Coal extraction history

Between 1720 and 1990, the mining basin of the North and Pas-de-Calais delivered more than 2 billion tonnes of coal, according to the site manager, though an evaluation report cites approximately 2.4 billion tonnes.

Number of shafts and subsidence

The extraction was done through 852 shafts, but the site manager estimates around 600. The mining activity created voids underground, leading to ground subsidence of up to 20 meters, as reported by the State Geological Service.

Subsidence ponds and World Heritage

Five subsidence ponds, including the Mare à Goriaux, are part of the World Heritage site. These ponds are stable and show no signs of disappearing. The Mare à Goriaux, covering 112 hectares, is home to about 200 bird species.

Scale of mining activity

Over 270 years, the extraction of 2.4 billion tonnes of coal averaged nearly 9 million tonnes per year. This amount, when divided by France's current population, exceeds 30 tonnes per person.

Underground infrastructure

The mining created a network of 100,000 kilometers of galleries, more than two and a half times the Earth's equatorial circumference. This network spans 120 km in length and 12 km in width, reaching depths of 1.2 km.

Surface impacts

Mining left 326 spoil heaps, hills of mining waste, across the area. These, along with subsidence areas, are physical traces of the mining history. Ground subsidence affected surface watercourses, causing them to change direction.

Formation of subsidence ponds

Subsidence ponds formed when water from underground rose to the surface after mining stopped. The Mare à Goriaux, for example, was formed from three marshy areas that gradually merged into one body of water.

Diverse origins of ponds

The five ponds included in the World Heritage site have different origins. The Mare à Goriaux formed from marshy areas, the Amaury Pond resulted from canal overflow, and the Argales Pond emerged from the sinking of a spoil heap.

Management of water

Pumping stations were installed to manage the rising groundwater, which interacts with pipelines and roads. These ponds are now recreational areas, offering the public a direct view of the post-mining landscape.

Variability in figures

The exact figures for coal extraction and subsidence vary, with estimates ranging from 2 to 2.4 billion tonnes and 20 to 25 meters of subsidence. A range of more than 2 billion tonnes and up to 20 meters is a more accurate representation.