Be Mindful of Valley Floor Avalanches This Spring

Spring has arrived! As we look ahead to the next 7 days a series of typically spring-like westerly fronts are forecast, much like what we saw batter parts of the country over the weekend. These fronts are expected to generate significant precip (rain/snow), combined with rising freezing levels, and strong winds.

Heavy rainfall has already soaked the snowpack, and will continue to, and we anticipate several large avalanche cycles through this period.

These avalanches are likely to run to the valley floor. This means trampers and hunters moving through valleys or accessing gullies or stream beds could be exposed to these avalanches.

While this is normal for springtime in New Zealand, this year there is a higher chance of avalanches running to the valley floor. This is in part related to the Persistent Weak Layer (PWL) that has been present throughout much of the Southern Alps. If an avalanche is triggered it may then awaken this PWL, low in the snowpack, resulting in an avalanche much larger than usual.

We recommend a very cautious approach to any valley travel over the next couple of weeks. Pay particular attention to what is above you, where you are stopping or camping, and of course, follow the advice on www.avalanche.net.nz. If you are heading to areas where there is no regional avalanche forecast, we recommend you follow the advice of the closest region.

A great way to decrease your exposure to these destructive valley floor avalanches is to wait for 24 hours after the rain and avoid runout zones in the valley floor (or being at the head of a valley) on the first hot day after the storm.

NZ Mountain Safety Council recommends:

• Avoid stopping in or below gullies.
• Avoid stopping in clearings where there is no tree cover above you or around you.
• Think very carefully about campsite choices in the valley, consider what is above you, and avoid runout areas such as gullies, small side streams or under cliff bands.
• Consider your timing, as these avalanches are more likely to occur during or within the first 24 hours of a storm, or on the first hot day after a storm.
• Check avalanche.net.nz and follow the terrain and travel advice.

Valley floor avalanche at the Whitcombe River, West Coast. PHOTO/KEVIN BOEKHOLT

Valley floor avalanche in Tasman Valley, Aoraki/Mt Cook National Park. PHOTO/GUY COTTER