Marmolada Glacier Collapse: what happened?

Yesterday, July 3rd 2022, disaster struck on the Marmolada, a 3343 m tall mountain in the Italian Dolomite Mountains, a southern subrange of the European Alps.
A piece of the glacier collapsed and 6 people are dead and in the latest news another 8 are injured. So what happened, where did it happen exactly and what was the (potential) root cause?

First of all: the Marmolada is an iconic mountain in Italy. It’s very popular amongst hikers and climbers and consequently, at least 18 people were in the direct area when the glacier collapsed. Some websites state that “a serac” broke off and caused the avalanche.
This is not true. A serac is a standing tower of ice – the Marmolada glacier doesn’t have seracs. Seracs are usually formed on large(r) glaciers with more vertical distance and lower temperatures: the Marmolada is in a hot area, and seracs would simply not stand long enough to survive. Also, the accumulation zone is simply not large enough to sustain seracs.
So what did happen? To better assess the situation, I compared the “before” (picture below) with “after”, a screenshot from a video posted on DW, a news website.

Before and after comparison of the Marmolada glacier, after the recent events on July 3, 2022 when the glacier collapsed.
A comparison in after-before. Never mind the snow cover on the lower picture from Google Maps, as it’s taken earlier in the season

The event happened on the northside of the mountain. Obviously, I would state as the south side doesn’t have any glaciers. The glacier collapsed and sent a large stream of water, ice and rocks down it’s slopes.
It happened exactly here (picture below), at roughly 3200m altitude.

The exact location of the glacier collapse on the Marmolada in Italy, July 32022.

The weather conditions were blistering hot: the freezing altitude was 4400 meter and under the dry conditions available, this must have meant a temperature of approximately 12°C at 3200m.
According to Peter Kuipers Munneke, a Dutch glaciologist (source: his Twitter account), 2 things would have contributed to the collapse of the glacier.
1. Accumulation of water in the glacier cracks, causing hydrostatic pressure and effectively tearing the glacier apart from the upper part (hydrofracturing). As the temperure was above 10°C, this seems a plausibel hypothesis, where melt water is exacerbating the melt of the connections between the cracks and losing them as a result.
2. Water on the bed rock, slightly lifting the glacier from the rocks and lubricating the surface. The normal friction with the bed rock is lost, causing a rapid slide down the mountain.

Losing so much ice in 1 event is spectacular and obviously dangerous. Glaciers collapse more often, although usually not as violent as this event. This glacier is in itself very special, as under normal conditions this glacier could not exist in this area. It lacks an accumulation zone, it’s in a warm area and the summers are hot & dry. The mountain is not specifally high either.
It’s for this reason that already in 2020 it was announced this glacier would disappear in about 15 years. It already shrunk by 80% (1954-2020). In recent years, over 10 hectares of surface is lost on an annual basis. This years winter drought and summer heat, combined with this tragic event, leads to an even faster retreat and disappearance of the glacier.

Events like this can happen in more places in the Alps, leading to a change in landscape and routes – and posing a threat on hikers and climbers. They are always unforeseen events – even on this glacier: the Marmolada glacier is the best documented and monitored glacier of Italy.

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