Fuel pollution threat persists beneath debris at Blatten

Around 150,000 litres of heating oil and fuel remain somewhere beneath Blatten’s debris field. The estimate comes as Canton Valais prepares for the village’s reconstruction, more than a year after the Birch Glacier collapsed and sent rock, ice and debris into the Lötschental Valley on May 28, 2025.

The slide buried about 90% of Blatten, including 130 houses and the parish church. It also swept cars, machinery, batteries, refrigeration units and household storage tanks beneath the new landscape. The debris blocked the Lonza River and created a lake behind the collapse. Oil slicks appeared on the water soon afterwards.

A new environmental study commissioned by Valais and reviewed by Swiss public broadcaster SRF puts the fuel volume beneath the buried area at around 150,000 litres. The estimate does not establish how much entered the environment. Some tanks may have survived intact, while other fuel could have leaked during the collapse or afterwards.

That uncertainty now forms part of the reconstruction timetable. Authorities consider pollution monitoring essential, while maintaining that the contamination risk does not make rebuilding impossible. Work was already under way in Blatten in August 2026, according to images cited by SRF.

The study identifies hydrocarbons as the main environmental threat beneath the rubble. Residents were asked to report heating oil tanks and other substances stored in their homes and buildings when the landslide struck. Authorities received 220 completed questionnaires, covering approximately 80% of the households and buildings buried by the disaster.

The responses recorded more than fuel. Residents reported motor and transmission oils, batteries, refrigerators, paints, solvents, gas cylinders and ammunition. These materials are dispersed through a debris cone created by a collapse that released about 9 million cubic metres of rock, ice and soil.

The study’s authors say a full recovery operation would be disproportionate because the pollutants’ precise locations are unknown. Excavating a huge and unstable mass to locate every tank and container could create further hazards, while the available evidence does not yet show widespread water contamination.

That assessment does not remove the need for controls. Water can move relatively easily through the debris cone, carrying dissolved pollutants or fuel residues into lower layers. Some substances could also emerge as gases or vapours when excavation and construction disturb buried structures. Valais is therefore examining whether drainage systems will be required in areas selected for rebuilding.

The first measurements have found no unusual contamination, but Valais is extending the watch. The environmental study warns that the oil slicks seen on the lake show that at least some heating oil and fuel escaped from the buried village. Researchers also warn that pollutants could eventually enter groundwater beneath or beyond the debris cone.

So far, water measurements have not detected anything out of the ordinary. The authors say that result cannot settle the issue because water continues to penetrate the debris and conditions may change as the rubble consolidates, drains or is excavated. Surface water and groundwater monitoring must continue over the long term and cover a wider area.

Canton Valais plans to expand the monitoring network across the entire Lötschental Valley, where Blatten sits. The approach reflects the valley’s connected water system and the difficulty of predicting how contaminants could move through a landscape reshaped by the collapse.

The programme will need to track both the lake and groundwater as reconstruction proceeds. New excavation, fill and drainage can alter water pathways. Authorities will also have to account for vapours and gases from buried materials when they assess construction sites and future public spaces.

Reconstruction will depend on how engineers handle the debris, not simply where they draw the new village boundary. Updated hazard maps identify areas where rebuilding is theoretically possible, including sections directly above the rubble that buried old Blatten.

Christine Genolet-Leubin, head of the Valais Department of the Environment, said it would be disproportionate to conclude that construction could no longer take place. She said the practical issue is determining how deeply workers excavate and how much material they place above the existing debris.

Those decisions will shape environmental protection as well as structural safety. Excavation could expose tanks, containers or contaminated soil. Filling and drainage could redirect water through the debris cone. Authorities are examining whether drainage systems will be needed in areas earmarked for construction, while monitoring will continue after buildings are completed.

The scale of the original disaster remains central to every decision. The 9-million-cubic-metre collapse destroyed homes, public buildings and infrastructure in a settled Swiss Alpine valley. Rebuilding therefore requires hazard mapping, geological engineering and a long-term pollution plan working together. The latest study gives officials a clearer inventory of buried materials, but it does not yet reveal the precise location or condition of every fuel tank beneath Blatten.