Glacier break leads to sea retreat
In the Swiss canton of Valais' Lötschental, the debris cone resulting from the collapse of the Lonza river's banks has allowed the river to carve new channels through its mass. At a press conference in Ferden, canton geologist Raphael Mayoraz reported a decrease in lake height behind the debris cone, dropping by one meter. Floating barriers have been installed to prevent the outlet from blocking, reducing the distressing volume of floodwater from approximately one million cubic meters to around 800,000 cubic meters.
The gradual draining of the water over the debris cone is good news, as it reduces the risk of the cone liquefying and causing a substantial amount of debris to flow down the Lötschental valley. Initial concerns of the unstable debris collapsing and sending rocks, ice, and rubble further down the valley have diminished, according to Mayoraz.
Looking ahead, weather conditions may pose a threat, with severe rain forecasted for several days, accompanied by melting ice on nearby mountains, which could destabilize the debris cone and increase the risk of a debris flow. Should such an event occur, it could put communities lower in the valley at risk.
Experts estimate that around a third of the nine million cubic meters of material that ended up in the valley after the glacier collapse is ice. The timing and possibility of this ice melting, along with the potential formation of cavities in the cone that could cause it to collapse, remain uncertain. Mayoraz warned that the cone is precarious, making it too risky to walk on.
The recent disaster was initiated by a collapse of rock material from the roughly 3,000-meter-high Kleine Nesthorn. After falling onto the Birsch glacier below, the glacier broke off last Wednesday and surged into the valley with massive amounts of ice, rock, and rubble. There is still loose material present at the breakaway points, indicating that the Kleine Nesthorn has not found equilibrium and continues to erode. Due to the steep terrain, further rockfalls could lead to more landslides.
Preparations have been made at the power plant in Ferden, some six kilometers downstream from the disaster area, to manage larger volumes of water or debris. The operator has partly emptied the reservoir to create space, and experts maintain that the dam will hold even under increased pressure. If a substantial amount of water collects, an alarm will sound when the reservoir is two-thirds full, giving residents of downstream villages Gampel and Steg time to evacuate. Both villages are near the point where the Lonza flows into the Rhone, where the river passes through relatively narrow concrete channels that can quickly overflow if flooding occurs. Residents have already packed their belongings, prepared to leave their homes at short notice, and will receive alerts via a warning app and sirens.
The Lonza water arriving at the Ferden dam is heavily polluted with sand and abrasion from the debris cone. In Gampel, excavators are working to deepen the drainage channels, as the sediment will settle further downstream.
Blatten, first mentioned in writing in the 15th century, lies almost completely buried under a meter-thick layer of debris at an elevation of around 1,500 meters. Even the church tower remains buried under this layer of rubble. Of the approximately 300 residents, only one local remains unaccounted for, with most having sought refuge elsewhere in the valley or with relatives.
The inhabitants have been coping with help from psychologists, as expressed by the Association for Psychological Emergency Aid in Upper Valais. They gather regularly for support. Mayor Matthias Bellwald expressed optimism concerning the rebuilding plans, stating that the community does not need pessimism or bureaucracy but practical solutions. He plans to present these plans with a timeframe soon.
The gradual melting of the ice in the debris cone could potentially rekindle concerns about debris flows, given the predicted severe weather conditions. The unprecedented disaster highlights the need for better environmental-science research, particularly in the field of weather-forecasting, to help anticipate and mitigate such events. As the weather shifts, it's crucial to monitor the stability of the debris cone and the surrounding mountains for any signs of instability to minimize the impact on the environment and the local population.
