hikes and art-therapy or meditation sessions, while other former mining land in the basin now hosts hiking and cycling routes, an artificial ski slope, an ultra-running trail and a vineyard known locally as 'Charbonnay.'
National Geographic also reports that unemployment in Lens fell from 15.5% in 2009 to a pandemic-adjusted 9.4% in early 2021, alongside the growth of small tourism and agritourism businesses in the area.
The slag heaps … are the national monuments to the miners.
— Bernard Lefrançois, former miner, quoted by National Geographic
Questions
Where exactly are the Loos-en-Gohelle slag heaps located?
They stand in Loos-en-Gohelle, a town in the Pas-de-Calais department near Lens, in northern France, according to Xataka and the Pas-de-Calais tourism board.
How tall are the twin terrils?
They reach about 186 meters above sea level, roughly 150 meters above the surrounding plain, which Xataka and the Pas-de-Calais tourism board describe as among the highest mining-waste heaps in Europe.
When were the heaps built and when did mining stop there?
The tourism board says most of the waste was piled up mainly between 1960 and 1970, with an added mound in 1970; Xataka reports that dumping on this specific site ended by 1986, while the wider mining basin's last mine closed in 1990, according to National Geographic.
What UNESCO status do the heaps have?
They are part of the Nord-Pas-de-Calais Mining Basin, which UNESCO inscribed as a World Heritage Site on 30 June 2012 as a living industrial cultural landscape, according to the Pas-de-Calais tourism board and National Geographic.
Can visitors climb the terrils today?
The Pas-de-Calais tourism board says one of the two cones is fully protected and closed to the public, while the other can be climbed via two marked viewpoints.
How the world is telling it
SpanishSpanish outlets such as Xataka frame the story as a striking before-and-after transformation, emphasizing that waste once seen as an industrial scar became, forty years later, a refuge for species normally found in warmer climates.
FrenchFrench local sources, including the Loos-en-Gohelle municipality and the Pas-de-Calais regional tourism board, present the terrils as a point of civic and heritage pride, focusing on protected status, regulated visitor access and ongoing biodiversity monitoring by the CPIE Chaîne des Terrils association.
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