By Imogen Foulkes
BBC News, Switzerland
Shrinking glaciers are causing tonnes of rock to break loose from one of Switzerland's most famous mountains, the Eiger, and crash into the valley below.
Upper Grindelwald glacier in 2000 and 1910 - the ice retreat is visible
On the east face of the Eiger, two million cubic metres of rock, enough to build two Empire State Buildings, is gradually splitting away from the main mountain.
Until recently, the rock was held in place by the ice of the lower Grindelwald glacier, but now the ice has melted, revealing a mass of unstable limestone.
Scientists say climate change is to blame for the disappearing ice.
In the 19th Century, the lower Grindelwald glacier stretched right down into the valley itself. Local people once even made a living from it, sending cartloads of ice to Paris, where the fashionable cafes used it in cocktails.
All over the Alps, glaciers have been shrinking, but what is worrying scientists most is the accelerated thaw that has taken place since the 1980s. During that time, Alpine glaciers have lost around 25% of their surface.
At Switzerland's Alpine Museum, an exhibition calling attention to the plight of the glaciers has just opened.
Entitled Glaciers in the Hothouse, the exhibition has dozens of pictures of Europe's glaciers from different periods in history. Organisers say the retreat of the last few years is the best visible proof of worldwide global warming.
Martin Grosjean, a specialist in glaciers and climate change at Berne University, says the current meltdown is simply not normal.
"We've got records on glaciers going back hundreds of years," he explained. "And it is completely normal for them to retreat and then grow, in response to the usual variations in climate.
"But what we are seeing now is extreme; an extreme reaction to extreme climate changes - it's a response to global warming caused by greenhouse gases."
For the time being, the Eiger's loose rock is not a hazard to local people because the boulders are crashing down into an uninhabited gorge.
Nevertheless Grindelwald's rescue services are on high alert. Many paths in the region of the glacier are closed, others have new signs warning that the frequent rock falls may cause dust clouds, poor visibility, changes in air pressure, and even small earthquakes.
Geologist Hansrudolf Keusen has spent much of the summer keeping a watchful eye on the Eiger. Each week, he surveys the loose limestone, and checks the water level in the gorge below.
Once a favourite tourist attraction, it is now closed, and the air is thick with the dust from fallen rock.
"In fact the biggest danger is down here," he said. "Not because a rock might fall on someone, because we've closed this area.
But the water in this gorge is the normal glacial melt water. If the falling rocks created a dam here, we could end up with a flood wave that could sweep down not just into Grindelwald, but all the way to Interlaken."
And even if there is no immediate danger, the consequences of such a huge rock fall are alarming to the thousands of tourists who flock to the resort of Grindelwald every year.
When 400,000 of those two million cubic metres fell down all at once, the village was shrouded in a thick cloud of dust for several hours.
Tourism is hugely important to Switzerland's economy, so officials are keen now to reassure visitors that everything is being done to ensure their safety.
"The Alps are not going to fall down overnight," said Hansrudolf Keusen. "They'll be with us for many years to come. But we do have to prepare for more events like this.
"We are already working on improving the safety on hiking trails, and on mountain railways. But at the same time, climbers and hikers will have to be more watchful too."
Europe's water tower
In the long term, however, scientists see the melting glaciers as problematic not just for Alpine tourist resorts, but for Europe as a whole.
Glaciers are also an important source of water; without them, summer water levels in Europe's rivers would drop substantially. In June, July and August, more than half the water in the Rhine is glacial melt water.
Tourists are warned about the risks of falling rock
Falling river levels would threaten crop irrigation, and obstruct freight traffic on Europe's waterways.
"Switzerland's glaciers are often called the water towers of Europe," explained Martin Grosjean. "They supply the rivers, and if there's not enough water in the rivers, you can't for example cool down nuclear power stations, that has a dramatic effect on power generation.
"Then there will be dramatic effects on agriculture because you won't have water to irrigate the crops.
"Glaciers are an important indicator of the water cycle. They show that the water available during the seasons is changing rapidly, and the question is how can society cope with long term water shortages."
That is a question that is becoming increasingly urgent; the most recent study into glaciers, from the University of Zurich, found that if global warming continues at its present rate, Europe's icecaps could be gone by the end of this century.
As the Swiss Alpine Museum puts it, we may be the last generation to be able to admire the "magnificent giants of ice".