Thunderstorms have hampered the search for more than a dozen hikers who remain unaccounted for a day after a huge chunk of an Alpine glacier in Italy broke off, sending an avalanche of ice, snow and rocks down the slope. The Italian prime minister, Mario Draghi, pledged on Monday night that his government would work to avoid a repeat of the tragedy in which at least seven people were killed. Eight people were injured at the Marmolada glacier – the largest Dolomites glacier that straddles the Veneto and Trentino regions – on Sunday afternoon. Thirteen people were still missing as of Monday evening. “Today Italy mourns these victims,” Draghi said during a visit to the site near the mountain town of Canazei. “This is a drama that certainly has unforeseen elements, but certainly also depends on the deterioration of the environment and the climate situation. Now we must take measures so that what happened on the Marmolas does not happen again in Italy.” At least four bodies, brought to a makeshift morgue at an ice rink in Canazei, have been identified. Three have been identified as Italian, including an experienced mountain guide who had been leading a group of hikers, and a 27-year-old man who sent a selfie to his brother 15 minutes before the avalanche plummeted down, hitting a popular hiking trail. According to media reports, those feared missing include Italians, three Romanians, one of French nationality, another from Austria, and four from the Czech Republic. Two of those injured are reported to be German. The Veneto president, Luca Zaia, said some of those hiking in the area on Sunday were roped together as they climbed. Sixteen cars remained unclaimed in the area’s car park, while authorities sought to track down owners through licence plates. It was unclear how many of the cars might have belonged to the already identified victims or to the injured, all of whom were flown by helicopter on Sunday to hospitals. Rescue operations were hampered on Monday due to a storm, before resuming with the use of drones. The thunderstorm forced Draghi’s helicopter to the site to be diverted, with the premier then travelling by car from Verona. “It is an unimaginable carnage,” a source told Rai News. “Some bodies will only be identified through DNA testing.” Prosecutors have opened an investigation against “unknown persons for culpable disaster”. What caused a pinnacle of the glacier to break off and thunder down the slope at a speed estimated by experts at nearly 200mph (300km/h) was not immediately known. But the heatwave gripping Italy since May, bringing temperatures unusually high for the start of summer even up in the normally cooler Alps, was being cited as a likely factor. “Temperatures have been well above normal levels for days and last winter there was not much snow, which basically no longer protects the glacier,” Renato Colucci of the National Research Council’s Polar Science Institute (Cnr-Isp), told Ansa. “This probably produced a large quantity of melted water at the base of that piece of glacier.” Jacopo Gabrieli, a polar sciences researcher at Italy’s state-run CNR research centre, noted that the long heatwave, spanning May and June, was the hottest in northern Italy in that period for nearly 20 years. “It’s absolutely an anomaly,” Gabrieli said in an interview on Italian state TV on Monday. Like other experts, he said it would have been impossible to predict when or if a serac – a pinnacle from a glacier’s overhang – could break off, as it did on Sunday. Alpine rescuers on Sunday noted that late last week the temperature on the 3,300-metre (11,000ft) peak had topped 10C (50F), far higher than usual. Operators of shelters along the mountainside said temperatures at the 2,000-metre (6,600ft) level recently reached 24C (75 F), hitherto unheard of heat in a place where people go in summer to stay cool. Pope Francis tweeted an invitation to pray for the victims and their families. “The tragedies we are experiencing with climate change must push us to urgently seek new ways to respect people and nature,” he said. Known as the Queen of the Dolomites, the Marmolada has lost more than 80% of its volume over the last 72 years, with the speed of its melt hastening over the last decade. Italian scientists warned in 2020 that the glacier could disappear within 15 years because of global heating. The Marmolada has been measured every year since 1902 and is considered a “natural thermometer” of climatic change. “This is the first time an event of this kind has happened on the Marmolada,” said Aldino Bondesan, a geophysics professor at the University of Padua and member of the Italian Glaciological Committee. “Studies of the Marmolada have been done, to see the variations in the thickness of the glacier and snow, and variations in its front, but I don’t think there has been a study dedicated to the danger of it breaking away as falls of this type have never been registered.” Low snowfall, combined with higher than usual temperatures in winter, have also contributed to the acceleration of the glacier’s melt. “This year we had a very particular year, maybe worse than in 2003 as we’re having high summer temperatures and we didn’t have winter snow or at least very little,” added Bondesan. “In June, the glaciers looked how they would normally look at the end of August.” The Italian Glaciological Committee monitors 200 of Italy’s 900 glaciers. In September 2019 and again in August 2020 homes were evacuated in a hamlet of Courmayeur, in the Aosta valley, following alerts that a huge portion of the Mont Blanc glacier, Planpincieux, was at risk of collapse. Planpincieux has been closely monitored since 2013 to detect the speed at which the ice is melting. In August 2018, a heavy storm unleashed a debris flow, killing an elderly couple when their car was swept from the road, which is currently closed. In the event of a collapse, it would take less than two minutes for the mass to reach the municipal road below.