Avalanche kills at least four in French Alps.

Four people have been confirmed dead, one has been injured and another is still missing following an avalanche near Entraunes in the Alpes-Maritimes Department in southeastern France, at about 1.00 pm local time on Friday 2 March 2018. All of those effected are reported to have been taking part in a guided off-piste ski tour near the Mercantour National Park when they were struck by the avalanche.

The approximate location of the 1 March 2018 Entraunes avalanche. Google Maps.

Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later.

 Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

The Alps have seen a number of avalanche related incidents this winter, largely due to high levels of snowfall. This is, in turn caused by warmer conditions over the Atlantic, which leads to higher rates of evaporation over the ocean, and therefore higher rates of precipitation over Europe, which falls as snow in cooler regions such as the Alps. This situation is likely to get worst this week after a significant cold front from the east brought plunging temperatures across Europe this week, which is expected to be replaced by a new wet front from the west over the weekend, depositing precipitation as more snow across the now cooler continent.

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Magnitude 4.9 Earthquake in southern France.

The Centre Sismologique Euro-Méditerranéen recorded a Magnitude 4.9 Earthquake at a depth of 5 km  in the  Hautes-Alpes Department of southeastern France, slightly before 9.30 pm local time (slightly before 7.30 pm GMT) on Monday 7 April 2014. This is a large quake for the region, and was found as far away as Marseille and Geneva, though there are no reports of any damage or casualties. 

The approximate location of the 7 April 2014 Haut-Alpes Earthquake. Google Maps.

The Alps are not static structures, but are a growing range of mountains being forced upwards by the impact of Africa into Europe, which is forcing the Adriatic Plate, underlying western Italy and the eastern Balkan Peninsula, further into the Eurasian Plate, causing folding and uplift in the rocks of central Europe. This movement is not smooth and continuous, but bumpy and jerky, as the rocks stick to one another while pressure builds up, then release suddenly causing quakes.

If you felt this quake you can report it to the Centre Sismologique Euro-Méditerranéen here. 

See also...

 Two children killed by landslide in the French Maratime Alps.

 Magnitude 2.9 Earthquake in northern France.

 Earthquake in the Auvergne Region, France.

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Two children killed by landslide in the French Maratime Alps.

Two children aged 7 and 11 were killed when a rock measuring approximately 5 m by 10 m fell rom an overhanging cliff onto a holiday challet where they were staying during a landslide at Isola in the Maratime Alps at about 5.00 am local time (4.00 am GMT) on Sunday 23 February 2014. Five adults from two families who were also staying at the chalet escaped with minor injuries, and were treated in hospital in Nice, 70 km to the south. The names of the affected families have not yet been released, but it is understood that the chalet was part of a British-built resort largely used by families from the UK.

 Rescue workers at the remains of the Isola Chalet on Sunday 23 February 2013. The Independent.

The incident happened after after a period of extended rain, combined with a sudden thaw in the area, which is primarily a ski resort at this time of year. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. When this is combined with a sudden thaw this can result in additional problems. As well as contributing additional water to any flooding, the thawing often affects ice in cracks in rock faces, which may have been weakened by the epansion of the water as it initially froze (ice occupies more space than an equivalent mass of water, due to its crystaline structre), but which have remained in place due to the adhesive properties of the ice, often resulting in quite large rockfalls.

Isola suffered a large rockfall in 2009, which trapped a large number of people, including many British tourists, when it burried a road connecting the chalet resort to the rest of the village. In January 2014, 2 people were killed when a rockfall struck a train in the Maratime Alps.

See also Over 100 people forced from homes by landslide in Dundee, Scotland, Magnitude 5.4 Earthquake off the coast of El Hierro, At least six dead as Atlantic Storm hits Britain and France, Supermarket destroyed by Italian landslide and Five dead and one missing as western Europe is hit by worst Atlantic Storm in a decade.

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