Mountain police on duty at Mont Blanc

Standing outside their yellow hut on a ridge 3,200 meters above sea level, two French gendarmes peer through binoculars at a group of foreign climbers making their way across a scree-littered stretch on what has become one of the deadliest routes to the top of Mont Blanc.

“Rocks, rocks!” one of the climbers suddenly yells, prompting them all to scurry for shelter in the Gouter corridor, on the most popular route to the summit of Europe’s highest peak.

Overcrowding on the mountain has again been severe this summer, with more than 300 people pitting their wits against the mountain each day despite the growing risk of rockfall as high temperatures thaw more ground at higher altitudes.

The heatwave that struck much of Europe in the past few weeks only heightened the risk — on Friday the bodies of three Italian climbers were found. That brought the death toll for this year’s climbing to 15, up from 14 dead and two missing last year.

Last month, authorities began turning away climbers who did not have reservations at the 120-bed Gouter refuge, which has been overrun by ill-prepared climbers who have found the challenge too exhausting.

The highly popular “Royal Route” up Mont Blanc is not considered a very technical climb, but officers say people can still quickly find themselves in over their heads while attempting the 4,810-meter peak.

Increased rock slides have even prompted local guides to stop leading clients up in recent weeks.

For those unwilling to put off their ascent, they are advised to start early to ensure they won’t have to tackle the Gouter corridor in the afternoon, when the risk of rockslides is greatest.