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March 2021

When Avalanches Become Historic

Unless you live in the mountains, especially high altitude mountains, you probably do not realize how many avalanches actually occur. The vast majority happen in remote areas with little damage to people or property.  
March 2019 was a record-breaking avalanche cycle for the Rocky Mountains in Colorado, with some catastrophic consequences. During the course of the month, scientists recorded more than 600 avalanches, breaking all previous records. Estimates suggest these accounted for only about 25% of the total avalanches.  
What made for this particular season and the significant number of slides? 

Early Season Setup 

Scientists studying the avalanches said it was not one particular factor, but really a series of events that spanned the entire winter. It started with an early-season setup. 
Snow began accumulating a little earlier than normal, with storms starting in October 2018. However, this was followed by a dry November, weakening the snow base, drying it out and weakening it for the rest of the season. 
The majority of the winter saw some frequent show, but not enough to trigger slides. This led to a lot of building snow on top of the weak base layer, adding weight that would eventually lead to what we saw in March. 

Late Season Storms 

What pushed the snow over the edge was heavy snow late in the season. This accumulated more weight quickly, on top of the fragile base layer that was already teetering with the snow from the rest of the season. Add to that the winds that accompanied these storms, causing massive change on the mountains very quickly. All of this combined to give you a dangerous situation. 
Are these likely to continue? Scientists do not know at this point. Without this particular combination of events, the 2019 season would not have been nearly so severe.